GIS-assisted FEFLOW modeling of groundwater moving processes within the Minqin oasis in the lower reach of the Shiyang River, Northwest China

Oases are specific landscapes and play very important economic roles in arid Northwestern China. Yet, the peripheral ecological systems around the oases are equally important to the oasis economic systems in terms of protecting the oasis from desertification and ensuring sustainable development of oases. However, the rapid increases in the population and steady progress in the society and technology since 1950s have greatly expanded irrigated agricultural production in the oases, resulting in a dramatic decrease in stream flow and associated increase in the groundwater withdrawal in arid Northwestern China. The overexploitation of groundwater formed groundwater table depletion cones and eventually lowered the groundwater table not only in the oases but also in the periphery of the oasis, resulting in an overall decrease in soil water content. In response to the soil moisture decrease in the periphery, some plant species relying on groundwater resource have been dying out and other more mesic species have been replaced with more xerosere species. In this paper, the groundwater flowing processes and the water-table fluctuating processes during the past 40 years were simulated to obtain the spatial and temporal distribution of groundwater table by means of the GIS-assisted FEFLOW modeling based on the hydrogeologic data obtained in the Minqin Basin. Several conclusions can be drawn from the simulated results. Firstly, the discharge and recharge of groundwater retained balanced and the groundwater table depth in the periphery area of the oasis maintained 2-3 m deep during 1960-1965. Secondly, the utilization of the groundwater dropped the groundwater table within the oasis to 5-10 m, leading to the formation of big groundwater depletion cones that started to influence the groundwater table of the periphery area in the 1970´s. Thirdly, the further overexploitation of the groundwater within the oasis has dropped the groundwater table to 10-20 m in the oasis and 7-10 m in- the periphery since the middle 1980´s