Watershed Monitoring and Modeling in Switzer, Chollas, and Paleta Creek Watersheds Kenneth Schiff Southern California Coastal Water Research Project

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

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

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

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

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?

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

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

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

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

Overland Flow Interception Storage Infiltration Interflow Upper Zone Storage Interception Storage Lower Zone Storage Groundwater Storage Deep Groundwater Evapotranspiration Active Groundwater Flow

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

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

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

Land use sites < 0.5"0.5" - 1.0"> 1.0"Total No. Agriculture3115 Commercial415 High density residential4217 Industrial5117 Low density residential213 Open space22 Recreational112 Transportation112 Natural loadings land use site events 30 natural site events Through 4/30/05 Sample Size For Land Use-Based Pollutographs Rainfall Quantity

Land Use Calibrations

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?

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

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

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

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

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

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, -