AN EXPERIMENTAL AND NUMERICAL STUDY OF FLOW PATTERNS AT A 30 DEGREE WATER INTAKE FROM TRAPEZOIDAL AND RECTANGULAR CHANNELS

Knowing flow pattern, especially stream tube dimensions at the vicinity of a lateral
intake is important to study flow discharge and sediment rate entering to the intake as well as to
better design a measure for controlling sediment entry into the intake. Previous studies have been
focused on intake from rectangular channels. In the present study, however, different experimental
tests were carried out at a 30 degree water intake installed at bank of a trapezoidal channel to
measure the three components of flow velocities; these data were then applied to calibrate the
numerical SSIIM2 model; by running the SSIIM2 model for different flow conditions, more data
were obtained. From the analysis of both experimental and numerical data the flow patterns
upstream of intake were plotted and the stream tube dimensions were obtained for all flow
conditions. It was found that the dividing stream width for intake from trapezoidal canal at the
bottom is less than it is for intake from rectangular canal for the same flow conditions; the width at
any elevation was found to depend directly on the diversion flow ratio. Relations for predicting
dividing stream width as a function of diversion flow ratio have been presented for intake from
both rectangular and trapezoidal cross sections. Also, computed secondary current strength at the
intake entrance, which is an effective parameter in transporting sediment to the intake, showed that
it is a function of flow diversion ratio and for intake from trapezoidal channel it is less than from
rectangular channel.