Optimization of hydraulic design of approach channel of spillway by hydraulic model studies

Abstract

The approach channel is intended to divert the flow safely from its original course and the diversion may be intended towards spillway, power intake or any other hydraulic structure. The hydraulic design of the approach channel involves determining cross-section dimensions of the channel for the design flood at a given flow velocity, slope and shape or alternatively determining the discharge capacity for the given layout and cross-section dimensions. Proper alignment of approach channel minimizes the head loss by reducing the oblique flows. Sometimes, the spillway approach channel is submerged with unconfined boundaries, asymmetrical in layout. However, these conditions are site-specific. Hydraulic model studies play a substantial role in testing these kinds of layouts to find out an optimum layout. Studies have been carried out on a 1:140 scale model of the spillway to optimize the layout of an unconfined, unlined, asymmetrical, and submerged approach channel by the assessment of velocity profiles and flow pattern in the approach channel for different shaped layouts. Studies indicated that the efficient layout of the approach channel is governed by its maximum available width and straightforward approach, prevention of lateral inflows by the provision of additional embankments and provision of suitable length of the guide bund.