300px|thumb|right|The Faraday Diversion Dam, [[Clackamas River. This dam slows a normally fast and shallow river for partial diversion to a hydroelectric dam. The diversion tunnel opening can be seen in the upper left.]]
thumb|right|The [[Imperial Dam diverting the Colorado River in the southwestern United States.]]
A diversion dam is a dam that diverts all or a portion of the flow of a river from its natural course. Diversion dams do not generally impound water in a reservoir; instead, the water is diverted into an artificial water course or canal, which may be used for irrigation or return to the river after passing through hydroelectric generators, flow into a different river or be itself dammed forming an on-ground or groundwater reservoir or a storm drain.
An early diversion dam is the Ancient Egyptian Sadd el-Kafara Dam at Wadi Al-Garawi, which was located about twenty five kilometres south of Cairo. Built around 2600 BC for flood control, the structure was 102 metres long at its base and 87 metres wide. It was destroyed by a flood while it was still under construction.
Classification
Diversion dams are a classification of dams distinct from storage and detention dams. Storage dams are used to store water for extended lengths of time. The stored water then can be used for irrigation, livestock, municipal water supply, recreation, and hydroelectric power generation. Detention dams are built to catch surface runoff to prevent floods and trap sediment by regulating the flow rate of the runoff into channels downstream. Diversion dams are used to raise the water level in order to redirect the water to the designated location. The diverted water can be used for supplying irrigation systems or reservoirs.
Purpose
Diversion dams are installed to raise the water level of a body of water to allow the water to be redirected. The redirected water can be used to supply irrigation systems, reservoirs, or hydroelectric power generation facilities. The water diverted by the diversion dam to the reservoirs can be used for industrial applications or for municipal water supply. Buttress dams require extensive steel framework and labor. As a result, buttress style dams are expensive to construct and are seldom built today.