Coastal Flood Maps. Chris Penney. Program Manager USACE Baltimore District 2 June US Army Corps of Engineers BUILDING STRONG

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1 Coastal Flood Maps Chris Penney Program Manager USACE Baltimore District 2 June 2015 US Army Corps of Engineers

2 There are two types of coastal flood risk maps They look different They communicate different things FEMA FIRM HES Storm Surge Flood Risk Map THIS CAN CAUSE CONFUSION

3 Multi program/agency effort to address confusion Detailed white paper and short factsheet Addresses purposes, differences, uses White Paper Factsheet

4 Hurricane Evacuation Study (HES) Storm Tide Flood Risk Area Maps Product of the HES HES supports State/Local hurricane evacuation/response planning Produces evacuation clearance times used to support evacuation timing/decision making

5 Storm Surge Flood Risk is the basis of coastal hurricane evacuations Run from water, hide from wind NHC SLOSH Model is used to identify flood risk areas from various hurricane scenarios

6 SLOSH MOM Dataset is used Provides overall picture of risk based on thousands of hurricane simulations Accounts for variation in factors that influence surge Category/Intensity is just one factor

7 MOM Approach is important for HES Provides overall picture of surge flood risk We don t know the specific characteristics of any approaching storm when long range planning Need to plan for the overall risk- all areas that may have a need to be evacuated during a hurricane threat

8 High resolution maps of risk areas created in GIS Using MOM dataset and ground elevation data Map shows at what category of storm the storm surge flood risk starts for an area Not probability based

9 HES Surge Risk areas are the basis and starting point for the development of pre-identified hurricane evacuation zones

10 HES Storm Surge Flood Risk Area Maps: Focused on population protection Not probability based Not intended for regulatory or insurance purposes Do not account for wave impacts

11 FEMA Flood Insurance Rate Maps Support the National Flood Insurance Program Focus on recovery and mitigation Focus on building losses

12 SLOSH Model not used for FIRMs ADCIRC Model used for recent updates Probability Based- 1% annual chance Basis of Base Flood Elevations- stillwater portion

13 Waves modeled for FIRMs Included in Base Flood Elevations Used to delineate Flood Zones for regulatory and insurance purposes Based on 1% annual chance water levels

14 Flood Insurance Rate Maps: Are statutory documents that support the NFIP Focused on Insurance and Regulatory Probability Based Include Waves, BFEs and Flood Zones Not intended for evacuation planning

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16 When the user understands the purposes and limitations of each map. HES Surge Risk Maps can support floodplain managers FIRMs can support emergency mangers

17 BUILDING STRONG

18 BUILDING STRONG

19 Why different storm surge models used? NHC and NHP need an operational model for forecasting and products like the MOM. Needs to be fast and cost efficient, with level of accuracy needed for evacuation planning and forecasting. SLOSH meets that need. Engineering/Design uses, FIRMs where insurance and regulatory considerations are at play, need higher level of resolution and detail. Less runs needed so speed not as important. ADCIRC meets that need.

20 Questions? Handouts Electronic copies of papers available NHC National MOM Viewer FEMA Map Service Center for FIRMs