Whale Rock Reservoir is Full

Last Friday, Whale Rock Reservoir reached 100% capacity and water flowed over the spillway for the first time since in 18 years! Just a few short months ago, at the beginning of 2023, the reservoir was only at 72.1% capacity. Before last week's storm, it was at 93.5% capacity. That’s a lot of rain in such a short period!

You will see the water flow to your right from Highway 1 as you approach the first Cayucos exit heading north.

💧 Whale Rock Reservoir is one of #SLOCity's three primary sources of drinking water. In fact, the City shares this reservoir as Whale Rock water is delivered to the three agencies through 17.6 miles of 30-inch pipeline and two pumping stations. If full, the reservoir would supply the City’s water needs for approximately 3 years.

💧Before March 10, 2023, Whale Rock had only spilled 12 times since it’s completion in 1961, according to data from the city of San Luis Obispo, which operates the dam and spillway. The reservoir is located on Old Creek Road and serves Cayucos, San Luis Obispo, Cal Poly and CMC.

💧 Whale Rock last spilled in the 2004/2005 winter season. With the ensuing drought years, seeing water flow down the spillway has become a rare sight in Cayucos.

💧 Whale Rock has a relatively small watershed and is fed by creeks, not rivers, which means a much smaller volume of water entering the reservoir during heavy rain events than is seen at larger reservoirs across the state.

💧 Preventative measures and inspections are routinely performed to ensure safe operations. The spillway is inspected by Division of Safety of Dams (DSOD) and by a geologic/engineering consultant yearly.

💧The concrete spillway is maintained regularly by staff and is measured at 850 feet long. Its design capacity is 9,500 cubic feet/second. Maximum recorded flows over the spillway were 600 cubic feet/second, which speaks to the low-stress the spillway has experienced when compared to design parameters.