Tisdale Weir

Flood Safety Compromised

by Tom Ellis

A study of flood events at Tisdale Weir and Bypass, south of Grimes, on the Sacramento River, was prompted recently by plans of Sutter Mutual Water Company to construct a large fish screen for their pumping plant at the south end of the weir. Tisdale Weir and Bypass are crucial to the security of the Colusa and Sutter Basins, as it provides relief of major flood flows in the main stem of the Sacramento River eastward into the Sutter Bypass.

Design flow capacity of the 4.6 mile long Tisdale Bypass is 38,000 cubic feet per second (cfs), and the design flow capacity of the Sacramento River below the Bypass is 30,000 cfs. The date chosen for the study of the flood event of January 4, 1997, when data on the division of flood flows between the main stem of the River below the Weir and the Tisdale Bypass showed a disturbing variance from design parameters. At peak flow on that date, flow in the River just downstream from the Weir was measured at 31,600 cfs, exceeding design capacity by 1,600 cfs. Meanwhile, at the same time, flow in the Tisdale Bypass was 20,000 cfs, well below the design capacity of 38,000 cfs. It is restricted by sediment accumulation and vegetative growth.

Checking history of sediment removal in Tisdale Bypass shows that during a four-year period (1984-1987), the Department of Water Resources removed 1,893,000 cubic yards of silt from within the Bypass channel. No major sediment removal has been done during the past 15 years. It has been calculated that there is currently over one million cubic yards of sediment in the Bypass east of Reclamation Road, presenting a very serious restriction to flood flows.

A letter concerning channel restoration in the Tisdale Bypass was written to the State Reclamation Board on March 17, 2003. Lead signatory on the letter was the Central Valley Flood Control Association. Eleven Sutter and Colusa Basin water supply and drainage districts also signed the letter. In response, the Reclamation Board agreed to meet with representatives of the involved districts to view the situation on June 27, 2003. At that time, the threat to public safety and the potential liability for substantial damages from backwater effects of restricted flood flows was pointed out to officials. It was suggested that the State needs to address this issue despite budgetary constraints.

In reply to these stated concerns, officials commented the current budget provides no funding to address this situation and they have little input into the budget process. They suggested we contact our local elected representatives and encourage them to act on our behalf to see that sediment and vegetative growth are removed.

From this meeting, I concluded that the Reclamation Board is either unwilling or unable to truly address this problem and there certainly is no sense of urgency. It is imperative that pressure be brought to bear if we are to be successful in getting the Tisdale Bypass cleaned. Therefore, I encourage all of you to contact your state legislators and your County Boards of Supervisors to enlist their help in this effort. Also, contact your local water and drainage district officials to encourage them to see that this effort is accomplished. If you need information on who to contact, call Family Water Alliance. For picture of Tisdale Weir debris click here.  Also see "A River Runs Through It".#