EVELOPMENT OF HEAD-DISCHARGE RELATIONSHIP FOR DRAINPIPE WEIR UNDER FREE FLOW CONDITIONS

A study was performed to test the utility of sharp crested weirs in subsurface drainpipes to measure discharge and to develop a head-discharge relationship for these weirs under free flow conditions. A horizontal sharp crested weir installed at the outfall of a subsurface drain, like a sump or a manhole, was simulated in the laboratory of COE in Water Resources Engineering. UET, Lahore. A set of known discharges was passed over the weirs and the corresponding heads were recorded above the crest. Based on the laboratory observations, a headdischarge relationship was developed for the horizontal crest for 8” diameter pipe. Sensitivity of the discharge coefficient relationship with respect to non horizontal installation of the weir (5 and 10 mm difference in elevation between the left and right corners of the weir) was also carried out. It appears that variation in the coefficient of discharge is small as compared to the values when the crest was horizontal. Generally, the coefficient of discharge of all the weirs decreased in the tilted position. It clearly show that the proposed weirs are useful in discharge measurement of subsurface drains.