MATTAWOMAN CREEK WATERSHED STUDY

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MATTAWOMAN CREEK WATERSHED STUDY

• CITIZENS ADVISORY MEETING
• 4 August 2002

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Water Quality Modeling

• Objective Application of the HSPF model to
  evaluate possible effects of existing future
  development on water quality in the Mattawoman
  Creek watershed

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Water Quality Modeling

• Models Utilized
• WMS-HSPF
• HSPE (expert system for calibration)
• GENSCN (scenario generator)
• Simulation time period (Apr 1998 Feb 2000)

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Modeling Tasks

• Data Collection/Model Input Development
• Hydrology Calibration
• Water Quality Calibration
• Run Scenarios

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Data Collection

• Meteorology
• Hydrology
• Water Quality
• Landcover/Landuse

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Meteorology

• Time Series Data
• Precipitation
• Potential Evaporation
• Air Temperature
• Wind Movement
• Solar Radiation
• Dewpoint Temperature
• Cloud Cover

• Data Sources
• Baltimore Washington International - BWI
• Washington Reagan DCA
• Patuxent NAS

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Hydrology

• Water Discharge Time Series
• Smithsonian monitoring station
• Soils
• Channel Geometry
• River Reaches
• Basin Delineation

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DNR 12-Digit Watersheds
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Watershed Delineation
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Water Quality Parameters

• Calibrated
• (TSS)
• NO3-N
• NH4-N
• Total N
• PO4-P
• Total P
• Smithsonian weekly composited samples

• Uncalibrated
• DO
• Chlorophyll
• Temperature

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Landuse

• Data Sources
• Towson 2000 - Calibrated Base Model
• MOP 1997 2020 Landuse
• Charles and PG County Zoning Buildout
• HSPF Land Segments
• Undeveloped land - PERLND
• Developed land IMPLND PERLND

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Undeveloped Land

• Forest
• Grass
• Barren
• Agriculture
• Wetland/Water

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Developed Land ( impervious)

• Low Density Development
• Low density residential (14)
• Medium density residential (38)
• High Density Development
• High density residential (65)
• Commercial (82)
• Industrial (70)
• Institutional (50)

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Scenarios Modeled

• 2000 - base calibrated model towson data
• 2020 - MOP landuse data
• Buildout - Zoning
• Forest
• Regulatory Compliance
• Enhanced Regulatory Compliance
• Stream Valley Protection

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Regulatory Compliance

• Existing Impervious Surfaces
• Assumes 25 are currently not treated for quality
  and quantity
• Assumes 25 reduction in existing untreated
  surfaces by 2020
• Assumes no reduction in existing treated surfaces
• ? Effective 6.25 reduction in existing
  impervious surfaces
• Future Impervious Surfaces
• Assumes 5 reduction in future impervious
  surfaces by 2020

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Enhanced Regulatory Compliance

• Existing Impervious Surfaces
• Assumes 25 are currently not treated for quality
  and quantity
• Assumes 25 reduction in existing untreated
  surfaces by 2020
• Assumes 10 reduction in existing treated
  surfaces with existing water quality treatment
• ? Effective 13.75 reduction in existing
  impervious surfaces
• Future Impervious Surfaces
• Assumes 15 reduction in future impervious
  surfaces by 2020

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Stream Valley Protection

• Assumes no future development within the stream
  valley
• Stream valley delineated at top of steep slopes
• Buildout (Stream valley protected lands)
• MOP 2020 data not provided in spatial format

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Discharge Past, Present, Future
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Discharge Scenarios
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Total N Load Past, Present, Future
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Total N Load Scenarios
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Total P Load Past, Present, Future
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Total P Load Scenarios
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TSS Past, Present, Future
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TSS Scenarios
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Limitations

• Space in watershed not addressed
• (lumped vs distributed model)
• Scenarios reflect the effects of reduction in
  impervious surfaces on water quality and quantity
• Direct effects of stormwater management on
  reducing peak discharges not reflected in future
  scenarios
• BMPs may have larger effects than modeled
• All conclusions based on MOP future growth
  projections current zoning practices

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Management Implications

• Buildout 2020 show large increases in pollutant
  loads
• increased N,P, TSS, lower DO ? adverse effects on
  biota
• Regulatory compliance alone does not have major
  influence on pollutent loads
• Reg compliance and enhanced scenarios will not
  change discharge significantly
• Reduced base flow and flashier flow regime ?
  adverse effects on biota
• Flashy flow regime needs to be addressed
• Stream valley protection results in highest
  pollutant removal
• may be greater than model results due to stream
  buffering lumped vs distributed)

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Conclusions

• Need to go beyond regulatory compliance for
  effective pollutant removal/peak reduction
• ? BMPs alone will not protect stream ecosystem
• Stream valley protection has greatest impact on
  reducing impacts to Mattawoman
• Reflects natural landscape
• Protects forest buffers and wetland filters
• Policy should reflect BMP use stream valley
  protection ? together will offset some of the
  impacts from development