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Patapsco/Back River SWMM Model

Patapsco/Back River SWMM Model. Part II – SWMM Water Quality Calibration Maryland Department of the Environment. Water Quality Calibration. General Aggregate Five Subwatersheds Focus on predominant land uses Calibrate EOS loads to literature values

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Patapsco/Back River SWMM Model

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  1. Patapsco/Back River SWMM Model Part II – SWMM Water Quality Calibration Maryland Department of the Environment

  2. Water Quality Calibration • General • Aggregate Five Subwatersheds • Focus on predominant land uses • Calibrate EOS loads to literature values • Calibrate Event Mean Concentrations • Detailed • Time series overlay • Comparative Analysis

  3. Water Quality CalibrationUrban TSS and Metals • Objective • EMC (statistics of wet-weather events) • Unit Load (annual) • Parameters • Buildup Rate (Linear - Calibrated) • Build Limit (Set high) • Wash-off Coefficient (Based on Literature) • Wash-off Exponent (Based on Literature) • Calculation • Load =  (Flow*Conc.) • EMC = Load /  Flow • Results • Unique Solution of Buildup Rate • Validation • Timeseries Comparision

  4. Water Quality Calibration Non-Urban Land Use (USLE) • Calibration Objective • Correlate with long term loading rate estimates • USLE – Estimates gross long term erosion rate • Parameters (Land use specific) R=Rainfall Energy (from BWI) K=Soil Erodibility (Soil type) LS=Slope Length Gradient Ratio (DEM) C=Cropping Management Factor (Landuse – Calibrated) P=Erosion Control Practice (Literature) • Delivery Ratio • Applied Based on Subwatershed Drainage to Baltimore Harbor • Parameter • Adjusted cropping management factor within recommended values

  5. Event Mean Concentration References

  6. Unit Load References

  7. Water Quality Data *All data collected by Baltimore City -DNR Core station TSS data available at stations 240, 230 and 211 (Data set contains mostly base flow samples) - Metals values not shown from 2/25/95 to 12/1/96 due to high detection limits

  8. SWMM Baseflow Concentration References Base Flow Data Source TSS Cr Zn Pb Baltimore County NPDES Report (2000) X Baltimore City NPDES Report (2001) X Baltimore City Wastewater Facilities Master Plan (1997) X X X Baltimore County DEPRM Watershed Monitoring Project (1997-2000) X MDE Upper Western Shore Monitoring Project (2001) X Concentrations

  9. Results

  10. Jones Falls

  11. Patapsco

  12. Back River

  13. Best Management Practices (BMPs) • Uncertainty and variability in EMC • Instream sites from NPDES Report • Timeseries comparison of model vs data show reasonable concentration magnitude agreement • BMPs not explicitly included in model • Established a baseline load scenario

  14. Sub-Watershed Loads

  15. Baltimore Harbor Watershed Land Use Loading Summary CBP TSS Results (93-97) Urban: 44.5% Crop: 28.4% Pasture: 4.1% Forest: 23.1%

  16. Comparative Analysis - Existing Studies

  17. SWMM Calibration Summary & Conclusions • Focus on predominant land use for model calibration • Calibrate EOS loads to mean literature values • Calibration urban EMC’s to reported mean landuse values • Overlay model with water quality timeseries data • Comparative Analysis • Model supports overall trends (Flow, TSS and metals) • Next - Sensitivity of water quality model to NPS Loads

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