Stormwater Master Plan

Client—City of Kelso, Washington

Gibbs & Olson completed the final phase of a stormwater master plan for the City of Kelso. Kelso’s aging stormwater system consists of various pipe sizes, ages and materials along with several roadside ditches for stormwater conveyance. Gibbs & Olson was hired to perform an analysis utilizing advanced stormwater GIS software. The analysis provides the City with a master plan that more accurately prioritizes their available resources for future stormwater projects.

Gibbs & Olson worked with the City on the first two planning phases that involved defining and mapping each stormwater basin within city limits using existing drawings and GIS data. For selected basins, Gibbs & Olson prepared an inventory of the existing structures and pipes, mapped the City’s stormwater system, conducted hydraulic modeling and analysis, evaluated materials and function, and made recommendations for improvements. The final phase continued data collection on the remainder of the City’s system, and Gibbs & Olson evaluated the entire system’s performance under large storm events using Storm and Sanitary Analysis. The final model analyzed and identified full pipe, surcharged structures, and surface flooding. Gibbs & Olson utilized the final modeling to prepare a stormwater master plan and developed a capital improvement plan that prioritizes the City’s resources on significant problem areas.