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The Problem:

Douglas County was tasked with investigating the potential location of the proposed community center on County property in Gardnerville. The likely site was situated within a primary Federal Emergency Management Agency (FEMA) -designated floodplain. A feasibility-level analysis was conducted to assess the possible impact on the Special Flood Hazard Area (SFHA) of Cottonwood Slough by constructing the community center at the chosen site. Because the impact on downstream structures is affected by the effective SFHA, FEMA did not permit any increase in water-surface elevation.

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The Solution:

A FLO-2D two-dimensional hydraulic model was used in the Manhard Pine Nut Creek hydrologic and hydraulic analysis prepared for the Town of Gardnerville. Following guidance from Douglas County personnel and their architectural consultants, the FLO-2D model was adjusted to block out cells affected by the proposed structure and fill area of the parking lot. Using the updated bathymetry, the model was operated, and the results were extracted.

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The Results:

The results and recommendations were presented in a report to the Douglas County Parks Department. Based on the findings of the study, the location of the proposed Douglas County Community and Senior Center was found to be feasible from a flood hydraulics perspective. A formal Conditional Letter of Map Revision application was prepared and submitted to FEMA to document the results of the two-dimensional modeling and demonstrate that the impacts from the project were mitigated through the design. Ultimately, a Letter of Map Revision application was completed to officially record the change to the floodplain caused by the improvements.