There is little question that we are in a drought. Sonoma and Marin Counties are now conserving water. Nearby Mendocino County is expected to have water problems. While Lake County isn”t in that dire condition yet, it could happen by the end of summer.
Clear Lake”s level is two feet below last year and by September the lake level could be reaching near zero on the Rumsey Gauge. How that will impact water users such as fishermen and lakeshore residents remains to be seen.
A little history on the lake”s level and water usage is in order. Unlike just about all other lakes where the lake level is measured by the altitude above sea level, Clear Lake is unique in that the lake level is measured by the Rumsey Gauge.
Many people don”t know how the Rumsey Gauge came into being. Prior to the building of the dam in 1914, outflow from Clear Lake into Cache Creek was controlled by a rock ledge called the “Grigsby Riffle.” The riffle is a rock ledge is located in a narrow canyon on Cache Creek about three miles from Clear Lake. Before the the dam was built, water would normally cease to flow over the riffle during the summer months.
In 1872 Capt. Rumsey decided to register the lake level but he needed to come up with a standard. He decided that when water ceased to flow over the riffle it would be called “Zero Rumsey.” Zero Rumsey is equal to a height of 1318.256 feet above sea level. When water was above the riffle it would be called a plus Rumsey, such as one foot, two feet and so on. Below the riffle, the lake level would be measured as a minus Rumsey. All measurements were based on zero Rumsey at the Grigsby Riffle.
However, he installed the actual gauge to mark the level of the lake in Lakeport. To this day, the lake level is still measured by the Rumsey Gauge. For example, today”s official reading of the lake level is 4.4 feet on the Rumsey Gauge. That means at the Grigsby Riffle the depth of the water is 4.4 feet.
Clear Lake is considered full when it reaches 7.56 feet on the Rumsey Gauge. The number was derived by averaging high water levels between 1873 and 1920. When the lake is full it holds approximately 1,155,000 acre-feet of water. An acre-foot of water is equal to approximately 326,000 gallons. When the lake level drops to Zero on the Rumsey Gauge the lake holds 842,000 acre-feet. That means between Zero and 7.56 feet there is 313,000 acre-feet of water in the lake. Yolo County”s allotment is 150,000 acre-feet of water when the lake is full. That adds up to about 3 1/2 feet of water on the Rumsey Gauge.
However, when the lake is somewhere between full and 3.22 feet on the Rumsey Gauge as of May 1, Yolo County”s water allotment is less. Yolo County gets no water if the lake level is below 3.22 feet on May 1.
In addition about 3.1 feet of water is lost due to evaporation. If it”s an usually hot summer the evaporation rate can be much higher. Yolo County can”t take it”s full allotment all at once. There is a monthly discharge rate that has been established. Plus, Yolo County can”t draw any water after Oct. 31.
In addition to Yolo County”s water allotment and the evaporation, lakeside residents have what are called riparian rights. Meaning that people who live along the lake”s shoreline have certain rights to the lake water for watering lawns, shrubs and other usage. As more people build on the lake their water usage will go up.
The lowest Clear Lake has ever been was back in 1977 when the lake level dropped to a minus 3.39 feet on the Rumsey. That year the lake level only reached a high of a minus .3 feet during the winter months. The total rainfall for that year was a meager 12.19 inches.
Whereas it”s doubtful that the Clear Lake will drop below zero on the Rumsey Gauge this year, it”s a sure bet that Indian Valley Reservoir will be drained nearly dry. This has occurred several times in the past.
In fact, the lake level is presently down about 45 feet. Yolo County owns all the water in Indian Valley Reservoir and uses it to supplement the water from Clear Lake.
Unlike Clear Lake where there are safeguards in place to keep the lake at a certain level, at Indian Valley Reservoir there are none. As long as Yolo County keeps a small pool at the dam they can take all the water they want.
This year, because of drier than normal year, it will take a lot of rainfall in the surrounding hills before there is a sufficient runoff to start filling Clear Lake. Many experts say that it will take at least six inches of rainfall before water starts to run into Clear Lake and it”s highly unlikely that will happen before December.
Drought and low lake levels all have an impact on fish and wildlife. It”s part of Mother Nature”s survival code and water plays a major part. The big fear is if we have two or three years in a row of continued drought, then we will really be in trouble.
