pond and wetland bmps, retrofitting detention basins
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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) - PowerPoint PPT PresentationTRANSCRIPT
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)
• Drainage Area: Minimum of 10 Acres (>25 Acres Preferred)
• Treat Water Quality Volume• Retrofit Opportunities• Maintenance
sediment removal
Inlet & outlet
vegetation
Wet Ponds – Primary Design Parameters
• Storage VolumeChannel Protection & Flood Control
• Detention Time (24-48 Hours)Water Quality
• Release RateChannel Protection & Flood Control
Wet Pond – Other Design Criteria
• Treat Up to 75 Acres
• Include Forebay
• Depth: 4-6 Feet
• Geometry Affects Performancedead storage
short circuiting
Extended Detention Pond
Wet Pond
Multiple Pond System
Pocket Pond
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
Wet Pond – Area Ratio
Area Ratio = Drainage Area
Pond Area
Should Be Less Than 100
For Maximum Efficiency
Wet Ponds – Pollutant Removal
Sediment………….. 50-90%
Total Phosphorus… 30-90%
Soluble Nutrients….40-80%
Lead……………….. 70-80%
Zinc…………………40-50%
Wet Pond Criteria
1. Minimum Contributory Area: 10 Acres2. Pretreatment: Sediment Forebay
Sized to Contain 0.1 inches per impervious area
3. Design to Treat Water Quality Volume4. Multiple Treatment Pathways Increase
Performance…Multiple Cells…Pond-Wetland Train
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
Types of Wetlands
• Shallow Wetland
• Extended Detention Wetland
• Pond-Wetland System
• Pocket Wetland
Component Design
Outlet Structure
Wetland Treatment Criteria
1. Surface Area: At least 1% of total Drainage Area
2. 25% of WQv 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”
Existing Conditions – (Pre-Construction)
Proposed Conditions (Post-construction)
Proposed Conditions (Post-construction)
Retrofitting Detention Basins
Conventional Detention Basins
• Designed For Flood Control & Channel Protection
large storm events (50 year…100 year)
• Do Not Control: runoff volumewater quality
• Do Not Provideaestheticswildlife habitat
Retrofitting Detention Basins - Benefits
• Pollutant Removal
• Water Quality Improvement
• Wildlife Habitat Creation
• Aesthetic Improvement
• Reduced Maintenance
Retrofitting Detention Basins - Modifications
• Modify Outfall Structurecreate two-stage release
treat small storms for water quality
• Eliminate Paved Low-Flow Channelsuse meandering vegetated swales
increase detention time for small storms
Retrofitting Detention Basins - Modificatons
• Use Stilling and Settling Basins at Inlets & Outlets
remove sediment & attached pollutantsplant with wetland plants
• Regrade to Provide Micro-Habitats
• Create Wetland - Pond Areas
Extended Detention Basin Conversion
Wet Pond Conversion
Proposed Conditions – Post Construction Construction