Green Infrastructure Flood Reduction Computations

Transcription

1 Green Infrastructure Flood Reduction Computations Stephen Sands, PE, CFM March 24, 2016 Water JAM 2010

2 Discussion Topics Siting success Watershed-wide computations Individual facility computations and calibration

3 Types of Urban Green Infrastructure Bioretention Permeable Pavement Subsurface Storage/Cistern Blue/Green Roof Stormwater Bumpouts /Tree Box Bioswales Wetlands Wetponds

4 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

5 Urban GI Siting Constraints Subsurface Utilities Drainage Pollutant Loading Ratio Community Support Landscaping Transportation Surface Structures Site Contamination Slope Suitable Soils Maintenance Access

6 Green Infrastructure Siting Water JAM 2010 NC AWWA WEA 2011

7 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

8 Green Infrastructure Siting Results Urban watersheds 50 to 200 acres Results varies based on drivers Coverage ranges from 15 to 40 percent

9 Discussion Topics Siting success Watershed-wide computations Individual facility computations and calibration

10 Dormont, PA Borough - Pittsburgh Most densely populated Established 1788 Population 9,000 Fecal coliform impairment Stormwater budget - $0 Borough-wide flood damage Grant funding

11 Watershed Conditions A = 47 acres, CN = 89 Water JAM 2010 NC AWWA WEA 2011

12 Watershed Conditions Water JAM 2010 NC AWWA WEA 2011

13 Watershed Conditions Water JAM 2010 NC AWWA WEA 2011

14 Green Infrastructure Screening Results Water JAM 2010 NC AWWA WEA 2011

15 NRCS Runoff Computations S = Losses = (1000/CN) - 10 Ia = Initial Abstractions = 0.2S Q = Runoff Volume = (P-0.2S) 2 (P -0.2S + S)

16 NRCS Runoff Computation Results 8.3 acres, CN = 98 2-year 2.92 inches GI Design Runoff Peak year 5.10 inches GI Design Runoff Peak year 6.83 inches GI Design Runoff Peak

17 NRCS Runoff Computation Results 9.6 acres, CN = 83 2-year 2.92 inches GI Design Runoff Peak year 5.10 inches GI Design Runoff Peak year 6.83 inches GI Design Runoff Peak

18 NRCS Runoff Computation Results Outlet 47 acres, CN = 89 2-year GI Design 0.2S Peak year GI Design 0.2S Peak year GI Design 0.2S Peak

19 NRCS Runoff Computation Results 100-year, 0.2 Ia Precipitation Loss Excess precipitation

20 NRCS Runoff Computation Results 2-year: GI Design 1.0 inch Precipitation Loss Excess precipitation

21 NRCS Runoff Computation Results 100-year: GI Design 1.0 inch Precipitation Loss Excess precipitation

22 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

23 Discussion Topics Siting success Watershed-wide computations Individual facility computations and calibration

24 Individual Facility Assessment Robust remote monitoring equipment Standardized equipment setups Regular site visits Annual monitoring results

25 Individual Facility Assessment Hydrograph Generation Runoff volume Peak discharge Routing Stage-storage-discharge Discharge through filter media Exfiltration to surrounding soils

26 Individual Facility Assessment Two cells Six inflows Area 8.6 ac Tc 6 min CN 75 Imp 24%

27 Individual Facility Assessment Water JAM 2010 NC AWWA WEA 2011

28 Hydrograph Generation Adjusted CN computation CN = 1000/[10 + 5P + 10WQ v 10(WQ v 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) (0.24 x 1.0)} 0.5 ] = 87.8

29 Hydrograph Generation 9 June 10, 2012 storm event cfs NRCS CN Adjusted CN Observed Minutes

30 Hydrograph Generation June 10, 2012 storm event cfs 5 4 NRCS CN Adjusted CN Observed Minutes

31 Hydrograph Generation June 10, inches Observed CN Adjusted CN Volume (cf) 19,718 1,710 16,230 Peak (cfs) May 8, inches Observed CN Adjusted CN Volume (cf) 34,644 13,440 42,900 Peak (cfs)

32 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 )

33 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

34 May 8, Storm Overflow Grate Water JAM 2010 NC AWWA WEA 2011

35 Routing Observations May 8, inches Infiltration Rate (in/hr) Outflow (cf) Observed , , , ,188

36 Discussion Topics Siting success Watershed-wide computations Individual facility computations and calibration

37 Green Infrastructure Flood Reduction Computations Stephen Sands, PE, CFM March 22, 2016 Water JAM 2010