Canal side weirs for water delivery to irrigation furrows

Abstract

The canal side weir system is a relatively new method for water distribution to irrigation furrows. The system consists of a concrete lined ditch (canal), equipped with small openings or weirs which deliver the design irrigation flow rate into individual furrows. This research aims at evaluating the proformance characteristics of this system through laboratory, field, and computer studies. A laboratory model was used to establish head discharge relationships for various weirs at different channel velocities. For sharp entranced weirs, discharge for a given head was found to be inverselly proportional to the magnitude of the channel velocity. At small heads (20-30 mm), discharge at 0.3 m/s velocity was found to be about 15% less than the corresponding discharge at zero channel velocity . For normal irrigation settings (head on the weir = 60-80 mm), the difference was about 6%. Streamline entranced weirs were found to have negligible sensitivity to changes in the channel velocity. Field evaluation studies revealed better overall proformance than conventional systems. For an operating system, an application efficiency of 86% with uniformity coefficient of 0.84 at 7% deficit was calculated. The components of loss were run-off 4% and deep percolation 10%.