The Capay Diversion Dam is at the heart of the District’s water delivery system, as this is the point where irrigation releases from Indian Valley and Cache Creek Dams are diverted into the canal headworks to bring water to farmers’ fields. Construction of the Capay Diversion Dam began in 1912 by the Clear Lake Water Company and was completed in 1913. The dam is a concrete, gravity structure with concrete headgates at each end, and is approximately 500 feet long and 15 feet high.
The Capay Diversion Dam was first constructed in order to build up water pressure so diversions into the headgates of the Winters and West Adams Canals could take place. At that time, pressure was created by constructing a temporary wooden check structure, or wall, on top of the dam. Water backed up behind the wall to create the necessary elevation to allow water to be diverted into the canals for delivery throughout the gravity-fed system. The wall was built every spring and removed after the irrigation season to let storm waters flow over the diversion dam. If everything went well, this process took about three days but could be interrupted by an early or late-season storm. A modern solution to this seasonal construction project was implemented in 1993 when a rubber dam was installed on top of the Capay Diversion Dam. At the time of its installation, the rubber dam was the longest in the world at 474 feet. From that point forward, instead of building the wall, the rubber dam could be inflated by an air compressor in a very short time.
Apron Repair
In the winter of 2003, it was discovered that the Capay Diversion Dam was in grave danger. Over time, creek bed deterioration undermined support for the downstream portion of the dam and a forty-five-foot length of the downstream portion, or apron, broke off. With a portion of the apron missing and erosion eating away at the underlying creek bed, the dam itself was in immediate jeopardy of catastrophic failure. Bringing in tons of gravel, grout and cement, the District completed an emergency repair. This patch solved the immediate problem, but was never considered a long-term, comprehensive solution. Given the age of the dam, the District prudently called in a team of specialized engineers to assess the condition of this critical structure in 2006.
The engineers’ analysis of the dam’s condition revealed that although the main portion of the dam was sound, decades of erosion and streambed degradation had damaged the downstream apron and its’ supporting bedrock. To remedy this, an apron replacement that extended it by 44 feet downstream along the entire length of the dam was completed in 2010. The result was a dam that is much more stable in order to withstand the destructive power of water and debris and will continue to serve the District for many more years to come.