Floodgates are used to control the water flow in rivers, streams, levee or reservoir systems, and for this reason floodgates are adjustable i.e.; in that they can opened and closed to varying degrees to allow the flow of water. Some floodgates are designed to set spillway crest heights in dams, to manage flow rates in canals or sluices, or floodgates can be designed to stop the flow of water entirely, or as part of a storm surge system. Most floodgates work by controlling water surface elevation that is being routed or stored. Floodgates are also known as crest gates, and are also used to higher or lower the water levels in main canals or rivers. Floodgates achieve this by letting more water flow into a detention basin, when the canal or river is nearing a flood stage. There are several types of floodgates and these are, Hinged crest gates, Bulkhead gates, Radial gates, Drum gates, Roller gates, Fuse gates and Clamshell gates.