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
Urban Drainage
Ponds Not Making the Cut Total Nitrogen Concentration (mg/l) 8 7 6 5 4 3 2 1 0 1.65 Inflow 1.20 Outflow Total Phosphorus (mg/l) 3.0 2.5 2.0 1.5 1.0 0.5 0.0 8.65 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
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
Impaired Urban Waters 18 Million 34 Million
Greens Mill Run Watershed Greenville Stream Length: 7.3 miles Watershed Area: 8600 ac. Impaired for Benthic Condition Excess Stormwater Runoff
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
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
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PICP: 10,800 sq. ft. Asphalt: 16,000 sq. ft. Impervious to Pervious Ratio: 1.5
Permeable Pavement Monitoring 17 in. No. 8 No. 57 No. 2 CURB
Sloped Permeable Pavement 450 4.5 1% Storage: ~2.5 inch event ~1 yr, 12 hr event ~10 yr, 1 hr event
Sloped Permeable Pavement 450 4.5 1% Storage: ~0.4 inches
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. 100 80 60 40 20 0 Impervious Lot Pervious Parking Lot
The REST of the story
Retrofit Site Selection 9 Initial Sites Incompatible Future Landuse Utilities Conflict Bioretention Site Wetland Site
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%
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
Bioretention 9,430 ft 2 Impervious Bioretention with Upturned Elbow Effective Design Storm Size: 0.28 in. % of Full Design: 46%
Bioretention Underdrain with upturned elbow Between Telecom and Electrical Banks Narrowed underdrain area by ~50% Low slope from drainage area
Rain Garden Rain Garden (In Situ sandy soil) Effective Design Storm Size: 0.63 in. % of Full Design: 78%
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
Stormwater Wetland Outlet Inlet 1 Outlet Inlet 1 Shallow Land Shallow Water Berm/ Landing Deep Pool Inlet 2 Inlet 2
nothing but holdin Contractor You know he s (Contractor) blind in one eye, right? Campus Facilities Manager (last day)
Stormwater Wetland Runoff Coefficient: 0.92 Effective Design Storm Size: 0.17 in. % of Full Design: 20%
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
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% 4.97 0.47 66.89 Bioretention Off-line 89% 95% 1.32 0.17 15.95 Grassed Bioretention On-Line 28% 98% 2.52 0.18 32.99 Wetland On-Line 0% 0% -0.10-1.34 35.08
25 20 15 10 5 0 Rain Garden PN ON NH4 NO2+NO3 2.50 2.00 1.50 1.00 0.50 0.00 Rain Garden TP DRP OP Total Nitrogen (lbs.-n/ac/yr) 6 4 2 0 20 15 10 5 0 20 Inflow Inflow Bioretention Outflow Grassed Bioretention Wetland Outflow Total Phosphorus (lbs.-p/ac/yr) 0.6 0.4 0.2 0 1.2 0.8 0.4 0 1.5 Inflow Outflow Inflow Bioretention Grassed Bioretention Wetland Outflow 15 1 10 5 0.5 0 Inlet 1 Inlet 2 Outlet 0 Inlet 1 Inlet 2 Outlet
Wetland Continued Research Bledsoe, G. & Peralta, A., Dept. of Biology, East Carolina University
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
Questions? Eban Z. Bean, Ph.D., P.E. Assistant Professor & Extension Specialist Urban Water Resources Engineering ezbean@ufl.edu EbanBean
Questions? Eban Z. Bean, Ph.D., P.E. Assistant Professor & Extension Specialist Urban Water Resources Engineering ezbean@ufl.edu EbanBean
Questions? Eban Z. Bean, Ph.D., P.E. Assistant Professor & Extension Specialist Urban Water Resources Engineering ezbean@ufl.edu EbanBean