1. WATERSHED MODELING IN SOUTHERN CALIFORNIA
Kenneth Schiff
Southern California Coastal Water Research Project

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

3. 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

4. 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

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

6. 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

7. LAND USE LOAD COMPARISON

9. Hardness = 100 mg/L CTR = 13.4 ug/L
Copper Loading From Ballona Creek ( )
Hardness = 100 mg/L CTR = 13.4 ug/L

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

11. 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

12.
Rubber
dam
To WRP

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

14. 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

15. 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

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

17. 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

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

19. Effectiveness of Cisterns
Cisterns only applied to specific land uses

21. 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

22. 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

23. 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)