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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

Patapsco/Back River SWMM Model

Part II – SWMM Water Quality Calibration

Maryland Department of the Environment

Water quality calibration
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

Water quality calibration urban tss and metals
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

Water quality calibration non urban land use usle
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

Water quality data
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


Swmm baseflow concentration
SWMM Baseflow Concentration


Base Flow Data Source





Baltimore County NPDES Report (2000)


Baltimore City NPDES Report (2001)


Baltimore City Wastewater Facilities Master Plan (1997)




Baltimore County DEPRM Watershed Monitoring Project (1997-2000)


MDE Upper Western Shore Monitoring Project (2001)



Best management practices bmps
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

Baltimore harbor watershed land use loading summary
Baltimore Harbor Watershed Land Use Loading Summary

CBP TSS Results (93-97)

Urban: 44.5%

Crop: 28.4%

Pasture: 4.1%

Forest: 23.1%

Swmm calibration summary conclusions
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