Effect of Bed and Side Slopes on Flow Measurements in Trapezoidal Free Overfall Channels

Abstract

The aim of the present investigation is to study the effect of both side and bed slopes on the flow over free overfalls in trapezoidal channels, three models of trapezoidal free overfall channels have been built and tested in a laboratory flume. These models had 0.1m bed width and 3.7m length with different values of side slope (m = 0.268, 0.577, and 1). Each model had four different bed slopes (S = 0, 0.0033, 0.01, and 0.02). A total of twelve series of the experiments were tested for different ranges of Froude number. Experimental results of all models showed that the variation of \({({Qm^{1.5}/\sqrt{gb^{5}}})}\) with \({({my_b /b})}\) for different values of side slope and different bed slopes is a simple power equation. It was observed that the values of \({({Qm^{1.5}/\sqrt{gb^{5}}})}\) increase with the increase in \({({my_b /b})}\) values. The correlation between \({( {my_b /b} )}\) with \({({my_c /b})}\) is found to be linear for different bed slopes. The ratio \({({y_b /y_c})}\) decreases with the increase of slope (S) with an average value of 0.729 for subcritical and supercritical flow on smooth beds of different slopes. An empirical expression is obtained for the variation of \({(Qm^{1.5}/\sqrt{gb^{5}})}\) with \({({my_b /b}),}\) and (S). The results of the present study have been compared with theoretical and experimental results obtained by other investigators showing well agreements.