storm drain mapping and impervious surfaces in sf bay urban areas

Storm Drain Mapping and Impervious Surfaces in SF

Bay Urban Areas

Impervious Surface Data Collection Workshop

Regional Board October 11th 2005

Lester McKeeSan Francisco Estuary Institute

San Francisco Estuary Institute

Regional Storm Drain Mapping

Objective• Map >24 inch diameter stormwater conveyance systems of the Bay

Area

Team• Christopher Richard - Oakland Museum of California• Janet Sowers - William Lettis and Associates Inc.• Robin Grossinger - San Francisco Estuary Institute• Trish Mulvey – Clean South Bay / SFEI Board

Period of Performance• 1993 - present


Progress


Linkages Between Storm Drain Mapping and Impervious data

• Planning at the Bay scale• Modeling runoff of water, sediment and contaminant loads for

improved problem definition during TMDL adaptive implementation

• Planning at the watershed scale• Modeling for drainage design• Modeling for understanding channel maintenance needs• Modeling to understand the processes of contaminant sources,

release, and transport


Other Uses(in the context of permits and TMDLs)

• Planning at the site scale• Performance standards in new development and redevelopment

(e.g. zero new EIA)• Education tool for increasing awareness of compacted soils* as TIA

• Planning at the community, regional or watershed scale• No net increase towards agreed upon thresholds• Alternative futures analysis (modeling to determine how best to get

to agreed upon thresholds)• Decision support for reaching hydro-modification or TMDL goals

(e.g. area of EIA disconnected annually)


Definition of an Impervious Surface (Arnold and Gibbons, 1996)

“Any material that prevents the infiltration of water into soil”

• Roads, rooftops, parking lots• Sidewalks, patios, bedrock outcrops, and

compacted soils*


Total Impervious Area (TIA)versus

Effective Impervious Area (EIA)

• TIA includes all impervious surfaces

• A portion of rain will infiltrate when it runs onto lawns, swales, or driveways

• EIA includes only impervious surfaces that drain to stormwater conveyances or receiving waters

• 100% of rain runs off EIA


Methods

• Direct• Digitization of aerial photography• Classification of remotely sensed (satellite) images• Collation of development / redevelopment plans

• Indirect (mathematical relationships)• Conversion of land use data• Conversion of population density data


TIA/EIA as an Indicator of Urban Impact to Surface Waters

• About 30-40 papers written prior to 2002

• See recent review articles:

• Paul and Meyer, 2001. Streams in the urban landscape.

• Gergel et al., 2002. Landscape indicators of human impacts to riverine systems.

• Brabec et al., 2002. Impervious surfaces and water quality: A review of current literature and its implications for watershed planning.


Linkage to Flow Hydrology? YES


% Impervious surfaces

1. Peak flow

2. Bankfull flow

3. Total volume

Location of TIA / EIA

• Lower watershed

• Upper watershed

Time from beginning of rain

Flow

Time from beginning of rain

Flow


Linkage to Physical Impacts? YES



1. Channel widening/ enlarging

2. Sediment loads

3. Stream temperature

Linkage to Contaminants? YES



1. Transmission of contaminants from sources

2. Contaminant loads

3. Eutrophication

Linkage to Biological Impacts? YES



1. Habitat quality and diversity

2. Insect/ invertebrate diversity

3. Fish numbers and diversity

Noticeable Impacts and Thresholds• Noticeable Impacts (see reviews Brabec et al., 2002; Gergel et al., 2002)

• Physical– Flow 5-50%– Channel form 2-30%

• Chemical 8-50%• Biological

– Fish 4-15%– Macro-inverts 8-15%

• Thresholds (Schueler, 1995; Arnold and Gibbons, 1996)

• Protected <10%• Impacted 10-30%• Degraded >30%


Summary (TIA / EIA)• Very good (if not best) indicator of urban impacts to

surface waters

• Need agreed upon regional definitions and methods

• Data can be used for planning at virtually every scale

• Data can be combined with storm drain mapping to develop watershed and regional hydrological models


Literature• Schueler, 1994. The importance of imperviousness. Watershed Protection

Techniques 1, 100-111.

• Schueler, 1995. The peculiarities of imperviousness. Watershed Protection Techniques 2, 233-238.

• Arnold and Gibbons, 1996. Impervious surface coverage: The emergence of a key environmental indicator. Journal of the American Planning Association 62, 243-258.

• Paul and Meyer, 2001. Streams in the urban landscape. Annual review of Ecology and Systematics 32, 333-365.

• Brabec et al., 2002. Impervious surfaces and water quality: A review of current literature and its implications for watershed planning. Journal of Planning Literature 16, 499-514.

• Gergel et al., 2002. Landscape indicators of human impacts to riverine systems. Aquatic Sciences 64, 118-128.


storm drain mapping and impervious surfaces in sf bay urban areas

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