The Pond Management Protocol. Tom Schueler Chesapeake Stormwater Network

Transcription

1 The Pond Management Protocol Tom Schueler Chesapeake Stormwater Network

2 Key Topics Pond Basics Evaluating Pond Functions Visual Indicators for Water Quality Visual Indicators for Dam Safety Techniques to Restore or Enhance Pond Performance

3

4 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

5 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

6 Wet Stormwater Pond

7 Dry Stormwater Pond

8 Evaluating Pond Performance A Simple Protocol for Ranking Pond Performance Based on Field Inspections

9 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 P Performing Ponds OP Over-Performing Ponds 56 to ~ to ~ variable rate depending on the nature of the pond retrofit enhancement

10 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

11 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

12 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

13 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

14 Loss of WQ Volume ED Dry pond Wet Pond Forebay PASS PASS Capacity Loss is Hard to Measure

15 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

16 WQ Volume ---Fails Full Forebay Full Pilot Channel

17 WQ Volume Moderate Sediment Accumulation Near Riser

18 Short Circuiting Indicator (or Inadequate Hydraulic Retention Time)

19 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

20 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

21 High Pool Elevation

22 High Pool Elevation

23 Clogs: High Pool Elevation

24 Riser Staining

25 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

26 Low Pool or Short Detention Time

27 Low Pool Elevation

28 Low Pool Elevation: Structural Sinkhole

29 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

30 Geologic Sinkhole in Pond

31 Geologic Sinkhole in Pond

32 Geologic Sinkhole in Wet Pond

33 Remediated Sinkhole

34 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

35 Vegetative Conversion Source KCI

36 Vegetative Conversion Source KCI

37 Vegetative Conversion

38 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

39 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

40 Geese Impacts

41 Invasive Plant Domination

42 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

43 Hyper-trophic Pond Conditions

44 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

45 Upstream Channel Erosion

46 Pilot Channel Erosion

47 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

48 Downstream Channel Erosion PASS FAIL

49 Nickpoint Compromising Outfall Pipe

50 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

51

52 Pond Retrofit Options

53 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.

54 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

55 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

56 Critical Pond Repairs

57 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!

58 EXISTING RETROFITS POND CONVERSION DRY POND CONSTRUCTED WETLAND

59 OTHER CONVERSIONS Adding Bioretention or Sand Filters to Dry Ponds

60 EXISTING RETROFITS BMP ENHANCEMENT Increase treatment volume, hydraulic residence time or other design elements to improve pollutant removal, such deploying a floating treatment wetland

61 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%

62 EXISTING RETROFITS BMP RESTORATION DREDGING AN UNDERPERFORMING POND TO RESTORE FULL PERFORMANCE

63 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

64 Questions and Answers