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Phelps Branch Sediment TMDL

Phelps Branch Sediment TMDL. Public Meeting Gene Yagow April 23, 2013. Overview. Impairment Watershed characterization GWLF sediment modeling Reference Watershed Approach TMDL components Allocation Scenarios. Water Quality Impairment. Biological Monitoring and Rating. Healthy.

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Phelps Branch Sediment TMDL

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  1. Phelps Branch Sediment TMDL Public Meeting Gene Yagow April 23, 2013

  2. Overview • Impairment • Watershed characterization • GWLF sediment modeling • Reference Watershed Approach • TMDL components • Allocation Scenarios

  3. Water Quality Impairment

  4. Biological Monitoring and Rating Healthy Impaired VSCI = Virginia Stream Condition Index

  5. Watershed characterization

  6. Watershed characterization Watershed segmentation Land use Soils Slope “Future Growth” Existing BMPs

  7. Watershed segmentation

  8. Land Use Distribution

  9. Future Growth • Simulation of a “future” land use condition • Assume growth is limited to the upper portion of the watershed • Developed land use increased by 15% (30 acres) • 1/3 of reduced acreage from Agricultural land use categories (10 acres) • 2/3 of reduced acreage from Forest categories (20 acres) • Allocated construction permit area as 5% of developed land uses

  10. The Reference Watershed Approach

  11. TMDL Target Load Reducing load in the impaired watershed to the target TMDL load is expected to restore the benthic community Example Reference Watershed TMDL Impaired Load Non-impaired Phelps Branch Watershed TMDL Reference Watershed

  12. Impaired and Comparison Watersheds Healthy VSCI Score Land use distribution Size Slope Elevation Physiographic region River basin Soil erodibility

  13. Reference Watershed

  14. HYSadj 4,252 ha Reference Watershed Area-adjustment Example HYS 20,789 ha TMB 4,252 ha

  15. GWLF Sediment Modeling

  16. GWLF Sediment Loads Cropland Pasture Categories Developed Land uses LDI = low intensity developed; MDI = medium intensity developed; HDI = high intensity developed TMDL

  17. TMDL Components

  18. Permitted Sediment Loads (WLA) General Concrete Permit *Average annual runoff simulated for the high-intensity Developed land use category. General Single-Family Household Permit (Alternative Domestic Wastewater Treatment) Construction Permits *Average annual load simulated for the Barren land use category.

  19. Phelps Branch Sediment TMDL Components • TMDL = WLA + LA + MOS • TMDL = area-adjusted load from reference watershed • WLA = permitted loads • MOS = margin of safety (10%) • LA = remaining load allocated for non-point sources

  20. Allocation Scenarios

  21. Allocation Scenarios • Sediment load reductions are required • from “Future” Conditions in Phelps Branch • To the target allocation load Target Allocation Load = TMDL - MOS = 2,010.4 – 201.0 = 1,809.4 tons/yr

  22. Potential Sediment Reduction Targets Pastures with stream access Eroding field roads Localized disturbed areas Construction sites Hydraulic effects of road crossings Urban storm water runoff

  23. Next Steps • Public comment open for 30 days • Finalize report and submit to EPA • Begin implementation planning

  24. Contact Information Gene Yagow Biological Systems Engr. Dept. 306 Seitz Hall (0303)Virginia TechBlacksburg, VA 24061 eyagow@vt.edu540-231-2538

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