Performance, applicability boundaries, and multi-mode construction of New-era Karez Engineering in Xinjiang of China

Xinjiang Uygur Autonomous Region is characterized by uneven spatiotemporal distribution of water resources, a high proportion of agricultural water use, and strong dependence on oasis stability during irrigation. Although large-scale water-saving irrigation, especially drip irrigation, has greatly improved water use efficiency, the marginal potential for water saving has gradually narrowed at the field scale. Therefore, it is often required to alleviate the water loss during diversion, conveyance, storage, and distribution in modern agriculture. The conventional Karez system in Xinjiang can represent the long-standing water-control strategy of “conveying water underground, relying on gravity flow, and reducing evaporation”, fully meeting the requirements of energy and water saving, and site-specific water resource use in arid irrigation regions. Since the 1990s, exemplified by the self-pressurized irrigation district of the 224th Regiment of the 14th Division in Xinjiang, the natural terrain elevation differences have been explored for self-pressurized pipeline water conveyance. It is often required for the modern engineering transformation of conventional Karez system. In this study, self-pressurized pipeline water conveyance was taken as the basic mode to evaluate performance, applicability boundaries, and multi-mode construction of New-era Karez Engineering in Xinjiang. Furthermore, 9 typical districts of self-pressurized irrigation were selected to investigate engineering data in the field. The practical performance of the basic mode was evaluated in terms of water conveyance efficiency, irrigation water use coefficient, water-saving effect, energy consumption, and operation and maintenance costs. The results showed that the water conveyance efficiency ranged from 83.84% to 91.17% in the 9 self-pressurized irrigation districts, with an average of 86.61%. Compared with pressurized irrigation districts under similar conditions, the self-pressurized mode increased water conveyance efficiency by a relative 16.09%. According to the similar net demand of irrigation water, annual water withdrawal was reduced by 65.2264 million m³, compared with the equivalent pressurized mode, whereas, the irrigation water use coefficient increased to 0.74-0.86. Meanwhile, pumping equipment was effectively reduced to realize significantly lower energy consumption, as well as operation and maintenance costs, due to its gravity-driven conveyance. Since the self-pressurized pipeline mode was far from widespread use in Xinjiang, its performance and applicability were constrained by natural terrain elevation, water source stability, pipeline network operation and maintenance, as well as the coordination between irrigation and drainage. Therefore, the modernization needs of irrigation districts were fully met for a sufficient elevation difference, stable water supply, low sediment load under complex pipeline maintenance, or low risks of drainage and salinity. Therefore, Karez Engineering was also required to integrate with modern pipeline networks, pumping stations, regulation and storage facilities, drainage systems, digital twins, and intelligent control systems, according to the underground conveyance, gravity-driven or low-energy flow, low evaporation, and site-specific water resources. Three technical modes were then proposed for typical regional practices. (1) Self-pressurized intelligent irrigation and drainage mode was represented by the Daheyanzi irrigation district, particularly for natural elevation differences and strong demands of irrigation drainage and intelligent operation. Self-pressurized pipeline conveyance, subsurface drainage, and digital monitoring were integrated with water and salt regulation in this mode. (2) The Ili River Valley mode the “low water source and high farmland” constraint to valley slope in irrigation areas. Technical pathway included hydropower generation, centralized lifting, high-level storage, and self-pressurized drip irrigation. (3) Yuepuhu mode was designed for pressurized irrigation districts of plain oasis with long-distance open-channel conveyance losses and decentralized field pumping facilities. Conveyance losses were reduced for high efficiency using pipeline replacement of canals, centralized pressurization, and metered regulation. With water saving and efficiency, Karez Engineering can be expanded into water source regulation in arid areas. In internal potential exploitation, the Shihezi mode focused on the identification, storage, and reorganization of potential water resources in spring overflow zones of piedmont alluvial fans, with emphasis on underground regulation, harmful-water control, and coordinated surface water–groundwater. For water-source augmentation, the formation-pressure-driven water-lifting mode explored the development and allocation of deep confined groundwater by utilizing natural formation pressure, high-elevation storage, gravity-driven pipeline conveyance, and intelligent irrigation. Overall, Karez Engineering of water resources regulation can be expected to shift from engineering water-saving into a multi-mode, multi-scenario, and system-oriented framework in arid regions. The findings can provide technical references for decision-making on the irrigation district, water security, and oasis ecological stability in Xinjiang of western China.