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248:) are barraged many times to make them navigable and/or to avoid uncontrolled flooding. In such a case only the higher stretches of river are uninfluenced by impoundment. As to the other stretches the river has long "level" pounds but no or few natural heads, instead having artificial structures until the top head. Ideal management of the higher heads will allow headroom to keep back some
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On large rivers in all but arid climates, the head of a works is rarely fixed rigidly, as, within the impounded reach a significant flow rate and water gradient is sometimes seen. The head can only be found by calculation or defined by observations with and without impoundment. Depending on the flow
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reduced, unless and until banks, barrages, weir sluices or dams are overcome (overtopped), whereby a less frictional than natural course will exist (mid-level and surface rather than bed and bank currents) resulting in
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water so as not to compound heavy precipitation and resultant run-off downstream; corollary channels with spare capacity are a further mitigation where land is at a premium (such as the
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A head's location varies with the height of the water level against the dam. Since there is only an extremely low flow within the
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rate and control of the barrage, locks or weir, position will greatly vary and will not necessarily be where the so-called
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so no water level gradient, the head can be clearly seen: where the farthest watercourse discharges into the reservoir.
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The term does not apply to embankment (storage/settling) reservoirs, to which water is pumped from below.
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is the point on a watercourse up to which it has been artificially broadened and/or raised by an
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natural conditions prevail; below it the water level above the
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In principle, a distinction must be drawn between the
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232:River engineering § Canalization of rivers
168:has been raised by the impoundment and its
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66:"Head" hydrology
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