Dams Designed to Prevent Flooding Could Backfire

A new study reveals that building dams to control flooding might actually increase the intensity of coastal flood events. Published in the Journal of Geophysical Research: Oceans, this research explores how dams in coastal estuaries—where rivers and ocean tides meet—affect flood risks. Despite their growing popularity as a response to climate change, sea-level rise, and salt intrusion, these structures may not always prevent flooding effectively.

The study, which analyzed over a century of data from Charleston Harbor in South Carolina, shows that coastal dams do not consistently reduce flood risks. Instead, their impact on flooding can vary based on factors like the duration of storm surges and water flow friction.

Lead author Steven Dykstra, an assistant professor at the University of Alaska Fairbanks, explains that although storm surges generally weaken as they move inland, the shape of an estuary can sometimes amplify them. Dams create an artificial barrier that reflects storm surge waves, potentially increasing their size and impact. Dykstra likens this effect to water sloshing in a bathtub, where certain wave patterns can cause the water to overflow.

Using Charleston Harbor as a case study, researchers applied computer models to 23 estuaries across various regions, including Cook Inlet in Alaska. The models confirmed that both the shape of the estuary and the presence of a dam significantly influence how storm surges and tides move inland. In some cases, waves in dammed estuaries become larger rather than smaller.

The study also found that even areas far from coastal dams can be affected by these structures. For example, in Charleston, the most severe storm surges were recorded more than 50 miles inland.

Dykstra notes the importance of awareness: many people may not realize they are in a coastal-influenced zone until a major flood event reveals it. As sea-level rise continues, more inland areas may experience the effects of coastal infrastructure. The study was conducted with contributions from Enrica Viparelli, Alexander Yankovsky, Raymond Torres from the University of South Carolina, and Stefan Talke from California Polytechnic State University, San Luis Obispo.