David Freyberg: If I could sort of focus people’s attention, I would focus attention on local dams, many of which are quite small, many of which are more or less invisible to the local community.
David Freyberg is a hydrological engineer at Stanford and expert on dams. He said – counting little dams in local communities – there are millions of dams in the U.S.
David Freyberg: Part of it is that we just have this aging systems of infrastructure out there and the decisions are the typical decisions that we make about power lines and pipe lines and sewers. Do we replace them? Do we remove them? Do we upgrade them?
Freyberg stressed considering dam removal on a case-by-case basis. He mentioned the Searsville Dam in California, where sediment has built up in the dam’s reservoir.
David Freyberg: The dam blocks the migration of fish, but the ecosystem that’s been created on the deposited sediment supports a very high density of nesting songbirds. So now we have this very interesting trade-off. If we remove the dam to facilitate passage of the fish, can we predict the consequences to the nesting songbirds?
He doesn’t know if both species can be protected.
David Freyberg: We have learned that there are no simple answers. These are very complicated systems. They don’t behave like natural systems so they are unusual systems.
Making decisions about smaller dams would probably have a bigger net impact than focusing on ‘problem’ or significant dams, said Freyberg.
David Freyberg: We’re getting close to the point of being able to have a better sense of prediction in terms of, if we fool around with the dam, what’s going to happen with the sediments, the vegetation, the water.
He said that right now, dam removal is as much a values question as a science question, because there’s no systematic way to analyze all the services a dam might provide, and also all their environmental costs.
David Freyberg: Because in the end we get into complex trade-offs between the value of agriculture, the value of recreation, for example, the value of diversity in our ecosystems, and these things are not easy to quantify in terms of dollars and cents.
He stressed that human intervention in the water environment is never impact-free.
David Freyberg: And the more we can understand those impacts, the better we can make decisions. As you peel off more layers, you just come to appreciate the complexity of our natural environment, and the value of trying to understand that environment to support these kind of decisions that have ramifications that go and on and on.