AN ASSESSMENT OF HYDRAULIC DESIGN OF MICROIRRIGATION SYSTEMS

The hydraulic design of micro-irrigation systems to achieve high syste m uniformity has led design engineers to over-design irrigation system s arbitrarily. Commonly used emitter flow variations of 10-20% are equ ivalent to a uniformity coefficient of about 98-95%, or a coefficient of variation of emitter flow of only 3-7%. The uniformity of a micro-i rrigation system is affected by not only hydraulic design but also man ufacturer's variation, grouping of emitters, plugging, soil hydraulic characteristics and emitter spacings, Among all the factors affecting the uniformity, the hydraulic design, with an emitter flow variation o f 10-20%, produces only a few percent change in uniformity. The manufa cturer's variation of micro-irrigation emitters ranges from 2% to 20%. The hydraulic variation will be less significant when an emitter with 10% or more manufacturer's variation is selected. The grouping effect will reduce the coefficient of variation to half or more if four or m ore emitters can be grouped together. The effect of hydraulic design i s also less significant with plugging situations, When there is no plu gging, the emitter flow variation from 10% to 20% in hydraulic design will reduce spatial uniformity only about 8% from 93% to 85% when the emitter spacing is designed as half of the wetting diameter in the fie ld. The hydraulic design criterion can be relaxed to 30% of emitter fl ow variation, q(var(H)), which can still achieve less than 20% in coef ficient of variation, or over 80% of uniformity coefficient in spatial uniformity of a micro-irrigation system. (C) 1997 Elsevier Science B. V.