1 / 26

Session 10: Post-Processing with GWLF

Session 10: Post-Processing with GWLF. Virginia Tech Biological Systems Engineering Department DEQ TMDL Modeling Workshop; Richmond November 19-20, 2013. To describe the various post-processing steps in TMDL development based on GWLF output. Objective. Process downstream sub-watersheds.

joshua
Download Presentation

Session 10: Post-Processing with GWLF

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. Session 10: Post-Processing with GWLF Virginia Tech Biological Systems Engineering Department DEQ TMDL Modeling Workshop; Richmond November 19-20, 2013

  2. To describe the various post-processing steps in TMDL development based on GWLF output Objective

  3. Process downstream sub-watersheds

  4. GWLF and Sub-Watersheds Modeling without sub-watersheds provides no spatial distribution of watershed characteristics, except as they relate to different land uses

  5. Modeling Sub-watersheds with GWLF TMB3 2,000 ha SDR = 0.1720 TMB2 1,000 ha SDR = 0.1845 Sub - Area TMB1 Total Watershed (TMB) 2,000 ha SDR = 0.1408

  6. Distributing Modeled GWLF Sub-watershed Loads TMB3 TMB1 TMB2 Total Watershed (TMB)

  7. Incorporate BMPs

  8. Representing BMPs in Models • Land use changes • Riparian pasture to buffer • Hi-till to Lo-till cropland • Source reduction • Livestock exclusion • Reduced PS discharges • Streambank stabilization • Application of removal efficiencies • DCR Ag Cost-share tracking • Chesapeake Bay Model accounting • Reductions from upslope land uses • Grass and forest buffers

  9. The load reduction fraction from a given landuse for any individual BMP can be thought of as: area of BMP / landuse area* reduction efficiency (acres) (acres) (fraction) The aggregate reduction fraction from all non-overlapping BMPs applied on a given landuse in a given watershed are then summed as a total reduction fraction. The remaining load fraction is referred to as the passthrufactor: passthru = 1 – total reduction fraction Since we simulate loads (not reductions) with the model, we apply the passthru factor to simulated loads to represent these BMPs. Incorporation of current BMPs Passthru factor = 1 – 0.09 = 0.91

  10. Incorporate point source loads

  11. NPDES Loads – Existing Conditions • NPDES Loads – Future Conditions • NPS Permitted Loads • Stormwater runoff permits • MS4 accounting • Sediment detention accounting Post-Processed Load Calculations

  12. VPDES Loads – Existing Conditions

  13. VPDES Loads – Future Conditions

  14. Stormwater load = area * runoff depth * concentration • Schueler’sSimple Method Runoff = Rainfall • Rv • where Rvis the runoff coefficient, defined as: Rv = 0.050 + 0.009 * (% impervious area) • Simulate runoff from the relevant land use categories • Barren • Developed NPS Loads – Runoff Estimation

  15. NPS Loads – Construction Site Runoff

  16. NPS Loads – Industrial Stormwater Runoff

  17. Area-weighted partitioning (post-processed) • Urban impervious • City – 36% • County – 64% • Different land uses (modeled) • Urban impervious (city) • Urban impervious (county) Alternative Simulation of MS4 Loads

  18. Develop Allocation Scenarios

  19. Aggregate Source Categories? Consider Reduction Exemptions? Determine Basis for Reductions Allocation Options

  20. Alternate Aggregation Options • More flexibility for implementation • Less specific targeting ability

  21. Permitted loads Source loads < 1-2% of Total Load Sources with very small UALs Area Load UAL HYSadj = reference TMB = impaired Possible Reduction Exemptions

  22. Consider exemptions Equal % Reductions Largest Source Loads Largest UALs Basis for Reductions

  23. TMDL Allocation Scenarios TMDL = WLA + LA + MOS Modeling Endpoint = TMDL - MOS

  24. Concentration-based Allocation Scenario Modeling Endpoint = Overall average TP concentration = 0.070 mg/L BMP Scenario 1 = Future Load + all Big Otter River IP BMPs. BMP Scenario 2 = BMP Scenario 1 + all Little Otter River sediment TMDL reductions. Allocation Scenario = BMP Scenario 2 + WWTP at current flow and 0.5 mg/L TP effluent limits.

  25. GWLF Allocation Exercise

  26. 26 Questions?

More Related