A flume is a channel with high sides built to convey water over a depression or ravine, acting like a bridge that carries water. The District has four flumes, all on the Winters Canal; without this critical infrastructure the District could not deliver water to over half of the distribution area. The four flumes, in order of their location downstream of the Winters Canal headgates, are the Lamb Valley, Almondale, Cottonwood, and Fredericks Flumes, all named for the sloughs that they cross over, except for Fredericks Flume which crosses over the Union Slough.
Drawings commissioned by the Yolo Water and Power Company indicate that the flumes were built before 1927, and it is likely that they were constructed in the same period that the Cache Creek and Capay Diversion Dams were built, circa 1914. Although the flumes are essential, they also act as bottlenecks along the Winters Canal because the maximum amount of water that the flumes can carry is 450 cfs. Because of this capacity limitation, water users below the Lamb Valley Flume are sometimes placed on waiting lists during hot summer months when water demand is high.
Over the years the flumes have surprised District staff with leaks and sink holes that have sprung up, some of which have led to short shutdowns of the Winters Canal while emergency repairs were completed. The Almondale and the Cottonwood flumes have already been repaired with an application of AquaLastic, a concrete repair system that addresses degradation and prolongs the life of infrastructure. The Lamb Valley flume is scheduled to be coated with AquaLastic in the spring of 2024. This treatment is expected to extend the life of these structures for an additional 8-12 years, but soon they will need to be replaced, as they remain vulnerable to failure due to age and erosion.
The flumes also help to support habitat in the sloughs, because the District delivers water via the sloughs to water customers along the sloughs. (The agreed upon delivery point is from the flume, but customers pick it up downstream in the slough.) In this way, the sloughs receive water during the dry season which aids riparian plants and animals.