Characteristics and Driving Factors of Drainage Water in Irrigation Districts in Arid Areas

Tarim Basin, the largest inland river basin in China, is facing declining runoff and deteriorating water quality due to agricultural reclamation. In this study, the spatial characteristics of drainage water in Tarim Irrigation District (which is in the upstream of Tarim Basin) are analyzed using long-term drainage, irrigation and agronomic data. The driving factors behind the spatial variations in total dissolved solids (TDS) are discussed along with the feasible approaches to reducing salt loads in the drainage waters. Cluster analysis reveals three distinct TDS clusters - Type-I (7436-9651 mg/l), Type-II (5899-7640 mg/l) and Type-III (3408-4084 mg/l) clusters. The spatial variations in TDS in the study area are not significantly influenced by irrigation water source, halide dissolution and ion exchange in soils or the wide use of water-saving technology. Reclamation of new arable lands, limitations on farmland areas or discharge canal lengths and the surrounding environmental conditions (such as reservoirs or wastelands) are the main factors driving the spatial variations in TDS in the region. It is suggested to reduce salt load in drainage waters by decreasing irrigation water amount, prohibiting reclamation of new farmlands, improving drainage systems and changing flow destination of drainage waters from rivers to deserts/wastelands. In-depth analysis of spatial variations in TDS along with the causes and countermeasures could benefit the optimization of agricultural drainage water and regional water management in the study area and other arid regions.