Dam spillover not anticipated through week in San Mateo County

Significant rainfall from this series of storms is raising the levels of the Crystal Springs Reservoir and there remains a 25% risk of reservoir spill later in January. If a spill occurs, rainfall flowing into the reservoir would flow out in addition to rainfall downstream resulting in high levels in San Mateo Creek. 

Emergency alerts to cellphones in the impacted area would be issued if evacuations are necessary in a worst-case scenario. SFPUC owns and operates the Crystal Springs Reservoir system on the Peninsula, which includes Lower Crystal Springs Dam on San Mateo Creek. When conditions allow, the SFPUC will conduct controlled releases of water out of Lower Crystal Springs Dam into San Mateo Creek to create space for expected rain inflow. The releases are planned with consideration of current rain and high tides to minimize impacts to San Mateo Creek. The goal is to reduce the potential for spillover during periods of extreme storms.

Rick Canepa, meteorologist for the National Weather Service said since Sunday, the atmospheric river that passed through the county this week brought 2 1/2 inches of rain in the area.

More rain is on the way, he said, starting with an unsettled weather pattern that will likely reach the county late Thursday night or early Friday morning with light rain. There will be continuous rain into Saturday, which could be heavy and could bring gusty winds. Throughout the rest of the week, temperatures should be moderate with lows in the 50s and highs in the low 60s. By Monday night, there will be a dry break with no rain through Tuesday, Jan. 17.

San Mateo Creek is fed from the Crystal Springs Dam off the Lower Crystal Springs Reservoir north of State Route 92. It runs through the watershed land, then turns into Hillsborough until it hits Arroyo Court in San Mateo. It heads underground at El Camino Real, then daylights briefly east of North B Street where it goes back underground at the Caltrain line to Claremont Street where it runs through a couple of tunnels then heads east through Gateway Park at Third Avenue and again goes underground at Highway 101. It resurfaces at Norfolk Street and meets the Bay at Ryder Park. 

The county urged people living along the creek to visit sandbag stations and report any downed trees on public property. The county said it will issue emergency alerts and offer shelter services should evacuations become necessary. The city of San Mateo and town of Hillsborough manage public sections of the creek, like clearing debris and vegetation from within the creek. However, the cities do not control the amount of water that enters the creek from either the reservoir or natural rainfall. City crews have been removing fallen trees and debris from the waterways during this storm and are continuing to clear areas to minimize blockages.

The reservoir is on the fuller side as the officials closed pipelines from the Hetch Hetchy Reservoir in Yosemite for maintenance, leaving the county to consume what water is currently stored in the Crystal Springs and San Andreas reservoirs. The Hetch Hetchy pipeline, which provides water to more than 2.8 million Bay Area residents, will be shut down until March 8 to allow for annual maintenance improvements. The project is a part of the San Francisco Public Utilities Commission’s and BAWSCA’s $140 million project to repair, upgrade and rehabilitate a 19-mile stretch of the mountain tunnel, the Moccasin Powerhouse and Reservoir and the San Joaquin Pipeline that is in need of repairs.

San Mateo residents can visit www.cityofsanmateo.org/floodprep for information on sandbags and storm safety. People can visit sfpuc.org/PeninsulaReservoirWetWeather for more information about the dam.