Abstract
In the present paper, the effects of side slopes, bed slopes and bed roughness on the flow over free overfalls in triangular channels have been studied experimentally. For this purpose, three models of triangular channels with free overfalls have been constructed and fixed in a 6m length laboratory flume. These three models had length of 244cm with different values of side slopes (Z) (0.8(H):1(V), 1:1 and 1.33:1). Each one of these models had four different bed slopes (S) (0, 0.0041, 0.0082 and 0.0123). For each bed slope, the bed was roughened with three particle sizes of sand (ds) (1.18mm, 2.36mm, and 4.75mm). The experimental testing program included sixteen series of experiments for each model. Four of them were for smooth beds and twelve for rough beds. A total of forty eight experiments were tested for different rates of discharge (Q). Experimental results of all models showed that Froude number (Frb) of flow decreases with the increasing of end depth ratio values (yb/yc) for different bed roughness, different bed slopes. The relations between the brink depth (yb) and the critical depth (yc) were found to be a simple linear formula for various bottom slope and different bottom roughness. An empirical expression was obtained for the flow over the free overfall in triangular channels for different bed slopes and roughness. The results of the present study have been compared with studies were obtained by other investigators, the comparison shows a very good agreement between them.
Highlights
The overfall is a weir with broad crest causing sudden change in water depth by free fall of water [1]
Delleur's et al study shows that when the value of more than 0.1, the end depth ratio (EDR) value will be smaller than the expected value due to the effect of roughness. (Rajaratnam et al, 1964) [4] present an experimental study on the various shapes of channels sections, they found that the value of the EDR is equal to 0.715 for confined rectangular channels, and for unconfined channels it is equal to 0.705
The aim of the present study is to investigate the hydraulic characteristics of the free overfalls of the triangular channels with an indication of the influence of the channel bed roughness, longitudinal bed slope and side slope on the depth of water at the edge of overfall as well as the relationship of this depth with critical depth
Summary
The overfall is a weir with broad crest causing sudden change in water depth by free fall of water [1]. 1936, is the first which pointed out the possibility of using the free overfall as a simple structure for measuring the discharge without requiring any calibration [2] He found that the end depth ratio (EDR) for critical flow in rectangular and horizontal free overfall channel equal to 0.715. (Beirami et al, 2006)[8] presented theoretical study for different free overfall channel sections with horizontal slopes by using momentum equation He found that the end depth ratio. The aim of the present study is to investigate the hydraulic characteristics of the free overfalls of the triangular channels with an indication of the influence of the channel bed roughness, longitudinal bed slope and side slope on the depth of water at the edge of overfall as well as the relationship of this depth with critical depth. The present study aims to find empirical equation to calculate the discharge for the cases studied in this research
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