Flooding is the natural result of the presence of too much water. To protect residential and agricultural areas, a number of flood defense technologies are utilized. Stopping floods from a river and stopping floods from the coast requires techniques unique to these areas. River flood water can be diverted or held back. Coastal flooding can be stopped by reducing the strength of strong waves. If flood defenses fail, temporary measures are used.
River Flood Defenses
To prevent rivers from overflowing the banks, flood defenses such as levees and reservoirs are used. Levees are usually high, cement walls that limit the flow of a river. Levees are typically used with rivers that are close to a sea. Reservoirs are large structures that interrupt the flow of a river and forms artificial lakes or ponds. Reservoirs can release large amount of water from a river and divert a flood from residential or agricultural areas.
Coastal Flood Defenses
To prevent flooding in coastal areas, defenses such as barrier islands, beach nourishment and sea walls are utilized. Barrier islands are natural strips of land that run parallel to a coastal line, sometimes for dozens of miles without a break. Barrier islands break waves that would otherwise flood an area. Beach nourishment is the movement of sediment from one location to another. Beach nourishment projects create beaches where there are none, or lengths a disappearing beach. The beach acts as a buffer between populated areas and rising water. Sea walls can be constructed as a wall or made of a range of material, such boulders. Sea walls are built to break strong waves to prevents flooding, especially during strong storms.
Emergency Flood Defenses
When other flood defenses fail, an emergency flood defense is the use of sandbags. Sandbags are usually burlap sacks that can be filled with sand or soil. The use of sandbags is temporary since water will eventually seep through the material used.