A New Approach to Analyze the Flow over Sharp Crested Curved Plan form Weirs

Weirs have widely been used for the flowmeasurement, flow diversion and its control in the open channels.Generally they are used as normal weirs of various shapes likerectangular, triangular, trapezoidal, etc. pose problems ofsubmergence upstream of the weir due to large afflux required topass the discharge downstream. Several weirs of modified planform like oblique weirs, diagonal weirs, Duckwill weirs, Labyrinthweirs etc. have successfully been used to control the afflux and toenhance their discharging capacity with minimum head over theweirs. Labyrinth weirs are folded in the plan view (i.e. the weircrest is not straight in plan form) to provide a longer crest lengthcompared to a normal weir having the same lateral space toincrease the discharge for a given operating head. For largereservoirs, the labyrinth weir is used as the overflow structure. Itallows the overflow sill to be raised for the same maximum level ofthe water and flood, and thus, increase the storage capacity of thereservoir. This paper contains the results of experimental studycarried out to analyse the flow characteristics of a sharp-crestedcurved plan-form weirs under free flow conditions in arectangular channel with weir height around 0.10 m and vertexangles ranging from 00 (i.e. normal weir) to 1200. The equationsfor the discharge coefficient of curved weirs have been proposed.The results show that there is a gain of about 50% in dischargeover a curved weir with vertex angle of 1200 as compared to anormal weir. Finally, equations for discharge coefficient for alltested curved weirs in a free flow situation have been proposed.