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Thinking Along New Channels

A central premise of most measures now taken to protect migrating Delta fish is being tested this fall during a series of experiments involving operation of the Delta Cross Channel. The results may reduce some of the conflict between protecting fish and Delta water quality.

The study, which is being funded by CALFED and conducted by an Interagency Ecological Program team, will focus on whether fish move with water or according to some other pattern. For example, they may move downstream at a constant rate, or only during certain times of day. The results could have important implications for operation of the channel, which allows Sacramento River water to pass into the interior Delta and improve the quality of exported water. Unfortunately, outmigrating juvenile salmon are also sucked into the interior Delta, where their prospects for survival are decidedly dim. For this reason, the channel gates are closed during migration periods. Closure for outmigrants between November and January last year led to serious water quality problems.

Hydraulic modeling studies have shown that water is forced into the channel primarily when the tidal stage in the Sacramento River is rising. The implication is that almost all of the water quality benefits associated with the channel could be achieved by opening the gates only when the tide is rising. However, how much that might benefit fish is still an unknown.

To help answer that question, on November 8th and 15th 160,000 juvenile smolt, marked for identification, will be released upstream of the channel - with the gates open -and then recovered by continuous midwater trawls over the following 48 hours. In addition, radio-tagging and sonar will be used to track fish movements. "We will know a lot more at the end of those two weeks than we do now," says EPA's Bruce Herbold. The study will also monitor the effect on water quality of operating the gates on a tidal cycle.

But it's the fish studies that may have the broadest implications. "A lot of the rules for Delta exports and flow are based on the assumption that fish move with the water," says Herbold. "If that's not the case then we've got a lot of work to do." Contact: Bruce Herbold (415)744-1992. CH

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