Redistribution Mechanism for Irrigation Water and Salinity in Typical Irrigation and Drainage Unit in the Hetao Irrigation District, China

This study clarified the migration and accumulation patterns of irrigation water and associated salt in a cropland irrigation and drainage unit and evaluated the water-use rationality of the irrigation and drainage unit in the Hetao Irrigation District. A typical lateral canal-scale irrigation and drainage system was selected, the planting pattern of which was complex and included interplanted crops and interlaced cultivated land and wasteland. The overall regional water balance model for the study area was established based on the monitoring data from a two-year field experiment from 2018 to 2019, and the dissipation of irrigation water and the redistribution of soil water and salt were investigated. The obtained specific water yield of the study area was 0.0443. In 2019, water conveyance losses from canals accounted for approximately 18% of the total water diversion, the irrigation water entering cropland through field canals (i.e., field irrigation) accounted for 77.2%, and surface drainage accounted for 4.8%. There is a lateral exchange of groundwater between different land types. After crops use irrigation water in the field, groundwater replenishes approximately 7% of the total water diversion to the field, wasteland consumes 6% of the total water diversion, and the utilization mode also is groundwater replenishment. In the cropland, evapotranspiration (ET) consumption accounted for 84.2% of the total water diversion, and salt accumulation accounted for 14.2% of the total salt introduced, whereas in the wasteland, ET consumption accounted for 6% of the total water diversion, and salt accumulation accounted for 44.2% of the total salt introduced. Although the wasteland area constituted only 5.43% of the total study area, it functioned as a salt storage area and played a vital role in dry drainage desalting. Maintaining an appropriate wasteland area and improving the drainage system could facilitate desalination and sustainable ecological development in the study area. The results provide a reference for water and salt regulation and modern ecological irrigation district management in similar irrigation districts.