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.

Agenda: 1. PWD Watersheds & Studies/Plans 2. Typical Procedure for Development of a

Comprehensive Stormwater Management Plan

• Coordinated efforts: – Act 167 SW Mgmt. Plans

• GIS Mapping, Watershed Hydrologic Modeling • Model Stormwater Ordinance • Plan of Action for SW Mgmt. & Retrofitting

– River Conservation Plans • Resource Inventory • Management Options (stream clean-ups, protect open space, protect

stream corridors) – Comprehensive Characterization Reports

• Water Quality Sampling • Habitat Assessment • Indicator Status Update

– Integrated Watershed Mgmt. Plans • Restore Impaired Water Quality • Multi-faceted Approach (Stream Restoration, BMPs, CSO Rehab)

– Stream Assessment Study’s – Trail Master Plans – Other Studies

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Act 167 SW Mgmt. Plans 2004 2013 2013 2008 2014

River Conservation Plan 2005 2011 2005 2007 2004 2001 1999

Comprehensive Characterization Reports 2004 2009 2010 2005 2007

Integrated Watershed Mgmt. Plans 2004 2013 2012 2005

Stream Assessment Study 2010

Source Water Assessment 2002 2007 2002

Other Studies 2003 2011

Timeline: Comprehensive Act 167 Stormwater Management Plans

– Darby-Cobbs Creeks Act 167 SW Mgmt. Plan (Delaware Co. Lead), 2004

– Development of Philadelphia Stormwater Standards from Darby-Cobbs Ordinance, 2005

– Tookany/Tacony-Frankford Act 167 Act 167 SW Mgmt. Plan , 2008

– 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)

Municipal Participation –

Data Collection Forms

Problems in the Watershed

• Floodplain encroachment • Undersized storm drains • Undersized stream channels • Erosion/Sedimentation • Water Quality/Pollution • Existing Ordinances • Others ????

Flooding

Undersized or Blocked Storm Drains

Erosion / Sedimentation Problem Area

Water Quality Problem Area

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

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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

Questions ? ? ? ?