November 19, 1993
The only thing that stops God from sending another flood is that the first one was useless.
Nicholas Chamfort(1741-1794)
The recent Mississippi floods have called into question the efficacy of great dams and levees. Why, despite all of the efforts in the past, did the Mississippi still devastate such a large area? Some people have even suggested that it would have been better if nothing had been done --no dams, no levees, no nothing.
I grew up during the peak of the government's dam building spree. We were told of the great benefits that each dam would have:
A dam would help in flood control, since water could be stored in the reservoir and released slowly.
A dam would produce electricity all year long, from the regular release of water through hydroelectric generators.
A dam would store water for use in households and for agriculture. Droughts would no longer be a disaster.
A dam would provide a lake for all sorts of recreation including fishing, water sports and boating.
In those days, preserving scenic rivers wasn't as much of a concern as was the need for cheap electricity to, among other things, make aluminum. Nor were scenic rivers as important as flood control and water for agriculture.
These things that dams are supposed to do, they can do. What we were not told was that, while a dam could do all of those things, it could not do them all at the same time.
For a dam to control flooding, the reservoir has to be as close to empty as possible before the rains or the snow melt. If it was empty and the water didn't come, it would be of no use for recreation, electricity production or irrigation. Conversely, if it was to be useful for electricity, irrigation or recreation, it would be of little value for flood control.
As a consequence, the people who manage water flow out of a reservoir make compromises which work most of the time. Obviously they didn't work in the Mississippi basin this summer.
California is fortunate in that much of the water stored behind our dams comes from snow melt in the Sierras. The snow can be measured toward the end of winter and predictions can be made as to the amount of run off. This allows the managers to empty the dam by just the right amount to receive the melt water. A sudden early heat spell can invalidate those predictions, but not to the extent of what happened in the Mississippi area.
California has a different set of conflicts. The main problem here is drought, not flooding. This conflicts with the production of electricity. In a time of drought, it is prudent to release just enough water to keep trout alive and to make nowhere near as much electricity as Pacific Gas and Elecric would like. This boosts people's electricity bills. Another problem is that water companies charge by the amount of water used. In a drought, not only can't they meet the demand for water, but they have less money coming in to meet expenses.
An additional problem during times of drought is the release of enough water to support the salmon and steelhead fisheries. Dams impede fish migration, despite all of the efforts to construct fish ladders to allow the fish to migrate past them.
Another conflict during drought years is balancing the needs of agriculture and cities against the need for water to maintain fish populations and to support fish migrations.
In short, every compromise that is made is bound to displease one group or another. What is the solution to all of these problems? DAMned if I know.