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Pond and Wetland BMPs, Retrofitting Detention Basins

Pond and Wetland BMPs, Retrofitting Detention Basins. WET PONDS. Wet Pond Treatment Processes. Settling Plant Uptake and Adsorption Infiltration Evaporation. Wet Ponds - Criteria. Provide Quantity and Quality Control (not volume control)

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Pond and Wetland BMPs, Retrofitting Detention Basins

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  1. Pond and Wetland BMPs, Retrofitting Detention Basins

  2. WET PONDS

  3. Wet Pond Treatment Processes • Settling • Plant Uptake and Adsorption • Infiltration • Evaporation

  4. Wet Ponds - Criteria • Provide Quantity and Quality Control (not volume control) • Drainage Area: Minimum of 10 Acres (>25 Acres Preferred) • Treat Water Quality Volume • Retrofit Opportunities • Maintenance sediment removal Inlet & outlet vegetation

  5. Wet Ponds – Primary Design Parameters • Storage Volume Channel Protection & Flood Control • Detention Time (24-48 Hours) Water Quality • Release Rate Channel Protection & Flood Control

  6. Wet Pond – Other Design Criteria • Treat Up to 75 Acres • Include Forebay • Depth: 4-6 Feet • Geometry Affects Performance dead storage short circuiting

  7. Extended Detention Pond

  8. Wet Pond

  9. Multiple Pond System

  10. Pocket Pond

  11. Wet Pond – Hydraulic Design • Design Pond Using Acceptable Methodology • NRCS…TR55…TR20 • Penn State Runoff Model (PSRM) • Modified Rational Method • Other • Hydrograph Routing Is Necessary

  12. Wet Pond – Area Ratio Area Ratio = Drainage Area Pond Area Should Be Less Than 100 For Maximum Efficiency

  13. Wet Ponds – Pollutant Removal Sediment………….. 50-90% Total Phosphorus… 30-90% Soluble Nutrients…. 40-80% Lead……………….. 70-80% Zinc………………… 40-50%

  14. Wet Pond Criteria • Minimum Contributory Area: 10 Acres • Pretreatment: Sediment Forebay Sized to Contain 0.1 inches per impervious area • Design to Treat Water Quality Volume • Multiple Treatment Pathways Increase Performance …Multiple Cells …Pond-Wetland Train

  15. Wet Pond Criteria • Pond Benches A. Safety Bench – 6%Maximum Slope B. Aquatic Bench – Maximum Depth 18” Below Normal Pool 6. Provide for Maintenance Access

  16. Types of Wetlands • Shallow Wetland • Extended Detention Wetland • Pond-Wetland System • Pocket Wetland

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