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Documentation of Event Damages and Recurrence Intervals in the FEMA BCA Module

This webinar provides guidelines for documenting event damages and recurrence intervals in the FEMA BCA Module for residential flood mitigation projects. Learn how to effectively use the DFA module to estimate flood risk and project benefits.

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Documentation of Event Damages and Recurrence Intervals in the FEMA BCA Module

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  1. Documentation of Event Damages and Recurrence Intervals in the DFA ModuleFEMA BCA Webinar (Intermediate)Presenter: John Squerciati, DewberryApril 2012 (Modified for Residential Flood Mitigation Projects March 5, 2013) 1

  2. Agenda Introduction Documenting Event Damages Documenting Event Recurrence Intervals (RIs) Documentation Dos and Don’ts Questions 2

  3. 1. Introduction • This Introduction answers the following questions: • Why did my BCA fail? (i.e., did not meet FEMA requirements for cost-effectiveness) • What is a Damage Frequency Assessment (DFA) module and how do I use it? 3

  4. Background: Why Did My BCA Fail? • All flood project BCAs need to determine flood risk to estimate project benefits. Higher flood risk means higher benefits, and vice versa. • Flood risk is based on flood recurrence intervals (RIs) and associated flood damages. • The FEMA BCAs submitted by your community used the Flood Module; which estimates flood risk for structures located in the FEMA floodplain as follows: • Flood RIs are based on the First Floor Elevation (FFE) of the structure relative to the Flood Insurance Study (FIS) profile data for the 10-, 50-, 100- and 500-year flood events • Associated flood damages are based on Depth Damage Functions (DDFs) associated with the project structure 4

  5. Explanation: Why Did My BCA Fail? • The BCAs reviewed by Dewberry did not meet FEMA requirements because the project risk – and therefore the project benefit – was too low for the project to be cost-effective • The most common reasons why the project risk was too low: • The FFE was 2 feet or higher above the 10-year flood elevation • The FFE was above the BFE (100-year flood elevation) • The structure was located outside the SFHA (100-year floodplain) • The computed Benefit-Cost Ratio (BCR) was less than 1.0 5

  6. What is a DFA Module? • The Damage-Frequency Assessment (DFA) module is a FEMA BCA approach which estimates flood risk for structures located in the FEMA floodplain or outside the floodplain: • Historic or expected flood damage event data • Recurrence Intervals (RIs) associated with the flood damage events 6

  7. How Do I Use the DFA Module? • Input the Following Information into the DFA module: • Project Information • Event Damages • Event Ris • Note:FEMA BCAs prepared using the DFA module sometimes fail due to insufficient or incorrect documentation of event damages and RIs 7

  8. Purpose and Target Audience • Purpose: Provide BCA users with FEMA-recommended examples and techniques to document damages and RIs for historic and expected events used in the DFA module. • Target Audience: IntermediateBCA Users - Preparers and Reviewers 8

  9. 2. Documenting Event Damages • DFA Software Ground Rules – Two Types of Damage Events • For Historic Damages, need a minimum of two known RI events or three unknown RI events occurring in different years • For Expected Damages, need a minimum of two known RI events 9

  10. Documenting Historic Damages • Historic Damage documentation sources: • Insurance Claims • Repair Records • News Articles citing credible sources 10

  11. Insurance Claims – Flood Events • Useful for documenting historic damages to insured properties from various hazard events • For flood events, Subapplicants can obtain flood insurance claim data on all properties insured under the NFIP through BureauNet (http://bsa.nfipstat.com) • Additional benefits may be estimated from flood claims data when other event information is available. • Be aware of Severe Repetitive Loss (SRL) Program properties. 11

  12. Repair Records • Useful for documenting historic damages to various facilities from hazard events • Repair records for residential buildings are typically limited to paid receipts for repairs or equipment rental • Repair records must: • be related to specific hazard events rather than scheduled maintenance or repairs, and • apply directly to structure(s) to be mitigated by the project • Always include complete copies of records organized in a spreadsheet when needed 12

  13. News Articles Citing Credible Sources • News articles can include nationally or locally published newspapers or newsletters that are printed or posted online • Credible sources – sources other than homeowner accounts • Make sure the articles indicate the specific dates and impacts to structures to be mitigated by the proposed project 13

  14. Documenting Expected Damages • Expected Damage documentation sources will vary based on the structure type and hazard to be mitigated • Building Damages tied to Flood Module Depth Damage Functions (DDFs) in FEMA BCA Software • Damages tied to Engineering Studies – Typically not done for residential building mitigation projects 14

  15. Building Damages Tied to FEMA BCA Software • FEMA Flood Module Depth Damage Functions (DDFs) • Flood damages to buildings can be estimated using DDFs based on the structure information (building type, number of stories, foundation type, size and BRV) as a function of flood depth above the First Floor Elevation (FFE) • Documentation Sources • DDFs can be documented from the BCA software or transcribed into a separate document or spreadsheet (recommended) • Structure information can be documented from various sources, including tax records, structure plans with dimensions, site photographs, engineering reports, and building cost data • Be sure to establish the correct reference point for the FFE 15

  16. 3. Documenting Event Recurrence Intervals (RIs) • DFA Software Ground Rules • For Historic Damage Events, need a minimum of two known RI events or three unknown RI events occurring in different years • For Expected Damage Events, need a minimum of two known RI events 16

  17. Historic Damage Events – Known RI Approaches • Approaches Listed in General Order of Preference • Flood Elevations or Discharges tied to Identified Flood RIs • Determined by Hydrologist or Other Qualified Agency/Expert • Estimated using Climataological Data • Estimated Using Rain Gauge Data 17

  18. Flood Elevations or Discharges tied to Identified Flood RIs • Documentation must include flood elevations and/or discharges from historic events as well as identified flood RIs that are used to determine the historic event RIs • Documentation Sources – Flood Elevations or Discharges • Both stream and tide gauge data can be obtained from the U.S. Geological Survey (USGS) website (http://waterdata.usgs.gov/nwis/sw) • Make sure the gauge data closest to the project structure(s) is used 18

  19. Flood Elevations or Discharges tied to Identified Flood RIs (cont’d) • Documentation Sources – Identified Flood RI Data • The USGS PeakFQ Program; which can be downloaded from the USGS website (http://water.usgs.gov/software/PeakFQ). • Refer to Section 2.1.2 of the Supplement to the Benefit-Cost Analysis Reference Guide for step-by-step instructions and a detailed example of estimating RIs using this approach 19

  20. Flood Elevations or Discharges tied to Identified Flood RIs (cont’d) • Documentation Sources – Identified Flood RI Data (cont’d) • FEMA Flood Insurance Study (FIS) Profiles and Discharge Tables or Transects; FIS data is available from the FEMA Map Service Center website (http://msc.fema.gov), then select Product Catalog from the top menu bar and search for the Effective FIS • When available, Hydraulics and Hydrology (H&H) Studies may be used where FIS data may be incomplete or out-of-date; must include complete copies of studies 20

  21. Flood Elevations or Discharges tied to Identified Flood RIs - Examples 21

  22. Determined by Hydrologist or Other Qualified Agency/Expert • Note that RI determinations may be limited for use in a specific geographic location, especially for large events such as Tropical Storm Allison (2001) or Hurricane Katrina (2005) • Documentation Sources • Post-event studies prepared by the U.S. Army Corps of Engineers (USACE) or the U.S. Geological Survey (USGS); must include complete copies of studies • Estimates prepared by a hydrologist; must include background data and/or calculations used to estimate RIs 22

  23. Estimated Using Climatological Data • This approach is often useful for estimating RIs of weather-related events such as or severe thunderstorms or other storms • Be sure to include complete records of all events • Documentation Sources • The National Climactic Data Center (NCDC) provides data on various weather-related events by county and is available online (http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwEvent~Storms); note the range of available data and include details on individual events • Climatological data from State or local sources 23

  24. Estimated Using Rain Gauge Data • Rain gauge data for historic damage events must be tied to flood RIs by a hydrologist or other qualified professional • Documentation Sources • The National Climactic Data Center (NCDC) records daily rainfall and other climactic data recorded by thousands of weather stations nationwide and is available online (http://www7.ncdc.noaa.gov/IPS/coop/coop.html); must include copies of all applicable data • NCDC also has Hourly Precipitation Data (HPS) data records available online (http://www7.ncdc.noaa.gov/IPS/hpd/hpd.html) • Analysis of rain gauge data prepared by a hydrologist; must include background data and/or calculations used to estimate flood RIs 24

  25. Historic Damage Events – Unknown RI Approach Unknown Frequency Calculator - Requirements • Minimum of three hazard events occurring in different years where either: • The frequencies/RIs of all events are unknown, or • The frequencies/RIs of up to two events are knownand have total inflated values that exceed the total inflated values of all the other unknown frequency/RI events • Analysis Duration based on the age of the structure or a minimum of 10 years; whichever is greater • No other way to tie historical events to known RIs 25

  26. Unknown Frequency Calculator • Documentation must include three historic event damages/losses and the date of construction for the structure to be mitigated • Documentation Sources • Historic hazard event damages/losses can be documented using approaches and sources listed previously for historic damage events • Date of construction can be documented using tax records, property appraisal, or included in a signed letter from a local official • NOTE: For multiple structures with different construction dates, the construction date of the oldest structure in the group must be used 26

  27. Analysis Duration Adjustments • Analysis Duration is a key component of the Unknown Frequency Calculator, and can present difficulties for structure(s) that are older or where the date of construction is unknown • Adjustments to Analysis Duration • A User Input Analysis Duration may be allowed when one of the following situations apply • Change in Local Flow Conditions • Replacement of Structure • NOTE: No historic events may be included in the BCA that occur before the start of the adjusted Analysis Duration 27

  28. Change in Local Flow Conditions • When local flow conditions have changed significantly over the life of a structure, it may be appropriate to adjust Analysis Duration • Documentation Sources • Documentation of change in local flow conditions may include: • Current and old FIS showing the before and after changes • Conditional Letter of Map Revision (CLOMR) or Letter of Map Revision (LOMR) • Hydraulics and hydrology (H&H) study that accounts for the change • Letter from city engineer or floodplain manager on community letterhead that addresses the changes in local flow conditions • Aerial photographs of the project area before and after the change in the watershed, or other photographs with dates showing increased development • Refer to Section 2.1.3 of the Supplement to the Benefit-Cost Analysis Reference Guide for step-by-step instructions and a detailed example of adjusting the Analysis Duration using this approach 28

  29. Change in Local Flow Conditions -Examples BEFORE AFTER 29

  30. Replacement of Structure • When a structure(s) to be mitigated are replaced or completely rebuilt, it may be appropriate to adjust Analysis Duration • Documentation Sources • Letter from a city engineer or building official on community letterhead with site photographs that includes the date and all details of the structure(s) replacement/rebuild • An engineering report with photographs that addresses the date and all details of the structure(s) replacement/rebuild • Current and old tax records with photographs that indicate the replacement of the structure(s) • NOTE: Partial rebuilding/replacement of a structure(s) is not acceptable documentation to adjust the Analysis Duration 30

  31. Historic Damage Events – Summary of Unknown RI Approach • Important Things to Remember About the Unknown Frequency Calculator… • This was intended to be a “last resort” approach • It is less likely to yield cost effective results for three historic damage events as the analysis duration increases (typically beyond 30 years) 31

  32. Expected Damage Events – Known RI Approaches Only • Estimated Event RIs based on Flood Module RIs in FEMA BCA Software • Estimated Event RIs from Engineering Studies – Typically not done for residential building mitigation projects 32

  33. Estimated Event RIs based on Flood Module RIs in FEMA BCA Softwaree • Flood Event RIs from Flood Module • Flood Event RIs are estimated in the Flood Module as a function of flood depth based on FEMA Flood Insurance Study (FIS) or equivalent Hydraulics and Hydrology (H&H) data • Documentation Sources • FIS Profiles and Discharge Tables or Transect data is available from the FEMA Map Service Center website (http://msc.fema.gov), then select Product Catalog from the top menu bar and search for the Effective FIS • When available, H&H Studies may be used where FIS data may be incomplete or out-of-date; must include complete copies of studies 33

  34. 4. Documentation Dos and Don’ts • Documentation DOs • DO provide all necessary supporting documentation for event damages, losses and RIs • DO provide complete copies of H&H studies and engineering studies • DO use FEMA Data Documentation Templates to organize documentation 34

  35. Documentation Dos and Don’ts (cont’d) • Documentation DON’Ts • DON’T assume the reviewer can access documentation online • DON’T forget to include an explanation of any assumptions made • DON’T use unreliable or non-credible documentation sources 35

  36. 5. Questions FEMA BCA Website • http://www.fema.gov/government/grant/bca.shtm FEMA BC Helpline Phone: 1-855-540-6744 E-mail:bchelpline@dhs.gov 36

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