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A MODEL FOR RIVER RESTORATION AND FLOOD MANAGEMENT

California's most recent floods only serve to reconfirm the lessons of the 1993 Midwest floods. The essence of a "flood management" approach is to change the objective from serial engineering and the desire to completely control floods to a more appropriate path: reducing hood hazards to life and property. Darns and levees are still very important, but they are not the only tools for achieving the goal of improving flood protection and restoring rivers.

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The floodplain of the Consumes River, January 1997

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An example of this approach can be found on the last undammed river flowing out of the Sierra Nevada: the Cosumnes. Hydrologist and former Friends of the River conservation director Betty Andrews and Dr. Philip Williams have devised a strategy for saving money, improving flood protection, and enhancing the natural resource values of this Central Valley stream. Their proposal shows that some

forms of flood management could even improve a unique river ecosystem and its floodplain.

Existing Problems

Except for recent regulations and mitigation requirements,

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most flood control activities along the Cosumnes River paid little or no attention to the natural environment. In an informal manner, agricultural levees were built along the river over the past 60 to 70 years. Unfortunately, those levees effectively cut off the river from its floodplain, eliminating multiple braids of the river and forcing it to remain within a single narrow channel.

By concentrating the river within an artificially narrow corridor,  the Cosumnes' levees actually increased the river's erosive forces, causing the channel bed to drop by up to 10 feet during the past 40 years. This deeper river channel helped create near-vertical stream banks, some towering 25 feet high, devoid of vegetation and

Except for some isolated areas, much of the Consumes River has been squeezed by agricultural levees

and undermining the single line of trees left at the top of the bank. The deeper channel has also meant a river devoid of its large gravel bars, which were once important spawning areas for salmon and steelhead. More importantly, the deeper channel also thhreatens to undermine adjacen levees.

The history of flood control on the Cosumnes River may have ultimately proved more damaging than it was protective. When the 1997 floods hit and the Cosumnes River recorded its largest flows ever, the 24 levee breaks along a fairly short stretch of river forced the evacuation of thousands of people.

Choosing the right path

Now, as Cosumnes River floodplain residents and area officials grapple with possible solutions, they can either embrace tradition or pursue a more effective strategy of reducing flood damages. By taking the standard path of levee replacement (which might seem inexpensive in the short run compared to other options) they will have to bear in mind the long-term expenses of channel maintenance. Continuing with the restrictive levee system will only continue to force the river to take deeper, more damaging bites out of its banks and channel. That, in turn, will require constant levee upkeep and maintenance.

The increasing costs of river bed and channel upkeep will only growwith time if traditional flood techniques are used. Not only could rip-rap and other typical channel stabilizing methods increase river velocities and further undermine streambanks, but such flows also could force costly upgrades to the bridge crossings that would be damaged by continuing to force river flows into the artificially narrow channel.

Finally, the loss of habitat, spawning gravels, and further degradation to what is one of the largest remaining stands of riparian oak woodland in California's Central Valley is in itself a cost. What is the price tag for damage to this important ecosystem should one decide to continue applying traditional flood control measures?

On the other hand, if the Cosumnes River could have additional floodplain storage areas it could significantly reduce downstream peak flows and flood hazards, while at the same time providing valuable ecosystem functions.

Setting back levees could reduce the incisive forces that are eating away at the river channel. Spreading those hood flows out across a wider area could reduce or reverse the damaging channel and bank problems, helping protect existing spawning gravels and riparian resources.

In addition, flood management alternatives that create a more resilient levee system away from the banks of the river will be less expensive to maintain in the long run and reduce the damaging flows that create so many erosion problems in the first place.

Of course, floodproofing homes and other structures so that they are elevated above the reach of destructive flood waters can also add to this flood protection mix. Relocating flood-prone houses and other structures would reduce the problems of flooding, and the need for environmentally damaging solutions.

Finally, broadening the floodplain along a river like the Cosumnes-rather than constricting it with levees could increase groundwater infiltration which, for a region like south Sacramento County, becomes increasingly important with each passing year.

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