Storm Drain Mapping and Impervious Surfaces in SF Bay Urban Areas

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Storm Drain Mapping and Impervious Surfaces in SF
Bay Urban Areas

• Impervious Surface Data Collection Workshop
• Regional Board October 11th 2005
• Lester McKee
• San Francisco Estuary Institute

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Regional Storm Drain Mapping

• Objective
• Map gt24 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

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Progress
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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

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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)

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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

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Total Impervious Area (TIA)versusEffective
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

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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

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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.

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Linkage to Flow Hydrology? YES

1. Peak flow
2. Bankfull flow
3. Total volume

Impervious surfaces
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Location of TIA / EIA

• Lower watershed
• Upper watershed

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Linkage to Physical Impacts? YES

1. Channel widening/ enlarging
2. Sediment loads
3. Stream temperature

Impervious surfaces
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Linkage to Contaminants? YES

1. Transmission of contaminants from sources
2. Contaminant loads
3. Eutrophication

Impervious surfaces
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Linkage to Biological Impacts? YES

1. Habitat quality and diversity
2. Insect/ invertebrate diversity
3. Fish numbers and diversity

Impervious surfaces
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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 lt10
• Impacted 10-30
• Degraded gt30

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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

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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.