The EFFECT OF HYDROPHYTES ON THE PERFORMANCE OF SECONDARY CANAL

Abstract

The hydrophytes in canal effect directly canal performance by reducing water velocity, enhances sedimentation and reduce canal cross section area which raise water level and reduces water flow. Indirectly the hydrophytes detaches from their origin and flow with water stuck with outlet and reduces its proportionality. In this regard a study was conducted on secondary canal known as Yar Husain Minor (YHM) of Maira Branch Canal, which is part of the Upper Swat Canal Irrigation System in Khyber Pakhtunkhwa, Pakistan. Maira Branch Canal and its secondary canal were designed for Crop Based Irrigation Operation (CBIO), which could supply irrigation water for maximum copping intensity (180%) even during peak periods of irrigation requirements. The current water allowance was 0.67 Ls^-1 ha^-1 (6.6 mm day^-1), which was based on the maximum crop water requirements. The several challenges for operation of YHM and other secondary canals of Maira Branch came from physical barrier mostly in the form of hydrophytes on the performance of YHM canal. Further challenges came from the fact that it receives water from River Swat which is turbid in summer and River Indus (Tarbela Reservoir) which is clear with low turbidity. This caused sedimentation and growth of hydrophytes in the YHM. Furthermore Triangular Profile Crump’s weirs were in all secondary canals including YHM for proportional division to the tertiary outlets (moghas). The study objectives were to investigate the effects of hydrophytes on canal capacity and at the outlets on the performance of the YHM. Hydrophytes growth was observed in head reaches of canal and samples were collected and were identified at the Department of Weed Science & Botany, The University of Agriculture Peshawar. Five types of aquatic weeds were identified. The hydrophytes growth in canal head reaches directly reduces the cross section by more than 50%. Indirectly the detached hydrophytes were get stuck in the outlets and affected its performance. Therefore, daily discharges were measured with/without detached hydrophytes at each outlet from staff gauging. Frequency was based on days stone hydrophytes present divided by total time. It was concluded that secondary canal performance was low due to hydrophytes. The hydrophytes and users interventions influenced the outlets performance by 80%. Trifurcators type outlets were more prone to influence by hydrophytes followed by bifurcators outlet.