As of last week, 11 out of the 17 major reservoirs in California reached over 90% capacity, well above their historic average levels, as the state's record snowpack continues to melt. But California's third-largest reservoir has yet to reach 60% of its total capacity.
Trinity Lake, located northwest of Redding in Shasta County, is at 58% capacity as of last Tuesday, just 78% of its historic average. When you compare that against most other major water supply reservoirs and nearby Shasta Lake, California's largest reservoir sitting at nearly 90% capacity, you begin to wonder why Trinity is so far behind.
According to Mary Lee Knecht, there are several main reasons why Trinity Lake continues to lag behind:
How the reservoirs refill
Trinity Lake has a small drainage basin
Snowfall in that region wasn't as strong
A federal law requiring releases due to the Trinity River Restoration Program
Trinity “is heavily dependent on snowpack; versus Shasta, which is mostly dependent on rainfall to fill,” Mary Lee Knecht, U.S. Bureau of Reclamation Region 10 public affairs officer, wrote in an email to the Chronicle.
Knecht points out that Trinity Lake has a small drainage basin where surface water like streams and snowmelt meet. With a small drainage basin, it takes longer to fill the reservoir, and likely more than one wet season to refill.
Snowfall in the Trinity region was just 120 percent above the historic average, unlike 200 to 300 percent in other areas in the state. When you compare Shasta to Trinity, the size of the drainage basins and the dependency on rainfall vs snowmelt to fill the reservoirs lies the big difference.
On top of all of that, fish restoration goals established in the Trinity River Restoration Program require releases from the reservoir to restore the fish habitat below Trinity Dam.
Other than Trinity Lake, Casitas Lake in Ventura County, is the only other major California Reservoir below its historic average at 74% capacity and 92% of its historic average.
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