1 / 34

Chesapeake Bay Modeling Perspectives for the Regulated Community

Chesapeake Bay Modeling Perspectives for the Regulated Community. Clifton Bell, P.E., P.G. Themes. Chesapeake Bay modeling framework is an remarkable set of tools. Impressive capabilities Important limitations TMDLs lead to an overreliance on models.

elden
Download Presentation

Chesapeake Bay Modeling Perspectives for the Regulated Community

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chesapeake Bay Modeling Perspectives for the Regulated Community Clifton Bell, P.E., P.G.

  2. Themes • Chesapeake Bay modeling framework is an remarkable set of tools. • Impressive capabilities • Important limitations • TMDLs lead to an overreliance on models. • Be prepared to advocate local achievements in model world.

  3. Primary purposes of the Bay modeling framework: Identify the: • Nutrient and sediment loads that will meet water quality standards in tidal waters. • Management actions that will achieve these loads.

  4. “The model” is actually many linked models and data processing tools

  5. Models developed, refined over 25+ years

  6. Models developed, refined over 25+ years

  7. Use of the model has also evolved • Originally used to predict “hypoxic volumes” in Bay • Estimate watershed-scale reductions (e.g., 40% reduction by 2000) • Track progress over large areas

  8. Use of the model has also evolved • Now trying to predict water quality at very specific locations and depths • Predict ≤1% changes in attainment. • Estimate local loads

  9. Some Important Strengths • Watershed model relatively well calibrated at Baywide and major tributary basin level • Water quality model relatively well calibrated for dissolved oxygen in critical deep water segments

  10. Modeling Process Uncertainty

  11. Modeling Framework is Conservativewith a Implicit Margin of Safety • Attainment controlled by small area, timing. • All WWTPs discharging at full permitted load • Conservative assumptions

  12. Conservative BMP Efficiencies

  13. Categories of Model Limitations • Limitations of the basic algorithms • Calibration errors • Overparameterization • Scale limitations • Input errors • Poor model behavior • Imprecision of management predictions

  14. Limitations of Basic Algorithms • Examples from watershed model: • Groundwater component crude • No explicit simulation of stream bank erosion • No mass balance of fertilizer

  15. Calibration issues • No calibration is perfect. • Quality of Bay model calibration varies greatly by parameter and location. • Watershed model partially calibrated to another model.

  16. Overparameterization

  17. Complex nutrient cycling algorithms

  18. Overparameterization x + y =100

  19. Highly Empirical Regional Transport Factors Edge of Stream Regional Delivery Factors In Stream Concentrations

  20. Phase 5.0 TP Calibrated Regional Factors

  21. Scale Issues • Watershed model lack resolution for accuracy at the local scale • Segmentation • Input data • Calibration Diane River Basin Hoffman County

  22. STAC Peer Review: 2008 “[The] current [watershed model]… is not appropriate for development and implementation of TMDLs at the local watershed scale. A major barrier appears to be the scale of information built into the [model]…”

  23. Input Errors • No benefit of agricultural nutrient management • Urban land use

  24. Poor model behavior • Many segments where the model doesn’t “behave”. • e.g., poor calibration • e.g., non-intuitive trends • Often the cause and its extent is undiagnosed.

  25. Summary so far The model is • Complex • Conservative • Imprecise

  26. So how precise are model predictions of future attainment, anyway? • Impossible to accurately quantify. • Bay program instituted the “1% rule”. • Field measurements are not this precise. • Laboratory measurement are not this precise. • Model is nowhere near this precise. • Lowest realistic estimates: • 5% for DO attainment. • 15% for chlorophyll-a attainment.

  27. USEPA’s Justification for “1 % Rule”

  28. How Will the Model be Used Post-2010? • Phase II WIPs • Quantify local loads? • Model “locked down” until 2017 • Tracking progress • Baywide • Major state tributary basin • Local level?

  29. Community Model Scenario Builder • Phase 5.3 watershed model publically available. • Scenario Builder • Tool for creating input to watershed model • Web version planned. • Can’t refine model scale.

  30. How Should Stakeholders Use the Model and Scenario Builder? • Don’t • Use current watershed model for local TMDLs. • Let current watershed model output drive Bay TMDL implementation at local level. • Let MS4 permits base compliance on current watershed model predictions.

  31. How Should Stakeholders Use the Model and Scenario Builder • Do • Track BMPs for input to watershed model. • Use current watershed to track progress at major tributary, state, and Baywide scale. • Base MS4 permit requirements on MEP. • Use refined models for local TMDL planning.

  32. How Should Stakeholders Use the Model and Scenario Builder • Do • Use watershed model to identify offsets and trades • Advocate new BMPs for inclusion in the Baywide model • New structural BMPs • Non-structural BMPs • Ordinances • Public education and outreach • Improved BMP maintenance

  33. Questions?

More Related