WATERSHED MODELING IN SOUTHERN CALIFORNIA Kenneth Schiff Southern California Coastal Water Research Project www.sccwrp.org

SCCWRP’s Watershed Research Themes Loads and concentrations Runoff mechanisms and processes Interactions with the coastal ocean Source tracking and identification Effectiveness of BMPs

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

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

WATER QUALITY MODELING FRAMEWORK Flow & Pollutant Inputs Flow & Pollutant Inputs Transfomations Dispersion Nitrification Flow & Pollutant Inputs Transport Uptake Decay Partitioning Instream Concentration Denitrification

30 land use site events 17 natural site events 34 mass emission Land use sites < 0.5" 0.5" - 1.0" > 1.0" Total Agriculture 3 1 5 Commercial 4 High density residential 2 7 Industrial Low density residential Open space Recreational Transportation Natural loadings (pollutograph) Natural loadings (microsampling) 8 12 Mass emission sites Arroyo Seco Arroyo Sequit Ballona Creek Coyote Creek Dominguez Channel LAR u.s. Arroyo Seco Los Angeles River San Gabriel River San Jose Creek Santa Monica Canyon Verdugo Wash Walnut Creek 30 land use site events 17 natural site events 34 mass emission site events Through 4/30/05

LAND USE LOAD COMPARISON

Hardness = 100 mg/L CTR = 13.4 ug/L Copper Loading From Ballona Creek (1990-2000) Hardness = 100 mg/L CTR = 13.4 ug/L

Most Likely BMPs from Stakeholders Cisterns Detention basins Load reduction Impervious reduction Wetland treatment Instream Impoundment Diversion

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

http://ca.water.usgs.gov/user_projects/sonoma/pics/rubberdam.jpg Rubber dam To WRP http://www.salinasvalleywatercoalition.org/images/rubberdam.jpg

Decadal Simulation Change in Load 20 MGD Diversion Volume -16 % Solids -3 % Copper -6 % Bacteria

Sensitivity Analysis Change in Load Volume -16 % -18 % -20 % Solids 20 MGD (13 cfs) 40 MGD (26 cfs) 50 MGD (32 cfs) Volume -16 % -18 % -20 % Solids -3 % -4 % Copper -6 % -7 % Bacteria

Effectiveness of Impoundment 5 ft dam retains 195 ac-ft of water 59% of storms > 195 ac-ft Storms > 195 ac-ft account for 99% of decadal storm volume 87% total decadal volume

Most Likely BMPs from Stakeholders Cisterns Detention basins Load reduction Impervious reduction Wetland treatment Instream Impoundment Diversion

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

Decadal Simulation Change in Load Cistern Volume -11 % Solids -8 % Copper -14 % Bacteria Dry weather loading not affected

Effectiveness of Cisterns Cisterns only applied to specific land uses

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

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

Percent of Storms Exceeding EXCEEDENCE RATE AT BALLONA CREEK 40% 35% 30% 25% 20% Percent of Storms Exceeding Thresholds for Copper 15% 10% 5% 0% 0.5 1 1.5 2 Rainfall Runoff Captured (in)