By Kevin Wilcox
A new joint intake and fish screen on the Sacramento River will provide water supply reliability and listed fishery species protection.
The joint intake on the Sacramento River will be about 46 ft. tall from river bottom and approximately 200 ft. long at the river face. The fish screens are a prominent feature. © MWH Global
July 29, 2014—Construction is under way on a new $44-million intake facility on the Sacramento River that will provide water to irrigate approximately 15,000 acres of crops and serve the residents of cities of Davis and Woodland, as well as the campus of the University of California, Davis. The intake features a complex fish screen system specially designed to protect the endangered Chinook Salmon, Steelhead Trout, and North American Green Sturgeon that migrate past the site.
The project is a joint effort of Reclamation District (RD) 2035, which provides irrigation for some of the rich agricultural lands of the Sacramento Valley, and the Woodland-Davis Clean Water Agency (WDCWA), which is a joint agency for the cities of Woodland and Davis that currently relies primarily on groundwater sources of diminishing quality. The existing intake of RD 2035 is the largest unscreened intake on the Sacramento River in California, and was identified by both state and federal agencies as a priority for facility improvement.
The two agencies awarded the engineering design of the project to MWH Global, headquartered in Broomfield, Colorado. MWH is also providing construction management for the project. MWH has been involved in the project since 2000, when RD 2035 first commissioned a feasibility study to look into installing fish screens on their existing intake.
The feasibility study for incorporating fish screens into the existing intake concluded that it would be prohibitively expensive and the permitting process would be complex and time consuming, according to Janet Atkinson, P.E., M.ASCE, a vice president of MWH who is the principal manager on the project. The existing intake is a century-old octagonal concrete structure, constructed in 1919, and is at the end of its useful life. Subsequently, the WDCWA began investigating the feasibility of constructing a water intake on the Sacramento River to replace its groundwater sources.
Construction is near the existing intake, an octagonal concrete structure constructed in 1919 that is at the end of its useful life. © MWH Global
"During the last decade, the water supply challenges of these two cities due to the water quality issues in their groundwater basin (their primary source of water) became evident. They looked at citing an adjacent, but separate, intake on the Sacramento River. After extensive coordination between these two agencies and in-depth engineering and environmental considerations, these two agencies agreed to have a joint intake on the Sacramento River to fulfill mutual interests and provide greater environmental benefits."
"Protection of fisheries is a huge element—and really the driving force behind this project," Atkinson says. "Over the years here in California there has been a lot of need and discussion on the protection of fisheries."
The new intake will be a reinforced-concrete structure, approximately 46 ft tall from the river bottom. The structure will span approximately 200 ft long at the river face. The structure will be founded on approximately 360 structural steel piles averaging about 50 ft in depth.
"When construction is completed, we'll have installed about 18,000 linear feet of piles," Atkinson says. "I think there are a lot of things interesting to engineers about river construction because that's probably one of the most challenging aspects of this project. In order to construct the project within the river the contractor is in the midst of constructing a temporary steel sheet piling cofferdam."
The fish screening system is also a formidable engineering challenge. Once complete, the system must meet exacting regulatory specifications that stipulate a maximum approach velocity of water to the screens of 0.33 ft per second.
"We have engineered the locations of the screens, and the size of the screens to meet those criteria. For this project there are 10 individual screen panels. They are each about 10 feet high by about 14 feet wide. The screens are high quality stainless steel. Behind the screens, inside the intake, there is a system of adjustable flow control baffles. Those baffle plates are vertically and horizontally adjustable. They are designed to allow the flow to be regulated to achieve a uniform flow through the screens," Atkinson says.
The screens, with slot widths of just 1.75 mm, are protected from river debris by a log boom system. Spaces between the screens are specially designed fish refugia, to give small fish a place to rapidly hide from larger, predatory fish that may gather at the screens.
Large brushes traveling at about 2 ft per second will continuously clean the screens. Inside the intake, a system of high pressure pumps and nozzles will blast away sediment, preventing it from building up in the intake wet well. The intake will house five large vertical mixed flow pumps for RD 2035 and four smaller, vertical turbine pumps for the WDCWA.
"What's interesting about this is because of the water delivery to two different agencies, it's operating under two sets of hydraulic operating conditions," Atkinson notes. The water for RD 2035 will be pumped a short distance into an open irrigation canal system, while water for the WDCWA will be pumped into a new pipeline and travel approximately four miles to the Woodland-Davis Regional Water Treatment Facility, also currently under construction.
Atkinson explained that MWH used computational fluid dynamics (CFD) modeling to test and refine the pumping station design and screen system. An earlier configuration with RD 2035 pumps on one side of the intake and WDCWA pumps on the other was discarded when CFD analysis revealed it would make it difficult to achieve the uniform approach rates required by regulatory agencies across the entire screen surface. Instead, the pumps will be arranged in a symmetrical pattern.
The RD 2035 and WDCWA are planning to commission the new intake in April 2016. Following that, they will begin demolition of the existing intake, which involves removing the structure and foundations and removing the conduit through the levee. All construction is expected to be complete by the fall of 2016.