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Managing Zone A Floodplains Jana Green, CFM Kim Dunn, P.E., CFM RAMPP FEMA Region III National Flood Insurance Program Essentials and Best Practices.

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Presentation on theme: "Managing Zone A Floodplains Jana Green, CFM Kim Dunn, P.E., CFM RAMPP FEMA Region III National Flood Insurance Program Essentials and Best Practices."— Presentation transcript:


2 Managing Zone A Floodplains Jana Green, CFM Kim Dunn, P.E., CFM RAMPP FEMA Region III National Flood Insurance Program Essentials and Best Practices

3 Topics of Discussion  Overview of Zone A Floodplains  Permitting Development in Zone A Floodplains  Estimating Flood Elevations in Zone A  Flood Insurance Implications  Letters of Map Change – Zone A Floodplains  Resources for more information 2

4 What is a Zone A Floodplain?  Area of the 1% annual-chance floodplain  Boundaries have been determined using approximate methodologies  No published Base Flood Elevations (BFEs) on Flood Insurance Rate Map (FIRM) or in the Flood Insurance Study (FIS) report 3

5 Zone A Challenges Without defined Base Flood Elevations:  Lowest floor elevations must be determined for permitting  Flood insurance rates may be higher based on unknown risk  Benefit-cost ratios for mitigation projects may be more difficult to calculate Water surface elevation needs to be estimated 4

6 Delineating A Zones  The paper FIRMs used:  topographic maps  soils analysis and mapping  historical information and high water marks  studies not completed by FEMA  More recently, Zone As are supported by automated hydrologic and hydraulic analyses  Not a detailed hydrologic and hydraulic study 5

7 Zone A Regulatory Requirements  Reasonably obtain and utilize any flood elevation data when reviewing and issuing permits  If the automated hydrologic and hydraulic analysis (model- backed Zone As) are available, use that as best available data  Use studies conducted by other federal or state agencies  Check to see if elevations have been determined for nearby development  Subdivision requirements:  Base Flood Elevations must be determined through a detailed study for proposed development larger than 5 acres or 50 lots, whichever is lesser 6 Permits are required for all development

8 Obtaining Estimated Elevations 1.Automated hydrologic and hydraulic (H&H) analyses 2.Other sources of data 3.Simplified methodologies  Contour interpolation (point-on-boundary)  Data extrapolation Remember, the floodplain administrator can always require a detailed study to establish a true Base Flood Elevation 7

9  Automated H&H analyses were run for Zone As  Elevation information exists in the model  Not detailed enough to be included on the FIRM  Can be used to estimate a 1% chance flood elevation Floodplain Administrators can use this as best available data for permitting in Zone A Zone A cross sections will soon be available online! 8 Automated H&H Data

10 9 or FEMA Engineering Library Availability of Automated H&H

11 State Sources for Automated H&H  Currently Region III hosts the data at  Data will be transitioned to State websites:  Maryland website:  West Virginia website:  Pennsylvania: 10

12 Other Sources of Data When automated H&H unavailable, check for other sources of elevation data:  Community Records  Development plans  Letters of Map Amendment (LOMA) for neighboring property  State or County agencies  Departments of Transportation (plans for nearby bridges)  Departments of the Environment (Stream restoration / erosion control projects)  Federal Agencies  Unpublished USACE, NRCS, or USGS studies  Preliminary FIRM data from FEMA 11

13 Simplified Methodologies Contour Interpolation Method  Based on an overlay of FIRM on topographic map  Estimate water surface elevation at the intersection of the contour  Confirm accuracy is acceptable 12

14 Simplified Methodologies Data Extrapolation Method  Extend water surface profile at the same slope  Transfer that elevation to the map view  Relevant within 500 feet of detailed study  No hydraulic structures (e.g. bridges, culverts) between end of detailed study and site 13

15 Using Elevation Data Once the BFE is established, development is required to comply with Section 60.3(c) of the NFIP regulations. 14  Residential: elevate lowest floor to the BFE  Non-residential: elevate or dry floodproof to BFE  Manufactured homes: elevate and anchor to BFE  Enclosures below BFE, must have adequate flood openings and be used only for parking, access, or storage. Openings Elevation of utilities and mechanicals Lowest Floor above BFE Yardley Borough, Bucks County, PA (from PEMA)

16 Flood Insurance Implications Mandatory flood insurance purchase requirements:  applies for all structures in or touching the floodplain that carry a federally-backed mortgage 15

17 Elevation Certificate  An Elevation Certificate is an administrative tool to provide elevation information necessary to:  record building elevations  demonstrate compliance with the NFIP  support a Letter of Map Change (LOMC)  determine proper flood insurance premiums 16

18 Elevation Certificate – Section E  Property owners can provide measurements that insurance agents can use to rate a flood insurance policy in Zone A  These measurements are not informative of risk or water surface elevations – should not be used for permitting purposes 17

19 Post-FIRM Zone A Rating No Base Flood Elevation Provided  Post-FIRM rating considers the elevations of the structure to determine rates  Top of Bottom Floor - Highest Adjacent Grade = Elevation Difference 18 Borough of Olyphant, PA - Post-FIRM structure (FEMA Region III)

20 Post-FIRM Zone A Rating Base Flood Elevation Information Available If a Base Flood Elevation is available from another source, Lowest Floor Elevation – Flood Elevation = Elevation Difference  Lowest Floor elevation is not an entry on the Elevation Certificate  It is determined by an insurance agent using information provided on the Elevation Certificate 19

21 Letters of Map Change in a Zone A 20  If flood elevation data is provided, FEMA will verify its reasonableness  If elevation data cannot be provided, FEMA will compute a flood elevation  This elevation determination may not be included on the determination letter

22 Reviewing Zone A LOMCs 21  If more detailed data is needed, the applicant may be asked to provide data such as:  Culvert/bridge dimensions  One or two cross sections  If supporting data is provided and is reasonable, it is incorporated into the hydrologic and hydraulic evaluation  If additional data is not provided, the determination may be based on more conservative methodology

23 Providing Cross Sections  For one lot, one cross section is usually sufficient  For a large lot or multiple lots, a cross section should be surveyed at each end of the parcel  Perpendicular to flow path  If property is upstream of a bridge, at least 2 cross sections are required  Should capture changes in channel characteristics: slope, roughness, etc.  Should reference vertical datum 22

24 Zone A LOMA 23 Page 1Page 2

25 LOMC Determination Documents The flood elevation used to complete a LOMC determination may or may not be displayed on the final letter.  Flood elevations are shown for:  Conditional Letters of Map Change  Non-removal determinations  Flood elevations are not shown for:  Removal determinations  Out As Shown determinations 24 Considerations When Elevations are Displayed

26 Zone A Permitting – Example One A resident enters the permitting office with the intention to build a house on a riverfront plot of land. The land is natural grade, and gently slopes down a hill from the main road to the stream channel. The stream has a history of flooding and its floodplain is mapped as Zone A. Suggestions  Recommend moving building site outside of the mapped Zone A floodplain  If possible, establish a flood elevation  Automated H&H if available, other sources of data, simplified methodologies, detailed study  Document how reasonably safe from flooding was established  Use high water elevations, add freeboard, use flood resistant materials, etc. 25

27 Zone A Permitting – Example Two You are permitting development for a 60 lot subdivision. 15 of the lots are located in a Zone A floodplain. 26

28 Zone A Permitting – Example Two Suggestions:  Recommend altering plans so houses will not be in the SFHA  Remember: If the development in the SFHA exceeds either 50 lots or 5 acres, flood elevation data is required 27

29 Resources  Visit the FEMA Library for:  FEMA 1-98 – Use of FIS Data as Best Available Data  The Zone A Manual: Managing Floodplain Development in Approximate Zone A Areas  FEMA Engineering Library for Models  HEC-RAS:  USGS Stream Stats:  FEMA GeoPlatform:  FEMA Map Information eXchange (FMIX)  (877) FEMA-MAP 28

30 Contacts 29 FEMA Region III Floodplain Management and Insurance Branch: Washington, D.C. Phetmano Phannavong, P.E., CFM 202-535-2248 Delaware Michael Powell, CFM 302-739-9921 Maryland David Guignet, P.E., CFM 410-537-3775 Pennsylvania Daniel Fitzpatrick, CFM 717-720-7445 Virginia Charley Banks, CFM 804-371-6135 West Virginia Kevin Sneed, CFM 304-957-2571


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