Vertical Pipe Intake (VPI) is employed as an intake structure for river or reservoir water withdrawal to supply potable and/or agriculture water. Vertical pipe intake is economical relative to other alternatives. VPI is usually installed near water surface and prevents coarse sediment entrance into the system. Strong vortex in VPI entrance is one of the difficulties encountered in vertical intake. This difficulty not only reduces efficiency of hydraulic structure, but also causes cavitations as well as vibrations. Moreover, it reduces discharge coefficient. The designer’s knowledge of important parameters helps him in correctly designing such structures. A set-up is prepared to study the effect of vortex on discharge coefficient. It consists of a storage tank, a stilling basin and headrace channel. The effect of air entry and wall clearance on discharge coefficient as well as submergence number are investigated. By analysing the results an optimum wall clearance is recommended. The results also show that: air entry increases submergence depth and reduces discharge coefficient.
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