Flow Characteristics through the Squared-Section Vertical Shaft Spillways

Abstract

This article aims to present the study of flow characteristics through the squared-section vertical shaft spillway for 5 patterns of the spillway entrance having different width-to-length ratios (m). Each spillway has the same perimeter length of the entrance and there are 3 different heights of the entrance (P) through the spillway above the channel bottom. The hydraulic models were constructed for this study to determine the discharge through the spillways with the flow conditions of free overflow downwards to vertical shaft and partly full condition in the outlet horizontal conduit. The assumption for the flow through the spillway was the same as the flow through high weir. The obtained data from the models were used to determine the spillway coefficient which can be used to analyze the relationships to the other variables that affecting on the flow characteristics. From the study it was found that the discharge through the spillway was directly proportional to the water level above the entrance of the spillway (H) by which the actual discharge was less than the theoretical discharge. The obtained values of spillway coefficient (C) from each pattern of spillway were found in the range 1.234 – 1.819 by which C is inversely proportional to H and for the consideration of any values of H it was found that C is directly proportional to m and P. The drainage efficiency of the spillway could be considered from the discharge coefficient (C_D) and were equal to 0.418 – 0.616 which rather low.