Dams are supposed to prevent floods. Some may make them worse
Dams are often built to control floods, but on certain kinds of rivers they may make big deluges worse, a new study finds. The finding suggests river managers might need to rethink their flood control strategies on silty and sandy lowland rivers.
In addition to storing water, engineers expect dams to reduce flood risks by modifying the river downstream. Because dams trap sediment, they release relatively clear water that cuts deeper into the river’s bed. This incision creates a roomier channel that can carry more water and prevent floodwaters from spilling over riverbanks.
By checking flood records from 1980 to 2015, the scientists discovered that the magnitude of moderate and large floods had in fact increased. Over the same period, however, the magnitude of smaller floods decreased—likely because the river’s deeper channel is better able to contain them.
More broadly, engineers should also pay more attention to the complex behavior of rivers when designing new dams, Pinter says. “It’s amazing how much we’ve gotten wrong by thinking that these big alluvial rivers are just pipes,” he says. “We continue to underestimate the importance of bedforms and roughness.”
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