Effect of hydraulic head and slope on water distribution uniformity of a low-cost drip irrigation system

Assessment of the effect of topography and operating heads on the emission uniformity distribution in drip irrigation systems is important in irrigation water management and could serve as basis for optimizing water use efficiency and crop productivity. This study was carried out to evaluate the effect of hydraulic head and slope on the water distribution uniformity of a low-cost drip irrigation system developed by the International Development Enterprises (IDE), a non-profit organization dedicated to ending poverty in the developing world. The drip system was tested for water distribution uniformity under varying system heads and slope conditions. The laboratory experiments were conducted at the facilities of the College of Engineering and Agro-industrial Technology, University of the Philippines Los Baños. A drum reservoir served as water supply for the IDE drip system. A sub-main of 10 m and lateral-sub holder of 10 m with adjustable slope was fabricated to enable slope variations during laboratory experiments. The drip system was operated at pre-specified operating heads of 1.0 m, 2.0 m and 3.0 m for slopes of 0%, 10%, 20%, 30%, 40% and 50% for the sub-main and 0% slope for the laterals. The discharge in each emitter was monitored for each chosen slope through direct volumetric measurements. The water distribution uniformity was then evaluated using the Christiansen's method and the Merriam and Keller's method. Mathematical relationships were then developed to characterize the effect of slope and heads on uniformity coefficient. We found that the coefficient of uniformity (UC) and the emission uniformity (EU) generally increase with increasing heads and decrease with increasing slope. The coefficient of uniformity generally followed a linear relationship with either head or slope. The UC and EU decrease substantially at submain slopes steeper than 30%. For level surface, a head differential of 0.5 m does not cause significant change in either UC or EU. For all slopes tested, we found that a head of 3.0 m with respect to the junction of the most upstream lateral may be considered to be optimum from both hydraulic and practical standpoints. On the basis of the results, appropriate recommendations were formulated to minimize non-uniformity of water distribution under field conditions in sloping drip-irrigated lands.