Discharge characteristics of orifice spillway under oblique approach flow

• Under straight approach flow, discharge capacities of the end bays are low compared to other bays.
• Flow passing through the bays of straight approach flow is higher than the oblique approach flow.
• Proposed equations give better prediction of discharge for flow through orifice type spillway.

Orifice type spillways are provided in the dam at lower level for facilitation in flushing of the sediment from the reservoir in addition to spilling the flood water. However, in most of the hydraulic structures, particularly in the earthen and rockfill dams, the spillway is not a part of the dam and it is provided on either of the banks of the river which results in oblique approach flow to the spillway that likely to affect the discharging capacity of the spillway. Presented in this paper is an experimental study for discharge characteristics of orifice type spillway under straight and oblique approach flow. Analysis of data indicates that discharge through the spillway decreases with increase of obliquity of the flow. The effect of the obliquity has been quantified and discharge equations for one, two and three simultaneous opening of the bays have been proposed.