The well-known approach of constructing dams to control flooding could actually lead to more severe coastal flood events, according to a recent research study. By examining over a century’s worth of data from Charleston Harbor, South Carolina, the researchers found that coastal dams don’t always reduce flooding. The impact of dams on flood risks can vary, influenced by the length of surge events and the friction from water flows.
The well-known approach of constructing dams to control flooding could actually lead to more severe coastal flood events, according to a recent research study.
This research, featured in the Journal of Geophysical Research: Oceans, explored the impact of dams in coastal estuaries, which are areas where rivers meet ocean tides. The construction of such large-scale structures is gaining traction worldwide, partly to counteract increasingly powerful storms, saltwater intrusion, and rising sea levels driven by climate change.
By studying data from Charleston Harbor, South Carolina, that spans over 100 years, researchers concluded that coastal dams do not always alleviate flooding. The risk of flooding can either rise or fall based on the length of a surge event and the resistance in the flow of water.
“It’s commonly thought that storm surges lessen as you move inland, but the shape of the basin can actually amplify it,” noted lead researcher Steven Dykstra, an assistant professor at the University of Alaska Fairbanks College of Fisheries and Ocean Sciences.
Estuaries generally have a funnel-like shape that narrows as they stretch inland. When a dam is added, it shortens the estuary’s length, creating a barrier that bounces storm surge waves back, pushing them further inland. The narrowing form also leads to minor reflections that vary with the surge duration. Dykstra likened these storm-driven waves to splashes in a bathtub, where certain wave patterns can cause water to overflow.
After analyzing Charleston Harbor as a primary example, the researchers utilized computer simulations to assess the flood response in 23 other estuaries located in various geographic regions. This included both dam-affected and naturally occurring estuary systems, such as Cook Inlet in Alaska.
The simulations validated that the shape of the basin and the changes created by a dam are crucial factors in how storm surges and tides progress inland. Under specific conditions, waves in areas with dams can increase in size rather than decrease.
The research also found that regions far from coastal dams might still be impacted by human-made infrastructure. In the vicinity of Charleston, the strongest storm surges frequently occurred over 50 miles inland.
“One concerning aspect is that people may not realize they are in an area affected by coastal influences,” Dykstra expressed. “As sea levels continue to rise, individuals far inland are learning that they are not immune to coastal effects, especially when severe flooding occurs.”
Other contributors to the study included Enrica Viparelli, Alexander Yankovsky, and Raymond Torres from the University of South Carolina, as well as Stefan Talke from California Polytechnic State University, San Luis Obispo.
