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

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

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

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Prelude to Todays Agenda

• Total Maximum Daily Loads (TMDLs) always benefit
  from more information
• Todays 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 todays meeting is to identify
  potential partnerships and collaborations

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Agenda For Today

• Background
• Goals of the project
• General approach
• - important considerations
• Next steps

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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

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Constituents of Potential Concern

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

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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?

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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

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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

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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

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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

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

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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

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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

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Sample Size For Land Use-Based Pollutographs
Rainfall Quantity
Land use sites lt 0.5" 0.5" - 1.0" gt 1.0" Total No.
Agriculture 3 1 1 5
Commercial 4 1 5
High density residential 4 2 1 7
Industrial 5 1 1 7
Low density residential 2 1 3
Open space 2 2
Recreational 1 1 2
Transportation 1 1 2

Natural loadings 4 11 15
33 land use site events
30 natural site events
Through 4/30/05
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Land Use Calibrations
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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?

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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

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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

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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

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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

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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

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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,

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