The City of Wenatchee SWMM modeling study determined conveyance system capacity and upgrades at various locations throughout the city's urban stormwater drainage network. The SWMM modeling was conducted by Mr. Joseph Brascher. Six different scenarios were modeled including both current and future land use conditions. SWMM was run on a continuous basis using 40 years of hourly rainfall data. Output from SWMM was then used to compute flood frequency information for each culvert in the drainage system network.

A total of over 1000 culverts were identified and modeled as part of the drainage system. Each culvert was evaluated for flood overtopping using both current and future land use information. Culvert sizes were upgraded to provide sufficient conveyance capacity where needed.

Fifteen separate SWMM models were constructed to simulate flood flows in the city's drainage system. For each model 40 years of hourly streamflow data were produced. Log Pearson Type III flood frequency statistics were computed from the SWMM simulated flow data. Simulated flow data were also used to identify how proposed flooding solutions would alter local and downstream flooding. This information was used to determine the benefits and costs of each solution.