Vision to Action: Creating and Using a Flood Risk Assessment for Identifying Mitigation Options

Transcription

1 Vision to Action: Creating and Using a Flood Risk Assessment for Identifying Mitigation Options Lisa Graff, CFM, GISP Clayton Ballerine, CFM Brad McVay, CFM, GISP University of Illinois Prairie Research Institute Illinois State Water Survey

2 Project Partners Illinois State Water Survey (ISWS) Illinois Department of Natural Resources, Office of Water Resources (IDNR/OWR) City of Rockford FEMA

3 City of Rockford, IL

4 Rockford Flooding

5 Flood Studies 9 detailed flood studies 5 approximate studies (best available)

6 Mitigation Interest Identified City of Rockford Updated flood studies revealed that flood risk had been dramatically underestimated on FIRM. Hundreds of structures were newly identified in the 1% annual chance floodplain of North Fork Kent Creek

7 Community Engagement and Risk Communication (CERC) Objectives: Recognize and enhance activities undertaken by CTPs to help build risk awareness and understanding at the local level. Increase a community's ability to communicate risk at the local level. Support local efforts to reduce natural hazard risk within a community or watershed area (e.g. complete mitigation actions). Keep communities and other stakeholders engaged throughout the Risk MAP process.

8 CERC Project Detailed, structure-by-structure flood risk data for each structure in the SFHA. First Floor Elevation Low Entry Elevation Average Annualized Loss Flood Depths Chance of Flooding Over a 30 Year Period Flood Risk Database

9 Scope of Work ISWS Multi-frequency Flood Depth Grids Percent 30-year Flooding Chance Grid HAZUS Level 2 Risk Assessment Database Maps of Priority Areas for Mitigation Action

10 Winnebago County Hazard Mitigation Plan The Risk MAP products and technical assistance will advance three of the stated goals: Flood proof, relocate, elevate, and demolish at risk structures. Map priority acquisition areas and those unsuitable for development. Map repetitive loss and substantially damaged properties.

11 Structure Identification What you need: Best Available Flood Inundation Data GIS Structure Inventory Building Footprints Parcel Data Assessors Information

12 Structure Identification: Cont.

13 Structure Identification: Cont.

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15 Surveyor Maps

16 Surveyor Forms

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18 HAZUS-MH: Loss Estimation Tool Program designed by FEMA for the purpose of providing communities with the means to identify and reduce risk from natural hazards

19 Levels of analysis Level 2 Level 3 Input detailed engineering data Combination of local and default hazard, building, and damage data Required user effort and sophistication Level 1 Default hazard, inventory, and damage information

20 User Defined Facilities (UDF) Table containing values for each structure Very specific format for upload Lat Long values to represent location User Defined Depth Grids 10%, 4%, 2%, 1%, and 0.2% annual chance floods

21 Filling in the gaps Tax exempt structures Missing attributes Replacement Cost Square Footage Number of Stories Year Built Design Level Foundation Type First Floor Height

22 Depth-Damage Curves Percentage of damage is calculated for each structure based on the depth of flooding. Based on Occupancy For buildings, first floor height For equipment, height above first floor Damage percentage is used to determine loss in USD Depth of flooding Depth used for damage estimation

23 Analysis Output Building Loss Content Loss Business Inventory Loss Percent Damaged for Structures Average Annualized Loss (AAL)

24 Average Annualized Loss Estimated long-term value of losses averaged on an annual basis Useful for estimating potential flood losses over a defined period of time Formula (10% 4%) *(Loss 10% + Loss 4%) / 2 + (4% 2%) * (Loss 4% + Loss 2%) / 2 + (2% 1%) * (Loss 2% + Loss 1%) / 2 + (1% 0.2%) * (Loss 1% +Loss 0.2%) / % * Loss 0.2%

25 Presenting Results Best Practice Results are ESTIMATES and should be treated as such Include a disclaimer Results should be rounded Results can be summed for an area or focused on individual structures depending on need

26 Keith Creek 1930

27 Keith Creek 2010

28 28 Keith Creek Mitigation Total #Properties Acquired #Properties Demolished

29 10% Annual Chance Depth Grid

30 4% Annual Chance Depth Grid

31 2% Annual Chance Depth Grid

32 1% Annual Chance Depth Grid

33 0.2% Annual Chance Depth Grid

34 Old FIRM vs New FIRM

35 North Fork Kent Creek Changes Since Last FIRM

36 History of North Fork Kent Creek 1890: Flooding destroyed nearly every bridge on North Fork Kent Creek 1890 Flood on Kent Creek at Winnebago Avenue (From Tinker Swiss Cottage Collection via the Rockford Public Library)

37 Recent Flood Events An analysis of recent rainfall events found the July 2010 event to be the largest experienced since Page Park Dam was completed. The 2010 event produced substantially less rainfall than the event shown on the Effective Maps Other major rainfall events within Rockford (2006, 2007 Keith Creek floods) were not focused over the North Fork Kent Creek Watershed NEXRAD Rainfall 2006 Flood Event On Keith Creek North Fork Kent Creek Watershed Outlined Red

38 10% Annual Chance Depth Grid

39 4% Annual Chance Depth Grid

40 2% Annual Chance Depth Grid

41 1% Annual Chance Depth Grid

42 0.2% Annual Chance Depth Grid

43 SUMMARY Collaboration with multiple partners: ISWS IDNR/OWR City of Rockford Build on HMP strategies Heightened risk awareness Demonstrate FEMA s commitment and follow through

44 Thank You For Listening! Rock River Rockford, National Show Ski Association Tournament