Assessment of Microirrigation Field Distribution Uniformity Procedures for Pressure-Compensating Emitters under Potential Clogging Conditions

Abstract

Highlights Distribution uniformity of the lower quartile ( DU lq ) was assessed in three microirrigation subunits with three procedures that used different locations and different numbers of sampled emitters. Using reclaimed effluent as the water source, performance was periodically measured for a total duration of 1000 h. Emitter clogging and the locations of sampled emitters greatly affected DU lq . None of the procedures accurately assessed DU lq if more than 4% of the emitters were fully clogged. Abstract . Proper water distribution uniformity is important for successful use of microirrigation systems. Consequently, consistent system monitoring and periodic distribution uniformity assessments can help determine the performance of a microirrigation system and identify possible problems that should be corrected. When using irrigation water with a greater clogging risk, such as reclaimed effluent, emitter clogging can seriously affect distribution uniformity. In this study, distribution uniformity was measured at three times (0 h, 500 h, and 1000 h of operation) in a microirrigation system that used reclaimed effluent. Emitter discharge values were obtained for each emitter in the system (three subunits consisting of four driplines each with 226 pressure-compensating emitters on each dripline), and the distribution uniformity of the low quartile (DUlq) was calculated for each subunit. These comprehensive DUlq values were compared with those calculated by three estimation procedures developed by Merriam and Keller, Burt, and Juana et al., which use different sampling locations and different numbers of sampling points. Results showed strong influence of emitter clogging and the location of the sampled emitters on DUlq values. Using this data set, the Merriam and Keller procedure had the greatest root mean square error (RMSE = 41.8%), the Burt procedure resulted in an intermediate value (RMSE = 5.9%), and the Juana et al. procedure had the lowest (RMSE = 3.2%) when most of the completely clogged emitters (about 1% of the total) were located at the ends of the driplines. Further speculative analysis in which complete clogging was allowed to migrate to the farthest distal emitters for the Burt and Juana et al. procedures indicated that none of the procedures accurately assessed the actual complete DUlq. These results suggest that none of these procedures alone are successful at assessing system-wide distribution uniformity when substantial clogging exists. Keywords: Drip irrigation, Effluent, Emitter clogging, Flow variation, Wastewater.

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