By Paul N.
Why is there so little water in the Twitchell Reservoir compared to other local reservoirs?
As of today [Thursday], the county states the Cachuma, Jameson, and Gibraltar Reservoirs are over or nearly 100% capacity. The Twitchell Reservoir is at 10.3%. Why is that?
Source: https://files.countyofsb.org/pwd/hydrology/Rainfall%20Reports/rainfallreport.pdf
“The water is stored in the reservoir during big winter storms and released as quickly as possible while still allowing it to percolate into the soil and recharge the groundwater. This means that the reservoir is usually far from full. It is estimated that the project increases reacharge by 20,000 acre feet per year.” https://www.usbr.gov/projects/index.php?id=193
Is this because Twitchell releases more water than the others?
Cachuma’s main purpose is water storage (same for upstream Gibraltar and Jameson), but Twitchell is a flood control reservoir. That means it is designed to stay near empty, such that there is more than enough space to temporarily store/slow down extreme flows during storms. The added benefit of releasing flows slowly and steadily, versus letting it all out at once, is groundwater recharge downstream.
I learned something new today. Thanks!