Experimental Investigation for Free Overfall of Flow in Semi-circular Channels

In the present paper, the effects of diameter, bed slopes, and bed roughness on free overfall flow of semi-circular channels were investigated experimentally. For this purpose, three models of semi-circular channels with free overfall were built and installed in a 6m long laboratory flume. These three models were 250 cm long and had varying diameters 160, 200, and 250 mm. Four different bed slopes (S) were used in each of these models (0, 0.004, 0.008, and 0.012). For each bed slope, three sand particle sizes were used to roughen the bed (1.18mm, 2.36mm, and 4.75mm). For each model, the experimental testing program contained sixteen series of experiments. They were divided into two categories: four smooth beds and twelve rough beds. Different rates of discharge (Q) were examined in a total of 192 tests. According to the experimental results of all models, the Froude number (F_r) of flow decreases as the end depth ratio ( y_b/ y_c) increases for various bed roughnesses. For varying bed slopes and bottom roughness, a simple linear formula was developed to relate the brink depth ( y_b) with the critical depth ( y_c). For various bed slopes and roughness conditions, simple empirical equations for the flow over the free overfall in semi-circular channels were found. The results demonstrate a good level of agreement.