DefinePK

Abstract

Barrages are used to divert the required water into canals and their design is said to be compromised if the required discharging capacity is reduced. In 2008, to restore tailwater levels, a sub weir was constructed downstream of Taunsa barrage, Pakistan. However, during 2010, the barrage didn’t pass its design flow and consequently its left marginal bund was breached. This study aims to investigate the effects of sub weir on the tailwater level, water heads, discharge coefficient and drowning ratio using FLOW-3D hydraulic models. The results indicated a maximum 15% rise in head water which further revealed an overestimation of water heads over the prototype sub weir. The analysis further indicated that from 12.09 to 24.19 m3/s/m discharge, the rate of change of water heads over the sub weir was found to be declined. Upon comparison, the simulated coefficients of discharge were found to deviate from the observed discharge coefficient and the maximum error reached 36 % at 12.09 m3/s/m. In conclusion, based on the results of numerical models, the operational conditions for the sub weir were not rationale which reduced the discharging capacity of the barrage and increased the drowning ratio.