Flow control structure
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A flow control structure is some type of construction that alters the flow of water in some way. As a group these are passive structures since they operate without intervention under different amounts of water flow and their impact changes based on the quantity of water available.
Flow control structures are know to have existed for thousands of years. Some built by the Chinese have been in continuous use for over 2,000 years. The Chinese used these structures to divert water to irrigate fields and to actually deposit silt in specific areas so that the channels were not blocked by silt build up. Structures like this required yearly maintenance to remove the accumulated silt.
More modern structures add to these basic principles. In Hawaii, there are numerous flow control structures that have been built to irrigate the Pineapple and sugar cane fields. The purpose of these structures is to divert water into the various canals and to keep them full. When over full, they either dump excess water back into streams or other canals. Among the simplest is a low dam across a shallow stream forcing all of the water to one side to allow it to be easily collect in a canal. This can keep a canal full even with very low flows in a stream.
Another simple device is a series of concrete piers installed in a spillway to slow down the descending water so that it does not cause damage at the bottom of the spillway.
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