PWD’s Systematic Watershed-wide Approach to Stormwater Mgmt. Jeffrey Featherstone, PhD Director, Center for Sustainable Communities, Temple University Paul DeBarry, PE, PH, GISP, D.WRE Director, Geospatial Data Technologies and Watershed Mgmt., NTM Engineering Joanne Dahme, General Manager Public Affairs, Philadelphia Water Department Richard Fromuth, P.E. Senior Research Associate, Center for Sustainable Communities, Temple University.
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PWD’s Systematic Watershed-wide Approach to
Stormwater Mgmt.
Jeffrey Featherstone, PhD Director, Center for Sustainable Communities, Temple University
Paul DeBarry, PE, PH, GISP, D.WRE Director, Geospatial Data Technologies and Watershed Mgmt., NTM Engineering
Joanne Dahme, General Manager Public Affairs, Philadelphia Water Department
Richard Fromuth, P.E. Senior Research Associate, Center for Sustainable Communities, Temple University.
– Pennypack Creek Act 167 SW Mgmt. Plan , 2013 – Poquessing Creek Act 167 Act 167 SW Mgmt. Plan ,
2013 – Wissahickon Creek Act 167 SW Mgmt. Plan , 2014
• The Watershed Stormwater Management Plans:
1. Evaluate Existing Studies/Data
2. Adjust DEM
3. Identify and Map Stormwater Problems
4. Map Streams
5. Map Obstructions
6. Collect Hydrologic Data
7. Develop Land Use Scenarios
8. GIS/Hydrologic Model Development
9. ID Stormwater Improvements
10.Develop Management Areas/Criteria
11. Develop Model SW Ordinance
12. Plan of Action
– 283 linear miles of streams
– 118 linear miles of streams – 73% Piped
Plans Have to Account for Past Neglect
Sample Comprehensive
Stormwater Management
Plan:
Wissahickon Creek
Watershed
Related Documents/ Studies: • An Integrated Watershed Management Plan • A Comprehensive Characterization of the Water Quality, Habitat and Biology • Sandy Run Act 167 Plan • River Conservation Plan
Related Documents/ Studies: •Floodplain Mapping Study: Sandy Run and Ambler Area Watersheds • Fort Washington Area Flooding and Transportation Improvement Study • A 'Special Area Management Plan’ • Detention Basin Inventory and Retrofit Program • Friends of Wissahickon Inventory
GIS Data Source County and municipal boundaries PennDOT, PASDA Road centerlines PennDOT or DVRPC Streams PWD Water bodies PWD, PAMAP Watershed boundary Delineated from LiDAR DEM from
PAMAP Wetlands U.S. Fish and Wildlife Service
National Wetlands Inventory (NWI), PWD
High Resolution Digital Ortho Photographs
PAMAP - 2008, DVRPC - 2010
Digital Elevation Model (DEM) LiDAR from PAMAP Program - 2008 Existing Land Use DVRPC - 2005 Future Land Use DVPRC, CSC Impervious Surface Areas PWD Hydrologic Soil Groups NRCS, PWD Geology USGS, PWD Obstructions PWD, CSC, FEMA, Municipalities Floodplains (FEMA Q3) FEMA
LiDAR data from PAMAP do not have stream break lines for small tributaries. This is needed for hydraulic modeling. Contractor (BAE) hired to add break lines for areas where hydraulic modeling and flood mapping is funded. (Ambler area at this time)
Existing detention basins were ID’d from aerial photography
Data was collected on the dimensions and outlet structures
Volumes were determined by overlaying LiDAR Contours on digital aerials and Stage- Storage-Discharge data was incorporated into the hydrologic model.
FEMA FIS data was collected and the floodplains utilized to ID problem areas, inundated structures, loss, etc.
Municipality Building Footprints in Floodplain 100 Year 500 Year
Abington 303 354 Ambler 90 91 Cheltenham 0 0 Horsham 0 0 Lansdale 16 32 Lower Gwynedd 104 124 Montgomery 6 6 North Wales 5 66 Philadelphia 5 16 Springfield 234 430 Upper Dublin 92 209 Upper Gwynedd 59 74 Upper Moreland 0 0 Whitemarsh 27 96 Whitpain 29 48 Worcester 0 0 Total 941 1546
Structures within Wissahickon Watershed Floodplains
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Stormwater Problems Flood Damage
Flood Insurance Payments: January 1978 – March 2010 Total paid claims = 610 Total payments = $26.2 Million
Flood Insurance Data provided by FEMA. Total claims payments do not represent all flood damage.
Obstructions
PWD field surveyed over 700 bridges, culverts, and dams in the watershed in 2005-2006. Half of these were determined significant obstructions to flow and resurveyed in 2012-2013. From the field measurements, obstruction capacities were determined and compared to flood frequencies.
Scour also reported
Bridge Culvert Dam
Obstruction Inventory
Tannery Run
Stuart Farm Creek
Rose Valley Creek
Obstructions
Obstructions
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Land Use Hydrologic Soil Group
GIS was used to overlay land use and hydrologic soil group for each subbasin to generate CN
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Curve Number Distribution for Wissahickon Subbasins
CN >85 CN 80-85 CN 75-80 CN 70-75 CN <70
Approximately 25 % of the watershed is covered by impervious surfaces such as roofs, parking lots and roads.
Curve numbers in this area to be evaluated further.
Trend
Residential
Non-Residential
Green Trend – Future land use based on population projections, no site-specific BMPs. Green – Future land use based on population projections and cluster housing, no site-specific BMPs. Future – Based on the Green land use projections and includes additional adjustments for storage from new or retrofitted detention basins, infiltration facilities, and riparian buffers.
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Existing Detention Storage Summed for each subbasin and added to the potential storage. The Curve number was then be adjusted.
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Hydrologic Model •HEC-HMS model •Inputs based on: - 2008 LiDAR from PAMAP - 2005 Land use from DVRPC - Soils data from NRCS, PWD - Stream and x-sect. data from PWD - 2008 Ortho imagery from PASDA - Storm Sewer Shed data from PWD •ArcHydro and HEC-GeoHMS used to prepare input for HEC-HMS model •137 subbasins delineated
•Average Drainage Area = 0.46 square miles
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Model Calibration The model was tested for multiple rainfall events and calibrated against observed flow data at stream gages. -Fort Washington -Philadelphia Design rainfall events were based on NOAA Atlas 14 precipitation frequency data.
Fort Washington Gage 40.8 mi2
Philadelphia Gage 64 mi2
The GIS data was exported to the HEC-HMS hydrologic model
Actual Storms - Storm Direction Influenced Hydrographs
Model Calibration Continuous (measured every 15 minutes) streamflow data is available at both USGS gage stations. Precipitation from several runoff-producing events will be run through the hydrologic model. The model will be calibrated so that it produces flows that are consistent with those measured by the USGS gages.
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8/2/09 3:00 AM 8/2/09 6:00 AM 8/2/09 9:00 AM 8/2/09 12:00 PM 8/2/09 3:00 PM 8/2/09 6:00 PM 8/2/09 9:00 PM 8/3/09 12:00 AM 8/3/09 3:00 AM
Rai
nfal
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nche
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Flow
(cfs
)
Date
Hyetograph/Hydrograph
MouthFt. WashingtonGage 18Gage 19Gage 21Wings Field (1-hr)C1648C5430C6611C3510AP069
Events were calibrated for both lag and peak at several points of interest (POIs).
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Event
Lag Time to Ft. Washington Gage (hrs) Peak Flow At Ft.
Washington (approx cfs)
Lag Time to Gage at Mouth
(hrs)
Peak Flow At Mouth (approx
cfs) Main Stem Sandy Run
Sep-04 3.5 11000 7 15200
Jun-06 4.25 6500 8.25 6800
Oct-09 3.75 1.75 3800 8 3200
Aug-09 7 1.15 6000 10.25 6000
May-09 3 2.5 2400 7 2000
Jun-09 2.25 4800 7 4600
Model Calibration The calibrated model output was be compared with peak flow estimates calculated using several widely accepted methods.
Peak and timing of hydrographs were analyzed at each POI
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Determine Management District
Assign Overall Management Districts
• District A = standard detention
• District B = alternate storm district
• District C = conditional direct discharge
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Tannery Run
Stuart Farm Creek
Rose Valley Creek
Hydraulic Model HEC-RAS Ambler portion of the watershed.
Sandy Run Watershed
Sandy Run Watershed
Model Ordinance: - ERSAM - SWM Site Plan Requirments - Groundwater Recharge - Water Volume Control - Channel Protection - Flood Control
Final Products: -Inventory of detention basins with proposed retrofits (Wm Penn) - Inventory of problem areas with proposed solutions (Wm Penn) - Final report - Model Stormwater Mgmt. Ordinance - FEMA flood flows - Basis for flood control projects - Plan of action to implement all various previously prepared programs