Dealing with Zone A Flood Zones. Topics of Discussion. What is a Zone A Floodplain?

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Claude Cobb
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Zone A Floodplains Resources for more information 2 What is a Zone A Floodplain?

1 Dealing with Zone A Flood Zones 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 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 3 1

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

information and high water marks studies not completed by FEMA Digital FIRMS supported by automated hydrologic and hydraulic analyses Not a detailed hydrologic and hydraulic study 5 Zone A Regulatory

2 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 Delineating A Zones The paper FIRMs used: topographic maps soils analysis and mapping historical information and high water marks studies not completed by FEMA Digital FIRMS supported by automated hydrologic and hydraulic analyses Not a detailed hydrologic and hydraulic study 5 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 Permits are required for all development 6 2

Obtaining Estimated Elevations 1. Automated hydrologic and hydraulic (H&H) analyses 2. Other sources of data 3.

administrator can always require a detailed study to establish a true Base Flood Elevation 7 Automated H&H Data Automated

Can be used to estimate a 1% chance flood elevation Floodplain Administrators can use this as best available data for

3 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 Automated H&H Data 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 Availability of Automated H&H or FEMA Engineering Library 9 3

Other Sources of Data When automated H&H unavailable, check for other sources elevation data: Community Records Development plans Letters of Map Amendment (LOMA) for neighboring property State or

USGS studies Preliminary FIRM data from FEMA of 10 Letters of Map Change in a Zone A If flood elevation data is provided, FEMA will verify its reasonableness If elevation data cannot be provided,

4 Other Sources of Data When automated H&H unavailable, check for other sources 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 of 10 Letters of Map Change in a Zone A If flood elevation data is provided, FEMA will verify its reasonableness If elevation data cannot be provided, FEMA may compute a flood elevation This elevation determination may not be included on the determination letter 11 Reviewing Zone A LOMCs 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 12 4

Providing Cross Sections For one lot, one cross section is usually sufficient

end of the parcel Perpendicular to flow path If property is upstream of a

channel characteristics: slope, roughness, etc.

Determination Documents Considerations When Elevations are Displayed The flood

5 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 13 Zone A LOMA Page 1 Page 2 14 LOMC Determination Documents Considerations When Elevations are Displayed 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 ldeterminations ti Flood elevations are not shown for: Removal determinations Out As Shown determinations 15 5

Models HEC RAS: www.hec.usace.army.mil USGS Stream Stats: http://water.usgs.

6 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: gov/osw/streamstats/ FEMA GeoPlatform: FEMA Map Information exchange (FMIX) (877) FEMA MAP 16 6

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8 500 End of detail study Detailed Methods 8

Managing Development in Approximate Zone A Areas FEMA Publication Guide for Approximate A zone areas Includes method to determine BFE Requirements for Developing BFE Data 44 CFR 60.

9 Managing Development in Approximate Zone A Areas FEMA Publication Guide for Approximate A zone areas Includes method to determine BFE Requirements for Developing BFE Data 44 CFR 60.3(b)(3) of NFIP regulations New subdivision proposals, including mobile home parks Greater than 50 lots or 5 acres, whichever is lesser MUST DEVELOP BFE DATA Requirements for Developing BFE Data If land is impacted by Zone A and meets criteria above, (50 lots or 5 acres whichever is less) BFEs must be calculated 9

10 Subdivision Alternatives May dedicate the entire zone A area as open space lot May not need a detailed flood study in this example Subdivision Alternatives Large lot subdivision may not need detailed study if building site is clearly above elevations of Zone A boundary 10

12 Hydraulics Normal Depth, Step Backwater Quick 2 12

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14 State Floodplain Management Agency (Emergency Management, Natural Resources, Water Resources, etc.) Quick 2 Normal Depth Example Problem Peak discharge, given Determine slope Determine Manning s n from chart and description i of channel and overbanks 14

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20 Three Cross section Step Backwater 20

21 Questions??? 21

ASFPM - Rapid Floodplain Mapping

ASFPM - Rapid Floodplain Mapping ASFPM - Nicole Cominoli Hydraulic Engineer USACE - Omaha District mary.n.cominoli@usace.army.mil June 3, 2015 US Army Corps of Engineers Mitigation = Risk Informed Decisions 2 The National Flood Insurance