Thursday, July 24, 2014

Capay Diversion Dam is key to Yolo County’s water works

The Capay Diversion Dam across Cache Creek is a simple concrete structure, 474 feet long and 15 feet 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. Courtesy photo

March 4, 2011 |

Slightly more than 3 kilometers 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 feet long and 15 feet 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 5 feet and increases its ability to divert water. The dam belongs to the Yolo County Flood Control and Water Conservation District (

Capay Diversion Dam 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 the dam 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 the Capay Diversion Dam. 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 result of having higher flows in summer than in winter is that carp and other large fish from Clear Lake become stranded in big pools in the creek in the 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 the Capay Diversion Dam, conditions are much less favorable for native fishes. In pools immediately below the dam, native pikeminnow, suckers and dace are still common. But habitat becomes increasingly less suitable downstream. 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 in summer is the red shiner, a recent invader from the east. At times, 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. While the Capay Diversion Dam is a barrier to upstream movement of these fish, it is likely that red shiner will appear above the dam, given a boost by anglers releasing bait.  It will then become one more threat to the fascinating native fish community of Cache Creek.

Update by Bob Schneider: A few years ago, the district discovered that the Capay Diversion Dam was being actively undermined as flood flows poured over the dam.  It was alarming!  In a large flood event, a key part of the district water delivery infrastructure literally could fall over.

The district undertook a series of studies to determine the extent of the problem and how best to renovate the dam. Last fall, that project was completed. You can see the repair work on the district’s web site in a one-minute time-lapse video. Take a look.

The Capay Diversion Dam is an underappreciated structure in Yolo County. This small dam diverts water that supplies our farms, recharges our ground water and maintains riparian habitat. It is a gravity system that needs no pumping. In the long term, particularly in light of climate change, this will become even more important.

In Yolo County, farms are a very large part of our visual open space. A reliable water delivery system is vital to maintaining our farms and that open space.

The board and staff at the district did a great job on this project. We thank them.

— Tuleyome a regional conservation organization based in Woodland. Peter Moyle is a fisheries expert at UC Davis and Bob Schneider is the senior policy director for Tuleyome. This column appears monthly.


Discussion | 2 comments

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  • mike tapiaMay 03, 2011 - 4:18 pm

    i hope yolo co flood control maintains a fish ladder or some flow over the dam for native salmon to return,have you seen the picture of the king salmon caught in capay, its in the general store. salmon always return to the stream they were boren right? not to mention salmon seen spawning in flooded fields and ditches in flood years. it looks like maybe to much water might be deverted, what did the e. i. r. report say californias largest lake, cut off from the ocean was an accepteble outcome? yolo brags about habitat restoration, there are no salmon in cache creek?

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  • mike tapiaMay 04, 2011 - 3:41 pm

    Salmon in Cache Creek Peter B. Moyle and Shaun Ayers Chinook salmon, steelhead rainbow trout, and Pacific lampreys all historically spawned in Cache Creek. Early records indicate that steelhead may have entered Clear Lake and spawned in tributary streams. Small salmon runs were recorded in the creek in the 1940s by Leo Shapovalov but there are few records since then. In November, 2000, however, a crew of UC Davis scientists collecting fish for mercury analysis found evidence of salmon spawning in the creek. The following is a description of the event by Shaun Ayers. On 11/29/00 we were collecting fish for mercury work just downstream of Highway 505 on Cache Creek when we came across a small salmon, moldy and very near death, swimming around in a pool. It looked like it had finished its work so I collected it as "evidence". In the next riffle we came across two others. I got a good look at one of them, a bright female with a well worn caudal fin. Within a few yards of where we found these two there was a freshly dug depression in the gravel measuring approximately 2.5 feet in diameter and 6-8 inches in depth. It was located at the tail end of a fast run between 2 riffles, the perfect type of place to get good water infiltration through the gravel. . . . A few days later we also saw a large hooked-jaw male dead on the bottom of a pool just upstream of Hwy 113 near Woodland. After finding these fish I did some investigation into how they made it up there. As far as I can tell, the most likely way for a salmon to get into Cache Creek is by the following route: Up the Toe Drain to the I-80 bridge. Just north of the freeway/railroad bridge they must work their way west across the Yolo Bypass through a series of waterways and irrigation ditches. I'm pretty sure this route works, as a friend of mine saw salmon trapped below a check dam on Willow Slough last year. Near the mouth of Willow Slough they are probably then getting into the waterway that parallels the western levee of the Yolo Bypass. They would then swim north to the outlet of the Cache Creek Settling Basin. During most of this fall there has been 15-20 cfs of Cache Creek water exiting the Settling Basin and flowing down the above mentioned waterway. The outlet structure carrying water under the Settling Basin levee is badly clogged with debris but does not appear to be completely impassible. The only other obstacle to upstream migration that I know of is a temporary bridge put in by a gravel company downstream of road 94b. It requires a 1-2 foot jump up into a culvert to get through. During our fish collection efforts this fall I was amazed at the consistent flow, good water quality, and abundance of spawning gravel throughout the lower part of the stream. At least this year, conditions on Cache Creek seem much more conducive to successful salmon spawning than those on Putah Creek. It's a shame that it is so difficult for the fish to get up there.

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