Possible Points: 140 for the element.
Purpose of Element: Communities that voluntarily adopt standards for mapping and delineating the regulatory floodway that are more stringent than those of the NFIP are granted credit under this CRS element. In general, the regulatory floodway is determined using computer models which map the 100-year flood event. Through this model, obstructions placed at the edge of the floodplain are simulated to gradually move closer and closer to the channel until the flood stage is one foot higher than the 100-year flood elevation. The area which would be inundated with water that is one foot higher than the base flood elevation under these simulated conditions is called the floodway (see page 410-22 for a figure describing the floodway determination process). The increase in flood stage above the base flood elevation is called the floodway surcharge (Louisville-Jefferson County, 2012). Because the NFIP requires that encroachment in the floodplain cause no more than a 1.0 foot surcharge, any mapping standard that requires a lower surcharge to be used to determine the floodway is credited (NFIP, 60.3 (c)(10)). In doing this, communities effectively expand the floodway. Most communities receiving credit for this are in states that have adopted a more stringent floodway rise, which tends to be anywhere from .5 to .01 feet.
Development in the floodway is highly regulated because living or working in a structure in these areas can be very dangerous due to the depths, and sometimes, high velocities that floodwaters reach in these areas. In addition, any development in the floodway (fill, storage of materials, new buildings) can increase flood risk for upstream and downstream property owners. Generally, development is prohibited in floodways unless it can be demonstrated that such development causes no-rise in base flood elevations. For more information see pages 410-21 - 410-24.
Impact Adjustment: Yes. This element is subject to an impact adjustment which is calculated based on several factors including: the area of the SFHA when the map is adopted relative to the area to which the floodway mapping standard applies, the community’s financial contribution to complete its flood study, and if the community has other higher standards for flood mapping. A full summary of the impact adjustment calculations for this element can be found on pages 410-29 - 410-31 of the CRS Coordinator’s Manual.
Potential to Double Count Credit: None.
Degree of Difficulty - Documentation: Medium. Creation of the impact adjustment map for this element may be a challenge for some communities. This is because it requires data that is not commonly maintained. In addition to the impact adjustment map, communities must assemble minor amounts of documentation for this element. The required documentation includes a copy the community’s Flood Insurance Study, floodway data table, and ordinance that formally adopt the higher regulatory standard.
Degree of Difficulty - Implementation: High. A significant amount of technical expertise is needed in order to complete the hydraulic modelling associated with delineating the floodway based on a new mapping standard. Finally, in order to receive credit for using a more restrictive floodway mapping standard, it must be formally adopted into a community’s floodplain management regulations. These are significant barriers that could challenge communities that are seeking to change the way in which they map the floodway. That said, these challenges can be overcome through a series of strategic actions that can be taken by communities. First, consultants can be hired to help assist smaller communities with the hydraulic modeling and GIS components of this element. Second, educating elected officials, floodplain homeowners, and the development community on the NAI benefits associated with implementing a more restrictive floodway standard can help to get the buy-in necessary to enact the new floodway standard.
Tip for Success:
- Communities in nine states (OH, MT, NJ, CO, IN, IL, MI, MN, WI) may automatically qualify for credit because of a state or locally-adopted floodway mapping standard that is more restrictive than the National Flood Insurance Program minimum. Communities in these states may be able to take credit for this element if they are: 1. compliant with relevant standards and 2. can produce the required documentation.
Co-Benefits Associated with this Element:
The benefits associated with having a more restrictive floodway mapping standard are not limited to ensuring that future development is resilient to flooding. Because development is significantly limited in the floodway, larger floodways mean that greater floodplain areas are preserved in their natural condition. When left in their natural state, floodplains improve water quality, stabilize streambanks and help to reduce channel erosion. Floodways in particular are usually inclusive of the all-important riparian bank area which are especially beneficial to fish and wildlife.