
We’ve discussed dam removal many times in the magazine and online. In some cases it’s a good idea—because the dam has outlived its usefulness, because it’s old and poses a safety hazard, or perhaps because it wasn’t well planned to begin with. Many dams were constructed without regard to the environmental consequences, such as impeding fish passage. But removal can also have consequences, as this Erosion Control article points out in detail; a freed river that tries to reoccupy its former channel could be disastrous.
That’s why this article in the Nature Conservancy Magazine is a welcome perspective on the issue. It also generally supports the removal of old and no-longer-useful dams, but it offers a particularly useful step-by-step guide to the necessary planning and follow-up. Planners must especially consider how the river’s new flow might erode existing structures and whether accumulated sediment behind the dam should be removed before the dam is.
New England has a particularly dense network of dams; Connecticut alone, even after many have been removed in the last few decades, has more than 4,000 remaining. In the Connecticut River watershed, there are an estimated 2,700 dams, and the river and its tributaries have, on average, one dam for every 10 miles of waterway. Removing them all is neither desirable nor possible—“You don’t want to spend your time unwisely” one Conservancy program director notes—so prioritization is critical. The Nature Conservancy, in partnership with other organizations, has created a database to do just that, based on factors such as habitat that will be restored and downstream obstructions that must be considered, to help jurisdictions decide which removal efforts will provide the greatest benefit.
Sometimes building a fish bypass is a less-disruptive alternative to dam removal, or can be used in conjunction with strategic removals. On Maine’s Penobscot River, a combination of removing two hydropower dams and building a fish bypass has opened up a long stretch of the river and fish populations have increased; before the work was done, the article notes, fish had been bred in captivity and trucked upstream.
An article in our January/February 2017 issue, “Helping the Fish to Cross the Road,” looks at the related issue of removing and resizing culverts in the Pacific Northwest to restore salmon habitat.
Janice Kaspersen
Janice Kaspersen is the former editor of Erosion Control and Stormwater magazines.