Green Infrastructure Flood Reduction Computations Stephen Sands, PE, CFM ssands@hazenandsawyer.com March 24, 2016 Water JAM 2010
Discussion Topics Siting success Watershed-wide computations Individual facility computations and calibration
Types of Urban Green Infrastructure Bioretention Permeable Pavement Subsurface Storage/Cistern Blue/Green Roof Stormwater Bumpouts /Tree Box Bioswales Wetlands Wetponds
Flood Reduction Features Storage/Runoff Reduction Infiltration Volume Control Design Storm 0.5 inch to 1.5 inch Maximum Storage Depth Vegetation Impacts Filter Media Impacts Bypass Storm Event
Urban GI Siting Constraints Subsurface Utilities Drainage Pollutant Loading Ratio Community Support Landscaping Transportation Surface Structures Site Contamination Slope Suitable Soils Maintenance Access
Green Infrastructure Siting Water JAM 2010 NC AWWA WEA 2011
S BANCROFT ST S " S " S 16TH ST S BANCROFT ST S " "S S CHADWICK ST S 17TH ST S COLORADO ST S BOUVIER ST S 18TH ST S CLEVELAND ST DORRANCE ST EARP ST ") Green Infrastructure Siting REED ST DORRANCE ST S CLEVELAND ST S CLEVELAND ST DORRANCE ST SEARS ST " " " " " " S S S S S S S GARNET ST S OPAL ST S WOODSTOCK ST S CAPITOL ST S LAMBERT ST EARP ST " " " " " " S S S S S ) " " " S S S " " " "" " S S S SS S "S " " " " S S S S " " " S S S POINT BREEZE AVE DICKINSON ST S 21ST ST S 19TH ST S 20TH ST CROSS ST GERRITT ST WILDER ST S WOODSTOCK ST S OPAL ST S GARNET ST S CAPITOL ST S LAMBERT ST "S " " " " " S S S S S " " " " " S S S S S " " " ) ) ) " " " S S S TASKER ST FERNON ST MOUNTAIN ST MORRIS ST Water JAM 2010 NC AWWA WEA 2011
Green Infrastructure Siting Results Urban watersheds 50 to 200 acres Results varies based on drivers Coverage ranges from 15 to 40 percent
Discussion Topics Siting success Watershed-wide computations Individual facility computations and calibration
Dormont, PA Borough - Pittsburgh Most densely populated Established 1788 Population 9,000 Fecal coliform impairment Stormwater budget - $0 Borough-wide flood damage Grant funding
Watershed Conditions A = 47 acres, CN = 89 Water JAM 2010 NC AWWA WEA 2011
Watershed Conditions Water JAM 2010 NC AWWA WEA 2011
Watershed Conditions Water JAM 2010 NC AWWA WEA 2011
Green Infrastructure Screening Results Water JAM 2010 NC AWWA WEA 2011
NRCS Runoff Computations S = Losses = (1000/CN) - 10 Ia = Initial Abstractions = 0.2S Q = Runoff Volume = (P-0.2S) 2 (P -0.2S + S)
NRCS Runoff Computation Results 8.3 acres, CN = 98 2-year 2.92 inches GI Design 0.04 0.50 1.00 1.50 Runoff 2.35 1.89 1.40 0.91 Peak 35 34 32 14 25-year 5.10 inches GI Design 0.04 0.50 1.00 1.50 Runoff 4.32 3.84 3.35 2.85 Peak 53 53 52 52 100-year 6.83 inches GI Design 0.04 0.50 1.00 1.50 Runoff 5.75 5.30 4.80 4.30 Peak 64 64 63 63
NRCS Runoff Computation Results 9.6 acres, CN = 83 2-year 2.92 inches GI Design 0.40 0.50 1.00 1.50 Runoff 1.44 1.05 0.69 0.37 Peak 22 18 11 3 25-year 5.10 inches GI Design 0.40 0.50 1.00 1.50 Runoff 3.13 2.68 2.75 1.82 Peak 41 38 34 28 100-year 6.83 inches GI Design 0.40 0.50 1.00 1.50 Runoff 4.47 4.00 3.54 3.09 Peak 51 50 48 44
NRCS Runoff Computation Results Outlet 47 acres, CN = 89 2-year GI Design 0.2S 0.5 1.0 1.5 Peak 103 100 85 68 25-year GI Design 0.2S 0.5 1.0 1.5 Peak 169 168 163 157 100-year GI Design 0.2S 0.5 1.0 1.5 Peak 209 208 204 198
NRCS Runoff Computation Results 100-year, 0.2 Ia Precipitation Loss Excess precipitation
NRCS Runoff Computation Results 2-year: GI Design 1.0 inch Precipitation Loss Excess precipitation
NRCS Runoff Computation Results 100-year: GI Design 1.0 inch Precipitation Loss Excess precipitation
Watershed-wide Observations 2-year: 10 to 40 percent peak flow reduction 25-year: 5 to 15 percent peak flow reduction 100-year: less than 5 percent peak flow reduction Set GI interception target to intercept initial rainfall Greater peak flow reduction in less urbanized sub-basins
Discussion Topics Siting success Watershed-wide computations Individual facility computations and calibration
Individual Facility Assessment Robust remote monitoring equipment Standardized equipment setups Regular site visits Annual monitoring results
Individual Facility Assessment Hydrograph Generation Runoff volume Peak discharge Routing Stage-storage-discharge Discharge through filter media Exfiltration to surrounding soils
Individual Facility Assessment Two cells Six inflows Area 8.6 ac Tc 6 min CN 75 Imp 24%
Individual Facility Assessment Water JAM 2010 NC AWWA WEA 2011
Hydrograph Generation Adjusted CN computation CN = 1000/[10 + 5P + 10WQ v 10(WQ v2 + 1.25 WQvP) 0.5 ] where: P = rainfall depth (inches) WQ v = runoff vol for water quality (inches) CN = 1000/[10 + 5(0.24) + 10(0.24) 10{(0.24) 2 + 1.25(0.24 x 1.0)} 0.5 ] = 87.8
Hydrograph Generation 9 June 10, 2012 storm event 8 7 6 cfs 5 4 3 NRCS CN Adjusted CN 2 1 0-1 0 200 400 600 800 1000 1200 Observed Minutes
Hydrograph Generation June 10, 2012 storm event 9 8 7 6 cfs 5 4 NRCS CN Adjusted CN Observed 3 2 1 0 780 800 820 840 860 880 900 920 940 960 Minutes
Hydrograph Generation June 10, 2013 1.45 inches Observed CN Adjusted CN Volume (cf) 19,718 1,710 16,230 Peak (cfs) 7.7 1.3 5.8 May 8, 2013 2.54 inches Observed CN Adjusted CN Volume (cf) 34,644 13,440 42,900 Peak (cfs) 7.2 5.8 11.6
Routing: Stage-Storage-Discharge Filter media discharge Darcy s Law equation, A f = (WQ v )(df) / [(k)(hf + df)(tf)] where: A f = surface area of ponding area (ft 2 ) WQ v = water quality control volume d f = filter bed depth k = coefficient of permeability (0.5 ft/day) h f = average head above filter bed (ft) = design filter bed drain time (days) t f WQ v /t f = Q o = A f (k)(h f +d f )/(d f )
Routing Observations Comparison of Instant Runoff to Routing Similar drawdown duration 1-hour storm event 65 to 80 percent of peak stage 24-hour storm event 30 to 40 percent of peak stage
May 8, 2013-2.54 Storm Overflow Grate Water JAM 2010 NC AWWA WEA 2011
Routing Observations May 8, 2013 2.54 inches Infiltration Rate (in/hr) Outflow (cf) Observed 622 0.5 23,814 2.0 7,011 4.0 2,283 5.0 1,188
Discussion Topics Siting success Watershed-wide computations Individual facility computations and calibration
Green Infrastructure Flood Reduction Computations Stephen Sands, PE, CFM ssands@hazenandsawyer.com March 22, 2016 Water JAM 2010