Winter Rains Bring Big Changes to Lake Cachuma
What will the impact of winter rains be? It’s too early to know for sure, but here are some of the ways in which winter storms might affect water quality at Lake Cachuma, and the drought.
During the winter rainy season that typically runs from November to April there is significant interest from the community regarding the affect of winter rains. The most common questions have to do with how rains will change conditions at Lake Cachuma, the effect on overall water supply, and influence on stage declarations. For updated rainfall totals, or to find current lake levels, click here.
How are the rains affecting water quality?
As a result of the Rey Fire in 2016, Whittier Fire in 2017, and the Thomas Fire in 2018, water quality conditions at Lake Cachuma are changing. Winter storms have washed ash, burned vegetation, and loose soil that has eroded from the burned slopes into the Santa Ynez River and the lake. Of particular concern is the steep area around the intake tower, which was severely burned during the Whittier Fire.
Further compounding this problem is that water levels at Lake Cachuma have risen and receded over eight years of drought, leading to the growth of vegetation in the lake bed. When winter storms submerge this growth it leads to natural decay, which further increases the concentration of organic materials in the lake. The nutrients in the lake contribute to algae growth in the warmer months of the year.
All this means that even as the community welcomes winter rain, the water at Lake Cachuma requires additional treatment at significantly increased cost.
How are the rains affecting the District’s water supply?
During the drought Lake Cachuma reached record lows, so this year’s rainfall has helped to improve surface water supplies. After the significant rainfall in January and February, the watershed is now saturated so that future storms will provide additional runoff into the Lake. It is predicted that additional storms in February and March could increase Lake Cachuma levels significantly.
What does this mean for the District’s Declared Stage III Water Shortage Emergency?
Despite the recent rains, as of early March the District has not received any additional allocation of Cachuma water from the US Bureau of Reclamation, who makes the allocations. The District currently has a 20% allocation, with a 35% allocation of water from the State Water Project.
The true impact of winter storms on available water supply often aren’t fully understood until late spring when lake levels and water supply can be assessed by the Federal and State government to determine how much deliveries to local water purveyors will be adjusted as a result. An announcement from the Bureau of Reclamation is expected as early as April when they determine whether there are sufficient supplies to make additional water available to agencies through a mid-year supplemental allocation. Depending on rainfall and snowpack conditions in Northern California, the State Department of Water Resources typically finalizes State Water Project allocations by the end of Spring.
With groundwater levels far lower than when we entered the drought eight years ago, it may be some time before the water shortage emergency is over. The District’s Drought Preparedness and Water Shortage Contingency Plan is based on both 12-month and 24-month evaluations of projected supply and demand, and the District looks to all of the four supply sources ahead of making decisions related to water supplies.