City of Oneida Drainage Study and Floodplain Map Revision

Higinbotham Brook is an urban watercourse with an approximately four-square-mile drainage area in the City of Oneida, New York, that experiences occasional flooding. The current FEMA floodplain mapping shows the 100-year floodplain well outside the brook. As a result, several residents adjacent to Higinbotham Brook are required to purchase flood insurance. The City of Oneida wanted a list of specific improvements to the brook that would reduce the occurrence of flooding and remove the flood insurance requirements within the watershed. To get FEMA’s concurrence on this list of improvements, the City of Oneida hired C&S to prepare and submit an application for a Conditional Letter Of Map Revision (CLOMR).

The first step of the CLOMR process requires the applicant to recreate an existing conditions model of the watercourse. This existing conditions model must predict similar results to the published flood insurance study (FIS) and floodplain map. This first step often involves the transferring of FEMA’s hydraulic model from an older software such as HEC-2 to HEC-RAS. C&S then prepared revised hydrologic and hydraulic drainage modeling of the Higinbotham Brook watershed. The revised hydrologic model used updated calculation techniques and reflected changes to land-use as well as changes to the operating procedure of an upstream dam. The revised hydraulic model included several watercourse improvements that would reduce the extents of the regulatory floodplain. These improvements include the replacement of key culverts and the creation of a park-like area that would function as a detention basin.

C&S submitted the CLOMR application to FEMA, where it went through a rigorous technical review. Following their review, FEMA issued the CLOMR, stating that if the improvements are made to Higinbotham Brook, the residents would be removed from the regulatory floodplain.