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Stories from the valley

Opening the Weirs

Contributed by Roberta Firoved

The weirs were opened for the first time in eleven years – an event that involved considerable media coverage and public interest. This has garnered West Sacramento some of the most attention since the humpback whales, Delta and Dawn, occupied the Port ship turning basin in 2007.

What does it mean to open the weirs? I never knew they existed until moving to West Sacramento in 1994.  Growing up on the Central Coast, we valued every drop of rain and never knew of structures for flood control. The weirs lower the water level in the Sacramento River to flood the Yolo Bypass bordering West Sacramento. The released water maintains levels in the river to mitigate against flooding Sacramento.

The Sacramento Valley would commonly flood after severe winter storms or when warm spring weather melted the Sierra snowpack at a rate the rivers could not contain. These flood events have been documented every 100 to 200 years. The most significant was the flood of 1981-82 with 43 days of rainfall after two decades of drought. The Sierra snowpack was at 10 to 15 feet followed by the warm atmospheric rivers storms – a scenario similar to the current events that lead to opening the Sacramento weir.

Planning began to control devastation from another flood of the magnitude experiences in 1861-62. Some thought that the City of Sacramento would never recover from that flood.

Opening the Weirs
Opening the Weirs

Today, approximately half a dozen weirs exist for flood control in the Sacramento Valley. The oldest is the Sacramento Weir and Bypass, completed in 1916. The 1,920-foot long structure consists of 48 gates that divert Sacramento and American River floodwaters to the west down the mile-long Sacramento Bypass to the Yolo Bypass. The river depth determines the number of gates to open the manage the river depth. Opening and closing the weirs is a manual process taking minutes to open and over an hour to close.

The Department of Water Resources operates the weir through regulations from the U.S. Army Corps of Engineers. Considerable management and communication occur to manage flood control through the weir system.

I rest much easier knowing that a system of flood management exists in the Sacramento Valley. The weirs cannot prevent a flood from every happening again. However, the likelihood is much less by maintaining the river at a manageable depth.