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Bypass Benefits
When winter rains swell the Sacramento River enough that it spills into the Yolo Bypass, the fish brought in with the overflows discover a new habitat--only to be stranded in the seasonal or perennial ponds left behind when the flows cease. The numbers of fish have been great enough to lure biologist Warren Shaul into monitoring their presence in the bypass on his own time for over four years, and to prompt the Department of Water Resources to propose a new study.
"You can look at the bypass in two ways," says Shaul, "as a golden resource for fish or a deathtrap." In d rier years, the Sacramento River can handle its flow without flooding. In wet years, however, the river overflows into two bypasses -- floodplain channels 2-3 miles wide and largely composed of agricultural fields that parallel the river. In wet years, the flow through the 60,000-acre Yolo Bypass near Knights Landing frequently exceeds that in the river, and so can the fish. "We pulled a net across a cornfield and got 40 juvenile Chinook--a huge density. In the river, we're sometimes lucky if we net any," says Shaul of Jones & Stokes. Fish like the native splittail minow (proposed for listing as threatened) and the endangered winter-run Chinook salmon can thrive in warm, food-rich shallows of the flooded bypass.
When the river drops below flood level, intake weirs abruptly stop flows into the bypass, disconnecting many ponds and agricultural ditches from flows left in the bypass' main drainage channel. Shaul thinks the weirs could be modified, possibly using radial gates, to allow more frequent spillovers at lower flows (more like a natural system). Shaul has found that even very small channels a few inches deep can help fish travel from the ponds to the main flow, and that creating more such small tributary channels would allow more fish to escape.
"Any changes to benefit fisheries must be compatible with flood management and not adversely affect marshlands and wildlife habitat," says Ted Sommer of the Department of Water Resources, pointing out that the Yolo Bypass is part the largest wetland restoration project west of the Mississippi. Such potential debates may be better informed if a proposed Water Resources study gets approved by the Interagency Ecological Program. The study would count fish, compare bypass habitat to the river, explore reasons why fish come and go, inventory the salmon races using the bypass, and closely examine where ponds and drainage networks are located and how they change with different phases of the flow.
Contact: Ted Sommer (916)227-7537 & Warren Shaul (916)737-3000
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