Restoring the “Natural River Process”
Continuing the Legacy

Written by Tom Evans

Historical Review

The rich alluvial soil of California’s Central Valley, an ample water supply and state-of –the art farming methods have made possible a food source that is a marvel to the rest of the world.

The valley, made up of the Sacramento and San Joaquin River Basins, produces one-fourth of America’s food—an essential part of our national security as we move into a dangerous future.

The abundance and variety of our food crops play a large part in California’s ranking as the world’s fifth largest economy.

Closer to home, our agricultural economy provides thousands of farm jobs, sustain many businesses that cater to farming needs and provides tax revenues to help operate local governments.

The vital role of agriculture in sustaining our economy and culture has existed in the valley for more than 100 years. Before that time, however, there was an entirely different picture.

In the last half of the 19th century, and before, the Central Valley was a vast overflow area. Winter rains overwhelmed the river channels each year and spread over the valley floor. In the flood years, the valley was truly an “inland sea.”

The floodplain supported vast areas of jungle-like riparian forests, willow thickets, marsh, wet meadows, grasslands and oak savannahs. It was a paradise for wild creatures, an ecosystem rich in variety and abundance of animal and plant species.

But for people trying to establish farms, and for those trying to build new towns the floods were ruinous. There was frequent loss of life and widespread destruction of homes and other property.

In the last half of the 19th century valley residents determined that the cycle of loss must end. They looked for ways to protect lives and establish a viable economy.

As the 20th century dawned, they had devised a remarkable system to harness flood flows in the Sacramento River and to reclaim fertile overflow areas for agriculture.

For most people, the choice was simple: flood protection and land reclamation were the overriding issues.

Levees, By-passes and Weirs

They realized it was not practical to build levees high enough, or place them far apart enough- to contain maximum flood flows. Too much farmland would be lost. A series of escape valves had to be installed in the system. These were called “weirs.” They provide openings in the levee through which peak flows can move into broad, leveed drainages called “bypasses.”

The designers were aware of an obvious fact: to maintain the carrying capacity of the river, the weirs and bypasses, it was essential to keep them free of obstructions, such as vegetation and debris. Today, it is our responsibility to continue the legacy of our forefathers in the maintenance and operation of this major waterway.

There are five of these weirs: Moulton in Colusa County, about 12 miles north of Colusa; the Colusa Weir at river mile 146, just north of that city; Tisdale weir at river mile 119, south of Grimes in Sutter County; Freemont at river mile 82, at the end of Sutter Bypass and the beginning of the Yolo Bypass; and the Sacramento Weir at river mile 63, just north of that city.

The Moulton and Colusa Weirs allow escape of flood flows into Butte Slough, which empties into the Sutter Bypass. Water that flows from the river at Tisdale also enters this bypass.

The mile long Fremont Weir, near the junction of the Sacramento and Feather Rivers, allows water from the Sutter Bypass to move into the Yolo Bypass.

An additional escape valve for peak flows in the Sacramento River is provided at the Sacramento Weir and Bypass, upstream from the junction of the Sacramento and American Rivers, This structure also conveys water to the Yolo Bypass.

Two other features of the flood control system are essential to its operation. One is the Knights Landing Ridge Cut, allows floodwaters from the west side watershed to drain into the Yolo Bypass. The other is the settling basin for Cache Creek and its entry into Yolo Bypass north of I-5.

The weir and bypass system has served well for nearly a century. For most of that time the floodways have been kept clear of snags and there has been periodic dredging. These practices were used to maintain the carrying capacity of river channels, weirs and bypasses. These measures, combined with construction of major reservoirs, have contained most flood flows.

Habitat Restoration

In more recent time the picture has changed drastically. During the last 30 years there has been growing concern about the ability of some species of plant and animal life to survive. The rapid growth of human population is exerting greater demands on available space and resources.

Laws to protect threatened and endangered species have been adopted at state and federal levels. Too often these laws have been crafted by legislators, and supported by interests, who are far removed – in distance and understanding- from the areas they would transform.

Some of the laws are being applied in ways that undermine safety features of the flood control system. In an effort to restore “natural processes” to the river, three dangerous concepts are being applied:

One is to restore riparian, jungle-like forests within the floodways to provide habitat for endangered species. There already is strong evidence that this practice may have contributed to a major flood in the vicinity of Meridian in 1997. A U.S. National Wildlife Refuge was developed within the Sutter Bypass, creating a backflow of flood waters. This is believed to have contributed to a massive levee wash-out.

The natural process also requires that snags be left in the river to become part of the habitat for fish. In addition to creating boating hazards, the snags cause islands of silt to form. These islands sometime divert river flows against the banks, causing more rapid erosion and a threat of levee failure.

Bank erosion is encouraged so that trees may be undercut and fall into the river to create fishery habitat. The time-proven method of placing rock on eroding banks to prevent wash-out is almost impossible to achieve because of environmental restrictions.

The Endangered Species Act is being applied in ways that seem to be punitive. If rock-facing, or rip-rapping is allowed, new habitat must be created to mitigate the work. The amount of habitat may range from three times the levee surface affected to an unlimited amount.

A recently proposed biological opinion by the U.S. Fish and Wildlife Service stated that the amount of mitigation would increase each year until the new habitat was created.

One result of this policy is that the cost of levee repair has become so expensive it usually is not undertaken—unless there is immediate danger of levee collapse.

Restoring the so-called natural process to the river already is causing adverse effects, including sandbars and snags. These create boating hazards and reduce the carrying capacity during flood flows. This situation contributes to the clogging of fish screens and the deposition of silt, not only during flood events, but during the normal irrigation seasons as well.

The weirs are being clogged with a build-up of silt and debris that greatly reduce their function as safety valves in the flood control system. At the Tisdale Weir, for example, the depth of silt build-up at the weir opening is four feet. The depth of silt in the Tisdale Bypass beyond is three feet.

The barriers of silt and debris prevent diversion of flood waters, as intended, and places downstream areas in greater peril.

There appears to be a likelihood that the river will be made more dangerous because of new habitat restoration plans. Two major programs proposed for the floodways would further limit the ability of the Sacramento and San Joaquin Rivers to convey flood water.

One of these programs is the Sacramento River Conservation Area plan. It proposes a continuous belt of riparian forest in the floodway from near Redding in Shasta County to Verona in Sutter County, a distance of 222 river miles. Bank erosion, siltation and additional large woody debris would be encouraged to restore natural conditions. All of these actions would reduce flood water carrying capacity and increase flood hazards.

The other program is the Comprehensive Study conducted by the U.S. Army Corps of Engineers and the State Reclamation Board—two agencies which have as a primary purpose the prevention of floods.

The Comp Study envisions habitat restoration programs in the floodways for both the Sacramento and San Joaquin Rivers. But it goes much further:

Flood Control vs. Habitat...the “conflict”

The Comp Study Team is aware that congesting the floodways with vegetation would be an invitation to disaster. To avoid that result, the study calls for a massive program of levee setbacks. This would lessen the height of flood flows while providing room for habitat restoration.

The great drawback in this concept is that it would consume vast amounts of farmland. The results would include losses in farm production and farm employment. Businesses that cater to agriculture would be diminished. Tax rolls, in mostly rural counties, would suffer. In some counties, which depend heavily on agriculture, the economy would be severely impacted.

The Comp Study also envisions levee setbacks for the Yolo Bypass to accommodate habitat restoration within the bypass. One of the habitat areas is the 4,000-acre Fazio Wildlife Refuge. The other potential habitat area is the 12,800-acre Glide Ranch, sold recently to the Nature Conservancy.

We have seen, from the Meridian example, that clogging floodways with vegetation can have disastrous results. The potential for calamity is even greater in the Yolo Bypass because its shallow gradient will allow a quicker rise in water elevation upstream from vegetative obstructions. Further, the Cities of Sacramento, West Sacramento, Davis and Woodland could be placed at peril from this backflow. In fact, all areas upstream from the obstruction would be in greater danger from flooding. The flow of water would be retarded in Putah, Willow and Cache Creeks and in the Sacramento, American and Feather Rivers…and all of their tributaries.

The lessons of history often are overlooked or ignored. A case in point is the great effort, between 1913 and 1938, to remove a “choke point” below Rio Vista to allow the escape of floodwater to Suisun Bay.

Dredges made a cut across Horseshoe Bend from north of Rio Vista to Collinsville to expedite movement of the water. According to the book, “Battling The Inland Sea,” the cut removed more soil than was excavated to create the Panama Canal. Because of renewed siltation, the channel is becoming a choke point again.

The choice to impose new habitat programs on vital water supply and flood protection systems has not been made by the people who live in the counties affected. The choice has been made in legislative halls and government offices far removed from future impacts. Not enough consideration has been given to the results likely to occur from actions by lawmakers and government agencies. There is a single-minded rush to restore habitat and deal with the aftermath at some future date. But shouldn’t the choice be made at the county level—by those who will be most impacted? Should those who stand to lose so much from restoration schemes be allowed to decide if such risks should be taken?

Shouldn't habitat restoration efforts be focused on public lands—which are already off the tax rolls—and in areas outside critical floodways? If you have an opinion, tell your supervisors and legislators. At least, you can make that choice.

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