Bull Creek Watershed Management Study · 2012-10-14 · BULL AND WEST BULL CREEK WATERSHED...

BULL AND WEST BULL CREEK WATERSHED MANAGEMENT STUDY

A CONCEPTUAL PLAN TO IMPLEMENT LOW-IMPACT DEVELOPMENT SOLUTIONS FOR BULL CREEK

NOVEMBER 2003

PREPARED FOR:

City of Austin, Texas

Watershed Protection and Development Review Department

P.O. Box 1088 Austin, Texas 78767

PREPARED BY:

PBS&J

6504 Bridge Point Parkway Suite 200

Austin, Texas 78730

Glenrose Engineering, Inc. P. O. Box 161270

Austin, Texas 78716-1270

Printed on recycled paper

Contents Page

Acronyms and Abbreviations ........................................................................................................................ v

1.0 LOW-IMPACT DESIGN, GOALS, AND OPPORTUNITIES .................................................................. 1-1 1.1 INTRODUCTION TO LOW-IMPACT DEVELOPMENT SOLUTIONS ..................................1-1 1.2 THE POTENTIAL FOR LID SOLUTIONS IN BULL CREEK.................................................1-2 1.3 GOAL 1: REDUCE EXTENT AND CONNECTIVITY OF IMPERVIOUSNESS.....................1-5 1.4 GOAL 2: ENHANCE PERVIOUS PERFORMANCE.............................................................1-6 1.5 GOAL 3: NATURAL AND OPEN STORMWATER CONVEYANCE .....................................1-9 1.6 GOAL 4: LENGTHEN TIMES OF CONCENTRATION.......................................................1-10 1.7 GOAL 5: PREVENT CONCENTRATION OF RUNOFF......................................................1-11

2.0 INVENTORY OF LOW-IMPACT DEVELOPMENT SOLUTIONS FOR RETROFITS .......................... 2-1

3.0 PUBLIC EDUCATION AND LID.............................................................................................................. 3-1

4.0 BENEFITS ASSESSMENT OF LID SOLUTIONS.................................................................................. 4-1 4.1 WATER QUALITY BENEFITS CONSIDERED .....................................................................4-1

4.1.1 Surface Water Hydrology .........................................................................................4-1 4.1.2 Surface Water Quality ..............................................................................................4-1 4.1.3 Groundwater Quantity ..............................................................................................4-2 4.1.4 Groundwater Quality ................................................................................................4-2

4.2 MODELING RESULTS FOR LID SOLUTIONS ....................................................................4-3 4.2.1 Analysis Approach....................................................................................................4-4 4.2.2 Land Use Data and Watershed Characteristics.......................................................4-5 4.2.3 LID Solution Scenarios Modeled..............................................................................4-7 4.2.4 Modeling Methods and Assumptions .......................................................................4-8

4.2.4.1 Goal Condition (5% IC).............................................................................4-8 4.2.4.2 Existing Condition.....................................................................................4-8 4.2.4.3 Rainwater Tanks.......................................................................................4-8 4.2.4.4 Rainwater Barrels (2 x 75 gallons each) ..................................................4-8 4.2.4.5 Rooftop Disconnections............................................................................4-9 4.2.4.6 Compost Soil Amendments for Pervious Areas .......................................4-9 4.2.4.7 Rain Gardens (Bioretention) for Non-Road Impervious

Areas ......................................................................................................4-10 4.2.4.8 Retrofit Smart Growth Road Dimensions ...............................................4-10 4.2.4.9 Impervious Cover (Road) Disconnections..............................................4-11 4.2.4.10 Bioretention for Streets...........................................................................4-12 4.2.4.11 Porous Pavement Roadway...................................................................4-13 4.2.4.12 Porous Curb and Gutter .........................................................................4-14 4.2.4.13 “SEA Streets” Equivalent (using SOS capture depth)............................4-14

4.2.5 Modeling Results....................................................................................................4-15 4.3 MULTIPLE BENEFITS ........................................................................................................4-27

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CONTENTS

5.0 FEASIBILITY............................................................................................................................................. 5-1

6.0 COST......................................................................................................................................................... 6-1

7.0 MAINTENANCE........................................................................................................................................ 7-1

8.0 CONCLUSIONS........................................................................................................................................ 8-1

9.0 BIBLIOGRAPHY....................................................................................................................................... 9-1

Appendices A Field Data Forms – LID Assessment of Tributary 6 B LID Cost Details

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CONTENTS

Figures Page

1 Ratio of Developed Condition to Goal Condition at Various IC Levels .........................................4-16 2 Runoff Volume for Existing and Goal Condition and with 11 LID Solutions for

Varying Levels of Impervious Cover..............................................................................................4-18 3 TSS Load for Existing and goal condition and with 11 LID Solutions for Varying

Levels of Impervious Cover ...........................................................................................................4-19 4 COD Load for Existing and Goal Condition and with 11 LID Solutions for Varying

Levels of Impervious Cover ...........................................................................................................4-20 5 Nitrogen Load for Existing and Goal Condition and with 11 LID Solutions for

Varying Levels of Impervious Cover..............................................................................................4-21 6 Baseflow Volume for Existing and Goal condition and with 11 LID Solutions for

Varying Levels of Impervious Cover..............................................................................................4-22

Tables

1 Bull Creek Potential Problem Sources and Solutions for Water Quality .........................................1-4 2 Inventory of Low Impact Development Solutions ............................................................................2-2 3 Estimating the Benefits of Low-Impact Development Solutions......................................................4-3 4 Percent of Bull Creek Watershed Area by Land Use ......................................................................4-6 5 Impervious Cover Component Percentages by Land Use ..............................................................4-7 6 Smart Growth Road Width Options ...............................................................................................4-11 7 SOS Ordinance Level of Capture ..................................................................................................4-15 8 Percent Toward Goal for LID Solutions Under Various Impervious Cover Levels........................4-23 9 Effects of Tank Size on Annual Capture Fraction .........................................................................4-24 10 Feasibility Scoring Matrix for LID Solutions.....................................................................................5-2 11 Summary of Estimated Cost to Implement LID Solutions per Acre.................................................6-1 12 Cost vs. Performance of LID Controls for the 40% IC Scenario .....................................................6-2 13 General Level and Cost of Maintenance Required for LIS Solutions..............................................7-1

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Acronyms and Abbreviations

BCCP Balcones Canyonlands Conservation Plan BWMS Bull and West Bull Creek Watershed Management Study

COA City of Austin EII Environmental Integrity Index

LID low-impact development NWI National Wetlands Inventory PAH polyaromatic hydrocarbons SFR single-family residential

TCEQ Texas Commission on Environmental Quality TNRCC Texas Natural Resource Conservation Commission, now the TCEQ WPDR COA’s Watershed Protection and Development Review Department

WSS Water Supply Suburban Watersheds

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1.0 LOW-IMPACT DESIGN, GOALS, AND OPPORTUNITIES

1.1 INTRODUCTION TO LOW-IMPACT DEVELOPMENT SOLUTIONS

Low-Impact Development (LID) solutions are small, decentralized water quality controls, which collectively attempt to mimic predevelopment hydrologic, soil, and vegetative patterns. After years of experimentation with what are now viewed as conventional stormwater controls (wet ponds, sand filters, detention ponds, etc.), it has been increasingly recognized that development using such controls does not allow its receiving waters to maintain the beneficial and natural qualities present prior to development. In other words, stream systems and water supplies appear to continue to degrade despite our best intentions in providing “end-of-the-pipe” controls.

In response, LID solutions were developed as an additional means of control, starting with the first applications in Prince George’s County, Maryland. LID solutions include such techniques as bioretention, bioswales, impervious cover disconnection, soil amendments, reforestation, and rainwater harvesting (see below for descriptions of these and other LID solutions). All take advantage of powerful and complex natural systems such as soil and vegetation to slow, detain, retain, infiltrate, and purify water discharged from developed areas. Instead of having the typical flashy peak flows during rainfall events seen in conventional developments, the hydrologic response in an area fitted with LID systems is muted and controlled. Flows are intentionally kept as diffuse and laminar as possible rather than be allowed to concentrate. (Conventional systems, on the other hand, rely on the use of concentrated conveyance systems to deliver water to a centralized control site.) LID practitioners seek to avoid the use of “end-of-the-pipe” controls such as traditional sand filters and wet ponds as these controls generally lack the ability to provide the full range of benefits offered by LID solutions. Pond Best Management Practices (BMPs) preside over greatly altered hydrologic regimes and often do not address dissolved pollutant parameters. However, LID users generally consider the use of both LID and conventional techniques in tandem in searching for complete solutions.

LID components are ideally planned prior to and constructed with initial development, not as an after-the-fact retrofit. LID solutions are physically integrated into the landscaping and basic infrastructure. However, in virtually all existing development to the present — including that of the Bull Creek watershed — no consideration of or provision for LID principles was ever made. Thus water has been intentionally concentrated in curb and gutter systems, moved to inlet structures and pipes, and discharged directly into waterways. Minimal opportunity for infiltration has been provided. In fact, the whole strategy of these designs is to drain away runoff as fast as possible, treating it as a nuisance or a danger. (LID designs treat water as a resource and an asset.)

The damage done by conventional development is significant and visibly obvious: water reaches waterways much faster and with proportionately greater erosive force than pre-development. The

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Low-Impact Development Solutions for Bull Creek

resulting scour enlarges channels, abrades away aquatic vegetation, and creates shifting gravel bars. The sediments introduced by this runoff and the pollutants which adsorb to them suffocate and contaminate riverine ecosystems, physically disrupting the pool and riffle sequences critical to fish and wildlife in a natural stream. Contact with soils which once removed or trapped these pollutants and retained water is minimized or eliminated. The impervious surfaces likewise collect and contribute additional pollutants (trash, oil and toxics from vehicles, leaf litter, atmospheric depositions of nutrients, bacteria, etc.) to the runoff and increase stream temperatures, depleting oxygen. The ecosystems affected are degraded and thereby reduced in both variety (biodiversity) and resilience and become more exposed to future runoff events.

LID designs seek an opposite result. They attempt to mimic, to the extent possible, the predevelopment hydrology of a site, thereby addressing the hydrologic impacts cited above for conventional development. To counteract the effects of impervious cover, LID solutions are considered at each step of the way in water’s path from roof and pavement to conveyance to waterway.

1.2 THE POTENTIAL FOR LID SOLUTIONS IN BULL CREEK

The Watershed Protection Department undertook a study of Bull Creek (among other watersheds) in 1999 entitled Water Supply Suburban Watersheds Report: Watershed Protection and Traffic Analysis (City of Austin (COA), 1999). This report evaluated the land development status, water quality protection strategies, and watershed assessments done to that point in Bull and other nearby watersheds. The study concluded that a number of factors combined to present a threat to the aquatic and riparian health of Bull Creek and the other Water Supply Suburban Watersheds:

• Nutrients • Pesticides and Herbicides • Hydrocarbons • Flow Regime • Siltation and Suspended Solids • Bacteria

The report also concluded that, due to extensive past development and the establishment of the Balcones Conservation Plan preserves, very little land remains undeveloped which might be urbanized. Therefore, water quality solutions would have to be retrofitted into existing development. Some attempts were made to identify conventional, end-of-the-pipe solutions — largely regional wet ponds in canyon low points (Loomis-Austin, 2000), but these efforts were later largely rejected when it became clear that many of these solutions might actually harm the environment more than they would benefit it (by blocking natural sediment transport, destroying riparian woodlands, etc.). Large-scaled ponds are also difficult to retrofit into existing development because there is seldom an appropriate, down-slope location for such controls. Only by purchasing and eliminating homes to make way for ponds could many subdivisions be treated by large ponds.

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A very different means of control was also proposed in the 1999 study, and that was that of LID. The study concluded:

The LID strategy could be applied to either existing or new development, or both. Along with public education, it offers one of the few options that can be used to control impacts from existing development, which accounts for the vast majority of problem sources in the WSS [Water Supply Suburban] watersheds (COA, 1999).

As noted in the introduction, LID solutions are inherently small-scaled and site specific. These features enable the potential for retrofitting into existing developments. But they also require a much higher level of attention to site-specific geographic characteristics (topography, soils, land ownership, etc.) than do larger scaled controls. The 1999 study did not address the specific sources of the pollutant types listed above. Therefore, in order to identify potential retrofits, a more detailed accounting of potential sources of hydrologic and water quality problems and the “lay of the land” in general was necessary.

Table 1 shows the potential sources of water quality problems, both physical (e.g., impervious cover, land uses, infrastructure) and human activities (e.g., site construction). Many of these sources can be treated with LID retrofits. Table 1 notes these in the shaded LID solutions column. Each source potentially addressed by LID is discussed below as to its presence, characteristics, and significance in Bull Creek.

The sections below combine an evaluation of the five goals of LID solutions with the potential problem sources noted above which may be addressed with LID approaches. In order to make a detailed determination of the existing developed condition, Glenrose Engineering staff conducted a field survey of all subdivisions in Tributary 6 of the Bull Creek Watershed (PBS&J, 2003) and many commercial properties. Tributary 6 was determined to be a suitable case study for the entire Bull Creek Watershed because it contains most of the main developed features of the Bull and West Bull Creek watersheds:

• Dominated by single family residential development • Commercial development along major roadways • Major Highway (Farm-to-Market (FM) 620) • Golf course

A field data form was used to note the characteristics of each area with respect to prospective LID solutions. The field data sheets are presented in Appendix A. This information was used in conjunction with physical data (e.g., impervious cover percent, land use type, recharge zone status, etc.) derived from geographical information system (GIS) coverages for the watershed to provide a basis for this LID analysis.

The following five goals were derived in part from a review of the seminal guidebook on LID: Prince George’s County, Maryland’s Low-Impact Development Design Strategies: An Integrated Design Approach (June 1999). These were taken as the basis for discussion of the condition and opportunities present in Bull Creek.

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1. Reduce Extent and Connectivity of Imperviousness. 2. Enhance Pervious Performance. 3. Natural and Open Stormwater Conveyance. 4. Lengthen Times of Concentration. 5. Prevent Concentration of Runoff.

Each of these five goals is addressed below in detail in conjunction with each of the Possible Problem Sources which were indicated in Table 1 as potentially addressed by LID solutions.

TABLE 1

BULL CREEK POTENTIAL PROBLEM SOURCES AND SOLUTIONS FOR WATER QUALITY Potential Problem Resulting Potential Solutions

Possible Problem Sources

Nut

rient

s Pe

stic

ides

and

H

erbi

cide

s H

ydro

carb

ons

Flow

Reg

ime*

Si

ltatio

n an

d Su

s p. S

olid

s Ba

cter

ia

Low

-Impa

ct

Dev

elop

men

t Pu

blic

Ed

ucat

ion

Exis

ting

BMP

Ret

rofit

s La

rge-

Scal

ed

Stru

ct. B

MPs

Other Impervious cover Rooftops x x x x x x Roadways x x x x x x x x x Parking lots x x x x x x x x x x Driveways x x x x x x x x Sidewalks x x x x x x Trails x x x x Pervious areas Residential landscaping x x x x x x x Commercial landscaping x x x x x x x Golf course landscaping x x x x x x x WW Mgmt. Sparse vegetation x x ? x x Compacted soils x x ? x x Erosion/channelized flows x x x x Infrastructure Closed runoff conveyance x x Open runoff conveyance x x Wastewater lines x x x W/WW CIP Wastewater lift stations x x x W/WW CIP Septic systems x x x W/WW CIP Underground storage tanks x Regulations Activities Site construction x x x Regulations Spills/Dumping x x x x x x Vehicle washing/soap x x Regulations Land Uses Auto-related businesses x x x Other hotspot businesses x x x x Fauna Pets x x x Livestock x x x Wildlife x x * Focus on Baseflow and Channel Forming Flow.

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1.3 GOAL 1: REDUCE EXTENT AND CONNECTIVITY OF IMPERVIOUSNESS

The monitored and modeled data examined in Section 2.0 of the Bull and West Bull Creek Watershed Management Study (PBS&J, 2003) showed the key, negative role that an increase in impervious cover has played in changing the water quality in Tributary 6 and in much of the watershed. Any solution to the resulting problems would thus require reversing the impacts of impervious cover.

However, not all impervious cover acts alike. Roofs have different characteristics than pavement, and the degree of “connectivity” is very important. Connectivity refers to how hydraulically connected impervious infrastructure is with the receiving waters. The more chance for disconnections, the better. For example, a roof might be connected directly to a concrete driveway which drains to a curb and gutter street drainage and on to a storm sewer pipe and into the creek. This scenario (very common in Bull Creek and most urban areas) provides virtually no opportunity for infiltration and treatment of the runoff in the soil. Only the other hand, the roof runoff might drain to a rock garden and then across a 100-foot landscaped or heavily vegetated buffer and then to a grassed swale and on to the creek. This scenario slows the water, treats it via settling and infiltration, and generally allows runoff from an impervious surface to be returned to a regime which mimics that of an entirely pervious area.

Roadways. Roads constitute the greatest source of connected impervious cover in Bull Creek’s residential neighborhoods. Virtually all of the streets in Tributary 6 have been built with curb and gutter and direct all runoff in concentrated flows to storm drains and/or single outfalls. The designs of these areas minimize rather than maximize overland flow and dispersed vegetative treatment of roadway runoff. They quickly and efficiently move rainfall runoff to centralized outfall points. The effect on water quality, baseflow, and stream habitats is decidedly negative. A key objective of LID design is to contain post-development impacts to pre-development levels. This may not be possible without substantial modification to street drainage infrastructure.

Residential roadways varied in width from 25 to 45 feet. The typical road width is 30 feet. The larger roads generally provided both two travel lanes for motorized vehicles and two bike lanes for bicycles. All of the roads are paved with either conventional (non-permeable) asphalt and/or concrete.

Any reduction in the extent and/or connectivity of road surface could improve watershed conditions. A variety of solutions could be implemented to accomplish this purpose. Notably, several roadways within Tributary 6 do feature relatively narrow widths (e.g., 25 feet) and/or have open, grassed swale conveyance. A retrofit to provide for roads of this configuration would help the watershed hydrologically. The presence of established examples of each in the area provides a model for future retrofits.

Rooftops. Most roofs in Tributary 6 were observed to be entirely disconnected. A small percentage of total downspouts were routed to driveways, which in turn drained to roadways and storm drain systems.

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However, most downspouts either went to landscaped pervious areas or drained to driveways which in turn drained to sheet flow onto pervious landscaped areas.

Many of the roofs constitute a high percentage of the total site imperviousness and the total site area. An assessment using GIS showed about 50 to 65% of residential impervious cover to be roof. Some hydrologic benefit could accrue from capturing roof runoff in cisterns, tanks, or rain barrels per rainwater harvesting, especially where roof runoff is currently being converted into channelized flow rather than sheet flow onto pervious areas. In such cases, rainwater storage could enhance the performance of the landscaped pervious areas. (This may be especially effective in areas with steep slopes and near ravines, which are numerous in Bull Creek.) However, currently, little roof runoff is not “connected” and such benefits would occur under the Enhance Pervious Performance section below.

Driveways. Many driveways drained, at least in portion, directly to roadways and into storm drain systems. Many driveways featured very extensive impervious cover. Virtually all driveways were made of impervious concrete rather than more pervious surfaces such as gravel. However, the solution would entail removal of concrete driveways (most in excellent condition, many built within the last 10 years, and all on private property) in favor of permeable surfaces. A program could be envisioned to educate folks about the advantages of a permeable driveway such that, over time as driveways were repaired and/or replaced, more permeable materials might be substituted.

Sidewalks. Some of the neighborhoods featured sidewalks. Most streets had sidewalks only on one side of the street. All of the sidewalks surveyed were concrete rather than made of more pervious materials. Many of the sidewalks were built such that a grassed buffer exists between the sidewalk and the road curb, providing for a large measure of sheet flow over vegetation and effective disconnection of this impervious surface. When future sidewalk repairs are necessary, Public Works could consider substituting permeable materials for the existing concrete walkways. Due to the small and relatively disconnected portion of total imperviousness that sidewalks represent, such solutions would not likely have a significant impact on watershed health.

Trails. Trails are not judged to be a significant source of water quality problems in Tributary 6. A modest length of trails exists in the Canyon Creek Greenbelt but represents a minor fraction of imperviousness in the watershed. Due to the narrow width and semiperviousness of the trails (essentially compacted earth, not pavement or asphalt) and proximity to much larger areas of pervious surface, trails repair for water quality does not appear to be a high priority from a water quality perspective.

1.4 GOAL 2: ENHANCE PERVIOUS PERFORMANCE

When in good condition, pervious surfaces effectively infiltrate stormwater, remove pollutants, and provide for creek baseflow. Pervious surfaces should be carefully maintained to provide these benefits and to offset the negative impacts of impervious surfaces. Most solutions involving pervious surfaces will

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also help lengthen times of concentration (Goal 4), a further benefit to erosion, water quality, and (usually) flood control.

Residential and Commercial Landscaping. A large percentage of the properties in Tributary 6 currently have what could be termed “intensive” landscaping practices. Such practices would include the extensive use of nonnative plant species (e.g., St. Augustine grass) and significant applications of water, fertilizer, pesticides, and herbicides to lawns to maintain these plants in good condition. These applications translate to increased loads of nutrients and toxics to creeks and receiving waters. Some construction contractors also clear some or all trees with heavy machinery and remove existing topsoil prior to construction. This machinery compacts what soil is left, and later red clay loam is typically imported as a topsoil. These soils are usually applied in very shallow depths (typically, 2–3 inches) and have minimal amounts of organic material (humus) which is critical to effective functioning of soils (plant health, water infiltration, air exchange, etc.). St. Augustine sod is then placed on the top. Soils impacted and changed in this way can act more impervious than pervious, and also require greater watering and chemical application to maintain a high level of lawn and plant health.

Intensive landscaping contrasts with a “low impact” landscaping approach which features native and adapted plants and minimal turf areas. Such an approach requires fewer chemical inputs (if any are used at all) to maintain its health and survival and also provides more habitat for native fauna. A shift to a Low-Impact Landscaping approach could be achieved through public education, use of compost soil amendments, and/or through an incentive program, such as seed money grants to convert conventional lawns into native, low-impact landscapes.

Golf course landscaping. About 5% of Tributary 6 is located in the Spicewood Golf Club. These lands are maintained in a traditional manner per golf course practices: short bermudagrass turf, regular watering regime, and use of pesticides, herbicides, and fertilizers to enhance the growth of this vegetation. This type of golf course maintenance has been shown to result potentially in significant loads of toxics and nutrients to receiving waters and saturated conditions due to frequent watering which lead effectively to an “imperviousness” surface. Golf course impacts, however, are beyond the scope of this present report. Discussion of the COA-owned wastewater pond on the golf course is included below in “Wastewater Treatment Plants,” under “Infrastructure.”

Sparse Vegetation. As a percentage of all properties, very few residential properties in Tributary 6 were observed to have poorly maintained pervious areas. Virtually all of these areas had a substantial and protective vegetated cover. Compared with solutions addressing impervious cover, little appreciable hydrologic benefit would likely occur were these areas to be more heavily vegetated. However, as noted above, a change in landscaping practices could possibly effect a change in water quality relating to nutrients and toxics.

Many of the residential areas had little to no tree canopy cover; these areas were covered by extensive lawn areas. Grassed lawns, especially those planted with hydric St. Augustine grass (a very common

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choice in Tributary 6) require more water and chemical inputs (fertilizers, pesticides, etc.) than do native species, especially when exposed to full sun most of the day. In these locations, trees could be planted to reduce the stress on the grassed areas below, lower the need for these inputs, and improve water quality.

An alternative approach would be to reestablish a more native vegetative condition, featuring native trees and a heavier understory of plants and associated leaf litter and mulch. Such vegetation would take virtually no chemical inputs and would provide a very complete land cover capable of intercepting and infiltrating a higher percentage of rainfall and runoff than would grassed lawns.

Erosion/Channelized Flows. Two separate areas were differently affected in terms of erosion and channelized flows from development: residential lots (stabilized with minimal effects) and storm drain outfall points (destabilized with significant impacts).

Lots. Due to the high percentage of vegetative ground cover (see above), little visible evidence of erosion or channelized flows was observed in residential or commercial lots during field reconnaissance. However, only a portion of the lots was visible from public roadways during the field survey. Some erosion and channelization of flows may exist behind the houses. Many of the houses are located directly adjacent to significant topographic relief (e.g., are located at the edge of cliffs) and it is likely that such placement lends itself to erosive, channelized runoff from roofs and driveways. Such problems could be addressed by rainwater harvesting, roof downspout disconnection, site regrading and terracing, and compost top-dressing. It is not anticipated that these problems are on the same level of magnitude and concern as those for the connected roadways.

Outfall Points. Once flows are concentrated by impervious cover, curbs, gutters, and storm drain systems, they have little opportunity for infiltration into the soil and proceed directly to waterways and receiving waters. The design of the street and drainage system of virtually all residential and commercial developments in Tributary 6 serve to maximize rather than minimize runoff concentration to outfall points. This in turn maximizes the impact of this runoff on receiving waters, including increased erosion.

Most of the development has occurred in the relatively flat uplands along hilltops. From this point, concentrated runoff is discharged down very steep ravines and other collection points. Once collected in this manner, it is very difficult to redistribute back as dispersed overland flow. If the streets and drainage systems are maintained in their present configuration, only conventional, end-of-pipe stormwater controls, such as retention ponds, can be envisioned to treat the water. The steepness of the terrain generally prohibits the practical application of such measures: construction would be difficult and damaging to the environment; maintenance access to the finished pond would be poor; and the ponds would still fail to address the fundamental hydrologic changes created by the development.

Some level of direct outfall protection can be envisioned to reduce erosion and improve water quality. For example, the outfall could be laid back further upslope and provided with a drop structure to reduce the energy of the water and protect the banks from erosion; the intervening pervious area created could be

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designed as a vegetative filter strip to infiltrate and treat some of the water. More extensive channel protection with reinforced earth lifts could also be used which would feature stabilizing vegetation which would in turn create a more stable stream geometry and reduce water quality problems. Loss of land and property could also be strategically prevented. However, such solutions alone would not correct the change in hydrologic regime caused by development.

These observations serve to reinforce the need to use LID solutions “higher in the watershed” rather than wait until water has been collected and directed to outfall points. Solutions which disconnect impervious cover and increase infiltration will assist in decreasing erosion from outfalls. However, in cases of existing, localized problems, a direct solution will likely be required.

Compaction. Compaction of soil dramatically reduces its ability to infiltrate rainfall runoff and provide for storage and treatment of this water. Compacted soils lack the biological health and complexity of better aerated, uncompacted soils and cannot sustain the same amount of protective vegetative cover. They essentially act as do impervious surfaces. The greatest amount of compaction generally occurs where soils have been subjected to high amounts of vehicle and/or foot traffic.

The field survey of Tributary 6 did not reveal many overt compaction problem areas. Such areas would be obvious from their lack of well established vegetation. However, discussion in “Residential and Commercial Landscaping” above, many cases of compaction and soil loss are masked by apparently viable grass cover. Some of the LID solutions, such as the application of compost soil amendments as a compost top-dressing on pervious areas, would help with whatever level of compaction does exist.

1.5 GOAL 3: NATURAL AND OPEN STORMWATER CONVEYANCE

Natural and open stormwater conveyance is superior to curb and gutter and closed (storm drain pipe) conveyance from a water quality perspective. Therefore, to the extent possible, existing open drainage should be preserved and existing curb and gutter and closed systems should be converted to natural and open drainage.

Closed Stormwater Conveyance. Most of the streets in Tributary 6 have curb and gutter drainage. These systems convey water along the gutters to centralized discharge points, usually into closed storm drain pipes or directly into waterways via curb inlets. As described above, this design does not take advantage of the infiltrative capacity of the soil and serves to speed up times of concentration. A North Carolina study found, for example, that streets with curb and gutter drainage had runoff volumes to receiving waters that were six times higher than that measured from streets with grassed swales (Bledsoe, 2001). For improved water quality, curb and gutter conveyance would either have to be replaced with an open drainage system or mitigated through some other means in order to restore a site to its predevelopment hydrology and the 5% impervious cover goal condition.

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Grassed Swales/Open Conveyance. This is the preferred approach to drainage for LID. However, once a street is built with curb and gutter drainage, only a major overhaul of the street’s structure will convert it back to natural conveyance. One advantage of curb and gutter systems is that they can be used in relatively confined spaces; grassed swales require more room along the roadway edge. Also, grassed swale conveyance requires that the street surface be raised above that of the swale bottom in order to drain via gravity. Curb and gutter streets offer a more hydraulically efficient conveyance than grass swales, allowing, in most areas, the street to be lower than the surrounding pervious areas. Redirecting curb and gutter to a swale in most cases would require raising the drainage flowline which in turn would effect many structural aspects of the site. This condition makes it very costly and difficult to retrofit a grassed swale. One possible solution would be to narrow the footprint of pavement on the road and use the converted pervious portion to create space for a grassed swale. This would reduce the area of impervious cover and provide open drainage. This approach has been used by the City of Seattle in its experimental SEA (“Street Edge Alternatives”) program.

An additional solution that could be considered would be to “daylight” the existing storm drain pipes in the watershed — convert them from subsurface pipes to open channels. This would allow more natural drainage which could slow the flows to less erosive velocities, lengthen times of concentration, and restore a more natural riparian habitat. However, with some exceptions, the storm drain networks observed during the field examination and map review were not extensive. The curb and gutter streets in many subdivisions act as the greatest proportion of drainage in the watershed, not a belowground pipe network. In most cases, only a short run of pipe at the bottom-most portion of a road was provided to drain the curb and gutter system to a ravine or drainageway. An additional difficulty in retrofitting most pipes to daylight their flows would be the severe topography of the watershed. Once the water has already been concentrated by wide, impervious streets with curb and gutter drainage, the outfall point is likely overwhelmed with quantity and velocity of flow — its conversion to “natural” drainage at this point would not address the fundamental problem of a substantially altered hydrologic regimen. (See “Erosion/ Channelized Flows — Outfall Points” above.)

Overland Flow. See “Enhance Pervious Performance” above.

1.6 GOAL 4: LENGTHEN TIMES OF CONCENTRATION

Urbanization and the addition of impervious cover usually dramatically speed the response time a watershed experiences in going from no rain to the point at which any given part of a watershed contributes to stream flows: affectionately know as the time of concentration (TOC). In an undeveloped condition, the headwaters of a watershed usually take much longer to begin contributing to the main stem, during which time runoff from lower in the watershed had already had time to move through; the slow movement of water throughout the watershed — much of it via overland flow — enables most of the water to infiltrate into the soil. In an urban setting, water is sped to the creeks via impervious surfaces and smooth, concrete drainage pipes and channels such that virtually all portions of the watershed contribute much more quickly, which greatly increases the volume, velocity, (reducing the TOC) and force of waters

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in the creek. In such a setting, runoff has very little opportunity to infiltrate into the soil for treatment or recharge as baseflow, water quality suffers, and channel erosion and flooding can dramatically increase.

The same techniques which are used for impervious cover (“Reduce Extent and Connectivity of Imperviousness”) and help pervious areas (“Enhance Pervious Performance”) will also help lengthen times of concentration.

1.7 GOAL 5: PREVENT CONCENTRATION OF RUNOFF

LID seeks to prevent the concentration of runoff. Once concentrated by impervious surfaces and hard conveyance systems, it is difficult to effectively restore the predevelopment hydrologic regime. Therefore, solutions should detain, retain, and infiltrate water as close to the source of additional runoff as possible. For example, runoff from impervious surfaces should be disconnected — directed across pervious areas rather than be allowed to proceed directly to an impervious street with curb and gutter drainage. The solutions listed above for the other goal categories address this concern.

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2.0 INVENTORY OF LOW-IMPACT DEVELOPMENT SOLUTIONS FOR RETROFITS

To determine the full range of options available for this approach, the project team evaluated the nationwide literature on LID. To these solutions were added some additional possibilities developed for this specific project. Table 2 presents the LID options identified for potential use in Bull Creek. The table summarizes the following for each solution:

• Description. Overview of the system.

• How It Works. Brief summary of the mechanisms by which water quality is improved.

• Benefits Provided. Water quality and additional benefits provided.

• Concerns. Main technical and institutional drawbacks possible.

• Comments for each solution. Additional comments where needed.

Please note that feasibility and cost issues are handled in subsequent sections, as is the quantification of water quality benefits.

Each could be combined with other options to create a given project. LID attempts to intercept, infiltrate, and treat water as soon as practical in its hydrologic path from rainfall to stream flow. Therefore, the inventory also starts at the first points of contact (roofs, lawns, etc.) and moves to conveyance systems (roads, swales, etc.) to the creeks (outfalls, enclosed creeks, etc.).

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Solution Type/Component Description How It Works Benefits Provided Concerns Comments Related Solutions1. Green Roof Roof with watertight liner and soil

medium to support vegetation; designed to retain a prescribed amount of water (e.g., a 2-inch rain).

Rainfall captured directly, retained on roof, used by plants.

Reduces runoff, cools roof and building, lowers energy consumption. Can be aesthetic.

Unproven in Austin. May be difficult to keep plants alive in hot season. More expensive retrofit than rain harvesting.

Could combine rain harvesting (e.g., from a higher roof level) for irrigation from impervious areas.

2. Rainwater Harvesting System: Tank Storage

Runoff from roof directed via gutters and pipes to a holding tank; water irrigated on dry days following storms. Tanks vary from 500 to over 10,000 gallons depending upon application and ability to use water.

Rainfall captured in tanks, later irrigated on plants or treated for domestic use.

Promotes infiltration, baseflow; lowers runoff & watering required. Flexible source of water for landscaping. Public education: help folks think about where their water is going.

Requires private owner/operator to maintain, thus minimal City quality control. Attractive to fraction of people willing to learn, perform these duties. Water quality function (store & release as much water as possible to maintain capacity) is in conflict with water conservation (longer storage until dry weather, incr. chance tank full during rains).

Seek passive discharge to ensure tank drains down, tank capacity kept high (e.g., soaker hose or drip irrigation). Is identified as a Central Texas solution.

Bioretention; site regrading; compost amendments, reforestation.

3. Rainwater Harvesting System: Rain Barrel Storage

Same as above but with smaller 75-gallon barrels. Existing component of City of Austin's water conservation program.

Same as above. Same as above. Smaller, less daunting to many than larger rain tanks, but small size may minimize positive impacts of use.

Expand COA program for rain barrels for Bull Creek.

See above.

4. Rooftop Disconnections Redirect water currently flowing from roof gutters to downspouts which flows to impervious surfaces and storm drain systems; allow to pass over pervious surfaces.

Runoff allowed to infiltrate into pervious areas which otherwise would run off in the storm drain system.

Promotes water retention, infiltration, & baseflow; lowers runoff & watering required.

Rooftops largely disconnected at present for many residences; more opportunity on commercial property, though less pervious space to irrigate on sites with high imperviousness.

Make sure pervious area adjacent; simple solution; possibly have a school class volunteer for work.

Site regrading; IC removal; compost amendments; rain gardens

5. Site Regrading/Terracing

Increase sheet flow, length of flow paths, etc. through the use of terracing and regrading of a site.

Runoff allowed to infiltrate into pervious areas which otherwise would run off as channelized flow.


Requires cooperation by, cost to private landowners & overhaul of at least a portion of a site's landscaping; invasive process will be rejected by some.

Bioretention; compost amendments, reforestation.

6. Compost Amendments for Pervious Areas

Apply compost to lawns, parks, & open spaces to improve soil properties. Complements many other solutions.

Helps compensate for years of soil compaction & topsoil loss with improved soil: more void space, organic content, stable nutrient content.

Enhances water retention in soil; lowers chemical maintenance requirements. Traps, neutralizes some types of pollutants.

Requires cooperation by, cost to private landowners; will be rejected by some.

Reforestation; impervious cover disconnections.

7. IPM & Xeriscape Demonstration Landscaping

Publicly accessible demonstration garden to educate citizens about non-polluting landscaping practices.

Shows by example how appropriate plant selection and soil preparation reduce the need for water, synthetic fertilizers, and pesticides. Promotes emulation of concepts on private lawns and gardens.

Lowers nutrient and toxic use on lawns and gardens which use same methods.

Outreach needs to be to those who use highly managed approaches; this population may be less interested in the approach and aesthetic used by the demonstration garden. Those most interested may already be using low impact techniques ("preaching to the choir").

City programs already emphasize methods; a Bull Creek demonstration project would provide a local example.

Compost amendments; retrofit landscape ordinance; reforestation, site regrading.

8. Reforestation Plant trees where few or none exist. Preference for disease-resistant native plants. Assumes use of mulch and/or ground cover establishment.

Trees improve hydrology by creating their own microclimate, soil retention by roots and leaf litter, and direct interception of rainfall.

Promotes water retention, infiltration, & baseflow; lowers runoff. Improves air quality, lowers temperature and "urban heat island" effects. Provides habitat & aesthetics.

Few concerns. Do have to ensure plants are watered and mulched for at least 2-year period to establish trees.

Dovetails with PARD programs for right-of-way plantings; need means to ensure plants watered for two years.

Compost amendments; retrofit landscape ordinance.

9. Impervious Cover Removal

Physically remove impervious cover and replace with vegetated pervious cover. Target unused parking space, roads, driveways, etc.

Directly addresses the most obvious cause of hydrologic disruption. Less impervious cover, less runoff, fewer water quality & quantity problems.

Promotes water retention, infiltration, & baseflow; lowers runoff. Lowers temperature and "urban heat island" effects. Improves aesthetics.

Must have cooperation of land owner, overcome perception that more impervious cover equates with more value for land; must also ensure that the new land use does not compact the soil and negate the benefits of the pavement removal.

Prioritize by connectivity of IC & proximity to waterways.

Compost amendments; retrofit landscape ordinance; reforestation, site regrading.

10. Retrofit Smart Growth Road Dimensions

Subset of Impervious Cover Removal: retrofit road widths to conform with Smart Growth road dimensions.

Permanently reduces footprint and impacts of impervious cover with highest hydraulic connectivity. Retrofits smaller widths to correct for roads installed under older code requirements.

Same as Impervious Cover Removal. Also provides traffic calming benefit (traffic slows with narrower roads) and, combined with tree plantings, increased shading and aesthetics along roads.

Will be resisted by those who want to maintain current traffic speeds--traffic will be slowed, esp. when two cars parked on either side of road. Will require extended construction: invasive process will be rejected by some.

Develop prioritization system (steep slopes, citizen complaints about traffic, etc.). Ensure neighborhood support; confer with Traffic Calming program. Use Transfer of Development Rights (TDR) mechanism to pay for using private projects & funding.

Convert curb & gutter to bioretention & swales; impervious cover removal; compost amendments; site regrading; vegetative filter strips; bioretention; alternative paving systems; reforestation.

TABLE 2INVENTORY OF LOW IMPACT DEVELOPMENT SOLUTIONS

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Solution Type/Component Description How It Works Benefits Provided Concerns Comments Related Solutions


11. Retrofitting City's Landscape Ordinance Into Parking Lots, etc.

Subset of Impervious Cover Removal: retrofit highly impervious parking lots with landscape islands with bioretention filtration.

Lowers imperviousness, provides retention for impervious cover with highest hydraulic connectivity.

Promotes water retention, infiltration, & baseflow; lowers runoff. Filters, traps, & neutralizes some types of pollutants. Lowers temperature and "urban heat island" effects. Provides aesthetics.

Requires cooperation by, cost to private landowners; invasive process will be rejected by some; difficult if parking availability is tight & compromised by loss of spaces for landscaping. Need sufficient gradient to drain system.

Would be on private property; landscaping agreed to be permanent feature of site; use bioretention in landscaped areas.

Site regrading; IC removal; compost amendments; bioretention; rainwater harvesting [for irrigation].

12. Impervious Cover Disconnections

Redirect water currently flowing from roads and parking areas directly to storm drain systems; allow to pass over pervious surfaces to infiltrate.

Similar to Rooftop Disconnections except targets asphalt and concrete. Runoff allowed to infiltrate into pervious areas which otherwise would run off in the storm drain system.


May be difficult to retrofit areas on steep slopes for fear of erosion and scour, potential for localized flooding.

Prioritize by connectivity of IC & proximity to waterways; find easiest, lowest cost solutions first.

Site regrading; compost amendments; bioretention.

13. Convert Curb & Gutter to Open Drainage

Remove existing curb & gutter road drainage and replace with open drainage (swales, vegetative filter strips, etc.).

Open drainage allows infiltration, slows runoff speeds & lowers downstream impacts. Closed drainage prevents infiltration, speeds runoff & increases downstream impacts.

Promotes water retention, infiltration, & baseflow; lowers runoff. Filters, traps, & neutralizes some types of pollutants.

Will be resisted by those who want to maintain existing aesthetic look of curbs; will likely have to be combined with narrower road widths to ensure sufficient space for swales (see concerns for "Retrofit Smart Growth Road Dimensions" above).

Could create a demonstration project to show how works, could be aesthetic; create a positive Hill Country connection with the design: "belongs in this place."

Impervious cover disconnections.

14. Pervious Concrete Curb & Gutter Systems [Ecocreto]

Replace existing curb & gutter road drainage with pervious concrete (e.g., Ecocreto) substitute.

Provides method between open drainage and conventional curb & gutter to promote infiltration without affecting road footprint.

Promotes water retention, infiltration, & baseflow; lowers runoff. Filters, traps, & neutralizes some types of pollutants.

Will require extended construction: invasive process will be rejected by some. May be difficult to retrofit areas on steep slopes: water may run off rather than infiltrate. Has potential to clog & will require street sweeping to maintain.

May require an underdrain system. Site specific due to gravity flow requirements.

Impervious cover disconnections.

15. Bioretention/Rain Gardens

Filtration device installed in landscaped area used to retain and filter water. Installed in pervious right-of-way or in road in chicanes, curb extensions or other traffic calming measures.

Provides retention and filtration of runoff. Water ponds on surface briefly after storm for greater storage. Similar to sand filter except uses soil & vegetation for more dynamic filtration medium. Presence of roots & high level of biological activity may help maintain infiltration ability, increase pollutant removal efficiency.

Promotes water retention, infiltration, & baseflow; lowers runoff. Filters, traps, & neutralizes some types of pollutants. Provides aesthetics.

Will likely require localized narrowing of road widths to locate facility (see concerns for "Retrofit Smart Growth Road Dimensions" above). Will be resisted by those who want to maintain current traffic speeds--traffic may be slowed. May be difficult to retrofit areas on steep slopes: water may run off rather than infiltrate.

Rain gardens are the residential equivalent of bioretention.

Site regrading; compost amendments; reforestation.

16. Vegetative Filter Strips Grassed area with level spreader to redirect channelized flows into laminar flow over pervious area for infiltration.

Runoff allowed to infiltrate into pervious areas which otherwise would run off as channelized flow.

Promotes water retention, infiltration, & baseflow; lowers runoff.

Must have cooperation of land owner; must also ensure that the new land use does not compact the soil and impede infiltration of runoff.

Integral component of many other LID solutions.

Site regrading; impervious cover removal; convert curb & gutter; compost amendments.

17. Infiltration Trenches Rock-filled trench designed to store and infiltrate runoff into the surrounding soil.

Zero-discharge design provides retention of runoff. Water ponds on surface briefly after storm for greater storage. Water migrates into adjacent native soil; helps site mimic natural hydrologic regimen.

Promotes water retention, infiltration, & baseflow; lowers runoff.

Has had problems with clogging of storagechamber. Provision of vegetative filter strip pretreatment is critical; probably best to substitute bioretention (plant roots in media provide dynamic, living counter to clogging) for infiltration trenches (largely inert media).

18. Pervious Concrete Road and Parking Systems [Ecocreto]

Replace existing road and parking lot pavement with pervious concrete (e.g., Ecocreto) substitute. Could be done for entire road or just the parking lane portion.

Allows infiltration, slows runoff speeds & lowers downstream impacts. Can be designed for zero-discharge or using an underdrain; helps impervious area mimic natural hydrologic regimen.

Promotes water retention, infiltration, & baseflow; lowers runoff. Lowers temperature and "urban heat island" effects. Lowers road noise from tires.

Will require extended construction: invasive process will be rejected by some. May be difficult to retrofit areas on steep slopes: water may run off rather than infiltrate. Has potential to clog & will require street sweeping to maintain.

Impervious cover removal.

19. Trail Repair Repair eroded or poorly designed trails.

Runoff from damaged or poorly designed trails redirected to stabilized areas and reduce erosion.

Lowers runoff. Reduces sediment load to waterways. Public education provided if done by volunteers.

Few concerns. May only address small, localized problems.

20. Daylight Storm Sewer Systems

Remove existing enclosed storm drain systems and replace with open swale or creek drainage systems; stabilize with vegetation, reinforce earth systems, etc.

Open creek systems and drainageways allow infiltration, slower runoff speeds & provide riparian habitat. Closed pipe drainage prevents infiltration, speeds runoff, increases downstream impacts, and provides no beneficial habitat.

Promotes infiltration. Restores habitat and creek function. Improves aesthetics. Public education from converting hidden, damaging infrastructure to a visible, functional one.

Will be resisted by those who want to maintain existing aesthetic look of subsurface drainage and/or do not like open drainage & water habitat. Will requireextended construction: invasive process will be rejected by some.

May be difficult to find extensive systems or significant runs of pipe in a watershed with steep topography. Outfall Protection (below) may be a better solution in most cases.

Erosion protection/detention at end of outfalls.

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Solution Type/Component Description How It Works Benefits Provided Concerns Comments Related Solutions


21. Erosion Protection at End of Outfalls

Provide energy dissipation and stabilization for untreated storm drain outfalls currently causing erosion. Could involve daylighting a pipe earlier (short of creek) to route over land for treatment.

Existing storm drain outfalls may discharge directly and uncontrolled energy into waterways, causing erosion and scour. Retrofitting can reduce these impacts.

Reduces erosion and scour. Protects riparian vegetation and habitat. Improves aesthetics.

Few concerns. May only address small, localized problems.

Bioretention; site regrading; compost amendments, reforestation.

22. Concrete Channel-Lining Removal; Replace with Natural Treatment

Remove concrete channel lining and replace with more natural equivalent, e.g., reinforced earth.

Similar to Daylight Storm Sewer Systems except targets open channels with hard armoring rather than enclosed storm drain pipes. Provides a more natural look, greater resilience, and fewer negative effects downstream.

Promotes infiltration, restores habitat and channel function. Improves aesthetics.

Will be resisted by those who want to maintain existing aesthetic look of hard lining of waterway (looks "less controlled").

Storm sewer daylighting; erosion protection/detention at end of outfalls.

23. Channel Protection and Stabilization with Natural Treatment

Remove concrete channel lining and replace with more natural equivalent, e.g., reinforced earth.

Same as above except no existing armoring to remove.

Same as above. Few concerns. Storm sewer daylighting; erosion protection/detention at end of outfalls.

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3.0 PUBLIC EDUCATION AND LID

LID solutions fundamentally affect small parcels of land distributed throughout a watershed. The vast majority of this developed property is privately owned and maintained. While publicly owned lands can and should be used for demonstration projects for public outreach, it is on these privately held lands that the fate of the watershed will rest. If effective practices can be used throughout the watershed to reduce runoff and pollutant loads, then the community’s goals can be achieved to preserve and protect the integrity of the watershed. If the hydrologic performance of these private lands remain essentially as it is today — i.e., like those of conventional urbanized areas throughout Austin, the watershed will continue to experience problems associated with a level of development and imperviousness well in excess of the goal condition of 5% impervious cover.

A number of barriers exist to the systematic implementation of LID practices. Many citizens living within Bull Creek may not recognize (or agree with!) the following:

• That water quality problems harm property values, wildlife, drinking water, aesthetics, and the long-term sustainability of natural and human communities.

• That a water quality problem exists in Bull Creek due to past and present development.

• That land use patterns and daily actions of the watershed’s inhabitants contributes to the problem.

• That LID solutions can be retrofitted and changes in behavior made to address these problems on a site-by-site basis.

• That technical and design resources (how-to manuals, brochures, demonstration projects, design workshops, etc., developed by the COA, citizens groups, etc.) are (can be made?) available to implement these practices.

• That financial resources to implement these practices should be made available by the COA through seed money and/or are worthy of being considered an investment by individual land owners.

• That improvements made by LID controls need to be maintained into the future to ensure that they function as designed and installed.

All of these themes are contingent upon an educated population which understands the issues and appreciates the value of protecting the watershed resource upon which they live and work. This points to the paramount importance of public education to provide a transition from the current lack of knowledge of these themes to one in which the daily actions of citizens and the design and function of the physical development in the watershed serve to preserve and protect the quality of this resource.

4.0 BENEFITS ASSESSMENT OF LID SOLUTIONS.

4.1 WATER QUALITY BENEFITS CONSIDERED

Water quality benefits for LID solutions were assessed for the following four groups of concerns:

Factor Model Parameters Purpose of Parameter Surface Water Hydrology

Average Annual Runoff Volume discharged from Site

Overall indicator of hydrologic impacts

Average Annual TSS Load discharged from Site

Overall indicator of sediment and turbidity impacts

Average Annual Uplands COD Load discharged from Site

Overall indicator of organics and toxic impacts

Surface Water Quality

Average Annual Uplands TN Load discharged from Site

Overall indicator of nutrient impacts

Groundwater Quantity

Average Annual Baseflow Volume produced from Site

Indicator of base flow, and thus spring flow and recharge volumes

Groundwater Quality

Qualitative approach: specify solutions which control Nitrate-Nitrogen (NO3)

Indicator of NO3 impacts to springs, salamanders, etc.

4.1.1 Surface Water Hydrology

Surface water hydrology deals with the interaction of precipitation — virtually all of it rainfall in Austin — on the land surface. As previously discussed, urbanization imposes impervious surfaces on the land which hinders infiltration of runoff into the soil and increase surface runoff to levels far above those of natural conditions. Addressing these fundamental changes in surface water hydrology presents the central challenge of water quality retrofits in Bull Creek. In large part, the other three important factors —surface water quality, groundwater quantity and quality — all react to the positive or negative forces created by surface runoff. Improvements in surface water hydrology therefore must precede and accompany improvements in these other factors. Moderation of surface water hydrology is also central to LID solutions, which focus primarily on infiltration and mimicking of the natural hydrologic cycle. The relationship between impervious cover and surface water quantity has been extensively monitored in Austin and is relatively well understood. This report uses the mathematical formulas developed by the COA and the LH-Hydro spreadsheet model to calculate Average Annual Runoff Volume.

4.1.2 Surface Water Quality

Surface water quality is partly a function of surface water hydrology. A large portion of pollutant loads are driven by water quantity: for many parameters, the proportion of a given pollutant in runoff (as expressed by Event Mean Concentrations) does not vary to a large degree whether there is little (low imperviousness) or a lot (high imperviousness) of runoff; but the fact that significant more runoff comes off of more highly impervious areas means that these areas will have dramatically higher pollutant loads than those with lower impervious levels. However, water quality is not merely a direct corollary of water

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quantity. Additional source controls are also needed, such as fertilizer, herbicide, and pesticide reductions. These types of pollutants come not merely from increases in runoff but from the increased presence of these substances in the environment due to their use in day-to-day activities, such as landscaping and automobile use. Most LID solutions improve surface water quality as well as correct surface water quantity via infiltration. The relationship between impervious cover and pollutant concentrations for various parameters has also been extensively monitored in Austin. This report uses the mathematical formulas developed from COA data (Barrett et al., 1998) to calculate loads for Total Suspended Solids (TSS), Chemical Oxygen Demand (COD), and Total Nitrogen (TN). See Section 2.2.2 of the Bull and West Bull Creek Watershed Management Study (PBS&J, 2003) for a more complete description of these pollutants.

4.1.3 Groundwater Quantity

Groundwater quantity is largely a function of surface water hydrology and location of recharge features. In the undeveloped portions of Bull Creek, the groundwater quantity is significant and robust; much of the headwaters of the watershed lies in the Northern Edwards Aquifer geologic formation. Water infiltrating these karst features serves to recharge innumerable small and large springs and feed the baseflow (groundwater) of the creek. In urbanized areas, the imposition of impervious cover limits the amount of water which can infiltrate into these recharge features and groundwater quantity, as expressed in baseflow, decreases. LID solutions can improve this situation by augmenting infiltration and consequent recharge and baseflow quantity. The relationship between impervious cover and baseflow quantity has also been monitored in Austin. This report uses the mathematical formulas developed by the COA to calculate Average Annual Baseflow Volume.

4.1.4 Groundwater Quality

Groundwater quality is a function of the cleanliness of infiltrating surface waters, relative location of recharge features, and type and depth of intervening soils (if any), and other means of pollutant removal (e.g., structural controls). Due to the complexity of these many interactions, groundwater quality is difficult to monitor and model. Presently, there are no available mathematical relationships for use to estimate quality levels for the various parameters tracked. This is unfortunate in that groundwater quality is a critical element in the maintenance of stream health in most systems, and especially in Bull Creek, which depends heavily on springflow. If water quality solutions are implemented which increase quantity but not quality of baseflow, the various aquatic communities dependent upon this springflow (e.g., the Jollyville salamander) may be negatively impacted. The key will likely be to ensure some minimum level of treatment of surface waters prior to their conversion to baseflow to conservatively assume that they will contribute, rather than hinder, stream health. Some pollutants, such as nitrates and pesticides, are so soluble that they are difficult to remove, even with a generous layer of intervening topsoil to provide treatment. Therefore, as with solutions to address surface water quality, source controls for fertilizers, pesticides will likely be necessary to protect groundwater quality. LID controls are a promising solution

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to this problem in that we will not be able to rely on end-of-the-pipe solutions to filter out these pollutants.

4.2 MODELING RESULTS FOR LID SOLUTIONS

An effort was made to quantify all LID solutions where possible in order to estimate their effectiveness relative to each other and to the goals established for the watershed. Table 3 shows which of the solutions were mathematically quantified and explanations where such quantification was not possible or desirable. In many cases, individual solutions were deemed components of larger strategies (e.g., terracing is a subset of bioretention or soil amendments) and/or defy reasonable quantification (e.g., trail repair). Eleven LID solutions, plus the goal condition and existing developed condition scenarios, were modeled.

TABLE 3

ESTIMATING THE BENEFITS OF LOW-IMPACT DEVELOPMENT (LID) SOLUTIONS

Solution Type/Component Comments Solutions Quantified with Model

1. Rainwater Harvesting System: Tank Storage Modeled. 2. Rainwater Harvesting System: Rain Barrels Modeled. 3. Rooftop Disconnections Modeled. 4. Compost Amendments for Pervious Areas Modeled. 5. Retrofit Smart Growth Road Dimensions Modeled. 6. Impervious Cover Disconnections Modeled. 7. Pervious Concrete Curb and Gutter Systems Modeled. 8. Bioretention/Rain Gardens Modeled as separate Bioretention (for streets)

and Rain Gardens (for lawns) options. 9. Pervious Concrete Road and Parking Systems Modeled.

10. Convert Curb and Gutter to Open Drainage Modeled as part of SEA Streets option (with bioretention and retrofit Smart Growth streets).

Solutions NOT Quantified 11. Green Roof Similar to Rain Harvesting. 12. Site Regrading/Terracing Component of others (e.g., compost

amendments, rain gardens). 13. IPM and Xeriscape Demonstration Landscaping See above. 14. Reforestation See above. 15. Impervious Cover Removal Similar to Retrofit Smart Growth Road

Dimensions. 16. Retrofitting COA’s Landscape Ordinance Into

Parking Lots, etc. Similar to Bioretention/Rain Gardens.

17. Vegetative Filter Strips Similar to rain gardens, compost amendments. 18. Infiltration Trenches Similar to bioretention. 19. Trail Repair Not a large-scale problem in Bull Creek

compared to urbanization. 20. Daylight Storm Sewer Systems Site-specific; limited opportunities in Bull Creek.21. Erosion Protection at End of Outfalls Site-specific; difficult to calculate/model benefits.

LID usually done higher in watershed. 22. Concrete Channel-Lining Removal; Replace with

Natural Treatment See above.

23. Channel Protection and Stabilization with Natural Treatment

See above.

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4.2.1 Analysis Approach

As noted above, the following five factors were tracked quantitatively for each solution on each site and compared with both the goal condition (5% IC) and the existing condition: runoff volume, TSS load, COD load, TN load, and baseflow volume. Pollutant loads were calculated as a function of runoff volume and pollutant concentrations.

Runoff Volume (Storm Flow) Estimation. Runoff volumes were calculated on an average annual basis using the “LH-Hydro” spreadsheet model. The following regression formula, based on COA monitoring data, directly correlates runoff to impervious cover:

Runoff Coefficient (percent of rainfall) = 0.3428*(IC percent)2 + 0.5677*IC percent + 0.0125

LH-Hydro was calibrated to this formula, and the outputs (runoff coefficients) generated for like impervious cover levels were very close in all cases. Both methods can be used to calculate average annual runoff volumes. LH-Hydro is based upon long-term historic data for a range of storm sizes and frequencies and can be adjusted not only for different impervious cover scenarios (like the regression formula) but also for different CN values and can calculate the benefits of constructing BMPs (e.g., detention and retention facilities) with differing capture depths.

Load Quantity Estimation. Pollutant loads for TSS, COD, and TN were calculated using relationships between impervious cover and mean pollutant concentrations. These regression formulas were developed by the COA based upon long-term modeling data.

TSS = 80 milligrams per liter (mg/L) for undeveloped lands (e.g., <= 5% impervious cover)

= 170 mg/L for developed lands

COD = 18.254+(97.72*IC percent) mg/L

TN = NO3 + TKN, where

NO3 = 0.82 mg/L

TKN = 0.6852+(1.4104*IC percent) mg/L

Average annual loads were derived as follows:

Load (lbs/yr) = drainage area x rainfall (32.5 in/yr) x runoff fraction (see below) x concentration (mg/L) x conversion factor (0.2267). Where:

Runoff fraction = Annual runoff volume (ac-ft/year, from LH-Hydro analysis) / (annual precipitation [32.5 in.] x drainage area (ac) / 12 inches)

Most LID solutions reduce the total quantity of runoff from a site and hence lower the associated pollutant loads carried by this runoff. In the cases of bioretention and porous pavement, the direct removal (filtration) of pollutants from runoff was also modeled (see discussion below for individual solutions).

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Baseflow Volume Estimation. Baseflow quantities from a given site were first calculated according to its overall impervious cover using the following equation determined by the COA:

Baseflow (percent of rainfall) = 0.0645−(0.1264*IC percent)

Note that this equation yields negative flows for sites with impervious cover in excess of 51%. In these cases, the baseflow was assumed to be zero (0).

Additional baseflow augmentation was credited for solutions which reduced storm flow volumes from existing levels. Some portion of this converted stormflow will be converted to baseflow (and the rest converted to evapotranspiration, etc.). The following formula was used to calculate this baseflow quantity:

Baseflow (percent of rainfall) = (0.0645−0.1264*5%) x (net decrease in storm flow)

This equation assumes that water prevented from becoming storm flow (the net decrease in storm flow) will stay on site and be converted to baseflow in the same proportion as it would on an undeveloped site (i.e., 5% impervious cover in this analysis). This assumption enables the benefits to baseflow to be accounted on sites who’s hydrologic properties have been improved by LID solutions (e.g., infiltration is encouraged with impervious cover disconnections or better soils) but who’s impervious cover remains unchanged. (Otherwise, the baseflow volume from the site would be assumed to remain unchanged as well, despite the implementation of the solution.)

Progress in Achieving Goals. The modeling results for runoff volume, TSS load, COD load, TN load, and baseflow volume were compared for each solution against both the goal condition (5% impervious cover) and the existing condition (buildout condition) to yield the degree of progress toward the goal condition. For example, the average annual runoff volume for a given tract of land was calculated to be 10 acre-feet per year for the goal condition, 100 acre-feet per year for the existing condition, and 50 acre-feet per year for “Solution A.” Solution A therefore brings the tract “back” toward the goal condition as follows:

1 – (solution volume – goal volume) thus 1 – (50 – 10) = 55.5% (existing volume – goal volume) (100 – 10) toward goal

Thus this hypothetical solution enabled this tract of land to go from 100 to 50 acre-feet, a lowering of 50 acre-feet, making the runoff 55.5% “better” (toward the goal) than it would have been without the control.

4.2.2 Land Use Data and Watershed Characteristics

The LID Conceptual Design methodology outlined above is structured to evaluate the efficacy of implementing LID solutions over large areas. It is a screening tool for subsequent individual, site-specific solutions. Thus, it shows whether it might be more effective to use one type of LID solution versus

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another (or a combination of solutions) for a given land use. Once the most effective solutions are identified, they may then be subjected to the rigors of a more site-specific analysis. These analyses are presented as individual Conceptual Designs.

A large variety and mixture of land uses exist in the Bull Creek watershed. The following table summarizes land use in the basin:

TABLE 4

PERCENT OF BULL CREEK WATERSHED AREA BY LAND USE

Land Use Percent of Watershed

Impervious-ness

Open space, preserve, undeveloped 50.6% None Single Family Residential (“SFR”) 29.8% Medium Transportation (“Road”) 8.5% High Commercial and Office (“Com”) 4.7% High Multifamily Residential (“MFR”) 4.3% High Industrial Park (“Ind”) 1.0% Medium Civic 0.9% Medium Other 0.1% Low Totals 100.0% Source[JMH1]: City of Austin GIS land use data, 2000.

Park and preserve land uses have minimal or no impervious cover and meet the goal of 5% impervious cover. Some LID projects could be envisioned for parks, but these, on the whole, would likely be demonstration type projects and would not be focused on the main contributing factors to water quality degradation. Few undeveloped lands remain in the watershed; these presently have (presumably) low imperviousness.

Single family residential represents the single largest developed land use. Note that a significant percentage of the transportation use (primarily road right-of-way) is located within single family subdivisions. Multifamily, commercial, office, industrial, and civic uses all have relatively high imperviousness and can contribute locally to water quality problems, though these uses are much less extensive than single family residential lands.

An analysis of watershed land use and impervious cover GIS information found a relationship between impervious cover from roofs vs. pavement (parking lots and roads) to be roughly equal in area. An additional portion of each site was deemed to be impervious according to a COA corrective function to account for sidewalks, driveways, and other features not represented in the GIS file. Using these relationships, the following generalizations for each land use pattern by impervious cover:

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TABLE 5

IMPERVIOUS COVER COMPONENT PERCENTAGES BY LAND USE

Impervious Cover Site

Totals Roads Roofs Other* Typical Land Use 20% 8.6% 8.6% 2.9% SFR, Civic 40% 17.1% 17.1% 5.7% SFR, Civic, Com, MFR, Ind 60% 25.7% 25.7% 8.5% Com, MFR, Ind 80% 36.4% 36.4% 7.2% Road

* Driveways, sidewalks, etc.

Land uses vary considerably in terms of impervious cover. The above table presents a range of impervious cover rather than attempt to assign one impervious cover value to each land use type. For example, single family residential subdivisions were typically found to have impervious cover levels between 20 and 40%, and this range of values is included in the analysis.

4.2.3 LID Solution Scenarios Modeled

The following 13 scenarios were modeled for goal condition, existing condition, and 11 LID solutions for each of the four impervious cover levels shown in the table above:

1. Goal Condition (5% IC)

2. Existing Condition

3. Rainwater Tanks (large tanks)

4. Rainwater Barrels (2 x 75 gallons each)

5. Rooftop Disconnections

6. Compost Soil Amendments for Pervious Areas

7. Rain Gardens (Bioretention) for Non-Road Impervious Areas


9. Impervious Cover (Road) Disconnections

10. Bioretention for Streets

11. Porous Pavement Roadway

12. Porous Curb and Gutter

13. “SEA Streets” Equivalent (using SOS capture depth)

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4.2.4 Modeling Methods and Assumptions

Various inputs and assumptions were necessary to model each of the scenarios. The sections below discuss the details of each scenario.

4.2.4.1 Goal Condition (5% IC)

Method: Used LH-Hydro to estimate average annual runoff for all tracts assuming 5% impervious cover. Some tracts are currently below 5% impervious cover and are expected to remain in this condition (e.g., park and preserve lands) and thus the actual percent impervious cover was assumed in these cases.

4.2.4.2 Existing Condition

Method: Used LH-Hydro to estimate average annual runoff for all tracts impervious cover derived from GIS or from extrapolations for buildout condition.

4.2.4.3 Rainwater Tanks

Method: Used GIS to count number of roofs (or extrapolated number using buildout assumptions). Used GIS to determine total roof area of buildings (roofs were distinguished from paved impervious areas). Assumed a tank volume in gallons equivalent to the square footage of roofs (e.g., 2,000-gallon tank for a 2,000-foot2 roof). The size of the irrigated area was assumed to be equal to the roof area of the house, both in square feet; this is conservative in that most yards are larger than the house footprint (although many systems may not irrigate both front and backyards). The maximum depth of irrigation was assumed to be 1.0 inch (typical landscaping guideline); obviously, if not enough water was available to irrigate, only that amount was used. A 5-day period following rainfall events of 0.5 inch rain or greater was assumed. The percentage of total annual rainfall to roof captured in system was calculated using a 45-year daily Austin rainfall record using the above assumptions. One-hundred percent of the site’s roof area was assumed to be retrofitted with rain harvest to show maximum impact — lesser percentages could also be envisioned (and are in fact more likely in practice). A de facto percentage impervious cover of the site was calculated by subtracting out any portion of roof imperviousness captured in the tank; thus, if the long-term simulation showed 60% of water being stored in the tank (and not lost to overflow), then 60% of the roof area was assumed to act as pervious cover and the total imperviousness for the site was recalculated accordingly. (An argument could be made that this portion of land should be subtracted from the land area entirely and not just declared pervious; for the sake of simplicity, this approach was not used. The accepted method is slightly more conservative.) The total runoff volume (ac-ft/yr) was then calculated using this de facto impervious cover level using LH-Hydro.

4.2.4.4 Rainwater Barrels (2 x 75 gallons each)

Method: Used identical assumptions and methods as used for rainwater harvesting, except the tanks were assumed to be two 75-gallon tanks for a total storage volume of 150 gallons. These barrels are the same as

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those used in the existing COA water conservation program. Obviously, for the more impervious sites (e.g., 80% impervious), there would likely be a much greater roof area than, say, the 20% impervious site and could therefore have more than two rain barrels for better effect. However, for consistency and simplicity, the same number of barrels was calculated for all modeling runs.

4.2.4.5 Rooftop Disconnections

Method: Used a technique from the Prince George’s County LID manual (Prince George’s County, 1999) for estimating the benefits of disconnecting impervious cover. The percentage of roofs disconnected prior to program assumed to be 90%, based upon Glenrose Engineering field work (most roofs were already largely disconnected). One-hundred percent of presently connected roof surfaces were assumed to be disconnected to gage the maximum potential impact. The additional percentage disconnected impervious cover was calculated by taking the current area of roof x the percent presently disconnected x percent disconnected by program divided by the total site imperviousness. The following steps were used:

• Calculate composite pervious CN (CN value) equation used in LH-Hydro for pervious areas at this impervious level

• Calculate percent of impervious site area (percent) (from GIS data)

• Calculate composite CN after disconnection (CN value) (using Prince George’s County method ratioing the above factors)

• Calculate composite pervious CN after disconnection (CN value) (math)

• Derive percentage CN value lowered through effort (percent) (math)

• Calculate total runoff volume (ac-ft/yr) with LH-Hydro using user-entered, lowered CN value for pervious area

4.2.4.6 Compost Soil Amendments for Pervious Areas

Method: The percent of total pervious area of each site amended with compost was assumed to be 100% to test the maximum effectiveness of this technique. (In practice, this high percentage might be difficult to achieve.) Few data nationally and no data locally were available to predict the decrease in runoff volume following the application of compost amendments. But the studies performed have documented a decrease in total runoff volume due to the increase in on-site storage in soil retention from the improved soil profile with compost amendments. Snohomish County in Washington state estimated a 17% decrease in total runoff volume from pervious areas following application of soil amendment for “conventional lawn” areas. Runoff volumes for existing conditions (see above) were therefore reduced by 17% proportionate to their percent perviousness.

440616/030329 4-9


4.2.4.7 Rain Gardens (Bioretention) for Non-Road Impervious Areas

Method: Rain gardens are the residential equivalent of bioretention systems. Rain gardens were assumed to serve the drainage area of all non-road impervious cover, i.e., roofs, sidewalks, and driveways. This area was reduced by 10% to reflect the fact that some impervious features will likely be down-slope of retrofitted rain gardens, such as sidewalks adjacent to roads with no intervening pervious cover for infiltration. The drainage area of the rain garden was calculated by adding the assumed impervious areas served and the rain garden footprint area. The total imperviousness of the rain garden area was calculated from the impervious area served and the pervious rain garden area. The capture depth for the facility was assumed to be 1.3 inches over all roof, sidewalk, and driveway areas (including those not served due to being downslope, i.e., the facilities were oversized to treat all impervious areas at 1.3 inches). A 1.3-inch capture depth is that required by the COA in Water Supply Suburban watersheds like Bull Creek for 100% impervious cover. The Water Quality Volume in cubic feet was calculated as 1.3 inches x impervious drainage area.

The size of facilities was calculated to ensure that they would physically fit on the site. This sizing method was taken from Claytor and Schueler’s Design of Stormwater Filtering Systems (1996). The planting soil depth (feet) was assumed to be 1.5 feet with no underdrain. The coefficient of permeability for planting soil bed was assumed to be 0.06 feet per day, which is typical for the tight clay soils native to the area. The average ponded depth over the rain garden basin was 3 inches, based on an assumed 6-inch maximum depth. A maximum time of 72 hours required for the Water Quality Volume to filter through the planting soil bed was imposed (reflects maximum time allowed by COA ECM for structural controls). The surface area of the bioretention planting bed was calculated in square feet and acres. The pond footprint as percentage of the total drainage area of the site and of the total pervious area of the site were also calculated (provided for comparison). The pond area was limited to no greater than the pervious area of the site. The total runoff volume from the rain garden drainage area was calculated using LH-Hydro. The percentage of total runoff volume from the drainage area captured in the rain garden BMP was calculated using LH-Hydro. The total volume of runoff to BMPs was thus calculated. One-hundred percent of the captured runoff was subtracted from the total site runoff since the facilities were to be designed with no underdrains (all water will infiltrate or evaporate).

4.2.4.8 Retrofit Smart Growth Road Dimensions

Method: Alternatives to standard road widths have been proposed in many communities, including Austin, to reduce impervious cover and achieve other goals. One proposal developed by COA staff for the Smart Growth program recommended that developers be given the options of using the following alternative, narrower road widths as shown in the following table:

440616/030329 4-10


TABLE 6

SMART GROWTH ROAD WIDTH OPTIONS

Pavement Width (feet)

Street Classification Existing Proposed

Average Daily Traffic (trips/day)

Width Reduction

(feet) Percent Change

Local – SF-1 to SF-2 30 26 <1,000 4 -13% Local – SF-3 to SF-6 36 28 <1,000 8 -22% Local – Side Street n/a 20 <1,000 10 -33% Residential Collector 40 36 1000–2000 4 -10%

These recommendations indicate that at least a 10% reduction in total road width — and thus total road area — is possible using this alternative system. The existing roadway area of each site was therefore reduced by 10%. LH-Hydro was used to calculate the total runoff volume given this lowered site impervious cover level.

4.2.4.9 Impervious Cover (Road) Disconnections

Method: Impervious cover disconnection calculations were made using a method developed by Prince George’s County to adjust CN values to evaluate the effects of disconnections (Prince George’s County, 1999):

CNc = CNp + (Pimp / 100) x (98 − CNp) x (1 − 0.5R) Where: R = ratio of unconnected impervious area to total impervious area CNp = composite pervious CN Pimp = percent of impervious site area CNc = Composite CN

First, based on field observation, a percentage of roads disconnected prior to program was made. All areas above 20% impervious cover were assumed to have 100% hydraulically connected roadway pavement as they generally have curb and gutter drainage. For the 20% impervious cover scenario, only 50% of the roads were assumed to be hydraulically connected because many of these streets have open drainage (swales). One hundred percent of connected roadway imperviousness was assumed to be disconnected in this analysis to show maximum impact — lesser percentages could also be envisioned (and are in fact more likely in practice). The ratio of unconnected impervious area to total impervious area (R) was calculated.

For example if site imperviousness was 40% roads (all connected) and 60% roofs and sidewalks and all of the roads were disconnected, then 40% of the impervious cover would then be assumed to be disconnected. The composite pervious CN (CNp) was calculated from polynomial equations used in LH-Hydro for pervious areas by impervious cover level. (This is a critical input since with LH-Hydro, the impervious CN is always 98 and the pervious CN is calibrated such that annual runoff matched field data

440616/030329 4-11


for Austin runoff; by using a pervious CN lower than the default value, a lower annual runoff total will be calculated.) The Composite CN (CNc) and composite pervious CN (CNp) after disconnection were calculated per the formula presented above with the inputs noted above. This lowered composite pervious CN (CNp) value was then entered into LH-Hydro to calculate the total runoff volume with the disconnections.

4.2.4.10 Bioretention for Streets

Bioretention facilities for streets were sized to capture runoff from roads. Generally, the first and fastest runoff from a site is that of the directly connected impervious cover. In residential cases (over 70% of the development in Bull Creek), almost all of this connected imperviousness is from the roads. Therefore, bioretention facilities could be built to fill up with road runoff and then bypass all subsequent runoff (presumed to be from disconnected sources). To gain acceptance and limit cost, we wanted to keep the size (footprint) of the bioretention facilities small enough to fit in the existing right-of-way. (Other LID solutions were developed to treat this disconnected water.)

Method: 100% of roads were assumed to be retrofitted with bioretention to model maximum potential. The capture depth over the roadway drainage area was assumed to be 1.3 inches, which is the capture depth required by the COA in Water Supply Suburban watersheds like Bull Creek for 100% impervious cover. This yielded a water quality volume in cubic feet. However, the actual drainage area will likely be the entire site, so the capture volume designed for the road was calculated for the larger site drainage area to yield an adjusted (and lower) capture depth. Thus, on a 20% impervious site (with less than 10% roads), the 1.3 inches of capture for the roads resulted in about a 0.11-inch capture for the entire site. (The overall site capture depth increased as the impervious cover assumed from roadways increased. For example, in the 80% impervious cover scenario, 0.47 inches of runoff is captured over the entire site.)

The size of facilities was calculated to ensure that they would physically fit on the site. This sizing method was taken from Claytor and Schueler’s Design of Stormwater Filtering Systems (1996). The planting soil depth (feet) was assumed to be 1.5 feet underlain with 12 inches of gravel with underdrain pipe. The coefficient of permeability for planting soil bed was assumed to be 0.50 feet per day, which is that of a good quality sandy loam with compost. The average ponded depth over the facility was assumed to be 3 inches with a maximum depth of 6 inches. A maximum time of 72 hours required for the Water Quality Volume to filter through the planting soil bed was imposed (reflects maximum time allowed by COA ECM for structural controls). The surface area of the bioretention planting bed was calculated in square feet and acres. The pond footprint as percentage of the total drainage area of the site and of the total pervious area of the site were also calculated (provided for comparison). The total runoff volume from the drainage area was calculated using LH-Hydro. The percentage of total runoff volume captured in the bioretention facility was also calculated using LH-Hydro.

The percentage of captured runoff that was actually retained was assumed to be 13%. This number was calculated in a separate analysis of bioretention facilities using a long-term (40-year) daily rainfall record;

440616/030329 4-12


the analysis showed that about 13% of the water captured by the facilities was retained and removed via evapotranspiration or deep soil loss. The remaining 87% of the water entering the facility passes through the underdrain (some of it during the storm event). This is the same dynamic as is seen with conventional sand filter systems. But both bioretention and sand filters will capture and slow runoff in this process, serving to diminish the negative impacts on stream channels below, but this is a different and less positive outcome than actual infiltration.

The total runoff volume from the total site was then calculated, subtracting the portion retained by the bioretention facilities from the original, existing runoff volume. All pollutant loads entering the facility were reduced by the following percentages to reflect the pollutant removal performance of bioretention (U.S. Environmental Protection Agency (EPA), 1999a):

Bioretention Pollutant Removal Performance Total Suspended Solids (TSS) 90% Chemical Oxygen Demand (COD) 93%1 Total Nitrogen (TN) 68%2 1 Uses low end of range of metals removal = 93−98%. 2 Uses low end of TKN removal = 68−80%.

4.2.4.11 Porous Pavement Roadway

Method: Porous pavement systems for roadways were sized according to the available road area. The greater the amount of roadway, the greater the capture volume available for this system. All (100%) road surfaces were assumed to be retrofit with 50% porous pavement and 50% conventional pavement. The driving lanes (middle of the street) would thus continue to be conventional pavement with the parking lanes converted to porous pavement. This resulted in capture depths approaching those of the required by the COA for Water Supply Suburban watersheds like Bull Creek. A greater (maximum) impact could have been modeled by assuming that all surfaces were to be porous, but this was judged to be a much less likely scenario. Lesser percentages could of course also be modeled to predict lower levels of implementation.

A locally available porous pavement system (“Ecocreto”) was used as the model to develop water quality volume calculations. Other systems are available, but this system has been used in recent cases for parking lots in the Austin area and the authors of this report were familiar with its design. (Generic pollutant removal performance assumptions were used from EPA documents.) The surface area of porous pavement was determined as 50% of the roadway area. (Additional paved surfaces, like driveways, sidewalks, and parking lots could also be converted, but were not considered in this present analysis.) Ecocreto systems typically specify an 8-inch gravel bed overlain with 4 inches of Ecocreto permeable concrete. Given the areal extent, depths, and void space of 40% for gravel and 15% for Ecocreto, a storage volume was calculated. The storage volume was divided by the total site area to calculate a capture depth for the system. (The storage volume was also divided by the road area only for purposes of comparison. Like the bioretention system for roads, it is likely that the roadway porous pavement systems

440616/030329 4-13


will largely fill with road runoff before runoff from other sources like roofs and pervious areas reach them.)

The total runoff volume from the drainage area was calculated using LH-Hydro. The percentage of total runoff volume from the drainage area captured in the pavement system was calculated using LH-Hydro. The percentage of captured runoff and retained was assumed to be 100% since the facilities were to be designed with no underdrains (all water will infiltrate). The total runoff volume from the total site was then calculated, subtracting the portion retained by the porous pavement from the original, existing runoff volume calculated for the site. All pollutant loads entering the facility were reduced by the following percentages to reflect the pollutant removal performance of porous pavement (EPA, 1999b):

Porous Pavement Pollutant Removal Performance Total Suspended Solids (TSS) 82%1 Chemical Oxygen Demand (COD) 82%2 Total Nitrogen (TN) 80% 1 Uses low end of range of TSS removal = 82−95%. 2 Metals removal characterized as “high”. Assume COD removal = 82% (same as TSS). 3 Uses low end of TN removal = 80−85%.

4.2.4.12 Porous Curb and Gutter

Method: This system is identical to that of the porous pavement for roadways (above) except the percent of roadways converted to porous pavement is that of the curb and gutter system of the road. Two (each side of road) curb and gutters were each assumed to be 2-feet wide; for the standard 30-foot-wide roads in Bull Creek, this results in 13.3% of the total surface area. This was used in place of the larger surface area of the porous pavement for roads systems (above). It resulted in a capture volume about 27% of that of the porous pavement for roads systems.

4.2.4.13 “SEA Streets” Equivalent (using SOS capture depth)

Seattle Public Utilities (SPU) of the City of Seattle, Washington developed an innovative retrofit approach for an existing single family residential street. They called their solution the “Street Edge Alternative” (SEA) and drew upon multiple LID techniques. SPU removed a portion of the roadway width to make room for a series of bioretention basins and engineered swales in the public right-of-way. Runoff from up to the 2-year rainfall event is now contained almost entirely on site. In the first year of monitoring, the system reduced total annual runoff by an impressive 97% over historic levels.

For this report, we modeled an SEA Street solution. Such a solution would like involve the same group of solutions used in Seattle: narrowed road widths, bioretention, and open drainage swales. The object would be to capture and retain as much runoff as possible. For the model, the capture depth assumed was that of the COA’s SOS Ordinance, required for development in watersheds within the Barton Springs Zone. The capture depths developed for this ordinance were developed to capture a very large percentage of all

440616/030329 4-14


annual storms, well above the levels currently required in Bull Creek (a Water Supply Suburban watershed). The following table presents the SOS Ordinance level of capture — assumed to be the level of capture to approximate a SEA Streets type of solution — and that of the existing Bull Creek requirements (for comparison):

TABLE 7

SOS ORDINANCE LEVEL OF CAPTURE

Capture Depth (inches) Impervious

Cover SOS

OrdinanceWater Supply Suburban

(including Bull) 20% 0.96 0.50 40% 1.32 0.70 60% 1.68 0.90 80% 2.04 1.10

Modeling of the SEA Streets solution was performed identically to that for Rain Gardens (Bioretention) for Non-Road Impervious Areas (see above). Ponded depths over the bioretention areas were thus assumed to be a maximum of 6 inches and so forth. The SOS level capture volume was assumed over the entire contributing area (not just the yard, as with rain gardens, or for the road, as with street bioretention). All of the water which does not bypass the facilities is assumed to be retained and infiltrated. The performance of these systems thus mirrors that of the rain gardens, except the capture depths were much greater. The size of the facilities required under these assumptions ranges from about 5% of the site area for a 20% impervious site to about 10% of the site area for an 80% impervious site.

4.2.5 Modeling Results

The Challenge. Scenarios were modeled for developed parcels with 20, 40, 60, and 80% impervious cover. Using the formulas presented above, the changes in flows and loads were calculated. Figure 1 shows the results of this analysis. The challenge is clear. Runoff from 20% impervious cover is 3.6 times greater than the undeveloped goal condition (5% impervious cover). This more than doubles assuming 40% impervious cover and increases to over 17 times the volume of the goal condition for 80% impervious cover. This illustrates the dramatic increases in runoff caused by increases in impervious cover. And the increases in pollutant loads as a result are even more dramatic. Thus, especially for the higher levels of impervious cover, a great deal will have to be done to retrofit these properties such that they “act” as though they only have the goal condition of 5% imperviousness. Baseflow changes do not appear as dramatic in this figure, though they are actually equally striking — the chart scale does not bring out these differences as clearly. However, the data show that at 20% impervious cover, there is only 70% of the undeveloped baseflow (30% loss), up to 80% loss at 40% impervious cover, and effectively no baseflow at all by 60% impervious cover. This is the context in which LID solutions must be retrofit: large volumes of water and pollutants need to be retained and infiltrated into the soil in order to meet the goal conditions, especially at higher impervious levels.

440616/030329 4-15

Figure 1

440616\030329 4-16

Ratio of Developed Condition to Goal Condition at Various IC Levels

1 1 1 1 1 0.7

4.15.

97.6

3.6

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9.9

18.7

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Goal Condition

20% IC

40% IC

60% IC

80% IC


LID Solution Impacts. Figures 2–6 show the gains made by the ten LID solutions at each of the impervious cover levels examined for storm flow, Total Suspended Solids (sediment), Chemical Oxygen Demand (toxics), Total Nitrogen (nutrients), and base flow respectively. Table 8 shows the progress towards the goal condition for each of the scenarios at each impervious cover level. As expected, the higher the level of imperviousness, the farther from the goal the resulting condition remains.

Seven solutions made sizeable impacts to hydrology and loads for some or all levels of imperviousness:

1. Rainwater Tanks

2. Compost Soil Amendments

3. Rain Gardens


5. Pervious Roads

6. Pervious Curb and Gutter

7. “SEA Streets” with SOS Capture

Each is discussed below in order of greatest overall effectiveness:

The Street Edge Alternative (SEA) Streets solution had by far the most effective modeling results of all solutions modeled. The reason for this is simple: this solution assumes the greatest capture and retention of runoff. The impact of retrofitting SOS-level controls would be great. LH-Hydro calculated that 88 to 92% of all annual runoff volume would be captured and retained in these systems. These modeling results may be conservative (i.e., the capture percentage may in fact be even higher and more effective). Like all of the LID solutions here investigated, the SEA Streets scenario is theoretical and as yet not attempted in Austin. A great number of site-specific variables would have to be worked out to implement this solution. A major concern would be the availability and access of an area sufficiently large and hydrologically suitable (i.e., downgradient) for the bioretention and engineered swales. Utility conflicts would also likely be a financially onerous design constraint. However, these modeling results are also especially instructive in that they examine the potential benefits of retrofitting Austin’s most protective water quality ordinance in the sensitive Bull Creek Watershed. Essentially, this solution allows the goal condition to be achieved or nearly achieved (and, in a few cases for some parameters, even exceeded) for all impervious cover levels — even in the 80% impervious cover scenario.

Pervious roads scored well in all categories. The modeling assumptions used provided for a very large space for implementation — half of all roadways. This extensive surface provides a voluminous space for water storage below. This solution even made notable gains when implemented at the 10% level, meaning that only 1/20th of the street surfaces would be converted (½ of 10%). This indicates the possibility of using this solution in targeted areas with still-perceptible results. These findings are intuitive: with impervious cover driving the negative hydrologic changes and with a much reduced level of impervious cover as the goal, the conversion of the most hydraulically connected of these surfaces — the roads — to

440616/030329 4-17

Figure 2

440616\030329 4-18

Runoff Volume for Existing and Goal Condition and with 11 LID Solutionsfor Varying Levels of Impervious Cover

0.0

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Goal Condition20% IC40% IC60% IC80% IC

Figure 3

440616\030329 4-19

TSS Load for Existing and Goal Condition and with 11 LID Solutionsfor Varying Levels of Impervious Cover

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Figure 4

440616\030329 4-20

COD Load for Existing and Goal Condition and with 11 LID Solutionsfor Varying Levels of Impervious Cover

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dD

isco

nnec

tions

Rai

n Ba

rrels

Roo

ftop

Dis

conn

ectio

ns

Exis

ting

Con

ditio

nChe

mic

al O

xyge

n D

eman

d Lo

ad (l

bs/y

r) p

er A

cre

Dra

inag

e A

rea


Figure 5

440616\030329 4-21

Nitrogen Load for Existing and Goal Condition and with 11 LID Solutionsfor Varying Levels of Impervious Cover

0

2

4

6

8

10

12

14

16

18

20

Goa

l Con

ditio

n

SEA

Stre

ets

Equi

vale

nt

Rai

n G

arde

ns

Perv

ious

Roa

ds

Bior

eten

tion

for

Stre

ets

Perv

ious

Cur

b &

Gut

ter

Rai

nwat

er T

anks

Soil

Amen

dmen

ts

Nar

row

er R

oads

Roa

dD

isco

nnec

tions

Rai

n Ba

rrels

Roo

ftop

Dis

conn

ectio

ns

Exis

ting

Con

ditio

n

Tota

l Nitr

ogen

Loa

d (lb

s-ft/

yr) p

er A

cre

Dra

inag

e A

rea Goal Condition

20% IC40% IC60% IC80% IC

Figure 6

440616\030329 4-22

Baseflow Volume for Existing and Goal Condition and with 11 LID Solutionsfor Varying Levels of Impervious Cover

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

Goa

l Con

ditio

n

SEA

Stre

ets

Equi

vale

nt

Rai

n G

arde

ns

Rai

nwat

er T

anks

Soil

Amen

dmen

ts

Perv

ious

Roa

ds

Bior

eten

tion

for

Stre

ets

Nar

row

er R

oads

Perv

ious

Cur

b &

Gut

ter

Roa

dD

isco

nnec

tions

Rai

n Ba

rrels

Roo

ftop

Dis

conn

ectio

ns

Exis

ting

Con

ditio

n

Bas

eflo

w V

olum

e (a

c-ft/

yr) p

er A

cre

Dra

inag

e A

rea


TABLE 8

PERCENT TOWARD GOAL FOR LID SOLUTIONS UNDER VARIOUS IMPERVIOUS COVER LEVELS

Full Implementation 10% Implementation

SCENARIO / SOLUTION TYPE 20%

IC

40%

IC

60%

IC

80%

IC

20%

IC

40%

IC

60%

IC

80%

IC

Goa

l C

ondi

tion

PERCENT TOWARD GOAL CONDITIONRunoff Volume (ROV) (ac-ft)

Buildout Condition 100% 0% 0% 0% 0% 0% 0% 0% 0%Rainwater Tanks 100% 29% 30% 29% 29% 3% 3% 3% 3%Rainwater Barrels (2 x 75 gals. each) 100% 3% 4% 0% 0% 0% 0% 0% 0%Rooftop Disconnections 100% 1% 1% 3% 3% 0% 0% 0% 0%Compost Soil Amendments for Pervious Areas 100% 19% 12% 7% 4% 2% 1% 1% 0%Rain Gardens (Bioretention) for Non-Road Imperv 100% 73% 56% 49% 42% 18% 15% 13% 11%Retrofit Smart Growth Road Dimensions 100% 5% 6% 5% 7% 1% 1% 1% 1%Impervious Cover (Road) Disconnections 100% 4% 7% 6% 4% 0% 1% 1% 0%Bioretention for Streets 100% 8% 7% 7% 7% 2% 1% 1% 1%Porous Pavement Roadway 100% 71% 68% 67% 69% 18% 16% 14% 13%Porous Curb & Gutter 100% 37% 32% 30% 30% 6% 5% 4% 4%SEA Streets Equivalent (SOS capture depth) 100% 100% 100% 100% 98% 56% 43% 36% 32%

TSS Load (lb/yr)Buildout Condition 100% 0% 0% 0% 0% 0% 0% 0% 0%Rainwater Tanks 100% 24% 28% 27% 28% 2% 3% 3% 3%Rainwater Barrels (2 x 75 gals. each) 100% 3% 3% 0% 0% 0% 0% 0% 0%Rooftop Disconnections 100% 1% 1% 3% 3% 0% 0% 0% 0%Compost Soil Amendments for Pervious Areas 100% 16% 11% 7% 3% 2% 1% 1% 0%Rain Gardens (Bioretention) for Non-Road Imperv 100% 60% 52% 47% 40% 15% 14% 12% 11%Retrofit Smart Growth Road Dimensions 100% 4% 5% 5% 6% 0% 1% 1% 1%Impervious Cover (Road) Disconnections 100% 3% 6% 6% 4% 0% 1% 1% 0%Bioretention for Streets 100% 49% 51% 51% 52% 12% 11% 10% 10%Porous Pavement Roadway 100% 53% 56% 57% 59% 14% 14% 13% 12%Porous Curb & Gutter 100% 28% 28% 26% 26% 5% 4% 4% 4%SEA Streets Equivalent (SOS capture depth) 100% 100% 96% 95% 95% 47% 39% 34% 32%

COD Load (lb/yr)Buildout Condition 100% 0% 0% 0% 0% 0% 0% 0% 0%Rainwater Tanks 100% 25% 28% 27% 28% 2% 3% 3% 3%Rainwater Barrels (2 x 75 gals. each) 100% 3% 3% 0% 0% 0% 0% 0% 0%Rooftop Disconnections 100% 1% 1% 3% 3% 0% 0% 0% 0%Compost Soil Amendments for Pervious Areas 100% 16% 11% 7% 3% 2% 1% 1% 0%Rain Gardens (Bioretention) for Non-Road Imperv 100% 63% 51% 46% 40% 16% 13% 12% 10%Retrofit Smart Growth Road Dimensions 100% 5% 5% 5% 6% 0% 1% 1% 1%Impervious Cover (Road) Disconnections 100% 3% 6% 6% 4% 0% 1% 1% 0%Bioretention for Streets 100% 53% 52% 52% 53% 12% 11% 10% 10%Porous Pavement Roadway 100% 55% 56% 56% 58% 15% 13% 12% 12%Porous Curb & Gutter 100% 29% 27% 26% 26% 5% 4% 4% 4%SEA Streets Equivalent (SOS capture depth) 100% 100% 96% 94% 94% 49% 39% 34% 30%

TN Load (lb/yr)Buildout Condition 100% 0% 0% 0% 0% 0% 0% 0% 0%Rainwater Tanks 100% 27% 29% 28% 28% 3% 3% 3% 3%Rainwater Barrels (2 x 75 gals. each) 100% 3% 3% 0% 0% 0% 0% 0% 0%Rooftop Disconnections 100% 1% 1% 3% 3% 0% 0% 0% 0%Compost Soil Amendments for Pervious Areas 100% 18% 11% 7% 3% 2% 1% 1% 0%Rain Gardens (Bioretention) for Non-Road Imperv 100% 69% 54% 48% 40% 18% 14% 12% 11%Retrofit Smart Growth Road Dimensions 100% 5% 6% 5% 6% 1% 1% 1% 1%Impervious Cover (Road) Disconnections 100% 3% 6% 6% 4% 0% 1% 1% 0%Bioretention for Streets 100% 44% 42% 41% 41% 10% 9% 8% 8%Porous Pavement Roadway 100% 59% 57% 57% 57% 16% 14% 13% 12%Porous Curb & Gutter 100% 32% 28% 26% 26% 5% 4% 4% 4%SEA Streets Equivalent (SOS capture depth) 100% 100% 100% 97% 97% 54% 41% 35% 61%

Baseflow Volume (BFV ) (ac-ft/yr)Buildout Condition 100% 0% 0% 0% 0% 0% 0% 0% 0%Rainwater Tanks 100% 9% 10% 13% 19% 1% 1% 1% 2%Rainwater Barrels (2 x 75 gals. each) 100% 1% 1% 0% 0% 0% 0% 0% 0%Rooftop Disconnections 100% 0% 0% 1% 2% 0% 0% 0% 0%Compost Soil Amendments for Pervious Areas 100% 6% 4% 3% 2% 1% 0% 0% 0%Rain Gardens (Bioretention) for Non-Road Imperv 100% 23% 19% 21% 27% 6% 5% 6% 7%Retrofit Smart Growth Road Dimensions 100% 2% 2% 2% 4% 0% 0% 0% 0%Impervious Cover (Road) Disconnections 100% 1% 2% 3% 2% 0% 0% 0% 0%Bioretention for Streets 100% 2% 2% 3% 5% 1% 0% 1% 1%Porous Pavement Roadway 100% 3% 3% 4% 6% 1% 1% 1% 1%Porous Curb & Gutter 100% 1% 1% 2% 2% 0% 0% 0% 0%SEA Streets Equivalent (SOS capture depth) 100% 38% 35% 44% 64% 18% 14% 16% 21%

440616\030329 4-23


storage and recharge, directly corrects the problem. An assumption that all of the road surface be converted to pervious pavement (instead of just 50%) would have made this solution even more effective — probably without equal as a retrofit. The pervious curb and gutter option scored well — about half as well as the larger pervious roads scenarios — which is impressive given the relatively narrow footprint (although assumed to extend the entire length of all roads).

Bioretention for streets had good performance for storm flow abatement and very good performance for pollutant load reductions. The numbers for runoff are not quite as good as the other top five solutions due to the fact that these bioretention units were assumed to have very small footprints and have underdrains. This does not allow water to be stored long enough for a high level of infiltration. It will serve to slow water down considerably as runoff is made to flow through 2.5 feet of soil and gravel, but this still does not perform with the same effectiveness as those solutions which actually infiltrate captured water. If these facilities could be designed and built to be larger for longer retention times, their performance numbers would improve. The rain garden bioretention solution does infiltrate captured water into the soil and thus had among the best scores for all solutions. Alone among all of the solutions examined, they allow significant improvements to base flow volume (rain tanks did score reasonably well, too). This solution, as modeled, may double-count some benefits that pervious landscaped areas already provide, but it is also likely that the performance of many (if not most) pervious areas could be significantly improved. Many of the soils have been compacted and many of the roofs are so large that their discharge is likely concentrated and difficult to infiltrate rather than diffuse. Rain gardens offer a means to address these issues and could be combined effectively with rain tanks, rain barrels, roof disconnections, and soil amendments.

Rain tanks performed well, though lower than the pervious pavement and bioretention options. The tanks were only assumed to be as large (volume in gallons) as the roof area was big (in square feet). Thus, a 2,000 square foot roof was assumed to have a 2,000-gallon tank (and water a 2,000-square-foot area). All of these variables could be changed to result in a more effective system. The following table shows the effects of varying the tank size on the annual capture fraction; the modeled assumption is shaded:

TABLE 9

EFFECTS OF TANK SIZE ON ANNUAL CAPTURE FRACTION

Relationship between Tank and Roof Size

Percent Annual Roof Runoff Captured*

Tank gallons = 1/4 roof sq. ft. 21.7% Tank gallons = 1/2 roof sq. ft. 36.6% Tank gallons = 1 x roof sq. ft. 53.6% Tank gallons = 2 x roof sq. ft. 70.6% Tank gallons = 4 x roof sq. ft. 84.7% Tank gallons = 10 x roof sq. ft. 96.5% * Assumes irrigated area same size as roof.

440616/030329 4-24


Large tanks in Central Texas are not uncommon. In some areas west of town, land owners prefer to build rain capture systems rather than drill water wells and depend on this water for their daily needs. These systems can be as large as 15 to 20,000 gallons. However, with this option, it was always difficult to make assumptions to model performance and not somehow include assumptions which refer to its ability to be implemented. Thus, rather than assume an 8,000 gallon tank for a 2,000 square foot roof — a system which might be considered small for some rainwater enthusiasts — we just assumed a 2,000-gallon tank. The percent captured thus fell from what would have been 84.7% annual capture to just 53.6% capture. But it is difficult to imagine (at present) that homeowners are all going to install 8,000-gallon tanks on their homes. In a way, the assumption of smaller tanks somehow accounts for the fact that few people will install these tanks, but those who do might elect for larger sizes.

Compost soil amendments for pervious areas made a sizeable impact at the lower (20 and 40%) levels of imperviousness. For sites with greater imperviousness, this solution could not be implemented across so large an area and potential benefits drop off. Actual benefits in practice would depend on a wide array of factors unknowable at present for this modeling, such as the impacts in the Central Texas area (the data used was from the Pacific Northwest, which has very different rainfall patterns) and the areal extent and depth which landowners would add the compost topdressing. This strays into the territory of feasibility, which is discussed in a subsequent section.

Four solutions made modest or minimal impacts to hydrology and loads for all levels of imperviousness:

1. Rain Barrels


3. Narrower Roads

4. Road Disconnections

Rain barrels scored modestly for an intuitively obvious reason: when compared with typical roof areas, they are too small to capture a very large percentage of runoff. For a 2,000 square foot roof, two 75-gallon barrels were modeled to capture only about 7.6% of annual rainfall from the roof. The larger tanks considered for the rain tank solution (above) of course capture a much greater percentage. But while big tanks will not likely to be a popular option right now for many property owners, the rain barrel solution does appear within reach. Austin’s rain barrel program for water conservation has been very popular. While this is a feasibility issue (discussed below), it is also indirectly a performance issue in that rain barrels might be a logical first step for many folks in learning about stormwater issues and what they can do about it. Once residents start thinking about smaller, achievable fixes, they may see and feel more able to tackle more ambitious — and hydrologically effective — solutions like rain harvest, soil amendments, and rain gardens.

Rooftop Disconnections were much in the same category as rain barrels. They were modeled to have very modest results (probably about a 1 to 3% improvement toward the goal condition for runoff volume) since most residential roofs are not now connected. Commercial roofs, on the other hand, are frequently

440616/030329 4-25


connected and thus modeled results showed more promise at higher impervious levels. But, again, we’re talking about incremental improvements and the building of public awareness. Both rain barrels and disconnections serve to increase property owners’ awareness of the fact that rain is running off and that you can do something about it — and actually use the water.

Road Disconnections were modeled to offer modest benefits on the order of about 5% reduction of storm flows and pollutant loads. Like many LID solutions, this solution appears to be one of many small steps which can be taken to improve conditions within a watershed. Some locations may be especially easy and inexpensive to retrofit in this manner: the deletion of a curb to allow water to drain on to an adjacent pervious surface. But much of the road infrastructure is built below the grade of the surrounding land and thus it may be difficult to redirect water in this fashion. Creative means may possible to catch water upslope and pipe or otherwise direct it to nearby pervious areas.

Narrower Roads were modeled to provide modest benefits, also on the order of about 5% reduction of storm flows and pollutant loads. Roads areas were reduced by 10%, presumably by a narrowing of one or both of the edges. Many roads were built to their current widths in compliance with existing standards of street design; these widths may be unnecessary and undesirable for the long-term use of the community. However, this modeling exercise does not give proper credit to the full impacts possible with this solution in combination with other solutions. With narrowed roads, street bioretention or porous pavement with a sizeable catchment area could be logically located in the vacated street area. The SEA Streets solution will require narrowed streets (and the elimination of curb and gutter drainage). Ancillary benefits would be the potential to plant additional landscaping for shade and beauty, and the reduced traffic speeds (traffic calming) which would result from the narrowed widths.

Modeling Note. With all of these results, it must be remembered that numerous assumptions were required to model each solution. In one of the most obvious cases, rainwater tanks had assumptions for roof size, tank size, irrigated area size, irrigated amount (inches applied), and even watering frequency. Obviously, if any of these factors had been changed one way or the other, it could have changed the results and made the solution perform better or worse compared to the other solutions. The project team attempted to apply reasonable assumptions — with clear documentation — in each case. Much more work could be done to offer insight into how each strategy could be best applied.

However, experience alone — actually building and experimenting with a variety of solutions — will provide the best means to test and modify these solutions. LID solutions, in many respects, are the stormwater equivalent of a climax forest in terms of diversity. Rather than have half a dozen end-of-the-pipe pond or filter options per past practice, LID solutions will be as varied as the countless properties in which they can be installed. Some will work better than others. (Some might not work at all!) But, as with complex ecosystems, redundancy is the key to success: have more than one organism (or BMP) try to do the job in case one fails for a time. Such a scenario may be the only means of ensuring that the watershed functions at maximum (or even minimally acceptable) hydrologic health over the long term.

440616/030329 4-26


4.3 MULTIPLE BENEFITS

Since LID solutions are tightly integrated into landscaping practices, they offer functions in addition to water quality improvements, such as improved landscaping, aesthetics, street shade, water conservation, habitat restoration, environmental education, and even traffic calming — all attractive benefits in an era of shrinking public and private budgets to accomplish these goals individually.

440616/030329 4-27

5.0 FEASIBILITY

LID solutions represent a new course for watershed restoration in Austin, Texas. Many of the elements have existed here for some time (e.g., open drainage, vegetative filter strips, and rain harvesting), but they have not generally been put to use in any comprehensive fashion as water quality retrofits. By design, the controls are placed in upslope, distributed positions where water first collects or concentrates. These areas include roofs and lawns, which are largely on private property. Therefore, the feasibility of implementing these solutions will revolve around the willingness of residential and commercial property owners to build, pay for, and maintain these solutions on their land. For those solutions not directly on private property, such as those built in the public right-of-way along roads, the COA will still have to consider and respect the opinions of those along whose properties these controls are built.

Table 10 presents a feasibility scoring matrix for the LID solutions considered in detail in this report. It examines the following sixteen factors:

1. Jurisdiction

2. Land Ownership

3. Land Availability

4. Access

5. Wetlands

6. Recharge Zone

7. Existing Trees

8. Flood Plains

9. Utility Conflicts

10. Physical Obtrusiveness

11. Cost to Community

12. Nuisance Potential

13. Visual Aesthetics

14. Multi-Use Benefits

15. Routine Maintenance

16. Long-Term Maintenance

Each factor is rated for each solution using a simple scoring system. The results of this analysis show that there is a wide range in feasibility for the eleven solutions. The most feasible solutions are those with the least amount of disruption and nominal cost to the public: rooftop disconnections and impervious cover disconnections. These two options essentially involve the redirecting of water without major changes to the landscape. (For this same reason, they are also among the least effective solutions.) They represent

440616/030329 5-1

Feasibility Considerations for Low Impact Development Solutions

Legal Environmental Community Acceptance MaintenanceLow Impact Development Solution

Juris

dict

ion

Land

Ow

ners

hip

Land

Ava

ilabi

lity

Acce

ss

Wet

land

s

Rec

harg

e Zo

ne

Exis

ting

Tree

s

Floo

d Pl

ains

Util

ity C

onfli

cts

Phys

ical

O

btru

sive

ness

Cos

t to

Com

mun

ity

Con

stru

ctio

n Im

pact

s

Nui

sanc

e Po

tent

ial

Visu

al A

esth

etic

s

Mul

ti-U

se B

enef

its

Rou

tine

Long

-Ter

m

TOTA

LS

1. Rainwater Tanks (large tanks) 1 -1 0 1 1 1 1 1 1 -1 -1 1 -1 0 0 -1 -1 22. Rainwater Barrels 1 -1 1 1 1 1 1 1 1 0 0 1 -1 1 0 0 0 83. Rooftop Disconnections 1 -1 1 1 1 1 1 1 1 1 0 1 1 1 0 1 0 124. Compost Soil Amendments for Pervious Areas 1 -1 1 1 1 0 1 1 1 -1 -1 1 0 1 0 1 0 75. Rain Gardens for Non-Road Impervious Areas 1 -1 0 1 1 1 0 1 0 -1 -1 1 0 0 0 0 -1 26. Retrofit Smart Growth Road Dimensions 1 0 0 1 1 1 0 1 -1 1 1 -1 0 0 1 1 1 87. Impervious Cover (Road) Disconnections 1 1 1 1 1 0 1 1 0 1 1 0 1 1 0 1 0 128. Bioretention for Streets 1 0 0 1 1 0 0 1 -1 -1 1 -1 1 0 1 -1 -1 29. Porous Pavement Roadway 1 1 1 1 1 0 0 1 -1 1 1 -1 1 1 0 -1 -1 6

10. Porous Curb & Gutter 1 1 1 1 1 0 0 1 -1 1 1 -1 1 1 0 0 -1 711. “SEA Streets” Equivalent (SOS capture depth) 1 0 0 1 1 0 0 1 -1 -1 1 -1 1 -1 1 -1 -1 1

Key to Scoring:Jurisdiction: -1 = conflicts; 0 = mixed; 1 = no concerns.Land Ownership: -1 = solution on private property or requiring land acquisition; 0 = solution on community ROW near private property; 1 = community/public lands.Land Availability: -1 = difficult to find suitable space to retrofit (e.g., large size, need downgradient location); 0 = moderate ability to find site; 1 = space not a constraint.Access: -1 = access difficult to build & maintain; 0 = moderate; 1 = easy/no constraints.Wetlands: -1 = Adverse effects likely (e.g., loss of water, reduction in area); 0 = adverse effects possible; 1 = no adverse effects.Recharge Zone: -1 = Adverse effects likely (e.g., introduction of polluted water to recharge); 0 = adverse effects possible; 1 = no adverse effects.Existing Trees: -1 = Adverse effects likely (e.g., loss of significant trees); 0 = adverse effects possible; 1 = no adverse effects.Flood Plains: -1 = Likely encroachment problems; 0 = potential encroachment problems; 1 = not a concern.Utility Conflicts: -1 = High problems/cost due to utility conflicts; 0 = moderate problems/cost; 1 = low/no problems/cost.Physical Obtrusiveness: -1 = large space/commitment needed on private property; 0 = moderate space/commitment; 1 = public space/commitment only.Cost to Community: -1 = high cost borne by private property owners; 0 = moderate private cost; 1 = public cost only.Construction Impacts: -1 = disruptive to community (e.g., traffic flow, noise, dust, length of time to build, etc.); 0 = moderate disruption; 1 = minimal/no disruption.Nuisance Potential: -1 = high nuisance potential (e.g., mosquitoes, dust, etc.); 0 = moderate potential; 1 = low/no potential.Visual Aesthetics: -1 = potential lack of acceptance to visual look (e.g., unconventional look, has weed problems, etc.); 0 = moderate potential; 1 = low/no potential.Multi-Use Benefits: -1= no multi-use benefits; 0 = potential multi-use benefits; 1 = multi-use benefits provided.Routine Maintenance: -1 = High requirements/cost for routine maintenance; 0 = moderate requirements/cost; 1 = low requirements/cost.Long-Term Maintenance: -1 = High requirements/cost for long-term maintenance; 0 = moderate requirements/cost; 1 = low requirements/cost.

TABLE 10FEASIBIILITY SCORING MATRIX FOR LID SOLUTIONS

440616/0303295-2


simple, modest solutions with modest impacts. They are also symbolic of LID solutions in that they reconnect the built environment to natural drainage mechanisms and are therefore instructive to the public.

A second tier of feasibility comprises those solutions which involve moderate cost and disruption to the private property owner and/or low profile footprints in the public right-of-way. Two are for private property: rainwater barrels and compost soil amendments. These options will require more commitment and maintenance than roof disconnections, but they essentially maintain the present physical look and layout of lawns and landscaping. The other three are adjustments to roadways: retrofit Smart Growth road dimensions. and porous curb and gutter, and porous pavement roadway. These are all much more involved (and costly) than rain barrels or soil amendments, but they are done in the public road right-of-way and do not ultimately change the geometry of the roads such that they intrude upon adjacent private property.

The third and most challenging tier of solutions in terms of feasibility are those options which require either substantial cost and maintenance by private property owners or major modifications to roadway infrastructure. Rainwater tanks and rain gardens will involve fundamental changes in lawn and watering practices and much greater financial input than the first and second tier solutions. Note that this challenge does not make these solutions difficult to implement, per se, but does make their widespread use more questionable. Bioretention for streets and the “SEA Streets” option are bold initiatives which will change the hardscape of both roads and drainage systems. Both have considerable multi-use benefits (traffic calming, street shade and beautification, etc.), but also will require more interaction with the community to ensure acceptance.

With all of these solutions, the COA will have to work closely with private property owners. It is assumed that all of the options proposed for private property would be strictly voluntary. The COA would do well to start with pilot projects with enthusiastic volunteers. When others saw the success — and none of these installations have to look wacky or outlandish as compared to a standard lawn—they could become more popular.

440616/030329 5-3

6.0 COST

This section discusses the costs to retrofit LID solutions into existing developed areas. First it must be noted that this exercise is very broad and speculative given the very nature of LID controls: they are very site-specific. For example, one application of bioretention for streets might be very straightforward and require no difficulty in excavation and connection to an existing storm drain. Another, of equal size, might encounter difficult soil and/or rock excavation and problems working around existing utilities. Costs will therefore greatly vary for actual projects. The figures given in this section are intended as general approximations. This does, however, give an idea of how different solutions compare against the others. This level of detail is appropriate for this generalized, watershed-wide LID Conceptual Design. Site-specific detail will be required for individual applications.

The following table presents the estimated costs to implement each LID solution for the four different impervious cover scenarios evaluated. Since the drainage areas of the scenarios were set at one acre, each cost attempts to show the cost for each solution per acre. All costs are rounded to the nearest $100, except those solutions which cost less than $1,000, which are rounded to the nearest $10. In cases where only one or a small number of solutions is implemented at a time, the costs may go up to the fact that many line items, such as mobilization and engineering fees, do not vary with a fixed percentage (i.e., some minimum cost to do the job is required, even if the job is very small). Appendix B presents a more complete list of the cost components used to derive the summary table below.

TABLE 11

SUMMARY OF ESTIMATED COST TO IMPLEMENT LID SOLUTIONS PER ACRE

Scenario Solution 20% IC 40% IC 60% IC 80% IC

1. Rainwater Tanks (large tanks) $ 5,000 $ 9,400 $ 13,400 $ 18,500 2. Rainwater Barrels 290 580 NA NA 3. Rooftop Disconnections 40 80 570 1,200 4. Compost Soil Amendments for Pervious Areas 15,500 11,600 7,800 3,900 5. Rain Gardens for Non-Road Impervious Areas 2,800 11,000 16,500 20,700 6. Retrofit Smart Growth Road Dimensions 10,700 21,400 23,000 32,700 7. Impervious Cover (Road) Disconnections 640 1,300 1,800 2,600 8. Bioretention for Streets 12,700 17,100 21,000 25,900 9. Porous Pavement Roadway 19,500 39,000 54,000 76,500 10. Porous Curb and Gutter 8,500 17,000 21,100 29,700 11. “SEA Streets” Equivalent (SOS capture depth) 169,800 305,400 320,100 434,900

As expected, those solutions requiring major modifications to existing roadway networks (e.g., bioretention and porous pavement) are likely to cost much more per acre than less extensive solutions. The following table contrasts cost and performance data for the LID solutions, sorted by cost per pound

440616/030329 6-1


removed of TSS. For simplicity, only the 40% impervious cover scenario is presented. This level of IC is closest to that of the majority of single family residential development and development in general in the watershed.

TABLE 12

COST VS. PERFORMANCE OF LID CONTROLS FOR THE 40% IC SCENARIO

Solution Cost/Acre

Lbs. of TSS Removed per Year

Percent toward TSS

Goal

Cost per Pound

Removed of TSS/Yr.

Rooftop Disconnections $80 2 1% $34 Rainwater Barrels 580 11 3 51 Impervious Cover (Road) Disconnections 1,300 22 6 60 Rain Gardens for Non-Road Impervious Areas 11,000 153 44 72 Bioretention for Streets 17,100 178 51 96 Rainwater Tanks (large tanks) 9,400 97 28 97 Porous Curb and Gutter 17,000 95 28 178 Porous Pavement Roadway 39,000 194 56 201 Compost Soil Amendments for Pervious Areas 11,600 38 11 308 “SEA Streets” Equivalent (SOS capture depth) 305,400 334 96 914 Retrofit Smart Growth Road Dimensions 21,400 19 5 1,137

This table shows the wide range in costs and performance1 for the modeled LID solutions. The three least expensive options — rooftop disconnections, rain barrels, and road disconnections — also offer the lowest cost in pounds of sediment removed. However, each of these solutions only achieves less than 10% of the distance desired toward the goal. The next tier of solutions cost about $10,000 to $17,000 to implement per acre: rain gardens, bioretention for streets, rain tanks, porous curb and gutter, and compost soil amendments. Of this group, the most cost-effective appear to be the two bioretention options: rain gardens and bioretention for streets. These solutions cost under $100 per pound removed of TSS and achieve a 40 to 50% improvement toward the goal condition. No other solutions have such positive numbers for these two important categories. The final group are the most expensive: porous pavement for roads, narrower roads, and the SEA Streets solution. All of these require extensive modifications to the built environment. As noted in the performance section above, the SEA Streets option is, by far, the most effective option in terms of returning urbanized areas toward the goal condition. However, it may be possible to combine a series of the other, less costly approaches to achieve a similar (if not quite as effective a) result.

1 Note that the performance of most solutions was similar for all of the pollutants modeled. For example, a control which

did well for TSS (shown in this table) generally did well in removing Total Nitrogen. This is due to the fact that most of these controls derive their effectiveness from reducing flow volumes, which in turn lowers pollutant loads. Therefore, the presentation of TSS is fairly representative of the other parameters of concern tracked in this report.

440616/030329 6-2

7.0 MAINTENANCE

Maintenance considerations for the modeled LID solutions are outlined by retrofit project. The following is a table showing the general level of cost and time commitment for each of the LID solution types.

TABLE 13

GENERAL LEVEL AND COST OF MAINTENANCE REQUIRED FOR LID SOLUTIONS

Level and Cost of Maintenance Required

Solution Routine Long-Term

Responsible Party for

Maintenance

1. Rainwater Tanks (large tanks) High High 2. Rainwater Barrels Medium Medium 3. Rooftop Disconnections Low Medium 4. Compost Soil Amendments for Pervious Areas Low Medium 5. Rain Gardens for Non-Road Impervious Areas Medium High

Property Owner

6. Retrofit Smart Growth Road Dimensions Low Low 7. Impervious Cover (Road) Disconnections Low Medium 8. Bioretention for Streets High High 9. Porous Pavement Roadway High High

10. Porous Curb and Gutter Medium High 11. “SEA Streets” Equivalent (SOS capture depth) High High

City of Austin

The following is a solution-by-solution description of the major maintenance tasks.


• Routine checks to ensure no mosquitoes or other undesired vectors are living in tank. Should not occur in well sealed system but should be checked.

• Routine checks (after significant rainfall events or at least quarterly) to ensure inflow pipes and outflow hoses not blocked. Will be obvious if not working correctly as water will not enter and/or exit tank properly.

• Clean debris screens over gutters periodically.

• Drain and clean tank occasionally to remove sediment and debris. Can be done with a swimming pool cleaning net through the top portal.

2. Rainwater Barrels

• Same as Rainwater Tanks (above), except barrels are smaller and can be inspected and maintained more easily. For example, for cleaning of accumulated debris, they can be emptied of water, rolled onto their side, and sprayed out with hose.

440616/030329 7-1



• Minimal maintenance except to (a) ensure that the pervious area to which the downspout discharges is well vegetated or stabilized (e.g., gravel) and not eroded, and (b) ensure that additional impervious cover is not added to undo and/or reconnect the disconnections.


• Minimal maintenance except to (a) possibly reapply compost where the ground has been compacted by foot or vehicle traffic, and (b) ensure that the compost is not washed off the site by channelized runoff (a concern whether compost was applied or not).

5. Rain Gardens for Non-Road Impervious Areas

• Ensure mulch is in place and sufficiently deep (3 inches). Replace every 6 months.

• Water plants if stressed from heat, lack of rainfall.

• Prune plants per standard practice for landscaping. Replace dead plants.

• Weed bed to control growth of unwanted plants.

• Water in the facility should infiltrate the system within 72 hours or less. If longer, the underlying soils may be too tight (e.g., heavy clay). Amend soil with compost. Should not occur if facility sized correctly (large enough).


• No additional maintenance compared to an existing, standard road. Is just narrower — and thus requires less resurfacing and sweeping maintenance.


• Ensure that the pervious area to which the downspout discharges is well vegetated or stabilized (e.g., gravel) and not eroded.

• Ensure that the vegetation is healthy; replace plants if necessary.

• Ensure that disconnection is maintained and not blocked or reconnected with curbing.

• May need to periodically enhance vegetated area with compost soil amendments to ensure health and infiltrative capacity.


• Ensure mulch is in place and sufficiently deep (3 inches). Replace every 6 months.

• Water plants if stressed from heat, lack of rainfall.

440616/030329 7-2


• Prune plants per standard practice for landscaping. Replace dead plants.

• Weed bed to control growth of unwanted plants.

• Water in the facility should infiltrate the system within 12 hours or less. If longer, the underdrain may be clogged. Unclog the underdrain using the clean out pipe per standard plumbing practices.


• Street sweeping twice per year minimum to remove sediment, trash, and debris from surface which could clog the underlying system. Frequency may be increased due to over hanging vegetation and or excessive dirt and pollutants, which may wash into or over and foul the surface of the pervious system.

• Power wash on an annual basis to flush silt or other contaminants. These sediment fines apparently cause little to no threat to the system when washed into the lower and larger aggregate.

• Ensure that dirt, sand, gravel or landscape material are not piled on the porous surface without covering the pavement first with a durable cover as to protect the integrity of the pervious surface

• Grade all adjacent landscaping to prevent the washing and or floating of materials (e.g., mulch, soil, etc.) onto or through the pervious surface.

• Flush spilled materials (e.g., chemicals, petrocarbons, etc.) from the system and/or use microbiological material to neutralize these spilled materials.

10. Porous Curb and Gutter

• Same as Porous Pavement Roadway above (except footprint much smaller.

11. “SEA Streets” Equivalent (SOS capture depth)

• Same as Bioretention for Streets above for bioretention component.

• Maintain grassed swales per standard practices used throughout COA (e.g., periodic mowing, trash removal, etc.).

440616/030329 7-3

8.0 CONCLUSIONS

A Good Start. LID solutions have not been implemented on a large scale in Austin. Most of these systems have been privately installed (e.g., rainwater harvesting tanks or barrels) by individual homeowners or businesses more for water conservation than for water quality or watershed improvement. Recently, a growing (but still limited) number of development design plans have been submitted proposing the use of pervious pavement, rainwater capture, and even bioretention. Thus, with no real publicity or encouragement as yet from the Watershed Protection and Development Review Department, some engineers and private citizens have discovered and wish to use these techniques. A major attraction of these solutions is that they can be more gracefully integrated into a site than traditional (and larger) end-of-the-pipe controls like sand filters. They also can be aesthetically beautiful, incorporating landscaping into both their presentation and function. These advantages bode well for their more widespread acceptance.

Need to Address Patterns of Large-Scaled Problems with Patterns of Small-Scaled Solutions Bull Creek is a big watershed and the temptation is to solve its problems with big conventional solutions. But these large-scaled solutions have frequently proven either infeasible due to spatial constraints (no room to locate them) and/or cause more environmental problems than they solve (e.g., destruction of habitat, interruption of sediment transport, etc.). A program to implement LID solutions will have to acknowledge the nature of the tools: they are, by design, small-scaled and distributed rather than centralized. The solution protocols presented in this Conceptual Design therefore addresses “patterns of problems” and suggests “patterns of solutions” rather than attempts to “solve” all of Bull Creek’s problems at one time. Many, many individual LID solutions will have to eventually be constructed to collectively address problems. Many more people will be involved in their construction and maintenance than with conventional BMPs.

The present Bull and West Bull Creek Watershed Management Study identifies and develops Conceptual Designs for seven site-specific solutions. Most of these will be LID solutions or will include LID components. However, it is acknowledged that these address only a few small areas in a 20,145-acre (31.5-square-mile) watershed. Therefore, it is especially necessary to develop a protocol for identifying additional locations for these solutions. This LID Conceptual Design provides that protocol, evaluates the prospects, benefits, feasibility, and cost of implementing LID solutions across the entire Bull Creek watershed.

Long-Term Commitment. A comprehensive program to implement LID solutions will require a long-term commitment of time and resources to be phased in. Such an effort could be coordinated to be done at the pace of standard repairs done on infrastructure to limit redundant costs. For example, rather than pay to rip out and rework a roadway currently in good condition, it would be more cost-effective to wait until the road is scheduled for maintenance anyway and add an LID component to save on mobilization costs and enable favorable economies of scale in materials, labor, and mobilization.

440616/030329 8-1


Site-Specificity. LID approaches are fundamentally different than conventional end-of-pipe controls. It will be impossible to develop a master plan to detail each and every installation. Instead, these controls should be built, like the controls themselves, in a piecemeal, dispersed and evolving process. The COA’s Watershed Protection & Development Review Department can play a key role in designing and installing prototype, example versions of these systems. These would logically be placed in high profile locations to maximize their public exposure to educate and inspire.

Ongoing Involvement with an Educated Public. If LID solutions are built such that they actually help meet the goals of restoring the watershed, it will have been because a vast percentage of them were built on private property. (Most of the existing development is on private property.) COA will not — and should not — have direct control over these solutions, because this would be intrusive, politically infeasible, and financially unsustainable. The COA will need to help initiate and sustain a public education campaign to help teach the public about these practices and encourage their use. Each will have to be designed, built and maintained to address individual sites. But the public education role by the COA would not be to install individual systems in all locations but rather to “train the trainers” — show individual, motivated persons in the community how to set up their own systems and how to show others to do the same. Potentially, a system of credits could also be used, wherein homeowners and commercial property owners could receive a credit on their drainage fee, a direct rebate, or some other arrangement. Given the overwhelming number of properties which would need to be retrofit, and given the sensibility of allowing a diverse group of people to experiment with and develop site-specific designs, such an arrangement would be necessary and beneficial for COA staff and citizens alike.

A “Bad News, Good News” Story. LID presents its own version of the classic “good news, bad news” story. The bad news is that a tremendous and unknown effort will be required to build enough LID solutions to meet the COA’s goal to restore Bull Creek. Such an effort will involve a seemingly unlimited number of participants on a vast number of properties at what could be a relatively high cost. The goal, if reached, will mean that the watershed will have been restored to a pre-development level of health and function, thereby helping to protect the natural beauty and ecological function of a large contributor to the water supply for the COA. The good news is that, at least in theory, this goal appears obtainable. Parcel by parcel, LID solutions can help the watershed return to this desired condition. And this apparently applies even for properties with relatively high impervious cover. This could never be said of the conventional end-of-pipe controls like regional water quality ponds, which only partially address the problems of the watershed, and this only in those few locations suitable and available for their construction. LID solutions would have been dramatically less expensive and difficult to build had they been included at the time Bull Creek developed. However, it does not appear that their effectiveness or use has been precluded. LID solutions remain a viable and attractive option for retrofit to restore the watershed. Indeed, the watershed will continue to function indefinitely at a suboptimal fashion until the built environment is modified to perform more sustainably. LID solutions provide this possibility. More experience is needed to evaluate their actual performance in the field and to learn from experience how best to design them. They deserve the opportunity to prove themselves.

440616/030329 8-2

9.0 BIBLIOGRAPHY

City of Austin Watershed Protection Department. 1999. Water Supply Suburban Watersheds Report: Watershed Protection and Traffic Analysis. Water Quality Report Series, COA-ERM 1999−02. November 29.

Claytor, Richard A. and Thomas R. Schueler. 1996. Design of Stormwater Filtering Systems. Silver Spring, MD: The Center for Watershed Protection, December.

Loomis-Austin, Inc. 2000. Integrated Solutions Development Study. Watersheds Master Plan. Phase II Final Report, vols. 1 and 2. For the Watershed Protection Department, Austin, Texas. June.

PBS&J. 2003. Pilot Study of Tributary 6, Bull and West Bull Creek Watershed Management Study. Prepared for the City of Austin, Texas. Document No. 020262. PBS&J, Austin, Texas.

Prince George’s County, Maryland Department of Environmental Resources Programs and Planning Division. 1999. Low-Impact Development Design Strategies: An Integrated Design Approach. June.

U.S. Environmental Protection Agency (EPA). 1999a. Storm Water Technology Fact Sheet: Bioretention. EPA 832-F-99-012, September.

⎯⎯⎯. 1999b. Storm Water Technology Fact Sheet: Porous Pavement. EPA 832-F-99-023, September.

440616/030329 9-1

Appendix A

Field Data Forms – LID Assessment of Tributary 6

UD Field Checklist

Location:

— Subwshed Number:

Th,r4-1~

Subdivision: &2V ~ak~sApprox. Age of Development: Headwaters:

Nearby Natural ResourcesV~o Spring

Salamander~~Cave/SinkhoIe/Karst Feature

~t.o Publicly Accessed Landsj~Other(eg~,wetfands, endangeredsp. habttat~:

Existing Structural ControlsFilterControf

Filter Stripv’ Other:

~ ~~bL%P.Ac.*b~ ~

NearbyPublic ResourcesParkSCITOOt N~6~ 1- ~ ~GreenbeltBCPOther (e.g., public easement):

DrainageType~‘.Jo Curb& GutterV Grassed SvvaleV Overland Flow

Existing hnpervious Cover PCI. AdjacentType Connected Perv. Cover OtherRooftops

L-~~~ Dnve~aysNoSidev~aIks

%~—Roads l-S~ RoadWdthParking Lots Spaces

—

~- & ~

Existing Pervious CoverSparse VegetationErosionlChannelized FlowsCompactionIntensive Landscaping PracticesOther:

Wastewater Disposal MethodSewer

VOn-SiteSystem 54*C._.

Potential Solutions0 Rain Harvest ~U Narrower Road[3 Roof Disconnect. Bioretention/Rain Gardens M ~ ‘4v.~&i oJ~*,~jo Site RegcadinglTerracing ~‘kI Natural Drainage/S~aies ~~Z~ompost Soil Amendment ,JJ~ ~ 0 Vegetative filter stripsE!~Low-Impact Landsca~ngN~fr,k$.~‘~‘M~ôD Infiltration trenches 90 Reforestation e~’&*, L~#... ~ Alternative Pavement Ee.u., Ecocreto]El IC Removal (Roads/Parking) ~> 2’ Outtalt Eiosiorr Protection

~ [3 IC Disconnect. (Roads/Parking) ~ ~ ~ .~‘.~ ‘&d~&c~~L-~ rt~&)~~ tLtr.~i.

Comments

ietdwork lnf tion

Date ~ (~~ Participants ~

LlOCtieckJistxls:8u11 LID Paae 1 of 1 8/1OIZD1

L~~WN~M-~.

itructural Controls ~)t~tJ E-Sand FilterFlood ControlVegetative Filter StripOther:

Wastewater Disposal Method

~,‘

_______ ~1l1e~tl_!~nkn

~ o’tt. ~( 1~’Lc~a4~’,v’2 *e~,vuJ6~t~-c~t-t+YT.

Location: C~SI,,M~~

Subwshed Number:

LID Field Checklist ‘7~.--~~m 7f,-~>1

‘75-~2-

Approx. Age of Development. 11-~2- Headwaters:

, ~ o4 , C~.4~1~11~Subdivision: A%~kL&t~.M~1k ~t’~iL~c £~t4.!,

Nearby Natural Resources}~-~ Spring

~-~/Salamander‘~fe~lk’j~4 cL4’AX~.~Cave/Sinkhole/KarstFeature Y1~4~~41~Lt

~~PubIicly Accessed Lands,~oOther(e.g., wetlands, endangered sp. habitat):

z~,4

Nearby Public ResourcesParkSchoolGreenbeltBCPOther (e.g., public easement):

Existing Impervious Cover Pat. AdjacentType Conn~cjed, Perv. Cover

_~ Rooftopsj~ Driveways_~_ Sidewalks t4~~

RoadsParking Lots

Other

~t~t~rU’

2S~3~’______Road Width______ ______ ‘~- Parking Spaces

2~.#S’,M4i4~~.2_çP (~‘ ~ ~ LL~N~r.&c~ Landscaping(~~4\U/”~) 4~-3b’c~?~

Existing Pervious CoverSparse Vegetation

— Erosion/Channelized FlowsCompaction

\/~lntensiveLandscaping Practices, ~$_Other:

Potential Solutionso Rain Harvesto Roof Disconnect.o Site Regrading/Terracingo Compost Soil AmendmentO Low-Impact LandscapingO Reforestationo IC Removal (Roads/Parking)o IC Disconnect. (Roads/Parking)

~ieIdworkI for ationDate__________ ____________

Comments:

O Narrower Roado Bioretention/Rain GardensO Natural Drainage/SwalesO Vegetative filter stripso Infiltration trencheso Alternative Pavement [e.g. Ecocreto]O Outfall Erosion Protection

eIU~v~L~~

DiIS~J~~rUV$L& ~. W~j~tAMA4~~ ~

Participants U M ft ~LlDChecklist.xls:BuII LID Page 1 of I 8i9/O1

LID Field Checklist

Location: ~. ,~ ~

Subwshed Number: Subdivision: 1i~ru.~,~uk~iV.

Approx. Age of Development: Headwaters:

Nearby Natural ResourcesSpringSalamanderCave/SinkholefKarst FeaturePublicly Accessed LandsOther (e.g., wetlands, endangered sp. habitat):

Existing Structural Controls ~‘4OI~(%Sand FilterFlood ControlVegetative Filter StripOther:

Nearby Public ResourcesParkSchoolGreenbeltBCPOther (e.g., public easement):

Drainage Type~JO Cuth&Gutter f\4L~&i~At~dI.

~/ Grassed SwaleL’ Overland Flow

Existing Impervious Cover Pct. AdjacentType Connected Perv. Cover Other

~“~ftops~.- Driveways

Pt~~ ‘~-

VRoads ~ 4-~~(y~- Width— Parking Lots ParkingSpaces

*~ Landscaping

~ ~L. uU ~j. *~Pt C.

Existing Pervious CoverVegetation

Erosion/Channelized Flows— mpaction

Intensive Landscaping Practices \ILA.A.\ t¼t1.~Y’&.~~hA~¼bLtte.~tj

Other:

Wastewater Disposal MethodCentral Sewer

t./ On-Site SystemOther/Unknown:

.~

Potential Solutions~ Rain Harvest ~kA~& riirQ~ (~,4~~~J4)D Narrower Road jV o ~.tj.tJ..u4~f v’~tLj~ c~~4~’O Roof Disconnection ~ L~Y~Bioretention/Rain Gardens ~ ‘—~ ~L-J.A.4. U~O Site Regrading/Terracing ‘°D Natural Drainage/Swales ~L’Compost Soil Amendment ) 0 Vegetative Filter Strips~‘iLow-lmpact Landscaping ~O Infiltration Trenchesl~”Reforestation ~è. ~ ~M’ ?~~‘~4MtJ Alternative Pavement [e.g., Ecocreto] p4u ‘.i..uAO IC Removal (Parking) Outfall Erosion Protection —.i~

O IC Disconnection (Roads/Parking) e-~

~ t ~Lk ~ ~ - K

cIJ~.*~~*~.4~ ~ kI~’. 4 G~UA.

Wieldwork lnf rmatiön~

1Date Participants

Comments:

LlDChecklist.xls:BuII LID2 Page 1 of 1 8/12w01

Potential Solutions~‘ Rain Harvestt~Roof DisconnecL~ite RegradinglTerracing t~w’~~v’tjt~.M~Compost Soil Amendment~‘Low-l mpact Landscaping~Reforestation ~ ~v’~’W,.U IC Removal (Ro~ids/Par}dng~l~’ic~sconnect.(Roads/Parking)

~ ~A)S O’).;i ~ ,~- MJJA

Narrower Road1/ Bioretention/Rain Gardens ‘~~*j..k1j.~t&~..;0 Natural Drainage/Sv.~lesLY~Vegetative filter strips’. &p~ s~fOh~U~O Infiltration trenchesC] Alternative Pavement Je.g., Ecocretojt~’ Outfall Erosion Protection r ~ Mi h..: ~4~e1~

Q3&%’~b~-1~tM

~ieIdworkInformation{~te 4~4(q~(~( Parlk~ipants JM~c-

ç ~ ~LLL ~

LID FieldChecklist

‘~w.I~J pt~b~-,~ ,Ta-4~.1~a,,~ted ~a~,L,e±c.

(~CL1Subdivision:Ca449mt (a4..1 S~A-.t~~ ~ \~j~Headwaters:

Exis~~Structural

~‘ ~J Control r~ ~&~‘~ Filter Strip

()~l~ ~J~’ v~Pi~~t~~Jendangered sp. hat)c~

~t,&1~y~~

Drainage Type?ir~A.W~ ‘~/Curb & Gutter

C,L~L~&~‘ ~‘ Grassed Swale ~Flow J ,~ ~

1

Pet. AdjacentConnected Perv. Cover Other

M~mL~4- I,

0 lv WdthSpaces

Wast~waterDisposal Meth&I‘I Central Sewer

~~çsu~&~ ~$~Ulw ~t~4 System

~1_ ~ ‘~p7(~~~ I ~4-~nc4/~4’t,t~e.i;~.~

Comments:

?x~.UL’~~~AM.k ~ ~ QA ~.k L t’t..k ck~uk~ ~ l.~.fr4MC’~- &i~*~~-.(~~ cbr~.M~’.~ *~t~Mj~~ VV~~ D.$ ~

L

LIDChecFth~xIs:BuIILID Paae 1 of 1 8/1Ot2OOl

k ~W ~ ~ ~ S

L~e

J1.JJ~ V.UD Field Checklist

Location: E~nk~’ ~ -~ ôp~~i-e~, ~rk~ , ~Y~MWVL, C~4u~iSr(~

Subwshed Number SubdMsion: ~jt~$i.~M (Auk~,Sd I~’~2J , Z.~’,2-7,

Approx. Age of Development: Headwaters:____________________________

Nearby Natural Resources Existing Structural ControlsSpringSalamander

/ Sand Filter ~- 6i~eS~ska~i~vi.

Control— Cave/Sinkhole/Karat Feature Filter Strip

Publicly Accessed LandsOther (e.g., wetlands, endangered sp. habitat):

Nearby Public Resources Drai ge TypePark & Gutter

7Schoci CM4AJI,~ /~.q&?JL.- ~l~4t-4~-t~t-fGreenbelt

SwaleFlow

BCPOther (e.g., public easement):

Existing Impervious Cover Pet. AdjacentType Connected____ Perv. Cover Other

I ö~ ~i~ij~Lk1A4~Wk ~At~~Driveways ~ i~ ~a..Lii GL.*.~’

dewalks ~ N ~.) 1 c~p w~a ‘~t3~ N WaY/i

Par$dng Lots Spaces

~rt 4S~~

Existing PerviousCover Wastewater Disposal MethodSparse Vegetation ~-‘~ Central Sewer

— Erosion/Channelized Rows System— Compaction

Intensive Landscaping Practices ~t& 6llIbt~l4I~ce-~-~�

Poten’tlaF SoTutionsU RatrrHaivest El NarrowerRoactO Roof DisconnecL 0 Bioretention/Rain GardensO Site RegradingfTerracing 0 Natural DrainagelSwaLes0 Compost Soil Amendment 0 Vegetative filter strip&O Low-Impact Landscaping 0 Infiltration trenchesO Reforestation 0 Alternative Pavement~e.g.,Ecocreto]O IC Removal (Roath/Parldng) 0 Outfall Erosion ProtectionU IC Disconnect. (Roads/Parking)

Comments:~ “&).W t~AM.& ~* &~~ U~v.kk( ~ ~ Or~&c&~M..a,

Fietdwor InformationDate__________ Participants JI.-~Uk ~ (~-

UDChkJi~.xfs:BuJILID Paae 1 of I e/1oe~o1

[ LID Field Checklist

I Location: Rain~j—tSubwshed Number: Subdivision: i

4 4e~øi /.~4jj(Oa4s A-d~’nApprox. Age of Development: Headwaters:

Nearby Natural ResourcesSpringSalamander ~

Cave/Sinkhole/Karst FeaturePublicly Accessed LandsOther (e.g., wetlands, endangered sp. habitat):

Existing Structural ControlsSand Filter ~ Nb I~’J ~Flood Control (~,j \~p~

- Vegetative Filter StripOther:

‘“~~‘)

Nearby Public ResourcesParkSchool j~JoM~GreenbeltBCPOther (e.g., public easement):

Drainage Type~,jD Curb & Gutter~ Grassed Swalev Overlanct Flow

Existing Impervious Cover Pcf. AdjacentType Connected Pen’. Cover Other

1./Rooftops~Driveways M~’1~ t~.u.l~c Sidewalks NOlJ~VRoads ~ 0 Road Width

— Parking Lots Parking SpacesLandscaping

* ~ c ~~Li4 ~ t.3 t..

Existing Pervious CoverSparse Vegetation ~ ~ f’r”~~~

— Erosion/Channelized Flows~ Compaction ‘,.,

~7lntensive Landscaping Practices ~ ~

Other:

Wastewater Disposal MethodSewer

~—‘ On-Site System s~c’t~Other/Unknown:

Potential SolutionsRain Harvest )( 0 Narrower Road V~&%~V.~~bAJt&~J~‘f~~)‘

O Roof Disconnection ~ Bioretention/Rain Gardens ‘~- L. ‘hAt tAt 4W~.O Site Regrading/Terracing 0 Natural Drainage/Swale~ (“ ~ I.

E~’CompostSoil Amendment 0 Vegetative Filter Strips j..~

!~-1.ow-lmpact Landscaping 0 Infiltration TrenchesI~Reforestation 0 Alternative Pavement [e.g., Ecocreto]O IC Removal (Parking) 0 Outfall Erosion Protection

-D IC Disconnection (Roads/Parking)

Comments:~ ~

Vieldwork lnf rmationDate~ ~it’i1oi Participants Jk~~C)c-C1

LIDCheckIist.xls:BuIl LJD2 Page 1 of 1 8/1301

LID Field Checklist

Location: I~L-k1V)t~..~ A-1c~ie..4- ~ô~vp~-(I CiLt,~.~~JSubwshed Number: Subdivision: ~ ~

Approx. Age of Development: ____________________ Headwaters:

Nearby Natural ResourcesSpringSalamanderCave/Sinkhole/Karst FeaturePublicly Accessed LandsOther (e.g., wetlands, endangered sp. habitat):

Existing Structural Controlsv’~ Sand Filter .2. pa’ia~c.~

~~~ff~~ntrolVegetative Filter StripOther:

Nearby Public ResourcesParkSchoolGreenbelt ,

BCPOther (e.g., public easement):

Drai1~~Type& Gutter

Grassed SwaleOverland Flow

Existing Impervious Cover Pct. AdjacentType Connected Pen’. Cover Other

V~Rooftops M.~. ~v Driveways Cw~u~J~t/i-_1.~.~&t &~&fr~.cJ. 1/

~ Sidewalks ~. c~1a~Ssst~ ~ ~ ~~Roads 4~~”RoadVv7dfh

— Parking Lots ParkingSpaces- ~ ~

c~v&~_~~

Existing Pervious CoverSparse VegetationErosion/Channelized FlowsCompactionIntensive Landscaping Practices £4 , ~ tc.~~Other:

ter Disposal MethodWa~~~a Sewer

On-Site SystemOthor/Unknown: -4 ~ WW

~A.tM*.~(AJl

Potential Solutions~ ‘~.4I&.4

’l~.I ~ ~1~arrower RoadL~’RainHarvest ~o R~Disconnection ~ ‘~‘~ -~F~” Bioretention/Rain Gardens t)’~ ~ ~ (~~.JL,Jt~i

~,)iteRegrading1Terraci~ ~ ~ ~ v~

Compost Soil Amendment ‘~~iativeFilter~ Landscaping Infiltration TrenchesO Reforestation Alternative Pavement [e.g., Ecocreto]O IC Removal (Parking) Outfall Erosion ProtectionO IC Disconnection (Roads/Parking)

c~~4 ~ ‘~7~%4,.tt3..&*~‘b.£~‘~~

~

Comments:

t$ ~‘9eldwor Information

,Date Participants ci (4 EF ~

00000

LlDCheckllst.xls:BuH LID2 Page 1 of I 8/13.01

‘c2. -c~’1

Cieldwork lnJ~grr~ation

1Date 2~/1/O~

t~j’

L

LID Field Checklist

Location: r ~ (c~,ç~~ 4~)~ ~~ ~

Subwshed No.: Subdivision: \LL,r ~ ~~~tjJr ~

Approx. Age of Development: - Headwaters:

Nearby Natural ResourcesSpring

~ Salamander 5i~e~‘ ( ~ ~ 1.~tt~S— Cave/Sinkhole/Karst Feature ~

Publicly Accessed Lands(e.g., wetlands, endangered sp. habitat):

Existing Structural Controls ~ ?Sand FilterFlood ControlVegetative Filter Strip

V Other: ~ ~

~ ~

Nearby Public ResourcesParkSchoolGreenbelt I\lQIJk~..BCPOther (e.g., public easement):

Drainage TypeV Curb & Gutter


Existing Impervious Cover AdjacentType Connected Pen’. Cover Other

‘/RooftopsV Driveways ~t~-

SidewalksRoads Width


~Existing P&vious Cover

VegetationErosion/Channelized FlowsCompaction~ Intensive Landscaping Practices P~Lnic.,wy~_~,L[~~jytS

Other:

Wastewater Disposal Method~— Central Sewer

SystemOther/Unknown:

Potential Solutions‘11~Rain Harvest ‘, ~ Narrower Road~ Roof Disconnect. [V Bkretenhon/Raui Gardens ~Jrk~ ~ t’~Li Site Regrading/Terracing U Natural Drainage/Swales ..4 ~3J~’ ~ ~kj.L ~U Compost Soil Amendment K LI Vegetative filter stripsU LN~im0aciLandsc~~ ç~u)v.‘1. ~&Li Infiltration trenchesU Reforestation [I Alternative P~y~.~nt[e.g., Ecocreto]U IC Removal (Roads/Parking) Li 6~lIE~ionProtectionLI IC Disconnect. (Roads/Parking)

Participants J~ft ‘~

LIDCheckIist.xls:BuII LID Page 1 of 1 8/8,01

LID Field Checklist

Location: ~ yr., ~p~i’?cJt~’sTi. / 1.p~,re~j1~Subwshed Number: Subdivision: L4.~.u-e,(Ci..~t.cJo~t~u&A,v. PJi~s~Z7~Approx. Age of Development: Headwaters:

Structural ControlsNearby Natural Resources EXi~~ Filter !SpringSalamander Flood ControlCave/Sinkhole/Karst Feature Vegetative Filter Strip ~Publicly Accessed Lands Other:Other (e.g., wetlands, endangered sp. habitat): 0~’~ s

/1~Nearby Public Resources Dr~in~neType~ ~ ~ ~

Park ~bVL ~Curb & ~ ~u~- I~School t’.~ok~~ ‘ %J Grassed Swale ~ VGreenbelt ~ Overland Flow ~ ~

BCPOther (e.g., public easement): l’i~l~•. I

Existing Impervious Cover Pct. Adjacent Q.. w~*.dJConnected Per.’. Cover Ofher’~

I.—..~eways L-~SidewaIks k ‘~__RoadVVidtt? ~ C~i~

‘Roads vc~Parking Lots Parking Spaces

LojuJt4 c~s~t~. ~ k~ ~. ~, Landscaping~

~ t’q~.. ~ ‘.‘~& ~‘ ~ ~‘~-44 ~A~•

Existing Pervious Cover Wastewater Disposal MethodSparse Vegetation Central SewerErosion/Channelized FlowsCompaction

I~~ntensiveLandscaping Practices ~ ‘¼~W.sL~— Other:

On-Site System.-~ OthorfUnknowni

~WS ~ -.e.ek.I

Potential SolutionsO Rain Harvest ‘b~O Roof Disconnedio1~iO Site Regrading/Terracing 0I~”CompostSoil Amendment 0~‘tow-lmpact Landscaping 0~eforestation ~*~L!J. \~‘k~’ IIMMJA4W4 0LW~C Removal (Parking) ~ tWJ&j ~4~oO IC Disconnection (Roads/Parking) ~‘~‘

Comm . ~‘-~ ~- ~ ~ ~ t ~m.d. t’~. ~ ~ ~ ~~ c~)~A~.3~ ~ q

e

m’ Narrower Road C~jh4.M.~h.QEl” Bioretention/Rain Gardens ~~.b%AJ_7t. ~ ~k

~. Natural Drainage/Swales ~J(A. ~ b t~.44\ 4JIIhLfr’J..

~ Vegetative Filter StripsInfiltration Trenches ~l~i ~Alternative Pavement [e.g., Ecocreto]Outfall Erosion Protection

VieldworK lnfqrmation

1Date ~L..L1~1 Participants JM (4 ~ ~ C C..—

‘1

ô.j~~

LlDCheckhst.xls;BuIi LID2 Page 1 of 1 8/1 3.01

LID Field Checklist

‘C

Location:

Subwshed Number:

Approx. Age of Development:

Subdivision: ~ ~ T’.~tqLHeadwaters:

Nearby Natural ResourcesSpringSalamanderCave/Sinkhole/Karst FeaturePublicly Accessed LandsOther (e.g., wetlands, endangered sp. habitat):

Existing Structural ControlsFilter

Flood ControlVegetative Filter StripOther:~ ~ ,4’ ~ rw~t.

o~u-~~

Nearby Public Resources

SchoolGreenbelt

(e.g., public easement):

Drainage Type& Gutter

~7 Grassed Swale~.- Overland Flow

Existing Impervious Cover Pct. AdjacentType_______ Connected Per.’. Cover Other

I’~~ftops~./Dnveways~.~.~s~&s_)k

Sidewalks IJtII~V Roads “— 2.6 RoadWidth

Parking Lots ParkingSpaces— Landscaping

G~$..~ ~ ~ ~ ~ “—n ~

Existing Pervious CoverVegetation

Erosion/Channelized FlowsCompaction

— Intensive Landscaping Practices t’.k~. ~O.J~Wv.Ct~&(~-

Other:

Wastewater Disposal MethodCentral Sewer

y On-Site System :Other/Unknown:

Potential Solutions)~ 0 Rain Harvest ~t0 Narrower Road~ 0 Roof Disconnection ~ I~’ B~retention/Rain Ga ens Cv.~..~ * bt. L~ ~ ‘u’..-.

, 0 Site Regrading/Terracing )cD atural Drainage/Swales ~‘~~J-$ ~.

EVCompost Soil Amendment ,~0/ Vegetative Filter StripsO J..ow-lmpact Landscaping ~eEJ~ Infiltration TrenchestY Reforestation ~ E~ Alternative Pavement [e.g., Ecocreto]

~ 0 IC Removal (Parking) Outfall Erosion ProtectionO IC Disconnection (Roads/Parking)

~ ~ ~ ~ ~Lf~’ ~Comments. ,

t .~j,,..’hA p 4.?.. ~‘ •

~

r~J ~&L~O ~oLk .wJ. ic‘9eldwork Info mation

I Date Participants ~)j4(.4- +-T) c_ £.~—

L~~J

LlDCheckflst.xls:BuII LID2 Page 1 of 1 5/13.01

LID Field Checklist

Existing Structural Controls_______ Sand Filter_______ Flood Control N_______ Vegetative Filter Strip________ Other:

Nearby Public ResourcesPark ~School ~ ~cJA’\~kGreenbelt ,..t3~-’&)J”~

— BCP ~Other (e.g., public easement):

-

Drainag~Type~ Curb & Gutter

Grassed SwaleOverland FlowOther:

~xisting Impervious Cover P~~Y.’-’ AdjacentType Connected Pen’. Cover Other

V Rooftops 1*y’~j—~________

~tDriveways ~y- t.LJJ ‘4.~&j ~Jt,p’.’.,,~~ G~3~UML~~4t~..SidewalksRoads ~ Road Width 4S .Sl~’Parking Lots ParkingSpaces

.

j ‘.P~x~-.&~‘.ci~ ~t ~~

Existing Pervious CoverSparse VegetationErosion/Chanrielized FlowsCompaction

~Intensive Landscaping Practices ~- AM..3.. ~Other: U~ki~~

Wastewater Disposal MethodCentral SewerOn-Site System

~t5 ‘~- ‘~5plk”cite- Ov~.Ptt~v~vo~_1~(.

Potential SolutionsO Rain Harvest (2~4k~ 0 Narrower Road ~ ‘~i~ ‘~‘*Jc ~A ~tP.4S~ ~

O Roof Disconnect. i~-~c- 0 rBioretention/Rain Gardens ~ P- ~ ~ .L*r~ ~‘.

O Site Regrading/Terracing —-—--~- 0 Natural Drainage/Swales ‘~-‘l- ~ ~ ~.4 -‘~‘-~

Compost Soil Amendment Vegetative filter strips~~‘~b ~ 0 tj~ifiltrationtrenchesO Reforestation 0 Alternative Pavement [e.g., Ecocreto] —~ ~ ~-‘~‘.

O IC Removal (Roads/Parking) ~ 0 Outfall Erosion Protection ~O IC Disconnect. (Roads/Parking) ~ Lc.~ç~’. ~

Comments: ~ (~I~ t.~ ~4’4.1kIL~ %J~ó~& \~t~~t~

~ieldworkI for ation,Date Participants Ak~ ~DL~

Location: ~ Vb~3~ .& ~ I7~~17g

Subwshed Number: T4”~P~L~ Subdivision: ~ ~ V\1AL~,c

Approx. Age of Development: ~ t~ ~~S~/aters: $&~.2~,.3~~#,74

Nearby Natural Resources~? Spring~u Salamander,~oCave/Sinkhole/Karst Feature

~~Publicly Accessed Lands~~Other (e.g., wetlands, endangered sp. habitat):

~~~1’ ‘.I~

I

LlDChecklist.xls:BuII LID Page 1 of 1 8)9.01

LIP Field Checklist .~ ~ -

Nearby Public Resources‘~“Park~ ‘~JU~~ ~ ~-~“

SchoolGreenbeltBCPOther (e.g., public easement):

Drainage TypeCurb & GutterGrassed SwaleOverland Flow


V’~Rooftopsi/Driveways

Sidewalksb Road Width


~p~&~M)

~ ~L~LAA~J.~1f1 ~ ~. ~3 ~ ~ ‘M~oExisting Pervious Cover Wastewater Disposal Method

Sparse Vegetation ~ Central SewerErosion/Channelized FlowsCompactionIntensive Landscaping Practices ‘—~p S%Jv4.-..k ~ ~Jv~3~tA.y&.~Other: NO

On-Site SystemOther/Unknown:

Potential SolutionsRain Harvest t~ç4ru~j IE( Narrower Roa~, ~ 4. ~ 4&~~

O Roof Disconnect. ~ 0 ~16i~tention/RainGardens ~ ~,4.. ~‘.&.~- S~...LO Site Regrading/Terracing 0 Natural Drainage/SwalesO C,QjLJj~jjj~nt 0 Vegetative filter strips

>~ 0 L~ JmQL~ç~jpg ~4iAA&~~ts’~ 0 Infiltration trencheso Relbrestation 0 Alternative Pavement [e.g., Ecocreto]O IC Removal (~e~s/Parking) 0 Outfall Erosion ProtectionO IC Disconnect. (Roads/Parking)

Comments:

~ieIdworkI fo ation

I Date ‘f~1/~ Participants ~JY(L.~

Location:

Subwshed Number: I Subdivision: (5j~ç1g~ ~ c~i. i~t

Approx. Age of Development: ~‘~‘~1- ZDD ( Headwaters:

4~cLd~r&l~~ (t~~ ~+~M.L~’\ i rtXI~J~~ i LNt~~‘4— t~�l ~

Nearby Natural ResourcesSpring

~Salamander ~ a~w5PtW ~‘ “~PCave/Sinkhole/Karst FeaturePublicly Accessed LandsOther (e.g., wetlands, endangered sp. habitat):

Existing Structural Controls_______ Sand Filter N,wE~:_______ Flood Control_______Vegetative Filter Strip

Other:

LlDChecklist.xls:BuII LID Page 1 of 1 8)9/01

SchoolGreenbeltBC P

~ieldworkIn ormation

1Date

LID Field Checklist ~-Ubo ,‘b~’-~1

~Location: ~ ~k. or~~ ~lSubwshed Number: 1~Y~)(~ Subdivision:

Approx. Age of Development: V~7g — Headwaters: 5pic~_wroI ~. ~u2( Ccee..4_ I~-L,1-I

Nearby Natural Resources Existing Structural Controlsy~Spring Sand Filter~SaIamander Flood Control,~vCave/SinkhoIe/KarstFeature Vegetative Filter Strip

~ Lz~1t~Av~.~kW~’ Other:Other (e.g., wetlands, endangered s~~itat?,~/~ ~•/ ~, c ~ (~x ~

Drainage TypeV Curb & Gutter



VRooftops 1~:&tA) ~43~‘Driveways ,(-S~— Sidewalks7Roads 4S’ RoadWidth 4o’~.’~

— Parking Lots ParkingSpacesLandscaping

~.

Existing Pervious CoverSparse VegetationErosion/Channelized FlowsCompaction

— Intensive Landscaping Practices— Other:

Wastewater Disposal MethodL.—tentral Sewer


~-Potential Solutionso Rain Harvest 0 Narrower Road ~-~_.- ~ IQ~4-.L1 ~%CJ.f

~o Roof Disconnect. 0 Bioretention/Rain Gardenso Site Regrading/Terracing )c. 0 ~ ~w~tJ..�’ t~~ML/~~4~~.~4L’4o Compost Soil Amendment 0 Vegetative filter strips ~ ~ c4-. ~. ~

O Low-Impact Landscaping 0 Infiltration trencheso ~forestation 0 Alternative Pavement [e.g., Ecocreto]~o IC Removal (Roads/Parking) 0 5ti~llErosion Protectiono ~coct. (Roads/Parking)

Comments:c~ -~&k W ~ G ~- ~è.~-t ~ ~ ‘.s#t~¼&~

.~ 4i. tJ.~j ~ ~ ~pfr..I~~t~$ ‘~ M’W~t.4o ~

Participants ç’) t’-{)c\- ~

LlDCheckiist.xls:BuII LID Page 1 of 1 8/9/01

&LA

‘l

LID Field Checklist ~-i’~ ‘~~-~i

Location: ~LkV,t)tJ~, ~ ~ ~ ~ ~

— Subwshed Number: 7’f’~° Subdivision: cc~N~.I&~~~c.k, &~.

‘

Approx. Age of Development: “7&-S~fr Headwaters:

Nearby Natural ResourcesSpring ~Salamander j\JUCave/Sinkhole/Karst FeaturePublicly Accessed LandsOther (e.g., wetlands, endangered sp. habitat):

Existing Structural ControlsSand FilterFlood Control N t/~V \/

Vegetative Filter StripOther:

Nearby Public Resources

School KGreenbelt IVv”~~’BCPOther (e.g., public easement):

Drainage Type,,./ Curb & Gutter

Grassed Swale- Overland Flow

Existing Impervious Cover Pct. AdjacentType Con ected Pen’. Cover Other

~j~SidewaIks . ~ ~~— Roads Road Width— Parking Lots Parking Spaces

~

Existing Pervious Cover ¶i~ ‘~ Wastewater Disposal MethodSparse VegetationErosion/Channelized FlowsCompaction

— Intensive Landscaping PracticesOther:

L.—’tentral SewerSystem

Potential Solutionso Rain Harvest 0 Narrower Roado Roof Disconnect. 0 Bioretention/Rain Gardenso Site Regrading/Terracing 0 Natural Drainage/Swaleso Compost Soil Amendment 0 Vegetative filter stripso Low-Impact Landscaping 0 Infiltration trenchesO Reforestation 0 Alternative Pavement [e.g., Ecocreto]o IC Removal (Roads/Parking) 0 Outfall Erosion Protectiono IC Disconnect. (Roads/Parking)

Comments:

Cleldwork lnf rmation

1Date ~‘(‘~O~ Participants ~t’&~c~ ( ~ c.c_LlDChecklist.xls:BuII LID Page 1 of I 8)9.01

~M ~1~•

LID FieldLocation: ~L4rt~w4. ~subwshed Number:

Approx. Age of Development:

Checklist

~v~,W1C~ 1t~~:1$(LO~S&~ ~

Subdivision: \tTU.tk~Q 2.0 ~2J\~ 44. ~Headwaters:

Nearby Natural Resources Existing Structural Controls ~ t~~,4ESpring FilterSalamander Flood ControlCave/Sinkhole/Karst Feature Vegetative Filter StripPublicly Accessed Lands Other:Other (e.g., wetlands, endangered sp. habitat):

Nearby Public ResourcesParkSchool T~-QJ~JJ.-Ir-L WL.~~A4~A..Greenbelt ‘~Wr. kt.tt\’Q..-t’h~.

Drain~9eTypeV Curb&Gutter

GrassedSwaleFlow

BCP(e.g., public easement):

AdjacentPen’. Cover

Existing Impervious Cover Pct.Type Connected

~ Rooftops ~Mv’ -

v~DrivewaysCb4.AX_r. ~ ~

i.’ Sidewalks ~~Roads (°‘Z)

Parking Lots ________

.~-:;~

V

_____________Other _______

~v RoadWidth ~ ~I _______ ParkingSpaces

_______Landscaping

Existing Pervious CoverSparse VegetationErosion/Channelized Flows

~3 ~~ompactionV. Intensive Landscaping Practices ~~ci.L.’. ~4 .4,’.

— Other:

Was~~ôMterDisposal MethodSewer


Potential Solutions

~‘ 0 Roof DisconnectionO Site RegradinglTerracing ioretention/Rain Gardens ~bV~-0 Natural Drainage/Swales ~

EY’Compost Soil Amendment ‘~. 0 Vegetative Filter Strips~Rain Harvest t~..-.A ~ d~ te ~ O~~&-tv-i:~t~’1.ow-ImpactLandscaping $ 0 Infiltration TrenchesO Reforestation I’c~. ru~~ 0 Alternative Pavement [e.g., Ecocreto]O IC Removal (Parking) 0 Outfall Erosion Protection

Disconnection (Roads/Parking)

Comments:

¶~ ~ ~~ ~ (I~4J’ 4S~J~*~~b Oi

~ CL~~L~~is.4Fieldworjc Infprmation

1Date ‘~II’-f1o1 Participants (JM{4 ‘4-

I,

LIDCheckIist.xls:BuII LID2 Page 1 of 1 8/14/01

Lit) Field Checklist

Location: ~ (.~i.kliw.~t~c’..p~1~G&.4S...-~- Subwshed Number: ‘l ti~., L Subdivision: Cpwi#s~*.MC~&t.-L.....

Approx. Age of Development: Headwaters:

Nearby Natural Resources

Salamander— Cave/Sinkhole/Karst Feature— Publicly Accessed Lands

Other (e.g., wetlands, endangered sp. habitat):

Nea~jyPublic Resources~‘ Park —~ ~

V’~chooI(~)

Existi9g Structural ControlsV1’ Sand Filter

Flood ControlVegetative Filter StripOther:

c.,,,~ ~4 ~ U~jp,~

{~i~ ,~~k-.-fL~~Drainage Type

& GutterGrassed Swale

GreenbeltBCPOther (e.g., public easement):

Flow

Existing Impervious Cover Pot. AdjacentType Connected Pen’. Cover OtherRooftops

l7DrivewaysSidewalks

— oads RoadWidth~— Parking Lots Parking Spaces

Existing Pervious CoverV’ Sparse Vegetation ç ~ SL’lk~($Ltt ( £cA#’~s.~

V’4Erosion/Channelized Flows J ~ ‘~fr~L\,~&pc.i4k~Compaction ‘4p ~~‘& ~{44.),,,Intensive Landscaping PracticesOther:

Waste~aterDisposal MethodV Central Sewer

SystemOther/Unknown:

Pote~ntialSolutionsL~(Rain Harvest 0 Narrower RoadO floof Disconnection Bioretention/Rain Gardens~‘ Site RegradinglTerracing 0 Natural Drainage/Swales~‘ Compost Soil Amendment IQ~Vegetative Filter StripsO Low-Impact Landscaping I!~ Infiltration Trenches

Reforestation Alternative Pavement [e.g., Ecocreto)O IC Removal (Parking) ‘* 1W~Outfall Erosion Prot~ç~on

Disconnection (Roads/Parking)

Comments:

~ieldworklnf rmation

Date ~jigro, Participants ~JM~4--t-ç)c (_—

LlDCheckiist.xis:BuII LID2 Page 1 of 1 8/1401

Appendix B

LID Cost Details

APPENDIX B

Estimated Cost to Implement Low Impact Development Solutions per Acre


Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR Comm/MFR CommRain Tank gal 0.80$ 3,750 7,500 11,250 16,000 Gutters & Pipes to Tank lin. ft. 20.00$ 60 90 110 130 Construction Subtotal $ - 4,200$ 7,800$ 11,200$ 15,400$ Contingency (20%) $ - 840$ 1,560$ 2,240$ 3,080$ COST incl. Contingency $ - 5,040$ 9,360$ 13,440$ 18,480$ Assumed No. of Homes/Buildings no. - 1.5 3.0 1.0 1.0 System Cost per Home/Building $ - 3,360$ 3,120$ 13,440$ 18,480$

2. Rainwater Barrels

Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR N/A N/AAssumed No. of Roofs each - 1.5 3.0 - - 75-gallon Rain Barrel each 50.00$ 3 6 - - Gutters & Pipes to Tank lin. ft. 3.00$ 30 60 - - Construction Subtotal $ - 240$ 480$ -$ -$ Contingency (20%) $ - 48$ 96$ -$ -$ COST incl. Contingency $ - 288$ 576$ -$ -$ System Cost per Home/Building $ - 192$ 192$ NA NA


Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR Comm/MFR CommAssumed Roof Area ft2 - 3,727 7,471 11,213 15,863 Assumed Downspouts per 2500 ft2 Roof no. - 4 4 4 4 Assumed Total Downspouts no. - 6 12 18 26 Assumed Pct. Downspouts NOT Currently Disconnected pct. - 10% 10% 50% 70%Assumed Total Disconnections to be Made each 53.00$ 0.6 1.2 9.0 18.2 Construction Subtotal $ - 32$ 64$ 477$ 965$ Contingency (20%) $ - 6$ 13$ 95$ 193$ COST incl. Contingency $ - 38$ 76$ 572$ 1,158$ Cost per Disconnection $ - 64$ 64$ 64$ 64$


Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR Comm/MFR CommTotal Volume of Compost Application yd3 60.00$ 215 161 108 54 Construction Subtotal $ - 12,900$ 9,660$ 6,480$ 3,240$ Contingency (20%) $ - 2,580$ 1,932$ 1,296$ 648$ COST incl. Contingency $ - 15,480$ 11,592$ 7,776$ 3,888$ Assumed No. of Homes/Buildings no. - 1.5 3.0 1.0 1.0 Cost per Home/Site $ - 10,320$ 3,864$ 7,776$ 3,888$

440616\030329 B-1

APPENDIX B

5. Rain Gardens (Bioretention) for Non-Road Impervious Areas

Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICExcavation yd3 $15.00 43 171 257 323 Planting Soil yd3 $40.00 21.43 85.58 128.31 161.33 Trees & Shrubs (native)--15-gal. each $120.00 2 8 12 15 Plants (1 gal. containers) each $7.00 24 93 139 175 Mulch yd3 $45.00 9 35 52 65 Construction Subtotal $ - 2,313$ 9,177$ 13,735$ 17,243$ Contingency (20%) $ - 463$ 1,835$ 2,747$ 3,449$ COST incl. Contingency $ - 2,776$ 11,012$ 16,482$ 20,692$ Assumed No. of Homes/Buildings no. - 1.5 3.0 1.0 1.0 Cost per Home/Site $ - 1,851$ 3,671$ 16,482$ 20,692$


Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR Comm/MFR CommExcavate and Remove Existing Curb, Road Surface, & Base yd3 30.00$ 16 32 48 69 Replace Removed Material with Topsoil & Compost yd3 40.00$ 16 32 48 69 Rebuild Stand-up or Ribbon Curb lin. ft. 25.00$ 249 498 498 705 Revegetate with Seed yd2 0.40$ 41 83 125 176 Construction Subtotal $ - 7,352$ 14,725$ 15,868$ 22,528$ Storm Drain and Utility Relocation & Repair Contingency (5%) $ - 368 736 793 1,126 Contingency (20%) $ - 1,470$ 2,945$ 3,174$ 4,506$ Engineering & Permitting (20%) $ - 1,470$ 2,945$ 3,174$ 4,506$ COST incl. Engineering & Contingency $ - 10,660$ 21,351$ 23,008$ 32,666$


Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR Comm/MFR CommModify Inlet Structures, Curb to Divert Flow to Pervious Area yd3 0.40$ 163 327 353 501 Regrade Receiving Pervious Area yd2 10.00$ 27 54 82 116 Apply Compost to Receiving Pervious Area yd3 40.00$ 5 10 14 20 Construction Subtotal $ - 535$ 1,071$ 1,521$ 2,160$ Contingency (20%) $ - 107$ 214$ 304$ 432$ COST incl. Engineering & Contingency $ - 642$ 1,285$ 1,825$ 2,592$


Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR Comm/MFR CommExcavation yd3 15.00$ 25.00$ 50.00$ 70.00$ 100.00$ Geotextile Fabric yd2 3.00$ 55.00$ 110.00$ 165.00$ 235.00$ Perforated PVC Underdrain Pipe lin. ft 12.00$ 25.00$ 50.00$ 74.00$ 105.00$ Gravel (for Underdrain) yd3 40.00$ 10.00$ 15.00$ 20.00$ 30.00$ Planting Soil yd3 40.00$ 15.00$ 30.00$ 45.00$ 60.00$ Replace Pavement on Perimeter yd2 3.50$ 190.00$ 270.00$ 330.00$ 390.00$ Build Curb on Perim. lin. ft 25.00$ 65.00$ 90.00$ 110.00$ 130.00$ Trees & Shrubs (native)--15-gal. each 120.00$ 1.00$ 2.00$ 2.00$ 3.00$ Plants (5 gal. containers) each 7.00$ 62.00$ 123.00$ 185.00$ 261.00$ Mulch yd3 45.00$ 2.00$ 4.00$ 6.00$ 8.00$ Overflow Storm Drain Inlet l.s. 2,400.00$ 1.00$ 1.00$ 1.00$ 1.00$ Outflow Pipe (12" PVC) & Connection to Existing Storm Inlet lin. ft 75.00$ 25.00$ 25.00$ 25.00$ 25.00$ Construction Subtotal $ - 9,049$ 12,231$ 15,018$ 18,502$ Contingency (20%) $ - 1,810$ 2,446$ 3,004$ 3,700$ Engineering & Permitting (20%) $ - 1,810$ 2,446$ 3,004$ 3,700$ COST incl. Engineering & Contingency $ - 12,669$ 17,123$ 21,025$ 25,903$

440616\030329 B-2

APPENDIX B


Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR Comm/MFR CommExcavate and Remove Existing Curb, Road Surface, & Base yd3 30.00$ 81 161 242 343 Gravel Base yd3 30.00$ 46 92 138 196 Pervious Pavement ft2 3.50$ 1,864 3,735 5,606 7,932 Rebuild Stand-up or Ribbon Curb lin. ft. 25.00$ 124 249 249 353 Construction Subtotal $ - 13,444$ 26,896$ 37,263$ 52,742$ Storm Drain and Utility Relocation & Repair Contingency (5%) $ - 672 1,345 1,863 2,637 Contingency (20%) $ - 2,689$ 5,379$ 7,453$ 10,548$ Engineering & Permitting (20%) $ - 2,689$ 5,379$ 7,453$ 10,548$ COST incl. Engineering & Contingency $ - 19,493$ 38,999$ 54,032$ 76,476$

10. Porous Curb & Gutter

Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR Comm/MFR CommExcavate and Remove Existing Curb, Road Surface, & Base yd3 30.00$ 21 43 65 91 Gravel Base yd3 30.00$ 12 25 37 52 Pervious Pavement ft2 3.50$ 497 996 1,495 2,115 Rebuild Stand-up or Ribbon Curb lin. ft. 75.00$ 124 249 249 353 Construction Subtotal $ - 5,846$ 11,740$ 14,519$ 20,514$ Storm Drain and Utility Relocation & Repair Contingency (5%) $ - 292 587 726 1,026 Contingency (20%) $ - 1,169$ 2,348$ 2,904$ 4,103$ Engineering & Permitting (20%) $ - 1,169$ 2,348$ 2,904$ 4,103$ COST incl. Engineering & Contingency $ - 8,476$ 17,022$ 21,052$ 29,745$

11. “SEA Streets” Equivalent (using SOS capture depth)

Consideration Units Unit Cost 20% IC 40% IC 60% IC 80% ICAssumed Land Use Type - - SFR SFR Comm/MFR CommNarrow Existing RoadwayExcavate and Remove Existing Curb, Road Surface, & Base yd3 30.00$ 16 32 48 69 Replace Removed Material with Topsoil & Compost yd3 40.00$ 16 32 48 69 Rebuild Stand-up or Ribbon Curb lin. ft. 25.00$ 249 498 498 705 Revegetate with Seed yd3 0.40$ 41 83 125 176 Excavation yd3 15.00$ 200 270 345 420 Geotextile Fabric yd2 3.00$ 470 650 825 1,000 Perforated PVC Underdrain Pipe lin. ft 12.00$ 212 291 370 449 Gravel (for Underdrain) yd3 40.00$ 55 75 95 115 Planting Soil yd3 40.00$ 120 165 210 250 Replace Pavement on Perimeter yd2 3.50$ 555 650 730 805 Build Curb on Perim. lin. ft 25.00$ 185 220 245 270 Trees & Shrubs (native)--15-gal. each 120.00$ 6 8 10 12 Plants (5 gal. containers) each 7.00$ 528 726 924 1,122 Mulch yd3 45.00$ 16 22 28 34 Overflow Storm Drain Inlet l.s. 2,400.00$ 1 1 1 1 Outflow Pipe (12" PVC) & Connection to Existing Storm Inlet lin. ft 75.00$ 25 25 25 25 Construct Open Drainage System (Grassed Swales)Excavation yd3 15.00$ 3,729 7,471 7,475 10,577 Regrading yd2 10.00$ 1,243 2,490 2,492 3,526 Revegetate with Seed yd2 0.40$ 1,243 2,490 2,492 3,526 Construction Subtotal $ - 106,146$ 190,863$ 200,073$ 271,799$ Storm Drain and Utility Relocation & Repair Contingency (20%) $ - 21,229$ 38,173$ 40,015$ 54,360$ Contingency (20%) $ - 21,229$ 38,173$ 40,015$ 54,360$ Engineering & Permitting (20%) $ - 21,229$ 38,173$ 40,015$ 54,360$ COST incl. Engineering & Contingency $ - 169,834$ 305,381$ 320,116$ 434,878$

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Bull Creek Watershed Management Study · 2012-10-14 · BULL AND WEST BULL CREEK WATERSHED...

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