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Published byStephany Rich Modified over 9 years ago
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Pond and Wetland BMPs, Retrofitting Detention Basins
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WET PONDS
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Wet Pond Treatment Processes Settling Plant Uptake and Adsorption Infiltration Evaporation
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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
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Wet Ponds – Primary Design Parameters Storage Volume Channel Protection & Flood Control Detention Time (24-48 Hours) Water Quality Release Rate Channel Protection & Flood Control
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Wet Pond – Other Design Criteria Treat Up to 75 Acres Include Forebay Depth: 4-6 Feet Geometry Affects Performance dead storage short circuiting
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Extended Detention Pond
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Wet Pond
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Multiple Pond System
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Pocket Pond
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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
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Wet Pond – Area Ratio Area Ratio = Drainage Area Pond Area Should Be Less Than 100 For Maximum Efficiency
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Wet Ponds – Pollutant Removal Sediment…………..50-90% Total Phosphorus…30-90% Soluble Nutrients….40-80% Lead………………..70-80% Zinc…………………40-50%
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Wet Pond Criteria 1.Minimum Contributory Area: 10 Acres 2.Pretreatment: Sediment Forebay Sized to Contain 0.1 inches per impervious area 3.Design to Treat Water Quality Volume 4.Multiple Treatment Pathways Increase Performance …Multiple Cells …Pond-Wetland Train
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Wet Pond Criteria 5.Pond Benches A. Safety Bench – 6%Maximum Slope B. Aquatic Bench – Maximum Depth 18” Below Normal Pool 6.Provide for Maintenance Access
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Types of Wetlands Shallow Wetland Extended Detention Wetland Pond-Wetland System Pocket Wetland
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Component Design Outlet Structure
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Wetland Treatment Criteria 1.Surface Area: At least 1% of total Drainage Area 2.25% of WQ v Should Be In Deep Water Zones (4’) 3.Minimum of 35% of Area: Depth of 6” or less 4.At least 65% of Area: Shallower than 18”
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Existing Conditions – (Pre-Construction)
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Proposed Conditions (Post-construction)
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Retrofitting Detention Basins
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Conventional Detention Basins Designed For Flood Control & Channel Protection large storm events (50 year…100 year) Do Not Control: runoff volume water quality Do Not Provide aesthetics wildlife habitat
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Retrofitting Detention Basins - Benefits Pollutant Removal Water Quality Improvement Wildlife Habitat Creation Aesthetic Improvement Reduced Maintenance
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Retrofitting Detention Basins - Modifications Modify Outfall Structure create two-stage release treat small storms for water quality Eliminate Paved Low-Flow Channels use meandering vegetated swales increase detention time for small storms
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Retrofitting Detention Basins - Modificatons Use Stilling and Settling Basins at Inlets & Outlets remove sediment & attached pollutants plant with wetland plants Regrade to Provide Micro-Habitats Create Wetland - Pond Areas
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Extended Detention Basin Conversion
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Wet Pond Conversion
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Proposed Conditions – Post Construction Construction
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