LAKE COUNTY — With the recent rains, Clear Lake has risen above its full level of 7.56 feet Rumsey.
The National Weather Service forecasted 4.1 inches of rain will fall between 4 a.m. today and 4 a.m. Thursday.
Utilizing these forecasts, the California-Nevada River Forecast Center in Sacramento has forecast that Clear Lake will rise to 8.5 feet Rumsey by Wednesday.
The Cache Creek Dam is currently releasing approximately 2,700 cubic feet per second (cfs), the maximum amount when Clear Lake is at this level. In perspective, 2,700 cfs will fill a typical in-ground, backyard swimming pool in one second, according to a press release provided by County of Lake, Water Resources Department.
Clear Lake”s natural outlet, Cache Creek, is too small to allow water to leave the lake as fast as it enters. The limited flow in Cache Creek causes Clear Lake to rise rapidly during heavy, prolonged rainstorms and does not lower lake levels very fast after the rains have stopped. Contrary to popular belief, the Cache Creek Dam does not cause Clear Lake to flood. The Cache Creek Dam is designed to release water at 21,000 cfs, however, Cache Creek can deliver less than 4,700 cfs when Clear Lake is at 11 feet Rumsey. These flows show that the dam can release almost 4 1/2 times as much water as can reach it during severe flood events on Clear Lake.
It is the narrow, shallow Cache Creek channel that slows the release of water from Clear Lake during a flood. Approximately 1 1/2 miles from Clear Lake, a rock ledge called the Grigsby Riffle crosses Cache Creek. The riffle is at a narrow point in the creek and limits the amount of water that may flow past it. The riffle controls outflow from Clear Lake. The riffle maintained lake levels prior to the construction of the dam in 1914.
Lake County Water Resources Department staff have been in communication with staff at the Yolo County Flood Control and Water Conservation District, the owner and operator of the Cache Creek Dam, regarding the lake level and operation of the dam.
In anticipation of rain, Yolo Flood began releasing water from the dam on Feb. 28, gradually increasing flow as the lake neared the full level. Since these releases began, nearly 1 foot of water has been released from Clear Lake.
