Presentation on theme: "Managing Zone A Floodplains"— Presentation transcript:
1Managing Zone A Floodplains FEMA Region III National Flood Insurance Program Essentials and Best PracticesJana Green, CFMKim Dunn, P.E., CFMRAMPP
2Topics of Discussion Overview of Zone A Floodplains Permitting Development in Zone A FloodplainsEstimating Flood Elevations in Zone AFlood Insurance ImplicationsLetters of Map Change – Zone A FloodplainsResources for more information
3What is a Zone A Floodplain? Area of the 1% annual-chance floodplainBoundaries have been determined using approximate methodologiesNo published Base Flood Elevations (BFEs) on Flood Insurance Rate Map (FIRM) or in the Flood Insurance Study (FIS) reportZone As are high risk areas shown on the FIRM that are subject to inundation by the 1% annual chance flood. The boundary of the Special Flood Hazard Area has been delineated on the FIRM; however, base flood elevations have not been determined, nor are floodways shown.Zone A floodplains are often called “approximate” zones. Some are more approximate than others – we will discuss technological advances in the delineation of Zone A floodplains in recent years, making them much less approximate.Mandatory flood insurance purchase requirements and floodplain management standards (local ordinance requirements) apply in Zone A floodplains.
4Zone A Challenges Without defined Base Flood Elevations: Lowest floor elevations must be determined for permittingFlood insurance rates may be higher based on unknown riskBenefit-cost ratios for mitigation projects may be more difficult to calculateWater surface elevation needs to be estimatedThese challenges can make it hard for you as a FPA to be able to identify and manage risk within your community. Zone A floodplains allow for a community to be aware of existing flood hazards without the associated costs of a detailed study. Historically the expense of full detailed studies was reserved for more densely populated areas, but due to development and urban sprawl, many formerly undeveloped Zone A areas now impact many insurable structures.Although there is no BFE published, an elevation is still needed to permit development and promote flood awareness. We will discuss some of the ways this can be accomplished.Not having a BFE available can result in increased flood insurance rates due to unknown risk. We will discuss how estimating a BFE can reduce flood insurance rates.
5Delineating A Zones The paper FIRMs used: topographic maps soils analysis and mappinghistorical information and high water marksstudies not completed by FEMAMore recently, Zone As are supported by automated hydrologic and hydraulic analysesNot a detailed hydrologic and hydraulic studyIn the images, you can see some of the differences between how older maps will depict Zone As compared to how they look on newer maps. Older FIRMs show floodplains that have less defined boundaries than newer Zone A floodplains backed by an automated model.In addition to topographic and soils data and historic information, there may have been studies completed to analyze flood risk that may not meet the specific criteria to have BFEs published on a FIRM; these can be mapped as Zone A areas or can provide information to evaluate when mapping Zone A areas.For the past ten years, Zone As are backed by automated engineering models.Ground surveys and detailed hydraulic analyses have not been completed in Zone A floodplains.
6Zone A Regulatory Requirements Reasonably obtain and utilize any flood elevation data when reviewing and issuing permitsIf the automated hydrologic and hydraulic analysis (model- backed Zone As) are available, use that as best available dataUse studies conducted by other federal or state agenciesCheck to see if elevations have been determined for nearby developmentSubdivision requirements:Base Flood Elevations must be determined through a detailed study for proposed development larger than 5 acres or 50 lots, whichever is lesserAgain, just because a BFE has not been established by FEMA on a FIRM or in a FIS, it doesn’t mean that one doesn’t exist. There are various places you can go to look for elevation information. Remember, as a Floodplain Administrator you reserve the right to require flood elevation information prior to issuing a permit and you MUST require elevation information for subdivisions of 5 acres or 50 lots, whichever is lesser.Permits are required for all development
7Obtaining Estimated Elevations Automated hydrologic and hydraulic (H&H) analysesOther sources of dataSimplified methodologiesContour interpolation (point-on-boundary)Data extrapolationRemember, the floodplain administrator can always require a detailed study to establish a true Base Flood ElevationThis is the order of preference for obtaining estimated water surface elevations.Automated H&H – sometimes referred to as “model-backed Zone As.”You can require detailed study - something to consider if the proposed structure is high value or subject to particular vulnerability (eg. you know it will be senior living and residents may have extra needs during an emergency.)
8Automated H&H Data Automated H&H analyses were run for Zone As Elevation information exists in the modelNot detailed enough to be included on the FIRMCan be used to estimate a 1% chance flood elevationFloodplain Administrators can use this as best available data for permitting in Zone AExisting flood elevation data for Zone As is already available in many locations. So before you attempt to develop an elevation, first – check to see if it has already been developed for you! There are a variety of sources available to obtain existing data, including data available through FEMA’s Engineering Library which will soon be available through FEMA’s GeoPlatform website.Caveats:Not available in all areas – Riskmap3.com will have data as it becomes available.Models do not typically reflect bridges, culverts, or damsMay underestimate water surface elevation and floodplain extent upstream of such structuresCross sections derived from topography (LiDAR), not field surveyed cross sectionsGeneral assumptions made of land use and roughness coefficientsA qualified engineer may use the Zone A model as the starting point for a more detailed analysis.Zone A cross sections will soon be available online!
9Availability of Automated H&H or FEMA Engineering LibraryFloodplain Administrators can most easily access and use this information for permitting at the RiskMap3 site (www.riskmap3.com). The full model, if needed, can be obtained via the FEMA Engineering library: https://www.fema.gov/national-flood-insurance-program-flood-hazard-mapping/engineering-library.Many Zone A streams in Region III have had engineering hydrologic and hydraulic models developed over the last 10 years. Your first option should be to obtain the flood elevations computed in those models. In most places where good quality digital topography is available, these models have been generated. Many of these are available online and most of the rest will be online soon.
10State Sources for Automated H&H Currently Region III hosts the data atData will be transitioned to State websites:Maryland website:West Virginia website:Pennsylvania:Elevation data is also available from a variety of state sources online, including these sources listed.
11Other Sources of DataWhen automated H&H unavailable, check for other sources of elevation data:Community RecordsDevelopment plansLetters of Map Amendment (LOMA) for neighboring propertyState or County agenciesDepartments of Transportation (plans for nearby bridges)Departments of the Environment (Stream restoration / erosion control projects)Federal AgenciesUnpublished USACE, NRCS, or USGS studiesPreliminary FIRM data from FEMAIf applying for LOMC, the reviewer will check for adjacent LOMAs.If a preliminary FIRM is available, this information can be used with caution: preliminary data is subject to change due to appeals until the Letter of Final Determination is issued. Therefore it is recommended that the more restrictive (i.e. safer) version of the FIRM be used but cannot be less than the effective. See FEMA Publication 1-98 for more details.Excerpt from FEMA 1-98 regarding Zone As and the use of preliminary FIRM data:For Zone A areas designated on the community's effective FHBM or FIRM, the BFE and floodway data from a draft or preliminary FIS constitute available data under Subparagraph 60.3(b)(4). The requirement at Subparagraph 60.3(b)(4) is an important floodplain management tool for reducing flood damages in areas where a detailed engineering study to develop BFEs and designate floodways on streams has not been conducted. Communities are required to reasonably utilize the data from a draft or preliminary FIS under the section of their ordinance that applies to this paragraph. A community is allowed discretion in using this data only to the extent that the technical or scientific validity of the data in the draft or preliminary FIS is questioned.When all appeals have been resolved and a notice of final flood elevation determination has been provided in a LFD, communities are required to use the BFE and floodway data for regulating floodplain development in accordance with 44 CFR 60.3(b)(4) since the data represents the best data available. This includes meeting the standards at 44 CFR 60.3(c), and (d) which includes the requirement that new construction, substantial improvements, and other development have their lowest floor elevated to or above the BFE (non-residential structures can also be floodproofed to or above the BFE). Communities must regulate floodplain development using the data in the FIS under 60.3(b)(4) until such time as the community has adopted the revised FIRM and FIS.
12Simplified Methodologies Contour Interpolation MethodBased on an overlay of FIRM on topographic mapEstimate water surface elevation at the intersection of the contourConfirm accuracy is acceptableOverlay FIRM on topographic data (make sure scale and projection match!)Confirm that the floodplain boundary generally conforms with contour lines AND the difference between the flood elevation on the left and right overbank are with ½ contour interval.Add ½ contour interval to account for inaccuracy of technique.It is better to survey in the field the location of the boundary and the elevation of the structure. If going to this expense, might as well survey cross section.Simplified methods can provide a good estimation of flood elevations, but it needs to be kept in mind that these are approximate methods. For this reason they can not be used for Elevation Certificates.Because it is approximate, freeboard is recommendedIt is important to use common sense and ensure that the result is reasonable – not just what a property owner might want to see.Simplified methods might be used as part of a tiered approach: eg. Do this first to see if a planned project is even feasible, then use a more detailed analysis for pre-construction design.
13Simplified Methodologies Data Extrapolation MethodExtend water surface profile at the same slopeTransfer that elevation to the map viewRelevant within 500 feet of detailed studyNo hydraulic structures (e.g. bridges, culverts) between end of detailed study and siteIf the subject location is only a short distance upstream of the end of a detailed study, you might be able to extrapolate the profile for a water surface elevation if:No structures (bridge or culverts) in between.No confluences in between.The general conditions of the stream are fairly consistent.Use common sense!This is taught in more detail in FEMA Course LP73.
14Using Elevation DataOnce the BFE is established, development is required to comply with Section 60.3(c) of the NFIP regulations.Residential: elevate lowest floor to the BFENon-residential: elevate or dry floodproof to BFEManufactured homes: elevate and anchor to BFEEnclosures below BFE, must have adequate flood openings and be used only for parking, access, or storage.OpeningsElevation of utilities and mechanicalsLowest Floor above BFEYardley Borough, Bucks County, PA (from PEMA)Once the BFE is established, development is required to comply with Section 60.3(c) of the NFIP regulations.Residential: elevating the lowest floor of residential structures to or above the BFE.Non-residential: elevate or dry floodproof commercial structuresManufactured homes: anchor and elevate manufactured home so that the lowest floor is at or above the BFE.If there are enclosures below the BFE, they must have adequate flood openings and be used only for parking, access, or storage.
15Flood Insurance Implications Mandatory flood insurance purchase requirements:applies for all structures in or touching the floodplain that carry a federally-backed mortgage
16Elevation Certificate An Elevation Certificate is an administrative tool to provide elevation information necessary to:record building elevationsdemonstrate compliance with the NFIPsupport a Letter of Map Change (LOMC)determine proper flood insurance premiumsThe point of this slide is to introduce the main uses of the Elevation Certificate. It may be used as an extremely useful administrative tool to document compliance with NFIP regulations and to support LOMC requests, but for this presentation, we will focus on its use when rating a flood insurance policy.To learn more about Elevation Certificates, you can access the Reviewing and Interpreting Elevation Certificates recorded webinar available through
17Elevation Certificate – Section E Property owners can provide measurements that insurance agents can use to rate a flood insurance policy in Zone AThese measurements are not informative of risk or water surface elevations – should not be used for permitting purposesSection E can be found on the second page of the Elevation Certificate.Usually, a surveyor or engineer completing an Elevation Certificate will need to tie into a local benchmark to provide building measurements that are absolute and referenced to a vertical datum.Section E can be completed by the property owner, who is required to find the highest and lowest points where the outside of the building touches the ground, and then measure the distance between those points and the building’s floor elevations.Property owners will need also to fill out Sections A, B, and F; you as the floodplain administrator may be asked for guidance with the map panel information and with understanding the various building diagrams.
18Post-FIRM Zone A Rating No Base Flood Elevation ProvidedPost-FIRM rating considers the elevations of the structure to determine ratesTop of Bottom Floor - Highest Adjacent Grade = Elevation DifferenceFor rating purposes, the more information the better. Having an EC filled out with the following information is better than not providing anything: Top of Bottom Floor, Highest Adjacent Grade, Lowest Adjacent Grade.Additionally, providing an estimated BFE is better than no estimated BFE.Borough of Olyphant, PA - Post-FIRM structure (FEMA Region III)
19Post-FIRM Zone A Rating Base Flood Elevation Information AvailableIf a Base Flood Elevation is available from another source, Lowest Floor Elevation – Flood Elevation = Elevation DifferenceLowest Floor elevation is not an entry on the Elevation CertificateIt is determined by an insurance agent using information provided on the Elevation CertificateThe lowest floor for insurance rating purposes may or may not be the top of bottom floor, depending on certain criteria.The lowest floor is something that a qualified insurance agent will determine because many considerations go into where exactly this elevation is. It isn’t simply just the floor that has carpet, or the floor where the bedrooms are located.Determining a base flood elevation or requiring one for new construction can have positive implications on insurance and eases the burden on the FPA.
20Letters of Map Change in a Zone A If flood elevation data is provided, FEMA will verify its reasonablenessIf elevation data cannot be provided, FEMA will compute a flood elevationThis elevation determination may not be included on the determination letterFor Zone A areas, a flood elevation must be determined to compare against the property information for a property-specific LOMC determination. Sources include:Local communities and countiesLocal and State natural resource and environmental protection or conservation agenciesU.S. Army Corps of Engineers or State transportation departmentsLocal engineersPreliminary FIRM and FIS data
21Reviewing Zone A LOMCsIf more detailed data is needed, the applicant may be asked to provide data such as:Culvert/bridge dimensionsOne or two cross sectionsIf supporting data is provided and is reasonable, it is incorporated into the hydrologic and hydraulic evaluationIf additional data is not provided, the determination may be based on more conservative methodologyIf a community submits a 1% annual chance flood elevation, it will be reviewed to make sure it has been calculated reasonably. If determined to be reasonable, future submissions will not need to reviewed. Community-determined 1% annual chance flood elevations should be submitted on communityletterhead; initial submissions should include relevant data and calculations for review.
22Providing Cross Sections For one lot, one cross section is usually sufficientFor a large lot or multiple lots, a cross section should be surveyed at each end of the parcelPerpendicular to flow pathIf property is upstream of a bridge, at least 2 cross sections are requiredShould capture changes in channel characteristics: slope, roughness, etc.Should reference vertical datumFor a large lot or multiple lots, at a minimum a cross section should be surveyed at each end of the parcel - more if distance is greater than 500’ or water surface difference is more than 1.0’ between cross sections.If in doubt of requirements for a specific site, contact FMIX and speak with the case analyst for clarification prior to paying for survey.Make sure the surveyed section goes through the house or proposed house location.A qualified engineer will be familiar with the appropriate methods and software to compute a WSEL:StreamStats hydrology:HEC-RAS - available directly from the US Army Corps of Engineers Hydrologic Engineering Center at:Or Normal Depth - Quick-2 Program ; Quick-2: only applicable in areas not affected by downstream obstructions or flow changes
23Zone A LOMAPage 1Page 2Every LOMC completed in Zone A will include this paragraph to explain the additional considerations that apply to Zone A.
24LOMC Determination Documents Considerations When Elevations are DisplayedThe 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 ChangeNon-removal determinationsFlood elevations are not shown for:Removal determinationsOut As Shown determinationsThe flood elevation is shown on conditional determinations because it is needed to ensure the development will be compliant.It is shown on non-removals to provide the detail about the flood risk since it remains in the SFHA.It should be stressed that the point of a LOMC is not to “get a BFE from FEMA.” The point of a LOMC is to determine whether a property or structure is located within the Special Flood Hazard Area.
25Zone 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.SuggestionsRecommend moving building site outside of the mapped Zone A floodplainIf possible, establish a flood elevationAutomated H&H if available, other sources of data, simplified methodologies, detailed studyDocument how reasonably safe from flooding was establishedUse high water elevations, add freeboard, use flood resistant materials, etc.When you do not have a BFE, you use what you have. It is usually better to make a more conservative decision than a less conservative decision when it comes to protecting against realized flooding risks. If possible, however, it is always best to determine the flood elevation.
26Zone A Permitting – Example Two You are permitting development for a 60 lot subdivision.15 of the lots are located in a Zone A floodplain.As you are aware, not every permit request is for a single structure or parcel. Sometimes you’ll see an application for a larger area and will need to consider the flood hazard risk when permitting development for those larger areas. This slide looks at an example of a request to put in a subdivision with many lots, some of which are located in Zone A.
27Zone A Permitting – Example Two Suggestions:Recommend altering plans so houses will not be in the SFHARemember: If the development in the SFHA exceeds either 50 lots or 5 acres, flood elevation data is requiredIf a flood elevation has been developed, permit the development under 60.3(c). A Letter of Map Revision may be requested so the FIRM can be updated with the new information.Good place for a higher standard, fewer lots and/or fewer acres.
28Resources Visit the FEMA Library for: FEMA 1-98 – Use of FIS Data as Best Available DataThe Zone A Manual: Managing Floodplain Development in Approximate Zone A AreasFEMA Engineering Library for ModelsHEC-RAS:USGS Stream Stats:FEMA GeoPlatform:FEMA Map Information eXchange (FMIX)(877) FEMA-MAP
29Contacts Phetmano Phannavong, P.E., CFM FEMA Region III Floodplain Management and Insurance Branch:Washington, D.C.Phetmano Phannavong, P.E., CFMDelawareMichael Powell, CFMMarylandDavid Guignet, P.E., CFMPennsylvaniaDaniel Fitzpatrick, CFMVirginiaCharley Banks, CFMWest VirginiaKevin Sneed, CFM