City of San Diego Low ImpactDevelopment Design Manual

LID SymposiumSeptember 2011

1

Jason Wright, P.E.

Jim Nabong, P.E.

Project Team

City Staff:• Sumer Hasenin• James Nabong

Tetra Tech Staff:• Scott Struck• Jason Wright• Chad Helmle

2

• Garbini and Garbini Landscape Architecture, Inc.

Presentation Outline

• Goals of the Project• LID Design Manual Contents

– Introductory Concepts– Site Assessment, Planning, and Site Design– Selection of Structural BMPs– Implementation Considerations– Appendices: Fact sheets, design templates

& more…

3

How do we make this… function more like this?

Overall Watershed-based Goal

4

Companion Manuals

• Storm Water Standards: clarifies criteria for compliance

• The LID Design Manual: clarifies acceptable LID design practices

• Compatible with the Street Design & Drainage Design Manuals

5

LID Manual Approach

6

• Provide design guidelines for Engineers, Planners, and Maintenance Staff– Links to Stormwater Standards– Provides Step-by-Step Planning

Process– BMP Selection Matrix

• BMP Sizing Tool• Detailed Design Guidance• BMP Design Templates (MS)• Fact Sheets/Plant List/O&M

Checklist

Low Impact Development Concepts

7

Under Natural Conditions Runoff is

Limited........But increases After

Development

Stormwater Management and LID Concepts

8

LID incorporated into traditional parking lot design minimizes alterations to natural hydrology.

Vegetated filter strips reduces pollutants washed into storm water.

Incorporating LID in CIP

9

Conceptual rendering of the University Avenue Mobility Plan.

Regional Considerations

10

Site Assessment, Planning, and Site Design

11

Step by Step Process – Step 1 (New / Redevelopment / Retrofit)

12

To Complete Step 1:Identify applicable zoning, land use, subdivision, and other regulationsIdentify setbacks, easements, and utilitiesIdentify targeted pollutants and pollutants of concern

Step by Step Process – Step 9 (Planned Site)

13

To Complete Step 9:Integrate conventional stormwater management needsFinish details and notesComplete the site plans

General Descriptions of BMP Practices

14

Pollutants

Removal processes

Settl

ing

Filtr

atio

n/st

rain

ing

Sorp

tion

Bio

accu

mul

atio

n

Bio

tran

sfor

mat

ion/

ph

ytor

emed

iatio

n

Oth

er (e

.g.,

phot

olys

is;

vola

tiliz

atio

n)

Sediment + + – – – –Nutrients + o + + + –Trash + + – – – oMetals + – + + + –Bacteria + (+) – + + & + *

Oil and grease – + + o + +

Organics + o o + + +Note: ( ) optional function; + major function; o secondary function; –insignificant function; & consumed by other organisms; * photolysis

General Descriptions of BMP Practices

15

Structural BMPs

Hydrologic controls Removal processes

Stor

age/

dete

ntio

n or

flow

atte

nuat

ion

Infil

trat

ion

Evap

otra

nspi

ratio

n Settl

ing

Filtr

atio

n

Sorp

tion

Bio

accu

mul

atio

n

Bio

tran

sfor

mat

ion/

ph

ytor

emed

iatio

n

Oth

er (e

.g.,

phot

olys

is;

vola

tiliz

atio

n)

Bioretention + (+) o o + o + + (o)Bioswale (+) (+) o o o o o o (o)Permeable pavement + (+) – – + – – – –Infiltration trench + + (o) o + o – – –Planter boxes + (+) o o + o (+) (+) (o)Sand filter o (o) – – + (o) – – (o)Vegetated filter strip – + + o o o – – –Vegetated swale (o) (o) o + + – – – –Cisterns/rain barrels + – – – – – – – –Note: ( ) optional function; + major function; o secondary function; – insignificant function

LID Selection – Structural BMPs

16

BioretentionArea Typically Served (acres): < 5Area Required for BMP: 4%–8%Major Maintenance: Mowing/plant replacementEffective Life Time: 5–20 yearsPollutant RemovalSediments: High Nutrients: MediumTrash: High Metals: HighBacteria: High Oil & Grease: HighOrganics: High

3. General Descriptions of BMP Practices

17

LID practice type

Bioretentiona Planter boxes Sand filter Vegetated swaleAttribute (no UD) (UD) (no UD) (UD)Contribute drainage area (acres) < 5 < 0.35 < 5 < 2Soil infiltration rate (inches/hour) > 0.5 < 0.5 N/A > 0.5 < 0.5 > 0.5Water table separation (feet) > 10 ft ≥ 2 ft N/A > 10 ft ≥ 2 ft > 10 ftDepth to bedrock (feet) > 10 ft ≥ 2 ft N/A > 10 ft ≥ 2 ft > 2 ftUnit slope < 2% N/A < 6% < 4%Pollutant Removal

Sediments High High High MediumNutrients Medium Medium Low LowTrash High High High LowMetals High High Low MediumBacteria High High Medium LowOil & grease High High Medium MediumOrganics High High Medium Medium

Runoff volume reduction High Medium Low Medium Low LowPeak flow control Medium Low Medium LowGroundwater recharge High Low N/A Medium Low LowSetbacks (ft) Structures > 10 ft > 10 ft

Steep slopes > 50 ft > 50 ft

LID Manual – Appendix B

– Design Details• Description

– Advantages / Disadvantages– Major Design Elements

– Characteristics and Functions• Based on Documented Research

• 9 Step Design Process• Photos, Design Templates,

Schematics,

18

LID Manual – Appendix B

• 9 Step Design Process1.BMP Configuration2.Determine the volume of water to treat3.Calculate the surface area required4.Determine the depth and type of soil media5.Design the inlet configuration6.Determine if an underdrain pipe is

necessary7.Select the appropriate overflow or bypass

method8.Select mulch and vegetation9.Additional considerations

19

LID Manual – Appendix B

20

LID Manual – Appendix B

21

LID Manual – Appendix B -Common Elements

22

LID Manual – Appendix C• Appendix C Design Templates

• Templates/details that can be used in designs

23

LID Manual – Appendix D

24

• Design Fact Sheets – Provide general description, example picture, considerations,

water quality benefits, but little explanation

LID Manual – Appendix E• Local Plant Listxposure, zones

25

LID Manual – Appendix F

26

Facility Inspection and Maintenance Check Lists

LID Manual Input Process Workshops

Engage key players January 2010 solicited initial input

on first draft

Charrette Exercise September 2010 Charrette Exercise using two

CIP projects to validate the manual steps

Coordinated with individual departments Incorporated Changes

Based on Feedback

Questions?