A floodplain is a land area immediately adjacent to a river, stream, or creek. It is an area that may be covered with water after heavy rainstorms. The floodplain collects and holds the excess water from storms, allowing it to be released slowly into the river system and to seep into groundwater aquifers, the underground layers of soil, gravel, or porous stone that yield and carry water. Floodplains, along with wetlands and shorelines, are considered to be critical areas for a river and its watershed.
Floodplains, also known as riparian zones or systems, can support particularly rich ecosystems, both in quantity and diversity of species. Soaking the floodplain’s soil releases a surge of nutrients – some left over from a previous flood and some resulting from the decomposition of organic matter in the current flood. Microscopic organisms thrive, larger species rapidly breed, and opportunistic feeders (especially birds) move in to take advantage. While the production of nutrients peaks and falls quickly, the emergence of new growth continues for some time.
Residential and commercial development projects in natural floodplains remove or reduce water storage capacity, and often cause flooding both up and downstream. Artificially controlling stormwater, in an effort to keep it out of the floodplain, causes the water to overflow riverbanks in other locations. This often creates floods of greater magnitude and danger. Building on floodplains increases the risk of property damage and life-threatening conditions. Diverting stormwater into channels forces the water to flow faster, and this both erodes topsoil and destroys habitats.