Watershed Monitoring and Modeling in Switzer, Chollas, and Paleta Creek Watersheds

1. Watershed Monitoring and Modeling in Switzer, Chollas, and Paleta Creek Watersheds Kenneth Schiff Southern California Coastal Water Research Project www.sccwrp.org

2. Prelude to Today’s Agenda • Total Maximum Daily Loads (TMDLs) always benefit from more information • Today’s presentation is mostly conceptual • - many of the details have not been finalized • Local stakeholders have extensive knowledge/experience • - SCCWRP has been instrumental in bringing unbiased technical information to TMDL development • One goal of today’s meeting is to identify potential partnerships and collaborations

3. Agenda For Today • Background • Goals of the project • General approach • - important considerations • Next steps

4. Background • Sediments at the mouth of several urban creeks draining to SD Bay are listed as impaired • - chemistry, toxicity, benthic community • Additional studies have focused the magnitude and extent of these impairments • - Chollas, Paleta, and Switzer Creeks • TMDL development for the contaminated sediments at these creek mouths would benefit from additional data • source analysis • linkage analysis

6. Constituents of Potential Concern • Trace metals • - copper, lead, zinc • Trace organics • - chlordanes, PAHs, DDTs/PCBs • Associated constituents • - organic carbon, suspended solids, hardness

7. Study Objectives • What are the concentrations and loads of contaminants of potential concern? • - can we differentiate among different sources? • What is the fate of the contaminants of potential concern?

8. General Approach • Utilize empirical data to estimate sources and loads of CoPC to affected areas at the mouth of Chollas, Paleta, and Switzer Creeks • Employ watershed models to supplement information on sources and loads of CoPC • Link to estuary models to help ascertain fates of CoPC inputs

9. Use of Empirical Data • Want to examine multiple potential sources • - urban watersheds and atmospheric deposition have been prioritized • Watershed inputs • Focus on wet weather • Use existing data wherever possible • MS4, Industrial, special studies • Collect new data as needed • - chlorinated hydrocarbons

10. Generalized Approach for Atmospheric Deposition • The possibility of inputs from atm dep is high • - urban air quality, localized sources • There are two methods for estimating deposition • surrogate surfaces • atmospheric concentrations and estimated deposition velocities • Focus will be direct deposition onto the water surface of affected areas • - deposition onto the watershed would be an interesting component

12. The Use of Watershed Models • Watershed models can be useful TMDL tools • Predict concentrations and loads from unmonitored storms or areas • critical conditions • margin of safety • Use to define source area contributions • - subwatersheds, land uses, municipal boundaries, etc. • Predict the effectiveness of future management actions • - cost efficiency of potential implementation plans

13. Temperature Wind Precipitation Dewpoint Solar Radiation Cloud Interception Storage Interception Storage Infiltration Upper Zone Storage Evapotranspiration Overland Flow LowerZone Storage Interflow Groundwater Storage Deep Groundwater Active Groundwater Flow

14. Approach to Building a Watershed Model • Physical data is needed for the model domain • - watershed delineation, stream properties, land use, etc. • Calibrate flow and water quality at small homogeneous land uses • Validate flow and water quality at the end of the watershed cumulative of all land uses

15. Special Considerations for Watershed Modeling • There are a number of different models available • - static, dynamic • We will use a dynamic model with short time steps • - one minute to one hour intervals • Shorter time steps enable predictions of within-storm management scenarios • - first flush, peak flows, flow duration

16. Data Collection Strategy for Wet Weather • Use previously collected data for land use information • - requires certain assumptions • Collect validation data at the end of each watershed • - requires local data for validation • Dynamic models necessitates dynamic water quality information • - requires multiple samples across the hydrograph

17. Sample Size For Land Use-Based Pollutographs Rainfall Quantity 33 land use site events 30 natural site events Through 4/30/05

18. Land Use Calibrations

19. Linking Watershed and Estuary Models • Estuary models can make predictions about hydrodynamic and particle transport • How much of the watershed inputs deposit in the estuary? • Ultimately, at a specific location in the estuary, where did the sediment contamination come from?

20. Special Considerations for Estuary Models • Two-way (tidal) flow • Hydrodynamic stratification • Particle dynamics • flocculation, settling, dispersal, mixing • Chemical partitioning • dissolution, precipitation • Sediment dynamics • flux, resuspension

21. Approach To Building An Estuary Model • Start easy and work towards the more complex • Dry weather, then wet weather • Calibration cruises • Hydrodynamic, particle, water quality, sediment quality data • Special studies for rate constants • Fluorescent dyes, sediment flux, particle size distributions • Validation cruises • Try to predict measured conditions based on calibration exercise

22. Summarizing • What are the sources and loads of contaminants of potential concern? • empirical measurements • watershed modeling • What is the fate of the contaminants of potential concern? • - estuary modeling

23. Immediate Next Steps • Need to prepare for wet weather sampling • Site and storm selection • Equipment prep and encroachment permits • Compilation of existing watershed data • physical, flow, and water quality data • Local partners? • Leverage existing monitoring • SCCWRP adapt to existing/planned studies • Incorporate tools or services developed by others

24. Longer Term Planning • Determine success of watershed modeling • Requires more data? • Model application runs • Begin preparations for estuary modeling • Hydrodynamic and water quality? • Primary special studies needed? • Ability to interface with other agencies

26. Approach To Building An Estuary Model • Physical data • geometry, bathymetry, substrate • Hydrodynamic data • Tidal and creek forcing, thermal and density stratification, velocity • Particle dynamics • Grain size, settling velocity, sediment resuspension • Water quality dynamics • Dissolved/particulate phases,