As we move into the fall months a number of people are curious about how far down Yolo County can draw the lake. The lake level is currently at 3.6 feet on the Rumsey Gauge. Clear Lake historically reaches its lowest level during the months of October and November.
Yolo County can take the lake level down to a plus-1 foot on the Rumsey Gauge. The Rumsey Gauge is a measurement of the lake level that was established back in 1872 when Capt. Rumsey created a gauge to measure the various lake levels. He came up with a standard that is still used today.
Rumsey decided that when water ceased to flow over the Grigsby Riffle, the lake would be at zero on his gauge. Zero Rumsey is equal to a height of 1318.256 feet above sea level. When water was above the riffle it would be called plus Rumsey, such as 1 foot, 2 feet and so on. Below the riffle, the lake level would be measured as minus Rumsey.
All measurements were based on zero Rumsey at the Grigsby Riffle, which is located on Cache Creek, about two miles from the dam. Yolo County was originally allowed to take the lake level down to zero on the Rumsey Gauge, however in 1978, eight years after Indian Valley Reservoir was built, Yolo County made an agreement with Lake County to stop taking water out of Clear Lake at plus-1 foot on the Rumsey Gauge.
Since Yolo County could draw an unlimited amount of water from Indian Valley Reservoir, it didn’t need as much water from Clear Lake. Of course, that doesn’t tell the whole story. Evaporation takes about three feet off the lake annually and if the weather is hotter than normal, it can be even more. Adding to the water draw is that homes around the lake can legally take an unlimited amount of water from the lake for their lawns and gardens. This is called “riparian rights.”
There have been only a few years when the lake level dropped to zero or a minus reading. When the lake is full at 7.5 feet on the Rumsey Gauge there is 1,155,000 acre-feet of water in the lake. At zero on the Rumsey, there is 842,000 acre-feet. If the lake is full by May 1, Yolo County can take 150,000 acre-feet of water. An acre-foot equals 325,879 gallons of water.
The lake normally doesn’t start to fill until after January and the maximum amount of runoff into the lake is completed by March during most winters.
Whereas Yolo County is limited to the amount of water it can draw from Clear Lake, that’s not the case with Indian Valley Reservoir. Yolo County owns all the water in the reservoir and annually draws it down to little more than a puddle. In fact, during the drought years of 1975-76 the reservoir was drained below the outlet and a siphon hose was placed at the dam to draw even more water out.
Lake County residents have been angry with Yolo County’s rights to the water in Clear Lake for many years. But in truth Lake County never really owned the water in Clear Lake because the lake belongs to the State of California. Lake County gave up its rights to the water in Clear Lake in 1912, when the Yolo County Water and Power Company applied to the State of California for 300,000 miner’s inches of water from Cache Creek, which flows out of Clear Lake. Lake County never protested this action and Yolo County was given the water.
In actuality, residents of Yolo County have claimed the water from Clear Lake all the way back to 1873.
The big question is if the lake will fill this winter. Some experts say that we are headed into another drought and it could be worse than two years ago. Hopefully the rains this year will come and the lake will fill. This would make local residents and Yolo County happy.
