BAY-DELTA CONVEYANCE CONCEPTS
Bay Delta Conservation Plan stakeholders have promoted a number of conceptual options for getting water around, through, or under the Delta to the state and federal pumps at Old River and Clifton Court Forebay northwest of Tracy.
Before deciding on the current subterranean “Twin Tunnel” configuration, these included a “through-Delta alternative”, an east-side canal (40 miles long), an “all-tunnel” alignment from near Hood to Clifton Court Forebay, and a west-side canal and tunnel option. All these options (including the Twin Tunnels) include multiple intake facilities outfitted with screens to reduce impacts to fish.
But these screens are little more than a “multi-headed Hydra,” as one fisheries biologist at Delta Flow Criteria Proceeding discussions put it. Why? Their functionality at such a large scale remains to be demonstrated. Indeed, they constitute a kind of red herring for salmon, a spurious “solution” to fish mortality that can be used to ram through destructive conveyance projects. Simply put, they are not a solution. They are a distraction.
Comparing Canal and Tunnel concept cross-sections, 1968 and 2009 (click either image to enlarge).
To get a sense of the scale of these canal concepts, we present cross-sections from a 1968 proposal and a more recent BDCP version. In 1968, the canal’s bottom width was 180 feet wide and its levee-to-levee width was about 440 feet. It would have had a maximum water depth of about 13.4 feet.
BDCP released a hypothetical cross-section of 340 feet at bottom with a levee-to-levee width of 540 feet. This canal would have a water depth of about 23.5 feet. This cross-section is about 54 percent larger than the canal cross-section considered in 1968.
And as shown in the BDCP image at right, the BDCP conveyance canal is much larger than the already sizable California Aqueduct.
As noted, state officials ultimately chose an underground Twin Tunnel conveyance project. (A triple-bore design was also considered.) The image at right shows conceptual cross sections for the original two–bore version.