Cull Canyon and Don Castro Reservoirs and Dams

Zone 2

Cull Canyon and Don Castro reservoirs were built and are maintained by the District for flood control purposes. Both the Cull Canyon Regional Recreation Area and Don Castro Regional Recreation Area are also popular East Bay swimming spots operated by the East Bay Regional Park District.

A major issue for both Cull Canyon and Don Castro reservoirs is siltation. Eroded silt—earth and debris—from upstream creeks continually fills in the reservoirs, which reduces the reservoirs’ capacity to hold stormwater. The siltation also jeopardizes water quality and impedes recreation. Originally, Cull Canyon Reservoir was 30 feet deep. Despite regular dredging, the reservoir is now only about 6 feet deep at the lowest point!

Silt removal is extremely expensive and prompts environmental problems due to the vast quantities of silt extracted. Limited disposal areas near the reservoirs and high transportation costs to a final disposal site are also challenges.

Additionally, Cull Canyon Reservoir was the subject of a seismic stability study, completed in 2006, that concluded the dam might be seismically unstable.

Until a permanent solution is found, the water level behind the Cull Canyon Dam has been lowered for public safety in accordance with the California Department of Water Resources’ Division of Safety of Dams interim requirements.

The District is currently exploring long- and short-term alternatives to deal with both the siltation and seismic problems for these reservoirs. There is no easy fix. The District has proposed projects to upgrade Cull Canyon Reservoir and Don Castro Reservoir. These projects have been incorporated into the Bay Area Integrated Regional Water Management Plan. The District is still seeking funding for these upgrades.

Ultimately, the solution will depend on public input, available funding, and engineering solutions.

The good news is that the swimming areas at both the regional recreation areas will remain unaffected.