DESCRIPTION
Chehalis will demolish the old wastewater treatment plant to create flood storage capacity in the floodplain of the Chehalis River. This portion of the project was Phase I which was for a grading plan with hydraulic analysis to demonstrate the positive impacts to the Chehalis River during flood stage.
The City of Chehalis retained Skillings Connolly, Inc. (Consultant) to assist in calculating the potential flood storage volume near the City’s wastewater treatment plant. For preliminary planning purposes, the City wanted to determine if excavation of more than 100,000 cubic yards of soil would reduce the flood stage near the wastewater treatment plant. Existing grade was modeled based on Lidar information.
The City of Chehalis then retained Watershed Science & Engineering (Consultant) to evaluate the potential impacts of removing the existing Waste Water Treatment Plant (including over-excavation for flood storage) on 100-year base flood elevations. The City used the results of this investigation to support the Flood Authority grant application for removal of the plant and associated fill.
