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For years many local residents didn’t understand what the Rumsey Gauge was, but with the ongoing drought, the Rumsey Gauge is on just about everyone’s lips. The history of the Rumsey Gauge goes back more than a 100 years and it is unique to Clear Lake.

Most lakes are measured by the their elevation. For example, when Indian Valley Reservoir is full the surface of the lake is 1,502 feet above sea level. Clear Lake is unique in that its elevation is measured at 1,318.26 feet, which is zero on the Rumsey Gauge. The lake level is based on that figure, which can be confusing because the lake is considered full when it’s at 7.56 feet Rumsey, or 1,325.82 feet above sea level.

While nearly all lakes are measured by their altitude above sea level, Clear Lake is measured by the Rumsey Gauge. Even today 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 located in a narrow canyon on Cache Creek about three miles from Clear Lake. Before the dam was built, water would normally cease to flow over the riffle during the summer months.

In 1872, Captain 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.” 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.

However, he installed the actual gauge in Lakeport and it’s used as a reference to the actual depth at the riffle, not the depth at Lakeport. To this day, the lake level is still measured by the Rumsey Gauge. For example, today’s (Thursday) official reading of the lake level is a minus-2.2 feet on the Rumsey Gauge. That means the depth of the water is less than zero feet at the Grigsby Riffle.

As for the individual who started the Rumsey Gauge, Capt. Dewitt C. Rumsey was from Yolo County. In 1852 he was the trail boss on cattle drives in the West. From what I have researched that’s where he received the title of “Captain.” In those days it was common to call the trail boss Captain. Rumsey was an important part of the history of Lake County. In fact, the town of Rumsey, located on Highway 16 in Yolo County, was founded by him. He also bought property in Lakeport. Rumsey Bay on Clear Lake is named after him. The actual location of the Rumsey Gauge today is Library Park in Lakeport.

Up until a few years ago the gauge was physically read each day by county personnel. Nowadays the U.S. Geological Survey Agency reads the gauge by remote telemetry.

Clear Lake is considered full when it reaches 7.56 feet on the Rumsey Gauge (that 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 are 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 because of evaporation. If it’s an usually hot summer the evaporation rate can be much higher. Yolo County can’t take its full allotment all at once. There is a monthly discharge rate that has been established. Yolo County also can’t draw any water after Oct. 31.

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