Evaluating Urban Stormwater Retrofits in the SE US Coastal Plain

Transcription

1 Evaluating Urban Stormwater Retrofits in the SE US Coastal Plain 2017 Florida Stormwater Association June 14-17, 2017 Eban Z. Bean, PhD, PE Assistant Professor & Extension Specialist Agricultural and Biological Engineering Urban Water Resources Engineering

2 Urban Drainage

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4 Ponds Not Making the Cut Total Nitrogen Concentration (mg/l) Inflow 1.20 Outflow Total Phosphorus (mg/l) Impairment, TMDLs, BMAPs Numeric Nutrient Criteria 0.35 Inflow 0.11 Outflow Paired sample results collected from 18 (N) and 23 (P) stormwater retention ponds in Florida. International Stormwater BMP Database

5 Urban Stormwater Impairments.so far Impairment Rate (of Assessed FL Water Bodies) 31% 59% 55% 80% Nutrients, Algal Growth, or Low Oxygen Coastlines Bays and Esturaries Streams and Rivers Lakes 1 st 1 st 2 nd 3 rd Pathogens 3 rd 7 th 3 rd 2 nd

6 Impaired Urban Waters 18 Million 34 Million

7 Greens Mill Run Watershed Greenville Stream Length: 7.3 miles Watershed Area: 8600 ac. Impaired for Benthic Condition Excess Stormwater Runoff

8 Watershed Development Trends ECU ~70% developed Development prior to 1982, few SCMs Upstream build out expected Largest single land owner: East Carolina University 2005 GMR LWP-RP

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10 Retrofit Challenges Lack of Financial or Regulatory Incentives Little Information on Performance in Florida Source Area & Receiving Area Compatibility Elevation Relative Areas (Undersizing) Soil Characteristics Existing Utilities Future Land Use Plans Site Aesthetics

11 N

12 N

13 PICP: 10,800 sq. ft. Asphalt: 16,000 sq. ft. Impervious to Pervious Ratio: 1.5

14 Permeable Pavement Monitoring 17 in. No. 8 No. 57 No. 2 CURB

15 Sloped Permeable Pavement % Storage: ~2.5 inch event ~1 yr, 12 hr event ~10 yr, 1 hr event

16 Sloped Permeable Pavement % Storage: ~0.4 inches

17 Pavement Performance March 2013 May 2014 Totals Rainfall: 64.6 in. Runoff: 38.4 in. Infiltration: 26.1 in. (38%) Storms: 101 events > 0.1 in. 15 events > 1.00 in. Max: 3.84 in Impervious Lot Pervious Parking Lot

18 The REST of the story

19 Retrofit Site Selection 9 Initial Sites Incompatible Future Landuse Utilities Conflict Bioretention Site Wetland Site

20 Grassed Bioretention 12,200 ft 2 Impervious Area Online Bioretention with Upturned Elbow (Unlined) Effective Design Storm Size: 0.34 in. % of Full Design: 41%

21 Grassed Bioretention Underdrains w/ upturned elbow Underdrain run below telecom bank Shallow storm sewer 18 in. btw inlet and underdrain inverts 9 in. ponding depth 9 in. media above invert

22 Bioretention 9,430 ft 2 Impervious Bioretention with Upturned Elbow Effective Design Storm Size: 0.28 in. % of Full Design: 46%

23 Bioretention Underdrain with upturned elbow Between Telecom and Electrical Banks Narrowed underdrain area by ~50% Low slope from drainage area

24 Rain Garden Rain Garden (In Situ sandy soil) Effective Design Storm Size: 0.63 in. % of Full Design: 78%

25 Stormwater Wetland Dry Detention 3,500 ft 2 Impervious Catchment 5.80 ac/252,500 ft 2 Permitted Stormwater Wetland Runoff from first 1 --> 16,000 ft 2

26 Stormwater Wetland Outlet Inlet 1 Outlet Inlet 1 Shallow Land Shallow Water Berm/ Landing Deep Pool Inlet 2 Inlet 2

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28 nothing but holdin Contractor You know he s (Contractor) blind in one eye, right? Campus Facilities Manager (last day)

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31 Stormwater Wetland Runoff Coefficient: 0.92 Effective Design Storm Size: 0.17 in. % of Full Design: 20%

32 Monitoring June 2015 August 2016 Rainfall: On-campus Weather Station Volumes: Water Levels in Basins and Underdrains Flow Rates: Weirs on Wetland Inlets and Outlet Flow meters on Bioretention Underdrains Water Quality: Inlets, outlets, and underdrains (as available) N species, P species, and Total Suspended Solids Wetland Inlet 1 Wetland Inlet 2 Wetland Outlet

33 Water Quality Results Inflow vs. Outflow (Underdrain): Concentrations not significantly different Loading Reductions Retrofit Watershed Runoff Reduction Inflows Reduction TN (lbs.) TP (lbs.) TSS (lbs.) Rain Garden Off-line 70% 100% Bioretention Off-line 89% 95% Grassed Bioretention On-Line 28% 98% Wetland On-Line 0% 0%

34 Rain Garden PN ON NH4 NO2+NO Rain Garden TP DRP OP Total Nitrogen (lbs.-n/ac/yr) Inflow Inflow Bioretention Outflow Grassed Bioretention Wetland Outflow Total Phosphorus (lbs.-p/ac/yr) Inflow Outflow Inflow Bioretention Grassed Bioretention Wetland Outflow Inlet 1 Inlet 2 Outlet 0 Inlet 1 Inlet 2 Outlet

35 Wetland Continued Research Bledsoe, G. & Peralta, A., Dept. of Biology, East Carolina University

36 Summary Growing Need to Address Legacy Stormwater Managment Large Challenges for Retrofitting Developed Areas Undersized Retrofits Can Reduce Runoff Volumes Infiltrate to Reduce Pollutant Loadings Flow Through Treatment Less Effective Opportunities for Improving Treatement

37 Questions? Eban Z. Bean, Ph.D., P.E. Assistant Professor & Extension Specialist Urban Water Resources Engineering EbanBean

38 Questions? Eban Z. Bean, Ph.D., P.E. Assistant Professor & Extension Specialist Urban Water Resources Engineering EbanBean

39 Questions? Eban Z. Bean, Ph.D., P.E. Assistant Professor & Extension Specialist Urban Water Resources Engineering EbanBean

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