Republic Presidents Bowl Stormwater Planning and Improvements

Varela helped Republic handle seasonal flooding and stormwater damage

The Presidents Bowl in Republic, Washington regularly experiences seasonal flooding. Surface runoff and high groundwater levels collect in the area, draining from a 350-acre upstream drainage basin. Much of the collected flow exits the area through old sanitary sewers, resulting in excess flow to the sewage treatment plant.

Varela worked with the City to acquire funding for planning and predesign from the Washington State Department of Ecology.

In 2018, planning began to develop alternatives and cost estimates to better handle stormwater. To understand the issues, site visits included late-night flow monitoring and flow measurement in both the sanitary and storm drain systems, as well as discussions with the Public Works Director.

The upstream drainage basin was defined using GIS techniques, volume and timing of runoff were estimated using the USDA SWAT+ computer model, and predesign for a new collection and conveyance system used the EPA SWMM computer model. 

Major alternatives to drain the basin included:
1) lining the sanitary system and constructing a new storm sewer or 2) converting the old sanitary sewer to convey stormwater and constructing a new sanitary system.

Infiltration BMP’s were also considered but site soil conditions are not suitable. Collected stormwater is discharged to an infiltration pond located about 3,000 linear feet downslope of the project area. These alternatives are being discussed with the City and Ecology in 2020.

Varela has worked with the City of Republic since 1985, planning and designing drainage improvements for Clark Avenue (State Highway 20), designing FEMA and FHA funded repairs after major flooding in the early 2000s, and completing Stormwater Master Planning for the City. These projects required coordination with WSDOT, the State Emergency Management Office, and FEMA. Design guidelines used for the evaluations included the WSDOT Hydraulics and the Ecology Eastern Stormwater Management manuals.

Planning for this project included developing design storms to calculate stormwater runoff flows and volumes, evaluating the City’s existing drainage system, identifying options, and developing design plans to repair the most severely damaged sections of the City’s drainage system.