Damned If You Dam, Damned If You Don’t

[question everything]

From Scientific American as reported on the WSJ:

Damned If You Dam, Damned If You Don’t

Environmental concerns have led the U.S. to pull down an increasing number of aging dams in the last decade, returning water to dry streams, birds to wetlands, and migratory fish to rivers. But environmentalists are also learning a torn-down dam can leave a host of challenges, writes Jane C. Marks, an ecologist at Northern Arizona University in Scientific American (no link available).

Sediment that has accumulated behind the dam can muddy the waters of a river, choking insects and algae that fish need to survive. Seeds buried in the sediment might unleash alien crops that kill local species and contaminated sediment might make fish poisonous. As a result, elaborate pipelines are sometimes required to get the finer sediment downstream to help stop erosion, while leaving coarse sediment upstream. Exotic fish can also suddenly become a problem.

A dam in Arizona had been blocking exotic fish such as bass and sunfish from getting into a creek. Biologists were concerned that, without the dam, local fish in the creek would be wiped out as the exotic fish arrived. So they temporarily removed the local fish, keeping them elsewhere, and poisoned the exotic fish in the creek. Once the exotic fish were dead, they returned the local fish to their former habitat.

Without dams to calm them, some rivers are once more prone to flooding. In France, local authorities have had to make up for decommissioning four dams in the Loire Valley with an elaborate weather-monitoring system to give four hours’ warning of a flood. Dams can cause dilemmas beyond the environment. Ms. Marks mentions how a father and son bitterly disagreed over the Loire dams’ removal. The father wanted the salmon and wild waters of his youth to return, whereas the son wanted to preserve the swims and boating trips of his youth.

[Porcupine]

1. Beaver dams were never an obstacle to fish...

and significantly slowed the amount of water entering major rivers from side streams during times of heavy runoff. The rivers ecosystems all evolved with beaver in them and we have killed most of the beaver.

Let the beaver regulate the water.