The Pond Management Protocol Tom Schueler Chesapeake Stormwater Network
Key Topics Pond Basics Evaluating Pond Functions Visual Indicators for Water Quality Visual Indicators for Dam Safety Techniques to Restore or Enhance Pond Performance
Beyond the Pond Checklist Why do we need a better pond inspection protocol? Our old approach flags potential problems but does not actually trigger maintenance activities (C.Y.A in case something goes real bad) Need to assess water quality function for BMP verification
Goals of the Pond Protocol Rapidly evaluate the function of stormwater ponds Use of rapid visual indicators to assess dam safety and water quality functions for wet and dry ponds Establish numeric criteria to trigger critical pond repairs Make cost-effective choices on how to manage your inventory of legacy stormwater ponds to optimize nutrient reduction and maintain dam safety
Wet Stormwater Pond
Dry Stormwater Pond
Evaluating Pond Performance A Simple Protocol for Ranking Pond Performance Based on Field Inspections
Pond Pollutant Removal Performance Levels Based on Field Inspections Code NP UP Performance Level Nutrient Removal (%) TP TN Non-Performing Ponds 0 0 Under-Performing Ponds 20 10 P Performing Ponds 55 35 OP Over-Performing Ponds 56 to ~70 1 36 to ~50 1 1 variable rate depending on the nature of the pond retrofit enhancement
Code NP Defining Factors for Non-Performing Ponds Pond Types Any Pond with a DS FAIL 1 Dry Pond Dry ED Pond w/ one WQ FAIL 1 Wet Pond w/ two WQ FAIL 1 DS: Dam Safety WQ: Water Quality ED: Extended Detention 1 Based on Field Inspections Using the WQ and DS Visual Indicators
Code UP Defining Factors for Under-Performing Ponds Pond Types Dry ED Pond Wet Pond w/ one WQ FAIL Self Converted Dry Pond WQ: Water Quality ED: Extended Detention
Code P Defining Factors for Performing Ponds Pond Types Wet Pond PASS Wet ED Pond PASS Dry Pond Conversion to ST Retrofit (wet or filter) ED: Extended Detention ST: Stormwater Treatment
Code OP Defining Factors for Over-Performing Ponds Pond Types Dry Pond Conversion to RR Retrofit Enhanced Wet Pond Retrofit ofloating Treatment Wetland osmart ED Above Pool oothers as Approved ED: Extended Detention RR: Runoff Reduction
Loss of WQ Volume ED Dry pond Wet Pond Forebay PASS PASS Capacity Loss is Hard to Measure
Loss of WQ Volume Indicators: Visible sediment or debris deposits neat dry pond inlet, pilot channel or outlet or wet pond forebay, benches or main pool Triggers: Estimated loss of more than a third of original pond water quality volume Remedy: Sediment cleanout or dredging
WQ Volume ---Fails Full Forebay Full Pilot Channel
WQ Volume Moderate Sediment Accumulation Near Riser
Short Circuiting Indicator (or Inadequate Hydraulic Retention Time)
Short Circuiting Indicator: Runoff is not fully treated during storms, either due to flow bypass or inadequate hydraulic retention time Triggers: Effective flow path from major inlet to outlet is > 0.5 length to width ratio Remedy: Pond Retrofit
High Pool Elevation Indicators: Low Flow pipes clogged by sediment/trash or plastic bags Riser staining Beaver activity Trigger: Pool elevations are more than six inches above normal pool elevation more than 3 days after a storm event Remedy: Relieve clogged pipes/trash racks
High Pool Elevation
High Pool Elevation
Clogs: High Pool Elevation
Riser Staining
Low Pool Elevation/Short Detention Time Indicators: Exposed Bottom sediments (wet) No evidence of sediment deposition (dry) Structural Sinkholes Trigger: Normal pool elevations more than six inches below normal pool for extended periods Remedy: Pond repair or retrofit
Low Pool or Short Detention Time
Low Pool Elevation
Low Pool Elevation: Structural Sinkhole
Geologic Sinkhole in Pond Indicator: Evidence of seepage into the pond bottom or embankment via sinkholes Trigger: Stormwater exits the pond through soils or voids and no longer goes out the design outlet Remedy: Sinkhole repair
Geologic Sinkhole in Pond
Geologic Sinkhole in Pond
Geologic Sinkhole in Wet Pond
Remediated Sinkhole
Vegetative Conversion Indicators Indicator: Shift from Turf to: Scrub Shrub Forest Emergent Wetlands Forested Wetlands Trigger: More than 50% of pond surface area does not meet its original landscaping objective Remedy: Bush Hog or Allow Self Conversion
Vegetative Conversion Source KCI
Vegetative Conversion Source KCI
Vegetative Conversion
Pond Management Choices for Self Conversion Require return to original landscaping objective Allow Self-Conversion but: Continue to mow embankment and maintenance access Expect increased frequency of FAIL due to clogged low flow pipes, WQV loss, or severe debris deposits at outlets
Invasive Species Indicators Domination by Invasive Plants (e.g., purple loosestrife, Phragmites, Japanese Knotweed, etc.) Trigger: plants infest more than 50% of pond surface area Large resident geese populations Trigger: >20 geese per pond acre
Geese Impacts
Invasive Plant Domination
Hyper-trophic Pond Conditions Harmful Blue Green Algal Blooms Takeover by Invasive Aquatic Macrophytes Cause: High Nutrient Inputs from CDA (e.g., fertilizer, sewage leaks, illicit discharges) Trigger: Permanent pool is stagnant, appears putrid, smells bad due to algal blooms or aquatic macrophytes over at least half of the wet pond surface
Hyper-trophic Pond Conditions
Upstream Channel Erosion Indicators: Severe Erosion in Pilot Channel Severe Erosion in Inflow Channels Trigger: Sediment load produced by channel erosion is diminishing pond storage capacity Remedy: Bank stabilization or pilot channel repair
Upstream Channel Erosion
Pilot Channel Erosion
Downstream Channel Erosion Indicators: Outfall stabilization is degraded Erosion threatens outfall pipe Nickpoints moving toward pond Trigger: Channel erosion is compromising the integrity of barrel or the embankment Remedy: Outfall and/or channel stabilization or regenerative stormwater conveyance
Downstream Channel Erosion PASS FAIL
Nickpoint Compromising Outfall Pipe
Dam Safety Visual Indicators Embankment Integrity Barrel/Riser Condition Emergency Spillway Condition Clogged Low Flow Pipes/Drains CSN will feature these visual indicators at its November 3 rd Webcast
Pond Retrofit Options
Maximizing Pollutant Removal The ability of retrofits to remove pollutants is based on three factors: 1. Type of stormwater treatment employed (ST and RR) 2. Amount of runoff depth captured by the practice 3. Total amount of impervious acres in the drainage area The best performing retrofits will use runoff reduction practices, maximize runoff volume captured and treat larger drainage areas.
Techniques to Restore or Increase Dry Pond Performance Technique Dam Safety Remediation Dry Pond Conversion to ST Dry Pond Conversion to RR "Smart" Dry Pond Retrofit Pond Repairs to get to PASS Upstream/Downstream Channel Protection Allow Self-Conversion * * no additional credit offered at this time Applies to: NP to P UP or NP to P UP pr NP to OP UP to P UP or NP to P UP to P NP to UP
Techniques to Restore or Increase Wet Pond Performance Technique Dam Safety Remediation Major Sediment Cleanout Retrofit: Increase WQv Floating Treatment Wetland Retrofit to Increase Residence Time Upstream/ Downstream Channel Protection Aquatic Management Practices Pond Repairs to go to PASS Applies to: NP to P UP or NP to P UP to P or OP P to OP NP to P UP to P UP to P UP or NP to P
Critical Pond Repairs
RETROFIT OF EXISTING PONDS 1. Pond Conversions 2. Pond Enhancements 3. Pond Restoration Can be the most cost effective type of retrofit since it represents existing stormwater infrastructure that you already own or control!
EXISTING RETROFITS POND CONVERSION DRY POND CONSTRUCTED WETLAND
OTHER CONVERSIONS Adding Bioretention or Sand Filters to Dry Ponds
EXISTING RETROFITS BMP ENHANCEMENT Increase treatment volume, hydraulic residence time or other design elements to improve pollutant removal, such deploying a floating treatment wetland
Design Enhancement: Floating Treatment Wetland in Existing Wet Ponds Pollutant Raft Coverage in Pond 10% 20% 30% 40% 50% TN 0.8% 1.7% 2.5% 3.3% 4.1% TP 1.6% 3.3% 4.9% 6.5% 8.0% TSS 2.3% 4.7% 7.0% 9.2% 11.5%
EXISTING RETROFITS BMP RESTORATION DREDGING AN UNDERPERFORMING POND TO RESTORE FULL PERFORMANCE
Use of Regenerative Stormwater Conveyance Retrofits at Outfalls Dry RSC practices can be used to solve gully erosion problems and serve as a retrofit below stormwater pipe and pond outfalls stormwater runoff Use runoff storage and the RR curve to determine removal rates Cabin Branch RSC project
Questions and Answers