Evaluate whether fill limitations, freeboard, or other requirements may help reduce flood risk from development.
The challenges with flooding in Region Seven and across Louisiana are widespread, with many contributing factors. These contributing factors include weather-related events — precipitation events, coastal storms, and tidal flooding — and are increasing in frequency, intensity, and duration. However, the effects of legal and policy decisions, including those relating to development and land-use patterns, drainage infrastructure, pervious and impervious surface area, and more, have also created challenges affecting where and how people can live and their overall resilience. Land use and development affect how readily water is (or is not) able to move through natural channels, and whether the natural environment has the capacity to accommodate changing flood patterns. Natural filtration capacity is lost as open space is converted to other uses. Development typically increases impervious surface areas, which leads to a greater velocity of stormwater runoff during precipitation events or other high water conditions, thus exacerbating flood risk. Sometimes, development also involves the use of earthen fill to elevate areas in the floodplain that are to be developed further. This is intended to reduce flood risk to the development itself by elevating the property. However, in some cases, this can actually exacerbate flood risk for surrounding (lower elevated) properties, and even the raised property itself, depending on the characteristics of the fill. That is, earthen fill can affect the overall ability of the land to store and convey water, increasing flood risks for upstream and downstream communities.See footnote 1
Given the significant impact of development on flood risk, it is important for local governments to have plans and regulations in place that seek to avoid or mitigate flood-related impacts from development as much as possible. Based on research and outreach conducted to inform the Regional Vision, drainage issues have been cited as a primary challenge by many of the parishes in Region Seven. It is also important for development and infrastructure itself to be designed with flood resilience in mind, particularly as some parts of Region Seven are experiencing historic growth, with recent escalations in the rate of permit applications filed.
This objective focuses on the need to evaluate and mitigate flood risk in areas that may be subject to new development. In addition, it encourages policymakers to consider whether existing standards are sufficient to protect new homes, as well as neighboring areas upstream and downstream.
Policymakers should contemplate policy options that impose stricter flood mitigation standards for new development, holistically and in the context of other factors, like housing needs and affordability, both of which can be affected by development regulations. Furthermore, the recommendations in this objective should also be considered in the context of flooding risks associated with existing homes and infrastructure, and the legal, planning, and policy mechanisms that can be implemented to help address these risks. The recommendations contained in this objective do not address this risk to existing structures, except to the extent that regulations discussed may also apply to substantial redevelopment.
How to Make Progress on This Objective
Informed by the latest data on local flood risk, local governments can seek to avoid or mitigate flooding from new development through one or a combination of three types of actions:
- Freeboard requirements;
- Limitations on fill; and
- Stormwater and drainage regulations.
As discussed in the Background for Goal Two, the National Flood Insurance Program (NFIP) establishes minimum standards for floodplain management and regulation within the Special Flood Hazard Area (SFHA, also referred to as the floodplain). Among these requirements is a minimum standard that building sites, subdivision proposals, and other proposed new developments in the floodplain are determined to be “reasonably safe from flooding.”See footnote 2 Supported by the latest available data and modeling, this standard can help local governments justify decisions to go beyond minimum NFIP requirements with respect to development proposed within a designated floodplain. Local governments may wish to consider these legal and policy options outlined above among the range of tools and approaches to reduce the risk of flooding to properties.
Much of the discussion below relates to technical classifications of how the Federal Emergency Management Agency (FEMA) defines geographic zones or areas of the floodplain under the NFIP based on factors like frequency and intensity of flood risk and proximity to the coast. These zones also have impacts on local land-use and zoning. This objective does not define each of these zones in text. For more information about each of these zones, see the Congressional Research Service’s Introduction to the National Flood Insurance Program. Additional definitions and information relating to the NFIP can be found in the Goal Two Background.
The minimum NFIP floodplain management standards require that “all new construction and substantial improvement of residential structures” in the regulatory floodplain (also known as the Special Flood Hazard Area or SFHA) be elevated at or above the base flood elevation (BFE).See footnote 3 However, given the growing frequency and intensity of flood events, including outside the SFHA,See footnote 4 some local governments have adopted or are considering incorporating new or enhanced freeboard requirements in parish and municipal ordinances.
Credit: Calcasieu Parish, Louisiana.
Freeboard refers to “an additional amount of height above the [BFE] used as a factor of safety in determining the level at which a structure’s lowest floor must be elevated or floodproofed to be in accordance with state or community floodplain management regulations.”See footnote 5 Freeboard can help account for unknown or unanticipated factors that can contribute to flood heights greater than the BFE, such as impacts from development in the watershed, wave action, blockage of infrastructure (e.g., bridges and culverts) by debris, or sea-level rise. Additionally, if a community that participates in the Community Rating System (CRS) program would like to work towards achieving a rating of eight or higher, they must have at least one foot of freeboard adopted.See footnote 6 Thus, freeboard not only reduces the risk of a structure flooding, it is also an explicit way to ensure that a parish or municipality can reap the full benefit of CRS points that are earned from activities to reduce flood insurance premiums across the participating community.
There are different ways that local governments can approach freeboard requirements, which are typically implemented in local ordinances including the floodplain ordinance. The following portion of this objective will contain potential provisions to be implemented or amended within an ordinance. While this list is not exhaustive, potential recommendations include:
- Raising the elevation requirements applying to the lowest part of a structure: Typically, elevation requirements either apply to the “lowest floor” (which may or may not include basements) or to the “lowest horizontal structural member of the lowest floor” (which can include components like HVAC systems and ductwork). The former is typical in the NFIP minimum criteria for SFHA A Zones,See footnote 7 while the latter is applied in V Zones as a stronger requirement, which mandates lower components of a structure to meet the elevation criteria.See footnote 8
Either of these standards could be applied in the context of a freeboard requirement, although the same freeboard requirement applied to the “lowest horizontal structural member of the lowest floor” would typically result in a more protective standard. Tangipahoa Parish applies a one-foot freeboard requirement based on the lowest floor (including basements) for new construction and substantial improvements of residential structures in areas of shallow flooding (AO/AH zones).See footnote 9
Description: An illustration of the difference between development standards applied in flood zones. Credit: Federal Emergency Management Agency.
- Specifying how structures may be elevated: There are multiple ways that structures can be elevated to meet freeboard requirements; in the absence of specific standards, this could include the use of compacted earthen fill, pier and beam construction, piling and columns, or other types of raised foundations.See footnote 10 As noted below, there are downsides to the use of earthen fill and its use for the purpose of structural support is generally prohibited in all SFHA V zones,See footnote 11 so local governments could specify alternative means of meeting freeboard requirements.
- Expanding the zones or areas where freeboard requirements apply: In considering freeboard requirements, local governments must determine the FEMA flood zones (e.g., A and V zones only, or broader) or other areas (e.g., parish or municipal overlay zones or districts) in which to apply the requirements. Expanding these areas to include more properties can directly help reduce flood risks, as structures will be required to be elevated higher above the identified floodplain. For example, Mexico Beach, Florida updated its regulations following Hurricane Michael to require one-and-a-half feet of freeboard in both the 100-year SFHA and 500-year floodplains.See footnote 12 St. Tammany Parish requires the lowest finished floor of structures built-in “areas of special concern,” which are defined by ordinance, to be “situated at least 24 inches above the crown of the road surface directly adjacent to and in front of the parcel.”See footnote 13 Jefferson Parish applies a minimum one-foot freeboard requirement in Zone AE for all new residential construction and substantial damage/improvement of residential structures.See footnote 14
Communities adopting freeboard requirements can receive points under CRS Activity 430, Higher Regulatory Standards — Freeboard (432.b), with the total amount of points depending on the extent of freeboard requirements (relative to the SFHA), the height of freeboard required, and whether or not fill is also regulated.See footnote 15
Limitations on Fill
For properties in the SFHA that are not in the designated regulatory floodway,See footnote 16 the placement of earthen fill is a common practice in the development community to help raise structures above the BFE.See footnote 17 Upon elevating with fill, property owners can petition FEMA to request that the area be removed from the SFHA, in which case requirements to comply with minimum NFIP floodplain management standards would no longer apply.See footnote 18 The same “reasonably safe from flooding” standard also applies when earthen fill is used to elevate an area proposed for development to or above the BFE. That is, when a map revision is sought to remove a filled area from the SFHA, the community must provide written assurance that “the land and any existing or proposed structures to be removed from the SFHA are ‘reasonably safe from flooding.’”See footnote 19
While the use of fill can help reduce flood risk for the structures built on top of the filled area, it can exacerbate flooding challenges for neighboring properties and communities as it “reduces floodplain storage capacity, can deflect waves onto neighboring property,” as well as having adverse impacts on environmental quality (e.g., wetlands, vegetation, and water) and functions such as drainage.See footnote 20 One option for local governments is to include additional restrictions or limitations on the use of fill in the SFHA and other areas that are environmentally sensitive or potentially at higher flood risk. These requirements, included in local floodplain management regulations, can take several different forms including:
- Prohibiting fill in certain areas: The NFIP minimum floodplain management standards require prohibiting fill in portions of the SFHA designated as floodways,See footnote 21 but local governments may choose to entirely prohibit the use of fill for new development in the floodplain or in specific areas that may be deemed higher risk or critical environmental areas. This approach also maximizes credit in the CRS Activity 430, Higher Regulatory Standards – Development Limitations (432.a), with total points adjusted based on the portion of the SFHA covered by the restriction.See footnote 22
- Implementing no-net-fill and other compensatory mitigation provisions: One alternative option to prohibiting the use of fill is to establish a no-net-fill requirement or other forms of compensatory mitigation requirement. These types of requirements are designed to ensure that any flood storage capacity lost due to the use of fill is compensated for by removing fill elsewhere to add storage capacity. For example, St. Tammany Parish generally prohibits net fill in “critical drainage areas” and on any lots or parcels 90 feet or less in width, except with an approved development plan.See footnote 23 Following Hurricane Harvey, Houston also extended its no-net-fill regulation to cover the entire 500-year floodplain. Compensatory mitigation requirements can also earn communities credit under CRS Activity 430, Higher Regulatory Standards – Development Limitations (432.a).See footnote 24
- Limiting the amount or total average height of the fill: Where fill is permitted, it is common to place restrictions on the amount of fill that can be used, which include limitations on average height and how far (horizontally) beyond the building footprint the use of fill may extend. Ascension Parish limits fill to 36 inches in height, and only within the foundation footprint on individual lots smaller than one-half acre; however, the parish is considering extending this limit to all development scenarios (including subdivisions and commercial lots).See footnote 25
Stormwater and Drainage Regulations
Aside from or in addition to freeboard requirements or limitations on fill, local governments may wish to implement other regulations that reduce flood risk through drainage infrastructure and stormwater management requirements. For example, parishes and municipalities can implement provisions requiring best management practices, requirements that properties retain a certain additional percentage of runoff relative to pre-development conditions, or promulgate provisions requiring that nature-based solutions or other features are included to provide adequate water storage capacity to accommodate a certain storm-frequency event. Iberville Parish requires that new development provide drainage infrastructure sufficient to accommodate a ten-year storm event. For commercial, industrial, institutional and certain multifamily developments, St. Tammany Parish requires a certain percentage reduction of pre-development peak runoff relative to the 25- or 100-year storm event, depending on the overall development size in acreage (e.g., with parcels five acres or larger required to reduce runoff by 25 percent for a 100-year storm event with on-site detention ponds required).See footnote 26 Based on the best available science and data, Region Seven parishes and municipalities might consider how future conditions could affect design storm events and whether to incorporate these anticipated changes into stormwater and drainage regulations.
Crosscutting Considerations and Practice Tips
When considering the most appropriate and feasible ways to minimize flood impacts from new development, decisionmakers may find the following crosscutting considerations and practice tips useful:
- Consider flood mitigation needs holistically
- Lead with data
- Engage communities and other stakeholders
- Coordinate with other authorities within the parish
These tips are based on priority implementation best practices and considerations most relevant to this specific objective and do not present an exhaustive list for regional and local planners and policymakers. In addition to this objective, decisionmakers should, at a minimum, also refer to Goal Five for crosscutting practice tips and considerations including the use of science and data related to flooding, drainage, and mitigation (Objective 5.2).
It is important to acknowledge that every jurisdiction will be starting from a different place and have a unique local context and needs, among other factors. Therefore, these practice tips could be adopted individually, collectively, or not at all. It will be up to policymakers to work directly with their communities and other key stakeholders and partners to assess and determine potential tools and approaches to implement this goal and objective.
- Consider flood mitigation needs holistically: Flood risks and potential solutions relating to new development should be considered comprehensively and in the context of flood risks to existing development and infrastructure needs to be identified by communities. Regulations affecting new development can be costly to implement, and ultimately affect the affordability of new homes; these costs should be considered alongside the flood mitigation benefits of strengthening standards and the overall housing needs and affordability concerns in a parish or municipality. Additionally, there may be greater concerns related to flooding of existing infrastructure, homes, and other properties, pointing to the need for parishes and municipalities to prioritize policy options that mitigate flooding in areas that are already developed.
- Lead with data: When considering the utility of development limitations and requirements for reducing flood risk, decisionmakers should ensure that they are relying on the latest data and science. This includes maps estimating flood depths and extent and precipitation estimates relating to the intensity, frequency, and duration of flooding and weather events. The Louisiana Watershed Initiative is also working with technical experts to develop hydrologic and hydraulic models for the state’s watersheds, which will support more informed decisionmaking when completed. Using accurate data and models in conjunction with a good understanding of uncertainties can help local governments justify decisions to place limits on the use of fill in the floodplain or implement freeboard requirements. For more information on prioritizing data needs related to flood mitigation, see Objective 5.2.
- Engage communities and other stakeholders: Decisions regarding development limitations or requirements designed to reduce flood risk from new developments and projects should involve robust community and stakeholder engagement. Community members, especially those who are resource-limited and Black, Indigenous, and People of Color (BIPOC) and low-income stakeholders, have direct knowledge about flood challenges their neighborhood is experiencing, and decisionmakers should seek to learn from individuals firsthand about their experiences and priorities. Additionally, decisionmakers should prioritize input from and transparency with the development community throughout the stakeholder engagement and implementation processes. Effective community and stakeholder engagement practices that decisionmakers can adopt in this context are discussed further in Objective 5.1.
- Coordinate with other authorities within a parish or municipality: As with Objective 2.2 and prioritizing open space preservation, intraparish coordination should also be prioritized when considering development limitations and requirements like fill restrictions and freeboard. Planning and environment departments are key partners, but decisionmakers should also identify any other relevant agencies or authorities (e.g., drainage districts, incorporated municipalities) in the parish that should be involved in order to provide greater policy consistency and coordinated implementation when possible. Making intraparish coordination standard practice can help avoid conflicting or duplicative regulatory or implementation efforts. Additionally, coordination within a parish and municipality (and across parishes and municipalities, if feasible) can help provide increased regulatory consistency to the development community.
The summaries below highlight resources and case studies available in Georgetown Climate Center’s Adaptation Clearinghouse that are relevant to this objective. They illustrate how many of the above benefits, practice tips, and planning, legal, and policy tools were or are being evaluated and used in practice in different jurisdictions. To learn more and navigate to the Adaptation Clearinghouse, click on the “View Resource” buttons.