In response to ongoing calls for greater water storage capacity, a study of the American River Basin has indicated that a high Sierra reservoir, strategically situated, could play a critical role in addressing California’s water issues.
California’s mounting concern to capture Sierra runoff has been accentuated by the state’s increasingly volatile weather patterns that fluctuate between droughts and floods. Despite this year’s robust Sierra snowpack, it stands as an exception, as climate projections predict more rainfall than snowfall in the lower mountains by the century’s end. Another pressing issue is the earlier runoff that necessitates extended management and storage of reservoir water during the arid summer months.
To mitigate these challenges, a new reservoir near Alder Creek in the Sierra is under consideration. Located just above Pollock Pines in El Dorado County and off Highway 50, this thoughtfully positioned reservoir could capture water during heavy rain events and from Sierra snowmelt, potentially augmenting Folsom’s total water supply by approximately 18%. As the water would be stored upstream of Folsom Lake, it would alleviate some of the operational pressure managers face in releasing water due to flood risks or compliance with environmental regulations.
There is great appeal for the Alder Reservoir location, which converges two granite formations and features a deep canyon. This setup would allow for cold water to be stored in a deep, narrow space, minimizing evaporation losses. The stored cold water could be released to address environmental needs of specific fish species downstream.
The provision of cold water is particularly crucial as Folsom is often the primary source for the Delta. Water managers frequently have to release water from Folsom to satisfy environmental water temperature regulations in the Sacramento-San Joaquin Delta. An upstream reservoir such as the one proposed at Alder Creek could help offset these cold water demands.
The proposed reservoir’s water would also serve the agricultural community of El Dorado County and, if necessary, could support cities like Folsom, Roseville, and the San Juan Water District, which currently rely on Folsom Lake’s water. The released water would travel via creeks, streams, rivers, and even the old gold mining flume system. The concept of this reservoir has been in discussion since 1916.
In 1916, the county was experiencing substantial agricultural growth, leading to the need to ascertain water supply solutions and explore methods to store rainfall and snowmelt. Of the 16 sites proposed at the time, the only one still being actively considered today is near Alder Creek.
The next steps to advance this project include initiating the feasibility study and economic analysis. The estimated cost of around $1.4 billion would be funded by local, state, and federal agencies, and the project is expected to take 10 to 15 years to complete.