Floodplains
Floodplains
Floodplains are the low-lying areas of land where floodwater periodically spreads when a river or stream overtops it banks. Riparian vegetation along streambanks and in the floodplain reduces the velocity of floodwaters, lessening the erosive force of the flood and capturing nutrient-laden sediment.
Floodplain soils absorb water during the wet season, then slowly releases moisture to plants and into the stream. This buffers the effect of peak runoff and keeps plants growing and streams flowing longer. Streambank vegetation also helps cool surface water temperatures, and creates important habitat for fish, waterfowl, and other wildlife species.
Flood waters bring moisture and a surge of new nutrients into the floodplain. Many settlements were originally built in or near floodplains because of access to drinking water and high soil fertility for farming. Over time, many riverside communities have chosen to control flooding by building upstream dams and levees, and by straightening the course of the river. Such drastic alternations protect developed lands from flooding, but they also permanently change a river’s ecosystem. Floodplains support many riparian species, such as New Mexico’s native cottonwood tree, which depend on regular small-scale flooding to survive and reproduce.
Today, communities are learning to create a healthier watershed by working in concert with nature. They can reduce flooding by rehabilitating upland water courses to slow down the flow and by constructing wetlands that intercept rainwater closer to where it falls, before large volumes of water reach the river. Water stored in floodplain and wetland soils is slowly released back to the surface over a longer period of time. That reduces flood volumes and keeps the river flowing longer into the dry season.
