SPATIAL VARIABILITY OF THE WATER DEPTH APPLIED BY FIXED SPRINKLER IRRIGATION SYSTEMS

Abstract The uniformity of water application is an important factor in the evaluation of sprinkler irrigation systems. This uniformity depends on the type of sprinkler and its operating conditions, such as the arrangement and spacing between the sprinklers in the area; velocity and wind direction during the period of water application and the pressure variation of the irrigation system. The objective of this study was to model, analyze and compare the structure of spatial dependence, as well as the spatial variability of the water depths applied by a sprinkler irrigation system with compensating and non-compensating sprinklers, using geostatistical methods and measurements of accuracy or similarity between the applied water depth maps. The experiment was carried out in an agricultural area, in the city of Cascavel-Paraná-Brazil. A total area of 10 × 10 m was used, with 04 compensating and 04 non-compensating sprinklers installed at a height of 1.5 m. For each type of sprinkler, water levels were measured in 100 collectors spaced 1 × 1 m in the study area in 32 trials. On each test sprinkling was carried out for one hour. The conditions of wind, temperature and air humidity were evaluated at the beginning of each test and at 10-minute intervals with a climatological station. As the geostatistical analysis showed the existence of directional trends, the coordinates were incorporated as covariates to the linear spatial model in the study of the spatial dependence of the average depth of the irrigation water for the two types of sprinklers. The spatial dependence structure that best fits the data when using the compensating sprinklers was the Gaussian model and when the non-compensating sprinklers were used, it was the exponential model. The spatial variability maps of average irrigation water depth (mm) of the trials, obtained by universal kriging, revealed that for both sprinklers there was an increase in the mean level average values in the northwest-southeast direction (135° in the azimuth system) in the area under study, influenced by wind direction and velocity during the execution of the experiment.

摘要 灌水均匀度是评价喷灌系统的重要指标。其均匀性取决于喷头类型及其运行工况，包括区域内喷头的布置形式与间距、灌水作业期间的风速与风向，以及灌溉系统的压力波动。本研究旨在借助地统计方法，结合施水分布图间的精度或相似性度量，对搭载补偿式与非补偿式喷头的喷灌系统的空间依赖结构，以及其施加的灌水深度空间变异性进行建模、分析与对比。
试验于巴西巴拉那州卡斯卡韦尔市的农田区域开展。试验地块总面积为10 m × 10 m，安装有4台补偿式喷头与4台非补偿式喷头，安装高度均为1.5 m。针对两类喷头，研究团队在试验区域内以1 m × 1 m的间距布设100个雨量收集器，共开展32组试验，每组试验的灌水时长为1小时。每组试验开始时及每间隔10分钟，通过气象站记录风速、温度与空气湿度等环境参数。
鉴于地统计分析显示存在方向性趋势，本研究将坐标作为协变量引入线性空间模型，以分析两类喷头的灌溉水平均深度的空间依赖性。适配补偿式喷头试验数据的最优空间依赖结构为高斯模型，而非补偿式喷头则适配指数模型。通过泛克里金（Universal Kriging）得到的各组试验灌溉水平均深度（mm）空间变异图显示，受试验期间风向与风速的影响，两类喷头对应的研究区域内，西北-东南方位（方位角系统下为135°）的平均灌水深度均呈现升高趋势。