Snohomish County PUD

Culmback Dam – Morning Glory Spillway Gate Raise

Spada Lake supplies raw water to much of Snohomish County and supports power generation at the Jackson Hydroelectric Project before discharging to the Sultan River and the City of Everett’s filtration system. As water demand increases and snowpack and precipitation become less predictable, interest has grown in storing more water in late spring for use during summer and fall. Because Spada Lake is formed by Culmback Dam and uses a morning-glory spillway, a seasonal spillway-raising gate was considered as a practical way to increase storage. The project aimed to develop an early-stage design concept for a system to raise and lower the spillway seasonally, and to examine the potential value and impacts of that added storage. This included reviewing cost-benefit tradeoffs at different storage heights, identifying needed structural analyses, assessing possible inundation effects around the lake, interpreting climate-related hydrology changes in the Sultan Basin, and summarizing operational considerations for making better use of increased summer water storage.