Harrisburg Flood Inundation Mapping Project – Many Agencies Working Together USACE Flood Risk Management and Silver Jackets Workshop 23 August 2012 Presented by Stacey Underwood, USACE and Mark Roland, USGS 1

2 Topics Background and Project Description Project Partners Description of Tasks Challenges Keys to Success Many Agencies, One Solution

Background/History of Flooding  City of Harrisburg has a long history of flooding as a result of heavy rain, snow melts and ice jams  Large portions of City and surrounding communities are in the 1% annual chance floodplain  Since 1746, there have been an estimated 46 observed floods (MARFC)  Major flood in 1936 brought a reported four to 15-foot depth of water what covered almost 1/3 of City  Flooding from Tropical Storm Agnes in 1972 brought a peak discharge of over 1 million cfs through Harrisburg  Similar major flooding in 1975, 1996, and recently in 2011 (5 th highest crest) 3

4 Harrisburg Flood Mapping Project Overview Flood inundation mapping tool to inform the general public, local officials and emergency mgrs of risk associated with a flood event Inundation map library will cover the City of Harrisburg and communities 10 miles upstream and 10 miles downstream of Harrisburg The maps will be tied to the NWS’s flood forecast point Map library will be displayed digitally on various map viewer websites Many Agencies, One Solution

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6 Primary Project Partners Federal  US Army Corps of Engineers (USACE)  US Geological Survey (USGS)  NOAA’s National Weather Service (NWS)  Federal Emergency Management Agency (FEMA) State  PA Emergency Management Agency (PEMA) Regional  Susquehanna River Basin Commission (SRBC) Local  The Harrisburg Authority Leveraging resources (funds and in-kind services) for total project cost of $235k Many Agencies, One Solution

Project Tasks  Data Collection (USGS lead) – deployed storm surge sensors prior to TS Lee, field surveys, researched and compiled existing data  Hydrologic Data Development (USGS lead) – Developed new rating curve for USGS Streamgage – Susquehanna River at Harrisburg, PA 7

8 Data Collection & Hydrologic Data Development Hydraulic Structures  9 bridges  Dock St. dam  Airport levee Data Sources  As-built plans  Field reconn.  HEC-2 Flood Insurance Study model Many Agencies, One Solution

Rockville RR bridge 9

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11 Data Collection & Hydrologic Data Development Channel bathymetry  USGS ADCP discharge measurements  As-built bridge plans  Flood Insurance Study Many Agencies, One Solution

12 Bathymetry Many Agencies, One Solution

13 Data Collection & Hydrologic Data Development USGS Streamgage Susquehanna River at Harrisburg, PA Extended rating curve to 125% POR peak discharge Many Agencies, One Solution

Data Collection & Hydrologic Data Development  2011 peak ranked 5 th highest (including Historic Peaks dating back to 1784) 14 Many Agencies, One Solution

Storm Surge Sensors  Onset HOBO U20 Water-Level Logger  USGS storm surge sensor housing unit 15 Many Agencies, One Solution

16 Storm Surge Sensors Many Agencies, One Solution

17 Storm Surge Sensors Many Agencies, One Solution

Data Collection & Hydrologic Data Development  1972 Hydrologic Atlas documented the flooding of Hurricane Agnes along a 20- mile reach extending from Marysville to Falmouth, Pa  Report was prepared by USGS in cooperation with PADER, SRBC, and USACE 20 Many Agencies, One Solution

21 Storm Surge Sensor Data Many Agencies, One Solution

Project Tasks  Hydraulic Model Development (USACE lead) –Developed HEC-RAS model for the study reach based on field survey data and high resolution Digital Elevation Model (DEM); model has been fully calibrated and verified. 22 #1: Match USGS Sensor and Gage Data for Lee #2: Match USGS Gage Elevation for Agnes #3: Match High Water Marks for Lee and Agnes #4: Match 1936 Flood USGS Gage Elevation and High Water Marks

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24 HEC-RAS Model Many Agencies, One Solution

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How good is it?  Mathematical model representing physical process!  Perfect? NO!!!  Pretty darn good? ABSOLUTELY! 26

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Project Tasks  Develop Flood Inundation Layers (USACE lead) – Using water surface elevations obtained from HEC-RAS modeled profiles, creating water surface profile to intersect with DEM ground surface profile to create inundation layers for each 1 ft. stage at the USGS gage.  Develop Depth Grid (USACE lead) –Developing depth grids for each of the inundation layers to display expected depth of flooding to nearest 1 ft. 28

Depth Grids 29

Project Tasks  Serve Maps on Mapviewers (SRBC, NWS) – The inundation map layers will be served on various mapviewers for public access – Susquehanna Inundation Map Viewer (SIMV) and NWS’s Advanced Hydrologic Prediction Service (AHPS), possibly USGS and USACE SimSuite 30

AHPS

Project Tasks  Outreach/Education (SRBC/NWS lead) – To ensure that the maps are understood and utilized such that appropriate action is taken during a flood event Stakeholder Meeting and Webinar – Were held to provide information on the project and for stakeholders to review/confirm hydraulic modeling/mapping is showing Lee and Agnes flooding accurately Public Meetings – Release map library and educate public on how to use it online Media Campaigns – When maps are released and at start of 2013 flood season Potential Resources – brochure, refrigerator magnet 34

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Challenges  Map Viewers Deciding which map viewers to load maps onto Learning the requirements for each viewer Funding for each viewer Deciding which to provide outreach materials for  Outreach Ensuring public is aware of and can easily use map viewers, and understand accuracy of the maps 36

Keys to Success  Multiple agencies are bringing diverse knowledge, expertise and resources  Good, timely data collection (thanks USGS!!) and model calibration were key  Outreach is an important component 37

Points of Contact  Stacey Underwood, USACE Baltimore District  Mark Roland, USGS

Questions? 39