4.0 Unit 4: BFE Considerations 4.1 Objectives At the end of this unit, you should be able to: List potential data sources for determining BFEs in A Zones. Describe contour interpolation and data extrapolation techniques used to determine BFEs. 4.2 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. 4.3 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. FEMA Publication 265 Guide for Local Community Officials in administering and enforcing floodplain management requirements Useful in determining BFEs in A Zones Quick 2abbreviated HEC-2 Windows version available 4.5 Simplified and Detailed Methods Simplified methods: Contour interpolation Data extrapolation (rarely applicable) Culvert hydraulics Detailed methods: Floodplain geometry (topography) Flood frequencyDischarge (hydrology) Flood dischargeStage (hydraulics) 4.6 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. 4.7 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. 4.8 FIRM + Topographic Map (Figure 8) FEMA 265, page V-4, description page V-3, Example 1 Pages 4-11 and 4-12 in your Participant Manual 4.9 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 = of the contour interval? Is the method acceptable at this site? What is the estimated BFE? In-class activity 4.10 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 4.11 at left bank 235 ft at right bank Contour interval is 10 feet EC provided has the Lowest Adjacent grade as 235 feet 240 235 + 5 = 240 BFE is 240 4.13 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 = of the contour interval? Is the method acceptable at this site? In-class activity 4.14 Data Extrapolation: Extend Profile 4.15 Data Extrapolation Criteria Site must: Be within 500 feet of the detailed study area. Have floodplain characteristics similar to the detailed study areafor example: The valley does not narrow rapidly upstream. There is no waterfall. Have no hydraulic structures such as dams and bridges. 4.16 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. 4.17 Detailed Methods Three key elements: Floodplain geometry (topography) Flood frequencyDischarge (hydrology) Flood dischargeState (hydraulics) 4.18 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 BFE Sta. 0 Elev. 500 Sta Elev. 475 Sta Elev. 475 Sta Elev. 475 Sta.4000 Elev. 510 Sta Elev. 450 4.19 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. 4.20 Activity: A Zone 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. 4.21 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) 4.22 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. 4.23 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) 4.24 Map Change Letters From FEMA Who receives the map change letter from FEMA? What is the difference between a LOMR and a LOMR-F? ZONE X X RM 2 ZONE X 512 ZONE AE WATER CREEK BFE LOMA LAG Above BFE BFE LOMR-F BFE LOMA LOMR-F 4.29 Failure To Request Map Changes 4.30 Remember... LOMA and LOMR-F applications require detailed methods of estimating BFEs. 4.31 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. 4.32 MT Forms Refer to the MT forms in the Forms Appendix in the back of your Participant Manual. In-class activity 4.33 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 4.34 MT Forms: MT-EZ (single lot LOMA) 3 pages 4.35 MT Forms: MT-1 (single or multi on fill, LOMA, CLOMA, LOMR-F, and CLOMR-F) 5 pages 4.36 MT Forms: MT-2 (LOMR) 20 pages 4.37 Submittal Documents Copy of recorded deed Tax Assessors 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 4.38 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. 4.39 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 4.40 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 4.41 Required Fees LOMAFee exempt All othersFees required Check the Web site for current fees: 4.42 Unit Summary Subdivision requirements in A Zones BFE data sources in A Zones Use of contour interpolation and data extrapolation as simplified methods to obtain a BFE Map change types Map change process The original 1804 Mississippi Territory included the lands that would eventually make up what states? 4.43 Mississippi Trivia 4.44