Section H. Strengthening Your Local Floodplain Management Program

In Section D, we learned that average annual flood losses have increased over the past century. In these times of increasing risks, it's important for communities to look at how they can go beyond the minimum NFIP requirements to better protect people and property. The federal regulations were developed more than thirty years ago to address nationwide goals. We know now that may not be good enough to address flooding experienced by all communities. There are several ways to strengthen your local floodplain management program, including adopting stronger regulations that account for local conditions and implementing actions that matter to your community.

The costs of settling for the minimums.

Graphic showing issues with minimum standards.

Simply put, assuming the minimum NFIP standards provide adequate flood protection ignores today’s reality. Embedded in that assumption is the notion that it’s acceptable for property owners to bear the future consequences and impacts of the community’s land use decisions to allow floodplain development. As flood risk changes, property owners may be burdened by increased flood damage. Recovery costs are consequently transferred from those who made (and benefitted from) those land use decisions to others, including victims, nonprofits, and multiple local, state and federal taxpayers.

Some of the ways the minimum requirements fall short of reducing future flood damage – and may instead be intensifying it – include:

  • Allowing floodplain development using flood hazard information that may be years old and not adequately account for future development that could increase flood frequency and depths
  • Allowing buildings constructed with their lowest floors "at" the minimum elevation (the 100-year or base flood elevation), without acknowledging that the methods used to model and estimate flooding have a number of simplifying assumptions, or that future flooding conditions will worsen
  • Allowing development activity to divert floodwater onto other properties, sometimes increasing velocities and flood depths
  • Allowing alteration of streams and rivers and allowing development that displaces water, which can increase flood depths

This section describes why robust local floodplain management programs can reduce damage and promote savings on NFIP flood insurance premiums. The section also offers brief descriptions of some ways communities can accomplish those objectives:

  • ASFPM's No Adverse Impact approach to floodplain management (Question 42)
  • NFIP's Community Rating System, which rewards communities that exceed the NFIP minimums with discounts on NFIP insurance premiums (Question 43)
  • Some of the more common ways communities strengthen their administration and flood damage reduction programs (Question 44)
  • Some regulatory options communities can adopt to strengthen their regulations to better guide development to achieve long-term goals (Question 45)

42. What is No Adverse Impact?

NAI Logo.ASFPM developed No Adverse Impact (NAI) to provide communities with options and ideas to avoid making flooding worse and creating other negative impacts to public health, safety and welfare. The program emphasizes communicating and promoting responsible floodplain development through community-based decision making. NAI floodplain management empowers elected officials and citizens to become better-informed stakeholders and promoters of "wise development."

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You can be a strong supporter of local floodplain management.

Elected officials can be strong supporters of better programs once they realize:

  • Their communities will pay the price of bad decisions over the long run
  • Federal and state minimum requirements are not sufficient to adequately protect their citizens
  • They may be liable for knowingly allowing flood problems to increase

Rather than view floodplain management as something imposed by the federal government, NAI promotes local accountability for developing and implementing comprehensive strategies and plans. Obviously, you do not want to see your constituents flooded or harmed because of the actions of someone else (including action or inaction by your community). But you may not realize that, as a local official, you have the power to do something about it.

How Does NAI Work and How Do We Learn More About It? The NAI approach helps communities identify the potential impacts of development and take action to mitigate those impacts. Use the NAI philosophy to shape your community's development management criteria:

  • Develop and adopt a comprehensive plan (or plan element) to manage development. Example: In the mid-1980s, Davenport, IA, along the Mississippi River, developed a Riverfront Conceptual Development Plan that concluded almost all buildings should be held back from the immediate river's edge to allow for a river trail. The plan's recommendations were adopted into the community's comprehensive plan and gradually incorporated into later plans and ordinances. After several subsequent floods, and almost 40 years of guiding development away from floodplains, much of the City's floodplain is now open space. The current comprehensive plan touts the wonderful amenities of the Mississippi River, without mentioning flood hazards.
  • Identify acceptable levels of impact. Some levels of flooding are acceptable, especially when areas prone to flooding are kept as open space. Where development has already occurred, it may not be feasible to avoid impacts of flooding at reasonable costs. In determining which future impacts to avoid, community leaders must weigh relative flood risks in different areas of their community, determine what infrastructure or resources can be flooded with little to no environment impact or taxpayer burden, and conclude what level of flood damage is acceptable.
  • Specify appropriate measures to mitigate adverse impacts during flood events. Example: The City of Poquoson, VA, successfully lobbied the state's General Assembly to allow regulation and enforcement of "No Wake" zones during flooding events. Fast moving cars and trucks traversing flooded streets were creating wakes and sending more water into flooded homes. The measure has reduced adverse impacts of flooding.
  • Establish a plan for implementation to reduce or eliminate adverse impacts over time.

Cover image of "NAI How To Guide for Regulations and Development" document.

NAI Resources

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NAI publications are available online (www.floods.org), including a toolkit and how to guides for regulations and development standards, hazard identification and mapping, education and outreach, planning, infrastructure, and mitigation. The NAI How-to Guide for Regulations and Development Standards describes many more restrictive regulatory standards, illustrating successful implementation through case studies.

NAI implementation actions may take a variety of forms, including:

  • Changes to requirements that govern floodplain/floodway, subdivision, grading/filling and stormwater
  • Changes to zoning to guide development away from floodplains or to reduce the density of floodplain development
  • Joining the NFIP Community Rating System (described in Question 43)
  • Seeking statutory authority to strengthen buildings codes with local amendments (or to gain authority to adopt building codes locally)
  • Establishing a mechanism to fund flood mitigation projects and identify and implement such projects (see Section B for an introduction to post-disaster floodplain management and mitigation)
  • Outreach to the community to improve understanding of and the need for progressive floodplain management (see Section C for more on communicating with citizens about floodplain management)

43. What is the NFIP's Community Rating System?

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CRS Overview

A short narrated introduction to the CRS suitable for viewers with little or no familiarity with the program is online: Community Rating System (CRS) Overview, Prerecorded Presentation. The presentation introduces 19 creditable activities and summarizes the commitments communities must make, including maintaining records and submitting annual reports, the steps you’ll need to take to start the application process and available assistance.

The NFIP's Community Rating System (CRS) was first implemented in 1990 and authorized by Congress in 1994. It is a voluntary incentive program that recognizes and encourages local floodplain management activities that exceed the minimum NFIP requirements. When participating communities undertake these activities, including adopting and enforcing regulations that exceed the minimum standards of the NFIP, NFIP flood insurance premium rates in those communities are discounted from 5 to 45 percent. Qualifying activities are those that meet the three goals of the CRS: (1) reduce flood damage to insurable property; (2) strengthen and support the insurance aspects of the NFIP; and (3) encourage a comprehensive approach to floodplain management.

In addition to reduced flood insurance rates, CRS communities and their citizens gain other non-financial benefits, including:

  • Residents and business owners have increased opportunities to learn about flood risk, evaluate their individual vulnerabilities, take action to protect themselves, and reduce the risk of flooding to their homes and businesses.
  • Activities that qualify for CRS credits enhance public safety, reduce damage to property and public infrastructure, and help minimize economic disruption and loss.
  • The opportunity to evaluate the effectiveness of their flood programs against nationally recognized benchmarks.

Map of CRS participating communities.

As of October 2018, nearly 1,500 communities were in the CRS, representing more than 70% of NFIP flood insurance policies in force.

Success Story Connection

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Roseville, California became the first city to earn a Class 1 CRS rating in 2006. It maintains this rating through outstanding public information, mapping and regulatory standards, flood damage reduction, and flood preparedness.


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CRS for Community Resilience (a.k.a. the CRS Green Guide)

ASFPM produced the CRS Green Guide and ancillary resources to encourage more communities to undertake voluntary, effective measures to increase flood resilience, offering a road map for CRS activities that strengthen natural ecosystems and reduce vulnerability to increasing flood risks.

How Do We Learn More About the CRS? Whether you're considering participating in CRS or looking to improve your rating, get started by downloading the FEMA brochure, NFIP CRS: The Local Official's Guide to Saving Lives, Preventing Property Damage and Reducing the Cost of Flood Insurance. Also, contact your NFIP State Coordinator and neighboring communities that are already in the CRS. Many CRS communities organize user groups to share experiences and provide help. Additional information and fact sheets about the CRS are at https://www.fema.gov/flood-insurance/rules-legislation/community-rating-system, and the Success with CRS webpage (https://successwithcrs.us/) profiles "real-life" examples of how CRS has helped communities across the U.S., explaining how some communities gained public support for a stronger program.

Community Incentives for Nature Based Flood Solutions: A Guide to FEMA’s Community Rating System for Conservation Practitioners

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This report from The Nature Conservancy explains and gives examples of how municipalities, states and other entities can plan and carry out projects that are integrated to not only reduce flood risk and yield NFIP premium discounts, but also result in critical environmental benefits such as larger green spaces, wildlife habitat, and living shorelines. The report includes a list of guides and decision support tools developed by federal agencies and non profit groups to help communities simultaneously embrace both the CRS and conservation and preservation initiatives. Learn more about The Nature Conservancy program that generated this and other guidebooks at coastalresilience.org.


44. What are some common ways to strengthen our approach to reducing flood risk?

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CRS Credits for Strengthening Programs

CRS credits may be available to participating communities that undertake these and other program elements that further the CRS goals.

Having good regulations on the books isn't enough. Communities must have effective programs with the right staff, sufficient budget to support administration, enforcement and staff training, and elected officials who support their floodplain managers (see Section G to learn more about effective floodplain management programs). The following additional ways to strengthen local floodplain management programs are briefly described below:

  • Flood Warning Systems
  • Floodway: More Restrictive Mapping Standard
  • Local Flood Hazard Maps
  • Mitigation Plans and Projects
  • Technical and Financial Assistance for Mitigation by Property Owners
  • Temporary Moratorium on Issuing Building Permits

Flood Warning Systems. The primary objective of flood warning systems is public safety, so emergency management officials can alert the public of impending conditions and decide when to close flood-prone roads and initiate evacuation orders. When warning systems provide credible advanced notice, citizens can be advised to take actions to minimize damage to property. Examples of actions include moving damageable contents out of floodable space (especially basements), moving cars to higher ground, implementing plans to install elements of dry floodproofing protection (e.g., installing special flood barriers across doors and other openings), shutting off gas and electricity, and relocating livestock to higher ground. While these actions don't eliminate damage to buildings, they can make recovery easier. Flood warning systems can be tied to very detailed evacuation plans when water monitoring stations (stream gages), flood depths and evacuation route elevations are carefully analyzed.

Floodway: More Restrictive Floodway Mapping Standard. FEMA uses computer models to simulate filling in the floodplain. Floodway boundaries are drawn when the model indicates the effects of the simulated filling would be to increase the flood depth by not more than 1 foot. Some states and communities work with FEMA to use a more restrictive standard, such as allowing no more than half a foot increase or zero increase. As a result, floodways in those communities tend to be wider, effectively limiting development in a larger portion of the floodplain. A more restrictive floodway mapping standard should be based on an examination of flood conditions and existing infrastructure in your community's floodplain.

Local Flood Hazard Maps. At a minimum, NFIP participating communities must adopt FEMA Flood Insurance Studies and Flood Insurance Rate Maps. However, nothing prevents the use of supplementary local maps and application of the floodplain management regulations to areas shown on those maps as subject to flooding. Communities develop and adopt supplementary maps:

  • To delineate areas known to flood that are not shown on FIRMs, including areas with ponding and inadequate local drainage
  • To delineate historic floods of record that affected areas outside the limits of the FEMA-mapped floodplain
  • To delineate areas subject to future flooding because of changing conditions, such as increased runoff from developing watersheds and more intense storms

Mitigation Plans and Projects. As with any long-term objective, having a well-thought-out plan of action is an important step towards meeting that objective. Most flood-prone communities have developed or participated in development of hazard mitigation plans, and many identify high-risk areas and evaluate options for mitigation projects in advance of the next damaging flood. Section B describes hazard mitigation plans, common mitigation projects and federal grant programs that may be available to support cost-effective projects.

Technical and Financial Assistance for Mitigation Projects by Property Owners. It's not surprising that many communities were established and grew up along rivers and shorelines. Many older communities have large numbers of buildings constructed long before the adoption of floodplain management regulations. Some communities seek federal and state funding to undertake projects to mitigate the effects of flooding (described in Question 10). Others decide waiting for highly competitive outside funding would take too long, and develop their own programs instead. For example:

  • Charlotte-Mecklenburg Storm Water Services, NC, developed retroFIT, a program funded by storm water utility fees to provide financial and technical assistance to homeowners who undertake flood damage reduction measures (elevation, relocation, demolition, wet and dry floodproofing, equipment elevation and basement abandonment).
  • South Holland, IL, funds and administers a Flood Assistance Rebate Program providing up to $2,500 to homeowners who invest in flood loss reduction projects (overhead sewers, foundation repairs and waterproofing, drain tiles, downspout diversion, flood walls, backflow devices and lift stations and others).

Temporary Moratorium on Issuing Building Permits. The natural reaction to damaging events is to "get back to normal." But doing that can mean allowing repairs and reconstruction without full consideration of options that contribute to long-term reduction in flood damage. Some communities impose a temporary, short-term moratorium on issuing permits to allow officials and property owners time to inspect structures in flooded areas and examine options (see Question 9 for examples of mitigation actions), including higher standards (described in Question 45). Especially when federal or state mitigation grant funds may be available, time is needed to evaluate the feasibility of obtaining funds. Funds may be used for a variety of projects that reduce future risk, including acquisition (buy-out), moving buildings to higher ground, elevation on higher foundations, retrofit dry floodproofing of nonresidential buildings, and some drainage projects. FEMA's mitigation funding programs are described in Question 10. While even a short-term moratorium may be unpopular with those anxious to rebuild quickly, the longer-term benefits of careful planning should not be overlooked.

Taking Time to Strengthen Regulations After Floods

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One benefit of a pause, or formal temporary moratorium on reconstruction, is the time it allows community officials to examine whether to modify their floodplain management regulations before reconstruction begins. Some communities do this even if they do not impose a moratorium. Property owners can exert pressure to repeal existing higher standards, which is another reason it’s important to have knowledgeable elected officials and staff who understand the long-term benefits of those higher standards.


45. What are some common ways to strengthen our regulations?

Your NFIP state coordinator is the best source of assistance for considering and adopting higher standards. FEMA Regional Offices may also offer advice. Remember – always have your NFIP state coordinator review proposed changes to your floodplain management regulations before adoption. In addition to their technical expertise, they may have sample language written to work with your existing regulations.

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Strengthening Regulations Involves Benefits and Costs

Your community should consider the pros and cons of higher standards. Each standard has its own pros and cons, but they share the following:

  • Pros: reduce flood risk over the long term; acknowledge community specific needs; contribute to overall resiliency and ability to recover after disasters; qualify for CRS credit points, which, in turn, lowers the cost of NFIP flood insurance – adopting ordinances should include whereas clauses that articulate the merits of higher standards
  • Cons: have some increased up front costs; may be difficult for property owners to internalize long term benefits; may be subject to pressure to repeal after flood events

The following common ways to strengthen local floodplain management regulations are briefly described below:

  • Coastal A Zone Like Coastal High Hazard Area
  • Critical Facilities Protection
  • Cumulative Substantial Improvement
  • Dry Land Access
  • Enclosure Limitations
  • Fill: Limitations on Use
  • Fill: Compensatory Storage
  • Foundations and Design Certification
  • Freeboard: Additional Height
  • Freeboard: Regulating Land Outside 100-Year Floodplain, But Below Freeboard Elevation
  • Hazardous Materials
  • Location Restrictions Based on Depth and Velocity
  • Low-Density Zoning
  • Lower Substantial Improvement Percentage
  • Manufactured Home Limitations
  • Preservation of Natural Areas
  • Repetitive Flood Loss (Substantial Damage)
  • Setbacks
  • Stormwater Management
  • Subdivision Design

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Building Codes and Higher Standards that Affect the Design of Buildings

Many of the higher standards described in this Guide affect the design of buildings. Communities in states that adopt building codes and mandate local enforcement should check with the NFIP state coordinator to learn how best to incorporate higher standards. Guidance and sample language to modify the International Codes are included in Reducing Flood Losses Through the International Codes: Coordinating Building Codes and Floodplain Management Regulations.


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Coastal A Zone

Learn more about Coastal A Zones, LiMWAs and higher construction standards applicable in these coastal hazard areas by downloading FEMA Limit of Moderate Wave Action Fact Sheets (English and Spanish).

Coastal A Zone Like Coastal High Hazard Area. Coastal high-hazard areas are flood-prone areas where breaking waves are expected to exceed 3 feet high during the base flood. These areas are called Zone V. Pounding waves are very destructive, which is why the NFIP has specific requirements for buildings in these areas to have piling or column foundations. The Zone V construction requirements are summarized in Question 36.

FEMA's post-flood field observations, engineering calculations and laboratory evaluations indicate breaking waves between 1.5 and 3 feet high cause more damage to common perimeter wall (crawlspace) foundations than is caused by similar flood depths without waves.

Map showing LiMWA line.Since 2009, FEMA's coastal flood studies evaluate wave conditions and delineate the Limit of Moderate Wave Action (LiMWA). The LiMWA is drawn where wave heights are expected to drop below 1.5 feet during base flood conditions (see graphic). The area between the LiMWA and Zone V boundary (or shoreline, if there is no Zone V) is called the Coastal A Zone (CAZ). When FEMA delineates a LiMWA on its FIRM, many communities elect to modify their ordinance to further protect development in the CAZ by requiring Zone V foundation design elements that prevent damage from breaking waves.

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Critical Facilities

Learn more about protecting critical facilities by downloading the FEMA fact sheet Critical Facilities and Higher Standards.

Critical Facilities Protection. Require new critical facilities to be located outside the mapped floodplain when feasible and if not feasible, require a higher level of protection (e.g., elevate at least 2 feet above the minimum elevation (the 100-year or base flood elevation) or above the elevation of the 500-year flood). Critical facilities include facilities communities consider essential to deliver services and protect public safety, such as emergency response facilities (fire stations, police stations, rescue squads, emergency operations centers, and emergency shelters), custodial facilities (jails, detention centers and long-term care homes), health care facilities (hospitals), schools and utilities (water supply, wastewater treatment and power). Protection for critical facilities may also include dry floodproofing some areas and adding high-capacity emergency generators and other elements to allow vital functions to continue.

Cumulative Substantial Improvement. Modify the basic "50% rule" (see Question 36 Existing Buildings, for minimum requirements) to track the costs of building improvements and repairs over a specified time period and require compliance with current flood protection standards when the accumulated costs add up to 50% or more of the market value of buildings. The NFIP minimum requirement for substantial improvement is a "one time" evaluation – each time an improvement is proposed or repairs are needed, the calculation comparing costs to market value is made. This inevitably leads some building owners to phase their large-scale improvements deliberately to avoid triggering the "50% rule." What this means is that owners invest over time, increasing value, yet the buildings remain at risk of flooding. Accumulating those improvement costs over a time frame of 1 to 5 years discourages owners from seeking sequential permits for deliberately phased improvements, while longer periods are selected by communities committed to long-term resiliency by bringing more nonconforming buildings up to code.

Dry Land Access. Requiring roads that serve new subdivisions, critical facilities and manufactured home parks to have the driving surface no more than a specified depth relative to the minimum 100-year or base flood elevation (typically 1 foot below) facilitates evacuation and access by emergency personnel. Care must be taken to provide for drainage, otherwise raised roads can block floodwater.

Enclosure Limitations. Areas below elevated buildings may be enclosed if used only for parking of vehicles, storage and building access (see Question 36 New Buildings, for minimum requirements). To discourage illegal conversion of enclosures, communities may adopt a limitation on size (e.g., less than 300 square feet for parking or less than 100 square feet for a stairwell and storage). Some communities require permit applicants to sign nonconversion agreements and record the agreements in property records to notify future owners of the restrictions on use. Other communities prohibit enclosures entirely to minimize obstructing flow, reduce the impacts of debris in floodwater, and minimize damage to elevated buildings.

Fill: Limitations on Use. In many communities, placement of compacted fill is a common way to elevate buildings. Sometimes individual buildings are constructed on fill and sometimes multiple lots are filled in order to redelineate the floodplain boundary. Using fill can have adverse impacts, including obstructing the storage and flow of floodwater, requiring removal of trees or other beneficial vegetation, causing local drainage problems and preventing infiltration of rain. Fill that is improperly or insufficiently compacted for structural support, or fill that is not "clean" and free of debris can more easily erode during floods, causing structural problems and contributing to waterway sedimentation. To prevent adverse impacts, some communities prohibit the use of fill to elevate buildings, or strictly regulate the content and compaction of fill based on anticipated future use to support buildings.

Fill: Compensatory Storage. Fill in riverine floodplains can displace floodwater and make flooding worse. Adding a requirement for off-setting, or compensatory, excavation when developers bring fill (dirt or compacted soil to raise a site) into flood-prone areas can reduce the impacts or eliminate the problem. Some communities specify a one-for-one compensatory excavation (one cubic yard of excavation for one cubic yard of fill) that must be handled on site. Other communities require engineering analyses to determine the adequacy of off-setting compensatory excavation. Another way to address the impacts of fill is to limit its use (see Fill: Limitations on Use).

Foundations and Design Certification. Recognizing the importance of designing to account for flood and wave loads in areas subject to high velocity wave action, the NFIP requires building foundations and designs in coastal high hazard areas (Zone V) to be certified by professional engineers or architects. Some communities require all building foundations in all flood zones, including slab foundations on fill, to be designed by registered professionals. This ensures designs account for site-specific flood conditions, such as flood depth, velocity, saturation and erosion of filled areas and potential for damaging debris impacts.

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Freeboard in Building Codes

State and local building codes based on the 2015 and later editions of the International Codes require at least 1 foot of additional elevation above the base flood elevation, although some states have eliminated this factor of safety. Communities considering adopting freeboard should first check their building codes. Some states allow communities to modify building codes to be more restrictive, including requiring more than just 1 foot of freeboard.

Freeboard: Additional Building Height. Many states and communities exceed the NFIP minimum lowest floor elevation (and dry floodproofing) requirement by 1 foot or more. This additional height, called freeboard, is the most common way communities strengthen floodplain management regulations. Freeboard provides a margin of safety against uncertainty, future increases in flood depths, and flood events that rise higher than the minimum 100-year (base flood) elevation. The higher buildings are constructed; the less flood damage they experience. This is reflected in lower NFIP flood insurance premiums (graphic). Most of the U.S. population lives in communities that have at least one foot of freeboard.

Building higher, whether just 1 foot or several feet, minimally increases the up-front cost of construction, a point often raised by builders contesting proposals to adopt freeboard. However, the long-term benefits of avoiding or minimizing damage plus lower annual insurance premiums, compared to the one-time cost, make freeboard a good investment (and attractive to future buyers). In many communities, when property owners have to elevate by more than just a few feet, they elect to raise buildings even higher to use the area underneath for parking.

Chart showing annual flood insurance premiums based on lowest floor height above BFE for AE and VE zones.

Costs and Benefits of Freeboard

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Learn more by downloading ASFPM’s brochure The Costs & Benefits of Building Higher, FEMA’s Higher Standards: Adopting Freeboard video, and FEMA Fact Sheet Building Higher in Flood Zones: Freeboard – Reduce Your Risk, Reduce Your Premium.

The National Institute of Building Sciences released Natural Hazard Mitigation Saves: 2018 Interim Report. This update looked specifically at the savings associated with compliance with the flood, wind and earthquake provisions of 2018 International Codes. One finding is that at least one foot of freeboard saves $6 for every $1 invested.

Freeboard: Regulating Land Outside 100-Year Floodplain, But Below Freeboard Elevation. While requiring additional building elevation (freeboard) is a fairly common higher standard applied to buildings in the mapped floodplain, much less common is applying floodplain management regulations to the land adjacent to the flood zone that is lower than the flood elevation plus freeboard (graphic). This approach is particularly appropriate where future conditions indicate increased flood risk, such as areas vulnerable to sea level rise and watersheds with significant development pressure. Remember: decreasing future flood vulnerability of a structure built today requires action today.

Graphic showing BFE plus freeboard.

Consider this example: a community adopts 2 feet of freeboard. Suppose Building B is "in" the flood zone and must be elevated 2 feet above the base flood elevation, but nearby Building A is just "out" of the flood zone and is allowed to be constructed at grade, with a basement. Now, suppose the next flood rises a foot and a half or 2 feet above the base flood elevation. Building B is not damaged, while Building A is inundated. Regulating land below the freeboard height applies the same factor of safety to all buildings subject to flooding up to that height, providing an equal level of protection to those who develop in areas just outside the FEMA-designated floodplain.

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Flooded waste ponds contribute to contamination of floodwater.

Ponds or lagoons that store animal wastes, coal ash and other processing byproducts may be overtopped during floods, or earthen berms and masonry walls may fail, releasing wastes into floodwater.

Hazardous Materials. Some hazardous materials pose risks to people and the environment if released into floodwater, and some hazardous materials are highly reactive when contacted by water, causing fires or explosions. The NFIP has no specific requirements for locating facilities that manufacture, store or handle hazardous materials in floodplains. Some communities do not permit such facilities, while others require applicants to demonstrate that alternative locations outside mapped floodplains are not available before processing applications. Some communities require these facilities to be protected to a higher level than homes and commercial buildings (e.g., freeboard of 2 or more feet, or above the 500-year flood elevation, whichever is higher). Emergency operations plans should be required, with detailed, specific actions to be taken by facility managers when flood conditions threaten.

Location Restrictions Based on Depth and Velocity. The NFIP minimum requirements for development do not require consideration of flood depths and velocities, and flood maps do not distinguish between areas with fast-moving or deep water during the base flood. While evaluation of site-specific conditions is required when designing buildings in Zone V, the same is not required in areas identified as Zone A/AE. Some floodplain areas are predicted to be inundated by 8 feet or more of floodwater and some floodplains in steep mountainous areas not only have very fast-moving flows, but experience rapid onset flooding (flash flooding). Deep floodwater and high-velocity flows pose risks to occupants and emergency services personnel involved in evacuation and rescue. Some communities recognize these very high-risk areas by restricting some or all development.

Low-Density Zoning. This planning approach helps guide development to less flood-prone areas, which limits investments in flood-prone areas and may raise awareness of flood hazards among real estate developers. Less dense zoning (more acreage per unit) in SFHAs also means fewer buildings, allowing more land area to remain unaltered and available to perform natural floodplain functions, such as storage of floodwater, groundwater recharge, and bio-filtration. Larger lots may also make it more feasible for buildings to be located outside of SFHAs or on higher ground.

Lower Substantial Improvement Percentage. The NFIP substantial improvement requirement ("50% rule") is described in Question 36 Existing Buildings. Some communities elect to adopt a cost-to-market value threshold of less than 50%. The result is that more buildings are brought into compliance, increasing overall community resilience. Barriers to successful implementation of this measure can arise after flood events, when lawmakers are pressured to return to the minimum 50% threshold. Before responding to calls for change, elected officials should review the history of the provision to understand the rationale behind initial adoption.

Manufactured Home Limitations. Manufactured homes are very vulnerable to flood damage, experiencing significantly more damage per foot of inundation than site-built homes. To provide a reasonable level of protection, some communities:

  • Require full elevation of replacement homes in older manufactured home parks and subdivisions, instead of allowing replacement homes to be installed on foundations that are just 36 inches high (described in Question 36 for minimum requirements)
  • Prohibit installation (or replacement) in floodways, except in existing manufactured home parks and subdivisions
  • Prohibit installation (or replacement) in coastal high hazard areas (Zone V), except in existing manufactured home parks and subdivisions
  • Prohibit installation (or replacement) in any flood hazard area
  • Prohibit new manufactured home parks or subdivisions from being created in flood hazard areas

Preservation of Natural Areas. Multiple objectives are achieved when undeveloped floodplain areas are identified for conservation or preservation, including development of greenways and passive recreation opportunities and protecting wetlands and wildlife habitat and corridors. Requirements for low-density zoning and subdivision designs can also be used to preserve natural areas. Preservation of natural areas and the beneficial functions of floodplains can be a critical part of a No Adverse Impact approach to floodplain management (see Question 42 for an introduction to the No Adverse Impact approach).

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Repetitively Flooded Buildings (Repetitive Loss)

The NFIP defines repetitive loss as "flood related damage on two separate occasions during a 10 year period for which the cost of repairs at the time of each event, on average, equals or exceeds 25% of the market value of the structure before the damage occurred."

Repetitive Flood Loss (Substantial Damage). The basic NFIP requirement for buildings that incur substantial damage (the "50% rule," described in Question 36 Existing Buildings) can be modified to require compliance when buildings are repetitively damaged by flooding. Communities do this more often when the nature of their flood risk is relatively shallow, yet frequent, which means applying the standard substantial damage definition is unlikely to reduce exposure to flooding over the long term. To qualify for NFIP flood insurance coverage called Increased Cost of Compliance (described in Question 33) when buildings are "repetitive loss" as defined by the NFIP, communities must adopt a definition for substantial damage and a requirement that triggers compliance with current standards when buildings sustain repetitive loss. It is important to understand that the repetitive loss provision must be enforced for all buildings that sustain repetitive flood damage throughout the mapped floodplain, not just those that have NFIP insurance policies or those that are seeking FEMA grant assistance.

Barriers to successful implementation of a repetitive flood loss measure can arise after flood events, when lawmakers are pressured to return to the minimum, which evaluates each damaging event without consideration of previous events. Before responding to calls for change, elected officials should review the history of the provision to understand the rationale behind initial adoption.

Setbacks. Many states and communities adopt setbacks (or buffers) to limit development within specified minimum distances from bodies of water. While the primary reasons may be related to water quality and riparian habitat protection, setbacks can also achieve flood loss reduction benefits by guiding development away from areas subject to erosion or deep floodwater. Depending on the objectives, setbacks may be measured from waterway centerlines, top of bank, normal high water, or the floodway boundary. This measure is particularly useful in communities with waterways that do not meet the FEMA threshold for study (typically less than 1 square mile drainage area), or waterways with only unnumbered Zone A without designated flood elevations or floodways.

Stormwater Management. Most stormwater management programs regulate increases in frequent rain event runoff from specific types of development, usually to achieve water quality objectives. Some programs also control the volume of runoff allowed to leave developed properties. When downstream areas are already experiencing flooding, some programs require new developments to control runoff from more severe rain events, such as storms that might result in the level of flooding used to delineate flood maps (the base, or 100-year flood). A variety of techniques are used to manage runoff, including detention basins (storing water to release after storms) and retention basins (holding water without release, perhaps to facilitate wetlands or groundwater recharge), infiltration (such as rain gardens, rock-filled trenches and porous paving). Rather than many smaller on-site facilities, some communities develop larger regional facilities designed to handle anticipated growth.

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Subdivisions and flood hazards

The American Planning Association’s 2016 PAS Report 584, Subdivision Design and Flood Hazard Areas, complements the 1997 PAS Report 473, Subdivision Design in Flood Hazard Areas. The newer report reflects a more comprehensive approach to reducing flood risks through subdivision planning and design.

Subdivision Design. Ordinances that regulate subdivision design can be written to guide development away from flood-prone areas through lot layout and open space requirements (see graphic). Developers may be required to set aside some or all of the mapped floodplain for open space, stormwater management, or recreational use. Lots can be platted to require building sites outside the floodplain or on high ground.

Graphic showing recommended and not recommended options for subdivisions near a floodplain.


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