CLOMR? What CLOMR? FEMA Floodplain Mapping Requirements for Dam Removal Projects – How Planning and Implementing Effective Strategies Can Minimize the Time/Cost of Compliance for Your Project

The Wood-Pawcatuck Watershed Association (WPWA) is undertaking work on the upper section of the Pawcatuck River (River) in Rhode Island to improve fish passage by removing the Lower Shannock Falls Dam, constructing a fish ladder at the historic Horseshoe Falls Dam, and constructing a nature-like rock ramp fishway at the Kenyon Mill Dam. The projects are located over a 2.5 mile reach of the River that had been studied in detail by FEMA as part of the National Flood Insurance Program (NFIP). FEMA requires towns or municipalities to apply for a Conditional Letter of Map Revision (CLOMR) to reflect the changes in flood risk that would occur due to dam removals or other major work on dams that will impact riverine hydraulics. In turn, many municipalities require project proponents to complete this potentially substantial and time consuming work effort. Understanding these requirements, the numerous challenges that can be encountered and successful ways to address the technical and administrative challenges can help a project stay on budget and schedule.
Combining these three separate construction projects that span across two jurisdictions into a single modeling analysis and CLOMR package provided a significant advantage in efficiency, time and cost for both WPWA and FEMA’s review contractor
(STARR). FEMA also benefitted significantly in its ongoing map modernization efforts by the project’s analysis using HEC-RAS in place of HEC-2, incorporating new topographic mapping and detailed bridge geometric information. Close coordination between the WPWA and its consultant was instrumental in providing the required information to FEMA for its review, such that technical questions and comments on the hydraulic model could be efficiently resolved.