The few streams that empty into the Central Plateau dissipate into the saline marshes. All streams are seasonable and variable. Spring floods do enormous damage, while there is little water flow in summer when most streams disappear. It can also be tapped by wells. Dams Dams have always played an important role in harnessing Iran's precious water reserves and the long-term objective of Iran's water resources development plan is based on the control and regulation of water resources through dams.
Dams also play an important role in flood control through routing of floods.
Several reservoirs behind the dams seem to offer good sailing and water-skiing facilities, but have not been used for recreation so far. The problem of water supply has been a constant preoccupation since the beginning of the country's history, thousands of years ago. Its inhabitants learnt to design and implement efficient techniques for harnessing limited water resources and for irrigation. Apart from the qanat, which was a major source of irrigation and domestic water supply for centuries, Iranians have in the past built dams of various types and weirs. Some of these head control structures, built as long as 1000 years ago, are still in good condition.