The Federal Emergency Management Agency (FEMA) promotes traditional flood control measures to be used with wetlands. The reason is that wetlands store water. So when water levels rise due to rain and flooding, wetlands are a great way to capture some of the water that would otherwise overwhelm traditional flood control systems. For example, the US Environmental Protection Agency estimates that one acre of wetland can store approximately three acre-feet of water. This is the equivalent of one million gallons. An acre-foot is one acre of land covered one foot deep in water. When wetlands are covered in trees and other vegetation, they are even more effective at slowing and capturing flood waters.
Keep in mind that some wetlands are more effective than others at capturing flood waters. Factors that determine effectiveness include: