ContentsPutah and Cache: Lower Cache Creek

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Irrigating with a Full Bladder

Peter B. Moyle

Slightly more than 3 km above Capay there is a dam across Cache Creek that is the heart of the water delivery system for Yolo County agriculture. Capay Diversion Dam is a simple concrete structure, 474 ft long and 15 ft high, built in 1914 and showing some wear and tear with age. In 1994 it was modernized with the addition of an inflatable dam, billed as the "longest single bladder dam in the world," on top of the old concrete. The inflatable dam, which can be raised or lowered in 30 minutes, raises the dam five feet and increases its ability to divert water. The dam belongs to the Yolo County Flood Control and Water Conservation District (www.ycfcwcd.org).

Capay Diversion Dam (CDD) takes water from Cache Creek and sends it throughout Yolo County by a network of 175 miles of canals, which start with the Winters Canal and the West Adams Canal at the dam. The canal system is capable of transporting fish long distances. Willow Canal, along the south boundary of Yolo County (near Davis), is part of the network and actually spills on occasion into Putah Creek. Thus, when inland silversides, introduced into Clear Lake in 1967, started their march through California, one of the first places they were found outside of Clear Lake, besides Cache Creek, was Putah Creek (in the early 1970s).

While Clear Lake is one of the oldest lakes in the world, it is also managed as a reservoir to deliver water to Yolo County. The "extra" water flows downstream in summer and is diverted at the Capay Dam. Thus, except during years of drought, Cache Creek above CDD had more flows in summer than it did historically. These summer flows were enhanced even further by the construction of Indian Valley dam and reservoir in 1976 on the North Fork of Cache Creek. The entire volume of this reservoir is available for use by the District after flowing down to CDD. The recreational rafting that is possible in Cache Creek Canyon in summer is mostly on water that is released from Indian Valley Dam. This water is both more plentiful and colder than the original creek water.

One by-product of having higher flows in summer than in winter is that carp from Clear Lake and other large fish from Clear Lake become stranded in big pools in the creek in winter. These fish become vulnerable as prey for bald eagles that winter now in the canyon. The eagles in turn attract birders and naturalists by the carload.

The reverse flow regime supports a fish fauna of the creek that is a curious mixture of native and alien species. One of the more abundant aliens is smallmouth bass, a favorite game fish, which tends to eliminate native fishes from streams where it is found. Somehow, the natives have managed an uneasy truce with this predator, so hardhead, pikeminnow, sucker, speckled dace, hitch, and other species are fairly common, as least for now.

Below CDD, conditions are much less favorable for native fishes. Not only do flows rapidly decrease downstream, but the channel becomes braided through miles of past and present gravel mining operations. In the shallow channels, the dominant fish is the red shiner, a recent invader from the East. It so abundant that it is likely suppressing populations of the remaining native fishes in the lower creek (hitch, pikeminnow, sucker, speckled dace) through competition and predation on larvae. The shiner was brought to Central California (under protest!) by bait dealers, who were authorized to do so by the California Fish and Game Commission. It is still a legal bait minnow. Unless given a boost by anglers releasing bait, the red shiner is probably unable to invade the rest of Cache Creek because CDD is a barrier to upstream movement of any fish.

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