EFFECT OF FLOW FLUCTUATIONS ON FREE DRAINING, SLOPING FURROW AND BORDER IRRIGATION SYSTEMS

The performance of free draining, sloping furrow and border irrigation systems which experience water supply fluctuations was evaluated over a wide range of field characteristics and soil types. The evaluation procedure initially determined the design parameters allowing for maxi mum application efficiency. The performance of the system was then cal culated for different inflow hydrographs. The basic model of the surfa ce flow process was the kinematic-wave model. It was first proven to h ave the capability for simulating border irrigation systems, and then successfully modified for cases where variations in the inflow tempora rily causes front-end recession. Two parameters of flow variation were considered; and increase or a decrease from an initial design flow co ndition. The requirement efficiency and uniformity were not significan tly affected by flow fluctuations of 25% or less of the design value. Further, it was shown that these fluctuations produced minor impacts r egardless of the time when the change occurred (for different soil typ es). Similarly, application efficiency changed less than 5% when the f low fluctuation was between 75 and 125% of the design flow and the flo w variation started after 75% of the total irrigation time had been co mplected. When the flow rates fell below 75% of the optimal design val ues and the fluctuations started before 50% of the cut-off time was re ached, the irrigation system performance parameters were significantly affected.