Tribal NPS modeling.ppt - University of New Hampshire · Today’s Discussion Topics • Some...

Watershed ModelingSome Simple Approaches

New England Tribal NPS Workshop

Mark Voorhees – US EPA New England

May 1, 2013

Today’s Discussion Topics• Some background on watershed modeling• Models to be discussed

– Impervious Cover Model– “Simple Method”– Pollutant Load Export Rates from literature– Derived Pollutant Load Export Rates using SCS Curve Number Model

– Load Duration Curves

• Best Management Practice Reductions

25/13/2013

Modeling Process Steps

• Step 1: Clearly define your purpose for using models?

• Step 2: Match the modeling approach(s) to fit your needs– Always use the simplest modeling approach possible

• Step 3: Apply model or modeling approaches to your watershed– Data compilation – GIS analyses expedite process– Selection of appropriate input values– Spreadsheets are very useful

3

Usefulness of Simple Modeling Approaches

• Simple approaches are typically empirically derived and are excellent for demonstrating relative changes in watershed processes due land‐use activities

• Educational and informative to guide development of sound land‐use planning and development regulations

• Capable of quantifying the relative benefits of implementing controls or policies

4

Great opportunity –not to be missed

Quick background on some important processes to be aware of

• Hydrology• Role of imperviousness – Impervious Cover Model• Regional rainfall patterns• Pollutant processes

– “build‐up and wash‐off”– erosion

• Water quality impacts – Long term (e.g., habitat degradation, eutrophication)– Short term (toxicity)

5

Hydrology and the developing watershed

Changes in Stream Hydrology as a Result of Urbanization

Source: Schueler, 1994

Runoff Yield and Imperviousness Cover

8

0.000.200.400.600.801.001.201.40

0 50 100

Stor

mw

ater

runo

ff yi

eld

-m

illio

n ga

llons

/acr

e.

Percent effective impervious

USGS Lower Charles River Sub-watershed Flow Gauging Program Water Year 2000

Stormwater runoff yield (million gallons per acre) vs. percent effective impervious cover(Breault, et. Al, 2002) (Zarriello et al, 2002)

Effects of Urbanization on Maryland Stream Cross Section

Source: Center for Watershed Protection, 2003

Consequently….

Increased stormwater volume & velocity

Stream widening & down‐cutting

Decreased base flow

And . . . more flooding!

Changes to Stream Geomorphology

Center for Watershed Protection’s Impervious Cover Model



New England Region Rainfall Patterns Important Points

• Most rain events are small in size;• Occur regularly (average about once every three days)

• The total volume and event size distribution are relatively consistent across New England Region

12

Precipitation Analysis

Percentage of Total Number of Rainfall Events Based on Size of Rain Events - Boston, MA

(1948-2004)

1.5-2.0 inches2%

1.0-1.5 inches5%

0.6-1.0 inches10%

0.0 - 0.2 inches55%

2.0 inches and above

1%

0.2-0.6 inches27%

0.0 - 0.2 inches0.2-0.6 inches0.6-1.0 inches1.0-1.5 inches1.5-2.0 inches 2.0 inches and above

Trash Nutrients

Pathogens

Heavy Metals

Oil & GreaseSediment

Pollutants

Today’s Discussion of Pollutants

• Nutrients – Phosphorus and Nitrogen• Trace metals ‐ Zinc as an example• Solids• However, methodologies are suitable to many other pollutants

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Stormwater Pollutants and Urban Runoff

• Phosphorus• Mostly associated with very

fine particles ~ 40 microns• Washed from impervious

surfaces with smallamounts of rainfall (0.3 inches)

• Stormwater controls must have filtration component to be effective

Nitrogen N Oxides are readily

washed off in early portion of rain events (first flush is typical).

Organic nitrogen can be a significant part of N load

High removals of SW nitrogen may require de-nitrification

• Trace Metals (e.g., Zinc)

• Highly associated with particulate matter

• Many are readily washed off of impervious surfaces

• High reductions can be achieved through settling practices.

Sources of Phosphorus & Nitrogen in SW

Solids and nutrients fromAgricultural Sources

Source:http://thinkprogress.org/climate/2012/09/20/879421/we-must-look-at-new-

options-for-reducing-water-pollution-from-agriculture/?mobile=nc 20

The Simple Method ‐ Calculating storm water pollutant loading from developed lands

• Use: Estimate stormwater runoff pollutant loads for urban areas

• Information needed for the Simple Method: • Sub‐watershed drainage area; • fraction impervious cover; • runoff pollutant concentrations; and• annual precipitation

http://www.stormwatercenter.net/monitoring%20and%20assessment/simple%20meth/simple.htm

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Simple Method Notes and Limitations

• Suitable for providing general planning‐level estimates of likely stormwater pollutant export from areas at the scale of a development site or sub‐watershed (areas for which base flow is non‐existent or very small)

• Most appropriate for assessing and comparing the relative stormwater pollutant load changes of different land use and development scenarios

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The Simple Method

• The Simple Method estimates pollutant loads for chemical constituents as a product of annual runoff volume and pollutant concentration, as:

L = 0.226 * R * C * A

Where: L = Annual load (lbs)R = Annual runoff (inches)C = Pollutant concentration (mg/L)A = Area (acres)0.226 = Unit conversion factor

23

Simple Method – Runoff Volume

• The Simple Method calculates annual runoff as a product of annual runoff volume, and a runoff coefficient (Rv). Runoff volume is calculated as:

R = P * Pj * Rv• Where: R = Annual runoff (inches)

P = Annual rainfall (inches)Pj = Fraction of annual rainfall events that produce runoff (usually 0.9)Rv = Runoff coefficient

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Simple Method – Runoff Coefficient• In the Simple Method, the runoff coefficient is calculated based on impervious cover in the subwatershed

• The following equation represents the best fit line for the dataset (N=47, R2=0.71).

• Rv=0.05+0.9Ia; Where: Ia = Impervious fraction

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Typical Percent Impervious Values for the Simple Method


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Table 5. Impervious Cover (%) for Various Land Uses

Land Use

Density Source

(dwelling units/acre) Northern

Virginia (NVPDC, 1980)1

Olympia (COPWD, 1995)

Puget Sound (Aqua Terra,

1994)

NRCS Rouge RiverModel

Default2

(USDA, 1986)(Kluitenberg,

1994)

Low Density Residential<0.5 6 - 10 -

19

100.5 - - 10 121 12 - 10 20

Medium Density Residential

2 18 - - 25

303 20 40 40 304 25 40 40 38

High Density Residential 5-7 35 40 40 - 38 40

Multifamily Townhouse (>7) 35-50 48 60 65 - 60Industrial -- 60-80 86 90 72 76 75

Commercial -- 90-95 86 90 85 56 85Roadway 80

1: NVPDC data measure effective impervious cover (i.e., rooftops are not included in residential data)

2: Model default values are approximately equal to the median of Olympia, Puget Sound, NRCS, and Rouge River data, with adjustments made where studies estimate impervious cover for a broad range of densities.

Simple Method Default Concentrations(see link below for possible defaults for TP and TN)


275/13/2013

Table 1: Pollutant Concentrations by Land Use: Total Suspended Solids (mg/l)Land Use

Source Residential Commercial Roadway Industrial Notes

Schueler, 1987 mean 1001 - - -This value reflects an estimate based on 25 data points from a wide range of watershed sizes. Data reflect instream concentrations. A small watershed size (i.e., 10 acres) was assumed to minimize the influence of the channel erosion component.

Gibb et al., 1991 mean 150 - 220 - These values represent recommended estimates for planning purposes and are based on an analysis of mean concentrations from over 13 studies from the US and British Columbia.

Smullen and Cave, 1998 median 55 55 55 55

This study probably represents the most comprehensive data set, with 3,047 event samples being included from across the nation. Data includes pooled NURP, USGS, and NPDES sources. The value is a median of EMCs and applies to general urban runoff (i.e., mixed land uses). The low concentration relative to other data can be attributed to the fact that, while NURP data represent small watersheds where channel erosion may play a role, NPDES data are collected as "end of the pipe" concentrations for very small drainage areas of a uniform land use. The NPDES concentrations were approximately 70% lower than concentrations from NURP or USGS.

US EPA, 1983 median 101 69 - - These values represent NURP data for residential and commercial land use. NURP data were collected in the early 1980s in over 28 different metropolitan areas across the US.

Claytor and Schueler, 1996 - - 142 124The roadway value is the un-weighted mean of 8 studies conducted by the FHWA. The industrial value is the mean value from 6 storms monitored at a heavy industrial site in Auckland, NZ.

Barrett and Malina, 1998 - - 173 -This data reflects a study of vegetative swales treating highway runoff in Austin, TX. Value represents average of the mean inflow concentrations measured at 2 sites. Data were collected over 34 storm events.

Caraco and Schueler (1999). Arid Climates 242 242 242 242

This value represents an average of EMC data collected from 3 arid climate locales (Phoenix, Boise, and Denver). A total of 90 data points are used, with each site having at least 16 data points. Value applies to general urban runoff (i.e., mixed land uses).

Driscoll, 1986 - - 242 -This value is the average of 4 median EMCs collected from highway sites in Nashville, Denver, Milwaukee, and Harrisburg. A total of 93 data points were used to develop value, with each site having at least 16 data points.

Shelley and Gaboury, 1986 - - 220 - This value is the median value of 8 highway studies from across the US. Some of the data from the Driscoll study (1986) is included.

Whalen and Cullum, 1988 228 168 - 108

These data are from an assessment of urban runoff quality that looked at NURP and State of Florida data. The NURP data are presented. Residential and commercial values are mean values for specified land uses and reflect between 200 and 1,100 sampling events depending on the parameter and land use. Industrial values are from 4 NURP sites and generally represent light industrial land use.

Model Default Value2 100 75 150 1201: Concentration based on a 10-acre drainage areaThe model default values represent best professional judgment, and give additional weight to studies conducted at a national level. Data do not incorporate studies on arid climates.

An example using the Simple Method Situation: A residential development is proposed for a sub‐watershed area within the Lake Bubaboo watershed. The project is proposed for a 35 acre area that is currently mostly forested. The LBA is concerned about increased phosphorus loading to the lake and is insisting that the project include an adequate level of stormwater control so that there will be no increase in annual phosphorus load to the lake.

Question:What would be the minimum percent reduction in annual phosphorus load that the proposed project’s stormwater management program would need to achieve in order to meet the LBA’s request?

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Example ‐ Project Information Area = 35 acres Annual precipitation = 43.5 inches

Existing conditions: Fraction imperviousness of forested sub‐watershed = 0.06 (i.e., 6% ‐paved

roadway through sub‐catchment)

Typical median stormwater TP concentration (C) for forested area = 0.10 mg/L

Proposed conditions: Fraction imperviousness of proposed residential development = 0.25 Typical median stormwater TP concentration (C) for residential area = 0.26 mg/L

5/13/2013 29

Example Calculations (continued)

Step 1: Calculate annual runoff volume for existing and proposed conditions using: R = P x Pj x Rv

Where: R = Annual runoff (inches) P = Annual rainfall (inches) = 43.5 inchesPj = Fraction of annual rainfall events that produce runoff =0.9Rv = Runoff coefficient (where Rv = 0.05+0.9Ia)Ia = Impervious fraction

Existing Conditions: R=43.5 x 0.9 x (0.05 + (0.9 x 0.06)) = 4.1 inches

Proposed Conditions: R=43.5 x 0.9 x (0.05 + (0.9 x 0.25))= 10.8 inches

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Step 2: Calculate annual phosphorus load for existing and proposed conditions using: L = 0.226 * R * C * A

Where: L = Annual load (lbs)R = Annual runoff (inches)C = Pollutant concentration (mg/L)A = Area (acres)0.226 = Unit conversion factor

Existing Conditions: L Exist=0.226 x 4.1 inches x 0.10 mg/L x 35 acres = 3.2 lbs P

Proposed Conditions: L Prop=0.226 x 10.8 inches x 0.26 mg/L x 35 acres = 22.2 lbs P

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Step 3: Calculate minimum percent reduction needed by proposed project’s stormwater management plan using:

% Reduction = [ (L Prop ‐L Exist)/L Prop ]x 100= [ (22.2‐ 3.2)/22.2]x 100= 86%

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Example of Annual Phosphorus Load Export Rates using the Simple Method

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Typical land use associated with

percent impervious values (1)

Percent Impervious

(%)

Annual Phosphorus load export rate developed from the Simple Method

(Schueler 1987) (lbs/acre‐yr)

TP EMC=0.22 mg/l

TP EMC=0.26 mg/l

TP EMC=0.30 mg/l

Rural residential0 0.10 0.12 0.135 0.19 0.22 0.2510 0.27 0.32 0.37

Large lot single family

15 0.36 0.43 0.49

20 0.45 0.53 0.61

Medium to high density residential

25 0.54 0.63 0.7330 0.62 0.74 0.8535 0.71 0.84 0.97

Multi‐family residential

40 0.80 0.95 1.0945 0.89 1.05 1.2150 0.98 1.15 1.33

55 1.06 1.26 1.4560 1.15 1.36 1.57

Light commercial/industr

ial

65 1.24 1.47 1.6970 1.33 1.57 1.8175 1.42 1.67 1.9380 1.50 1.78 2.05

Heavy commercial

85 1.59 1.88 2.1790 1.68 1.98 2.2995 1.77 2.09 2.41100 1.85 2.19 2.53

Annual rainfall for Boston 43.5 inches used to calculate export rates

Unit‐Area Loading or Pollutant Load Export Rate Method

This method uses published yield‐values to estimate annual average pollutant loading for a specific land use

Simple straight‐forward approach works well with spreadsheets and information from GIS watershed data layers

Information needed: Inventory of watershed areas by land use Reported pollutant load export rates (e.g., literature, TMDLs and watershed loading analyses)

5/13/2013 34

Unit‐Area Loading Method Method: Multiply area of land‐use by the unit‐area export rate for the pollutant of interest;

Usefulness and limitations: This method is useful for estimating the relative magnitude of runoff pollutant loading from various land‐use based sources in a watershed;

This method is least likely to give accurate results because of the uncertainty of fit between the catchment of interest and the data collection location(s);

5/13/2013 35

Some Literature derived Runoff Pollutant Load Export Rates

http://cdm16658.contentdm.oclc.org/cdm/singleitem/collection/p267501ccp2/id/1999/rec/4

36

Table 3‐12: Typical Pollutant Loadings (Ibs/acre‐yr) From Different Land Uses ( Taken from Fundamentals of Urban Runoff Management: Technical and Institutional Issues. 2nd Edition, 2007

By: Earl Shaver, Richard Horner, Joseph Skupien, Chris May, Graeme Ridley)

Land‐Use TSS TP TKN NH3‐N NO2&NO3 BOD COD Pb Zn Cu Cd

Commercial 1000 1.5 6.7 1.9 3.1 62 420 2.7 2.1 0.4 0.03

Parking Lot 400 0.7 5.1 2 2.9 47 270 0.8 0.8 0.06 0.01

High‐Density Residential 420 1 4.2 0.8 2 27 170 0.8 0.7 0.03 0.01

Medium‐Density Residential 250 0.3 2.5 0.5 1.4 13 50 0.05 0.1 0.03 0.01

Low‐Density Residential 65 0.04 0.3 0.02 0.1 1 7 0.01 0.04 0.01 0.01

Highway 1700 0.9 7.9 1.5 4.2 n/a n/a 4.5 2.1 0.37 0.02

Industrial 670 1.3 3.4 0.2 1.3 n/a n/a 0.2 0.4 0.1 0.05

Shopping Center 440 0.5 3.1 0.5 1.7 n/a n/a 1.1 0.6 0.09 0.01

Source: Based on Table 2.5 in Burton and Pitt, 2002

Example Calculation using Pollutant Load Export Rates

• Estimate the annual total nitrogen (TN) load that discharges from storm drain 1 (SD1) to Calvin Bay.

• Step 1. A delineation of the contributing drainage area to SD1 using storm drainage maps and the land‐use data‐layer in GIS indicates the following inventory:– 11.5 aces commercial – 4.7 acres high density residential (HDR) ; and– 3.1 acres of parking lots

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Example Calculation using Pollutant Load Export Rates (continued)

• Step 2: Select appropriate load export rates (LER). Table 3.12 does not provide rates for TN but does for TKN and NO2 & NO3 (TN = TKN + NO2 & NO3)– Commercial: TN‐LER = 6.7 + 3.1 = 9.6 lbs/ac/yr– HDR: TN‐LER = 5.1 + 2.9 = 8.0 lbs/ac/yr– Parking Lot: TN‐LER = 4.2 + 2.0 = 6.2 lbs/ac/yr

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Table 3‐12: Typical Pollutant Loadings (Ibs/acre‐yr) From Different Land Uses ( Taken from Fundamentals of Urban Runoff Management: Technical and Institutional Issues. 2nd Edition, 2007

By: Earl Shaver, Richard Horner, Joseph Skupien, Chris May, Graeme Ridley)Land‐Use TSS TP TKN NH3‐N NO2&NO3 BOD COD Pb Zn Cu Cd

Commercial 1000 1.5 6.7 1.9 3.1 62 420 2.7 2.1 0.4 0.03Parking Lot 400 0.7 5.1 2 2.9 47 270 0.8 0.8 0.06 0.01

High‐Density Residential 420 1 4.2 0.8 2 27 170 0.8 0.7 0.03 0.01Medium‐Density Residential 250 0.3 2.5 0.5 1.4 13 50 0.05 0.1 0.03 0.01Low‐Density Residential 65 0.04 0.3 0.02 0.1 1 7 0.01 0.04 0.01 0.01

Highway 1700 0.9 7.9 1.5 4.2 n/a n/a 4.5 2.1 0.37 0.02Industrial 670 1.3 3.4 0.2 1.3 n/a n/a 0.2 0.4 0.1 0.05

Shopping Center 440 0.5 3.1 0.5 1.7 n/a n/a 1.1 0.6 0.09 0.01Source: Based on Table 2.5 in Burton and Pitt, 2002

Example Calculation using Pollutant Load Export Rates (continued)

• Step 3: Calculate TN loads for each land‐use area:– Commercial: 9.6 lbs/ac/yr x 11.5 acres = 110.4 lb/yr– HDR: 8.0 lbs/ac/yr x 4.7 acres = 37.6 lb/yr– Parking Lot: lbs/ac/yr x 3.1 acres = 19.2 lb/yr

• Step 4: Sum TN Loads:– SD1 TN load = 110.4 + 37.6 + 19.2 = 167.2 lb/yr

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Suggested Phosphorus Load Export Rates when percent imperviousness is unknown

40

Annual Phosphorus Load Export Rates by Land Use when Percent imperviousness is unknown

Land use (source) TP load export rate (lb/ac/yr)

Agriculture ‐ general*(1) 0.45Commercial **(2) 1.50

Forest (3) 0.12Freeway (2) 0.80

High‐density residential (2) 1.00Industrial (2) 1.30

Medium‐density residential (2) 0.50Low‐density residential (rural) (3) 0.27

Open space (3) 0.27

Sources: (1) Budd and Meals 1994; (2) Shaver et al. 2007; (3) Mattson and Isaac 1999

* Agriculture includes row crops, actively managed hay fields and pasture land.

** Institutional type land uses such as government properties, hospitals, and schools are included in the commercial land use category for the purpose of calculating phosphorus loadings.

Suggested Phosphorus Load Export Rates when Imperviousness is known

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Table 1. Proposed Phosphorus Load Export Rates (PLER) for various stormwater runoff source categoriesPhosphorus Source Category by Land

Use Land Surface Cover Phosphorus Load Export Rate, Kg/ha/yr Comments

Commercial (Com) and Industrial (Ind) Impervious 2.0

Derived using a combination of the Lower Charles USGS Loads study and NSWQ dataset. This PLER is approximately 75% of the HDR PLER and reflects the difference in the distributions of SW TP EMCs between Commercial/ Industrial and Residential.

Pervious See* DevPERV

Multi‐Family (MFR) and High‐Density Residential (HDR)

Impervious 2.6 Largely based on loading information from Charles USGS loads, SWMM HRU modeling, and NSWQ data set

Pervious See* DevPERV

Medium ‐Density Residential (MDR)Impervious 2.2 Largely based on loading information from Charles USGS loads,

SWMM HRU modeling, and NSWQ data setPervious See* DevPERV

Low Density Residential (LDR) ‐ "Rural"Impervious 1.0 Derived from Mattson Issac and subsequent modeling by Tetra Tech

for Optimization study (composite rate 0.3 kg/ha/yr)Pervious 0.2

Highway (HWY)Impervious 1.5 Derived from Shaver et al and subsequent modeling by Tetra Tech

for Optimization study (composite rate 0.9 kg/ha/yr)Pervious See* DevPERV

Forest (For)Impervious 1.0 Derived from Mattson Issac and subsequent modeling by Tetra Tech

for Optimization study (composite rate 0.13 kg/ha/yr)Pervious 0.1

Agriculture (Ag)Cover Crop/Grazing 0.8

Table C‐4 of NH Lake TMDL Reports (Cited source: Reckhow et al. 1980)Row Crop 2.2

Hayland ‐ no manure 0.4*Developed Land Pervious (DevPERV)‐

Hydrologic Soil Group A/B Pervious 0.2Derived from SWMM HRU modeling with assumed representative TP concentration of 0.3 mg/L for pervious runoff from developed lands. TP of 0.3 mg/L is based on NSWQ dataset, TB‐9 (CSN, 2011), and other PLER literature.

*Developed Land Pervious (DevPERV) ‐Hydrologic Soil Group C Pervious 0.5

*Developed Land Pervious (DevPERV) ‐Hydrologic Soil Group D Pervious 0.8

Source of Table : See Attachment 1 to Appendix F to 2013 Draft New Hampshire Small MS4 General Permit: http://www.epa.gov/region1/npdes/stormwater/nh/2013/Appendix‐F‐Small‐MS4‐NH.pdf

Model Simulated Pollutant load Export Rates Using the Curve Number Method

• EPA used P8 model to simulated average annual runoff yields for a variety of pervious surfaces (e.g., million gallons/acre/year)

• P8 model is a continuous simulation model that uses hourly rainfall data to generate runoff volumes for a long‐term period (e.g., 10 years)

• P8 uses the Curve Number method to estimate runoff volumes from pervious surfaces

• The Curve Number method was developed by SCS (now NRCS) and is a commonly and widely used empirical model suitable for many land covers including agriculture 42

Model Simulated Pollutant load Export Rates Using the Curve Number Method

• Average annual pollutant load export rates can be calculated using the model simulated runoff yields multiplied by a pollutant concentration (or a range of concentrations)

• The runoff yields reflect regional climatic patterns;• This method allows the user to estimate annual loadings that reflect

regional climatic conditions and the users choice for quality

430.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

20 30 40 50 60 70 80 90 100

Average An

nual Run

off Y

ield, M

illion

gallo

ns/acre/year

Curve Number

P8 Model Simulated Average Annual Runoff Yield Using the Curve Number Method ( Boston MA, Hourly rainfall 1998‐2002), MG/acre/yr

Curve Number Method and Model Derived Export Rates

• The Curve Number method is widely used in the design of stormwater controls

• Commonly used for agricultural sources• Use of the derived export rates based on annual runoff yield is useful for planning purposes and estimating relative differences among source categories and relative benefits of management options.

44

Curve Number Method to Generate Generic Runoff Flow and Load Export Rates For New England

45

Curve Numbers by Land Cover and Hydrologic Soil Group

United States Department of AgricultureNatural Resources Conservation Service

Part 630 HydrologyNational Engineering Handbook

Chapter 9 Hydrologic Soil-CoverComplexes

For a more complete list of curve numbers see the above document found at this link:

http://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17758.wba

Hydrologic Soils are identified in soil surveys

46

Runoff Curve Numbers

The specified SCS Curve Number (CN) reflects an area‐weighted‐average of the pervious areas, which

generally reflect land cover and soil hydrologic group.

The following table lists typical CN values as a function of land use, hydrologic condition, and soil group:

Curve Number by Hydrological Soil Group

Land Use Hydrologic Condition A B C D

Grassed Areas Good (>75% Cover) 39 61 74 80

Fair 49 69 79 84

Poor (<50% Cover) 68 79 86 89

Meadow / Idle Good 30 58 71 78

Woods Good (thick forest) 25 55 70 77

Fair 36 60 73 79Poor (thin, no

mulch) 45 66 77 83

Construction Site Newly Graded 81 89 93 95

Impervious 98 98 98 98

Pervious area HSG A well drained soils

Pervious area HSG B moderately drained soils

Pervious area HSG C limited permeability

Pervious area HSG D poorly drained soils

Tabulated Model Calculated Annual Export Rates

• Spreadsheet generated tables of export rates for various curve numbers and pollutant concentrations

Export rate = runoff yield (MG/ac/yr) x concentration (mg/L) x 3.7854 x 106L/MG x 1 lb/454,000 mg

47

P8 model simulations ‐Boston, MA hourly precipitation, 1998‐

2002

Runoff yield,

MG/acre/yr

Annual Phosphorus Load Export Rate lb/acre/yr

Average Annual Flow Weighted Total Phosphorus Concentration, mg/l 0.025 0.05 0.1 0.2 0.3 0.5 0.7 1.0

curve nu

mbe

r

30 0.002 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.0240 0.007 0.00 0.00 0.01 0.01 0.02 0.03 0.04 0.0550 0.018 0.00 0.01 0.02 0.03 0.05 0.08 0.11 0.1560 0.042 0.01 0.02 0.03 0.07 0.10 0.17 0.24 0.3570 0.083 0.02 0.03 0.07 0.14 0.21 0.35 0.48 0.6980 0.157 0.03 0.07 0.13 0.26 0.39 0.65 0.91 1.3190 0.318 0.07 0.13 0.26 0.53 0.79 1.32 1.85 2.6598 0.748 0.16 0.31 0.62 1.25 1.87 3.12 4.36 6.23

100% by P8 1.052 0.22 0.44 0.88 1.75 2.63 4.39 6.14 8.77MG = million gallons, Average annual rainfall = 43.5 inches

Tabulated Model Calculated Annual Export Rates

48


2002

Runoff yield,

MG/acre/yr

Annual Nitrogen Load Export Rate lb/acre/yr

Average Annual Flow Weighted Total Nitrogen Concentration, mg/l 0.5 1.0 1.5 2.0 3.0 5.0 8.0 10.0

curve nu

mbe

r

30 0.003 0.01 0.02 0.02 0.03 0.05 0.08 0.13 0.1740 0.007 0.03 0.05 0.08 0.11 0.16 0.27 0.43 0.5450 0.017 0.08 0.15 0.23 0.31 0.46 0.77 1.22 1.5360 0.034 0.17 0.35 0.52 0.70 1.05 1.75 2.79 3.4970 0.063 0.35 0.69 1.04 1.38 2.08 3.46 5.53 6.9280 0.129 0.65 1.31 1.96 2.61 3.92 6.53 10.44 13.0590 0.303 1.32 2.65 3.97 5.30 7.95 13.25 21.20 26.5098 0.426 3.12 6.23 9.35 12.47 18.70 31.17 49.87 62.34



2002

Runoff yield,

MG/acre/yr

Annual Total Suspended Solids Load Export Rate lb/acre/yrAverage Annual Flow Weighted Total Suspended Solids Concentration, mg/l 25.0 50.0 75.0 100.0 150.0 200.0 400.0 1000.0

curve nu

mbe

r

30 0.002 0.4 0.8 1.2 1.7 2.5 3.3 6.6 16.540 0.007 1.4 2.7 4.1 5.4 8.2 10.9 21.7 54.350 0.018 3.8 7.7 11.5 15.3 23.0 30.6 61.3 153.160 0.042 8.7 17.5 26.2 34.9 52.4 69.9 139.7 349.370 0.083 17.3 34.6 51.9 69.2 103.8 138.4 276.8 692.180 0.157 32.6 65.3 97.9 130.6 195.8 261.1 522.2 1305.690 0.318 66.3 132.6 198.8 265.1 397.7 530.2 1060.4 2651.198 0.748 155.9 311.8 467.8 623.7 935.5 1247.3 2494.7 6236.7


Example Calculation using Model Generated Export Rates

• Estimate the annual TSS load from a 10 acre pasture with HSG C in fair hydrologic condition.

• Assume a median TSS concentrations of 70 mg/L

• The Curve number is 79• Using the export rate table, the annual runoff

yields for CNs 70 and 80 are 0.083 and 0.157 MG/acre/yr, respectively. Interpolating, the runoff yield for CN 79 is 0.150 MG/acre/yr

• The export rate for CN 79 and TSS conc. of 70 mg/L = 0.150(MG/ac/yr) x 70 (mg/L) x 3.7854 x 106L/MG x 1 lb/454,000 mg = 88 lbs/ac/yr

• The estimated annual TSS load from the pasture = 10 acres x 88 lb/acre/yr= 880 lbs yr

Runoff Curve Numbers

The specified SCS Curve Number (CN) reflects an area‐weighted‐average of the pervious areas, which

generally reflect land cover and soil hydrologic group.

The following table lists typical CN values as a function of land use, hydrologic condition, and soil group:

Curve Number by Hydrological Soil Group

Land Use Hydrologic Condition A B C D

Grassed Areas Good (>75% Cover) 39 61 74 80

Fair 49 69 79 84

Poor (<50% Cover) 68 79 86 89

Meadow / Idle Good 30 58 71 78

Woods Good (thick forest) 25 55 70 77

Fair 36 60 73 79Poor (thin, no

mulch) 45 66 77 83

Construction Site Newly Graded 81 89 93 95

Impervious 98 98 98 98

Pollutant Load Duration Curves

http://www.kdheks.gov/tmdl/basic.htm 50

Flow & Fecal Load Duration Curves

http://www.crwr.utexas.edu/gis/gishydro09/using_an_HIS.html 51

Load Duration Curves

• Flow Duration Curve Load Duration Curves• Data intensive (not really a simple approach):

– need long‐term flow record or a calibrated continuous simulation hydrologic model

– Abundant water quality data and/or calibrated watershed water quality model

• Useful for understanding the nature of contributing sources and for which management activities are needed– dry weather (low flow) & wet weather (high flow)

http://water.epa.gov/lawsregs/lawsguidance/cwa/tmdl/upload/2007_08_23_tmdl_duration_curve_guide_aug2007.pdf

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Reduction Credits forStructural Controls

Develop estimates of long‐term cumulative performance using regional climate data

Stormwater Best Management Practices Performance Analysis by Tetra Tech Inc.

Develop and calibrate models to performance data

Simulate long term performance varying the capacity of controls

Validate results with literature review

Charles River Stormwater BMP

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0.25 0.75 1.25 1.75 2.25

Perc

enta

ge re

mov

al fo

r TSS

BMP size (controlled depth of runoff)

BMP Performance Curve Concept

40%

0.65 in 0.90 in

BMP I

BMP II

Size BMPs from established curves developed from calibrated models and detailed performance data

Provides long‐term cumulative performance estimates based on BMP design capacity

Eliminates the need for detailed modeling and evaluation in individual applications

Land simulation(SWMM)

Surface runoff generationand pollutant wash off

BMP simulation(SUSTAIN/BMPDSS)

BMP Treatment

Precipitation

BMP Performance Curve: Gravel WetlandLand Use: Commercial

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Depth of Runoff Treated (inches)

Pollu

tant

Rem

oval

TSS TP Zn

Scheme for BMP Performance Curve Development

Generation of BMP Performance Curvesfor New England Region

Surface Infiltration (6 infiltration rates)

Infiltration trenches(6 infiltration rates)

Bio-filtration

Porous pavement with underdrain

WQ Swales(non-infiltration)

Gravel wetland

BMPs

Enhanced Bio-retention** Optimized for N and P removal

– Curves not yet final

BMP Performance Curve: Infiltration TrenchLand Use: Commercial

(Soil infiltration rate 0.17 in/hr)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2


Pollu

tant

Rem

oval

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Run

off V

olum

e R

educ

tion

TSS TP Zn Volume

BMP Performance Curve: Gravel WetlandLand Use: Commercial

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2


Pollu

tant

Rem

oval

TSS TP Zn

BMP Performance Curve: BiorententionLand Use: Commercial

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2


Pollu

tant

Rem

oval

TSS TP Zn

BMP‐Performance Extrapolation Tool (BMP‐PET)BMP‐Performance Extrapolation Tool (BMP‐PET)

Questions ?Mark VoorheesUS EPA – (OEP06‐4)[email protected]

58

Thank you

Additional reference and information sources

• USGS National Map: http://nationalmap.gov/viewer.html (Data include: Elevation, Orthoimagery, Hydrography, Geographic Names, Boundaries, Transportation, Structures, and Land Cover, while products include: US Topo and Historical Topo Maps. The National Map Viewer also allows visualization and identification queries (but not downloads) of Other Featured Data, to include Ecosystems, Protected Areas, Gap Analysis Program Land Cover, Hazards, Weather, Wetlands, Public Land Survey System, and National Park Service Boundaries.)

• You can find Soil Data here: http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx

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• Report on the development of Stormwater BMP Performance Curves for New England Region (Tetra Tech, Inc., 2010). http://www.epa.gov/region1/npdes/stormwater/assets/pdfs/BMP‐Performance‐Analysis‐Report.pdf

• Spreadsheet tool for using the curves and instructions. http://www.epa.gov/region1/topics/water/swtoolsresources.html

• Upcoming EPA tool : http://www.epa.gov/ord/gems/stormwater.htmTo be released later this month). It will be available on this page: http://www.epa.gov/research/waterscience/water‐models‐data‐tools.htm.

• Also, check out Watershed Assessment, Tracking & Environmental Results Tool (WATERS) (under Watershed Tools).

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