Unit 4: BFE Considerations

1. Unit 4: BFE Considerations

2. Objectives • At the end of this unit, you should be able to: • List potential data sources for determining BFEs in Approximate A Zones. • Describe contour interpolation and data extrapolation techniques used to determine BFEs.

3. Objectives (Continued) • At the end of this unit, you should be able to: • Identify the purposes of letters of map change. • Identify forms needed to apply for different types of map changes. • Describe errors commonly found on map change application forms.

4. Approximate A Zone Elevations • Detailed studies are not available. • Simplified methods can provide estimated BFEs. • If you lack confidence in simplified estimation methods, require property owners to provide BFEs based on detailed studies.

5. Simplified and Detailed Methods • Simplified methods: • Contour interpolation • Data extrapolation (rarely applicable) • Culvert hydraulics • Detailed methods: • Floodplain geometry (topography) • Flood frequency—Discharge (hydrology) • Flood discharge—Stage (hydraulics)

6. Contour Interpolation and Data Extrapolation • Both are simplified methods, and cannot be used to support LOMA and LOMR-F applications. • Contour interpolation overlays topographic maps on the FIRM. • Data extrapolation extends flood profiles beyond the detailed study area. • At least one other method plus previous flooding history should be used.

7. Contour Interpolation • Obtain a topographic map of the site. • Reduce/enlarge to FIRM scale. • Overlay Zone A floodplain boundary on the topographic map. • Does floodplain boundary follow contour lines within acceptable limits? (Elevations of left and right overbanks must be within one-half of the contour interval of the map.) • If accuracy is acceptable, determine the BFE.

8. FIRM + Topographic Map (Figure 8) FEMA 265, page V-4, description page V-3, Example 1Pages 4-11 and 4-12 in your Participant Manual

9. In-class activity Interpreting Figure 8 • Find Example 1 paragraph on page V-3 (page 4-11 in your Participant Manual). • What is the contour interval of Figure 8? • At the structure site, what is the elevation of the left (upper) bank on the map? • What does the map show as the elevation of the right (lower) bank? • How many feet = ½ of the contour interval? • Is the method acceptable at this site? • What is the estimated BFE?

10. FIRM + Topographic Map (Figure 9) FEMA 265, page V-5, description page V-4, Example 2 Pages 4-12 and 4-13 in your Participant Manual

11. In-class activity Interpreting Figure 9 • Find Example 2 paragraph on page V-4 (page 4-12 in your Participant Manual). • What is the contour interval of Figure 9? • At the structure site, what is the elevation of the left (upper) bank on the map? • What does the map show as the elevation of the right (lower) bank? • How many feet = ½ of the contour interval? • Is the method acceptable at this site?

12. Data Extrapolation: Extend Profile

13. Data Extrapolation Criteria • Site must: • Be within 500 feet of the detailed study area. • Have floodplain characteristics similar to the detailed study area—for example: • The valley does not narrow rapidly upstream. • There is no waterfall. • Have no hydraulic structures such as dams and bridges.

14. Data Extrapolation Steps • Determine the location of the site on the flood profile for the detailed study area. • Extrapolate the last segment of the flood profile that has a constant slope to the location of the site. • Determine the BFE from the extrapolated profile.

15. Detailed Methods • Three key elements: • Floodplain geometry (topography) • Flood frequency—Discharge (hydrology) • Flood discharge—Stage (hydraulics)

16. Sta. 0 Elev. 500 Sta.4000 Elev. 510 Sta. 1100 Elev. 475 Sta. 3100 Elev. 475 Sta. 2100 Elev. 475 Sta. 2600 Elev. 450 Topography • Geometry of cross-section of the floodplain • Vertical coordinates (elevation) • Topographic maps • Field-surveyed cross-sections • Increased level of detail on topographic map = increased accuracy of floodplain delineation

17. Hydrology and Hydraulics • Hydrology gauges peak rate of stream flow during a flood throughout a watershed. • Hydraulics predicts water surface elevations that occur at a particular site during a flood. • QUICK-2 is a software program that performs hydraulic calculations.

18. In-class activity Activity: Zone A Data Sources • Purpose: Determine appropriate sources for existing data in unnumbered A Zones. • Work with others in your group to resolve each of the following questions or situations. • You may use the Flood Data Sources table that follows the questions as a resource.

19. Letters of Map Change Procedures • Not enough funding to map all with detailed methods • Two types of analysis done: • Detailed analysis (developed and developing areas) • Approximate analysis (undeveloped areas)

20. In-class activity Activity: Map Change Acronyms • Purpose: Ensure that you understand the meaning of some map-related acronyms. • Work with others at your table to write the words represented by each acronym. • Then choose a definition from the choices listed. Write the letter of the definition in the space to the left of the acronym. • You may use the course glossary as a reference.

21. Map Change Letters From FEMA • LOMA (MT-1 surveyor) • C-LOMR-F (MT-1 surveyor) • LOMR-F (MT-1 surveyor) • C-LOMR (MT-2 engineer) • LOMR (MT-2 engineer)

22. Map Change Letters From FEMA • Who receives the map change letter from FEMA? • What is the difference between a LOMR and a LOMR-F?

23. Structure Site

24. Situation 1: What LOMC Applies? BFE

25. Situation 2: What LOMC Applies? BFE

26. Situation 3: What LOMC Applies? BFE

27. Failure To Request Map Changes

28. Remember . . . • LOMA and LOMR-F applications require detailed methods of estimating BFEs.

29. Map Change Process • Community endorsement of the map change process is very important. • For any map change letter other than a LOMA, a local official must sign the request.

30. In-class activity MT Forms • Refer to the MT forms in the Forms Appendix in the back of your Participant Manual.

31. Map Change Request Forms • MT-EZ: Single lot/existing structure, no fill, no change to BFE or floodway (LOMA) • MT-1: Single or multiple lots/structures, proposed structures or fill, no change to BFE (LOMA, CLOMA, LOMR-F, CLOMR-F) • MT-2: Series of 12 forms to request a LOMR

32. Submittal Documents • Copy of recorded deed • Tax Assessor’s Map • Certified Site Plan/Boundary Survey • Copy of the effective FIRM • FIRM with property accurately plotted • FIS Flood Profile • Signed/Dated Property Information Form • Elevation Certificate

33. In-class activity MT-1 Sample Submittal Documents • Refer to the MT-1 forms in the Forms Appendix. • Locate each of the forms listed on the previous visual. • Pages 4-52 through 4-58 in your Participant Manual show examples of forms for an MT-1 submittal.

34. Elevation Certificate

35. Generic Problems: MT Forms • All forms not submitted • Forms not completed • Confusion about definitions • Lowest Adjacent Grade • Lowest Floor Elevation • Lowest Lot Elevation • Only lowest floor elevation submitted

36. Generic Problems: MT Forms (Cont.) • Applicant request for the lot only, not for the actual/planned structure • Recordation data missing from deed or plat • Plat or tax map insufficient to locate property on FIRM • Plat not certified

37. Required Fees • LOMA—Fee exempt • All others—Fees required • Check the Web site for current fees: • http://www.fema.gov/fhm/frm_fees.shtm