If your project will impact the official Federal Emergency Management Agency (FEMA) or local floodways or floodplains, it will require floodplain permitting through the local Floodplain Administrator (typically a City or County employee). In certain localities, such as Boulder and Fort Collins, the local Floodplain Administrator also has jurisdiction over local floodplains and floodways. Any project that will alter Federal or local floodways and/or floodplains should undergo a hydraulic analysis to determine the impacts of the proposed improvements. The type of permit needed is often dependent on how significant the floodway/floodplain impacts are. A hydraulic engineer can assist you both with determining this impact and communicating with the Floodplain Administrator during the permitting process.
Each city/town, and some counties, have their own set of floodplain development regulations. For example, the City of Loveland requires that the finished floor elevation of new buildings be above the 100 year base flood elevation. On the other hand, the City of Fort Collins has regulations for the elevation of new structures that vary by river (ranging from 12″ to 24″ above the 100 year base flood elevation).
If you determine that your project will require floodplain permitting, hydraulic analysis is often required to identify the extent of the impacts. A hydraulic analysis is done by hydraulic engineers and it estimates the impacts of your project on the existing floodway and floodplain. Based on the outcome of the analysis, the project will either need to pursue a NoRise Certification or a Conditional Letter of Map Revision (CLOMR). This permitting process can often be a lengthy and expensive (several thousand dollars) process, but it ensures that the work you do does not have a negative impact on your neighbors. It also ensures that work done by other property owners does not negatively affect the floodplain on your property. If you are not sure if your project will require Floodplain Permitting, reach out to your local floodplain administrator, watershed coalition or a hydraulic engineer. Floodplain administrators are typically city or county employees and can be contacted through the appropriate agency’s website.
In cases where the work in the floodway will result in a zero-rise or a decrease in base flood elevations, it may be possible to avoid the step of the CLOMR. A zero-rise or no-rise means that hydraulic modeling shows the project will not cause a negative impact to the floodplain (or less than a 0.5 foot rise if there is no floodway defined). In these instances where the hydraulic analysis can show that a project will not cause a rise in the floodplain, the project can achieve a No-Rise Certification. This process is typically much less expensive and take less time than a CLOMR process. The local Floodplain Administrator is responsible for making the decision whether a CLOMR is required in these cases. If you are pursuing a No-Rise Certification, your engineer should talk with the local Floodplain Administrator early in the process so that they have a clear understanding of the project and its impacts.
However, when projects will cause a rise in the floodway or floodplain, they will have to undergo a full CLOMR process and receive comments regarding the impacts of the proposed project. A CLOMR is typically prepared by the hydraulic engineer and presents the projected floodway/floodplain impacts.
A survey of the final condition must be produced after construction, from which a new hydraulic analysis is created. The new hydraulic analysis is then submitted to the local Floodplain Administrator in the form of a Letter of Map Revision (LOMR). Once accepted, the official FEMA Flood Insurance Rate Map (FIRM), Flood Boundary and Floodway Map (FBFM), or both, are updated by FEMA to reflect the new floodway/floodplain conditions.
For some cases in which a no-rise certification is achieved but the floodway and/or floodplain is significantly affected, the local floodplain administrator may still require a LOMR process after construction. A LOMR review process can cost several thousand dollars.