A study performed by the U.S. Geological survey and published in Science reveals that rivers respond quickly to dam removal. In the past forty years, more than 1000 dams have been removed from US rivers due to safety concerns, sediment buildup, and inefficiency. According to Jim O’Connor, a geologist with the U.S.G.S. and lead author of the study, “rivers quickly erode sediment accumulated in former reservoirs and redistribute it downstream, commonly returning the river to conditions similar to those prior to impoundment." Because of this, more and more dams are coming down as a means of river restoration.
A national effort is underway between several US agencies and universities to better understand and document the effects of dam removal. A major finding is that river channels stabilize within only months or years after dam removal. Fish and other biological factors seem to respond quickly as well. Migratory fish especially will move upstream and utilize the habitat that was previously inaccessible.
As the number of dam removals increase both in the US and overseas, this effort to understand the consequences of dam removal becomes more pressing. Scientists seek to use the information gathered to guide dam removals in the future. "As existing dams age and outlive usefulness, dam removal is becoming more common, particularly where it can benefit riverine ecosystems," said Gordon Grant, Forest Service hydrologist. "But it can be a complicated decision with significant economic and ecologic consequences. Better understanding of outcomes enables better decisions about which dams might be good candidates for removal and what the river might look like as a result."