WATERSHED MODELING IN SOUTHERN CALIFORNIA

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WATERSHED MODELING IN SOUTHERN CALIFORNIA

• Kenneth Schiff
• Southern California Coastal Water Research
  Project
• www.sccwrp.org

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SCCWRPs Watershed Research Themes

• Loads and concentrations
• Runoff mechanisms and processes
• Interactions with the coastal ocean
• Source tracking and identification
• Effectiveness of BMPs

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Modeling Advantages

• More complete characterization of pollutant
  concentrations and loads
• All storms of a year, wet vs. dry years
• Source attribution
• Subwatershed, land use, municipal boundaries
• Assess management scenarios
• - Effectiveness, cost efficiency

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Water Quality Modeling In Southern California

• Watershed-scale water quality models already
  exist
• - HSPF, SWMM, EFDC, LSPC, etc.
• Virtually none were built in California
• Not necessarily designed for arid or urban
  environments
• Previous time scales largely insufficient for
  urban applications
• Need minutes to hours for within storm
  applications

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WATER QUALITY MODELING FRAMEWORK
Flow Pollutant Inputs
Flow Pollutant Inputs
Transfomations
Dispersion
Nitrification
Transport
Flow Pollutant Inputs
Uptake
Decay
Partitioning
Instream Concentration
Denitrification
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30 land use site events
17 natural site events
34 mass emission site events
Through 4/30/05
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LAND USE LOAD COMPARISON
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Hardness 100 mg/LCTR 13.4 ug/L
Copper Loading From Ballona Creek (1990-2000)
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Most Likely BMPs from Stakeholders

• Cisterns
• Detention basins
• Load reduction
• Impervious reduction
• Wetland treatment
• Instream
• Impoundment
• Diversion

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Impoundment and Diversion Assumptions

• Rubber dam at end of Ballona Creek
• 5 ft high
• Overflows during storms
• Retained volume is diverted flow to WRP
• Constant diversion of 20 MGD

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http//ca.water.usgs.gov/user_projects/sonoma/pics
/rubberdam.jpg
Rubber dam
To WRP
http//www.salinasvalleywatercoalition.org/images/
rubberdam.jpg
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Decadal Simulation
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Sensitivity Analysis
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Effectiveness of Impoundment

• 5 ft dam retains 195 ac-ft of water
• 59 of storms gt 195 ac-ft
• Storms gt 195 ac-ft account for 99 of decadal
  storm volume
• 87 total decadal volume

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Most Likely BMPs from Stakeholders

• Cisterns
• Detention basins
• Load reduction
• Impervious reduction
• Wetland treatment
• Instream
• Impoundment
• Diversion

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Cistern Application Assumptions

• Distribute cisterns on specific land uses
  throughout watershed
• Public
• Open
• Transportation
• Commercial
• Cisterns capture all rainfall for an average year
  (12)
• Cisterns store rain and pollutants up to their
  capacity and then bypass to the stream
• Cisterns emptied during the summer
• Used for irrigation, no net increase in dry
  weather runoff

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Decadal Simulation
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Effectiveness of Cisterns
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Summary

• Watershed models are a powerful management tool
• Extrapolate to unmonitored times/locations
• Requires effort to ensure you believe them
• Calibration and validation
• Wet and dry weather
• Provides invaluable insight into evaluating
  management action effectiveness
• Cost efficiency

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Soon To Be Released

• More detailed and involved BMPs
• Design storm for water quality
• Function of hydrology
• Function of BMP cost
• Linked estuarine models
• Contaminated sediments

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EXCEEDENCE RATE AT BALLONA CREEK
40
35
30
25
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Percent of Storms Exceeding Thresholds for Copper
15
10
5
0
0
0.5
1
1.5
2
Rainfall Runoff Captured (in)