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Karst Waters Help Resolving Drought in Northwest China’s Arid Region
Major breakthrough have achieved in finding deep buried karst water in a Northwest China’s Special Program of Groundwater Resources. The Program started two years ago was carried out by the former Ministry of Geology and is now succeeded by the Ministry of Land and Resources. It is supported directly by the State Council. Fig.1 Location of exploration wells with high yield karst water The findings are at the eastern part of Northwest China’s Arid Region. It is in the neighbouring areas of Ningxia, Nei Mongol , Shaanxi, Gansu Provinces (or Autonomous Regions), and characterized by extensive Loess cover hundreds meters thick (Fig.1). It is thus called as Loess Plateau covering some 200,000 km2, and is the broadest of this kind of landscape in the world. In the north of the Great Wall, there is a 20,000 km2 Mu Us Desert. Geotectonically, it is underlain by the Ordos platform, where Lower Paleozoic carbonate rocks (Cambrian and Ordovician) are overlain disconformably by Permo-Carboniferous Coal measures , followed by Mesozoic Red Beds, Neogene Red Clay and Quaternary loess. The paleokarst on the surface of lower Paleozoic carbonate rocks is one of the most important natural gas reservoirs in China . The southern part of the Loess Plateau is bordered by the active Wei River Graben, where geothermal springs are often seen, and frequented by earthquake. The Wei River Plain is the cradle of ancient China’s culture, with its Xian city as the historical capital of many Dynasties. The Loess Plateau has long suffered from water shortage because of low annual rainfall ranging between 500mm at South (Xian) and less than 200mm at the North (Mu Us Desert), and bad water quality of shallow aquifers. Fig.2 Hydrogeological cross section of Well No.Y1,Fuping, Shaanxi The first breakthrough happened in early 1997, when the Y1 exploration well completed in Fuping County at the southern part of the Loess Plateau(Fig.1). It is 778m deep, but 200m are in Loess, with an addition of 300m in Neogene clay and gravel. 238m of the lower part in the well are in Ordovician Limestone Karst Aquifer (Fig.2). Pumping test gives a discharge of 5320m3 per day, with a drawdown of only 1.89m (Fig.3). The potential yield of the well is estimated to be 13300m3 per day. The TDS is 1.18g/L, while the water temperature is 43°C, obviously related to geothermal. The second well (Y2) was completed early 1998, near Qianxian county, also at the southern part of the Loess Plateau (Fig.1). It is 800.03m deep with a potential yield of 5000m3/D. The water temperature is 22 °C. In July 1, 1998, rich karst water was also found in the northern part of the Loess Plateau. The 175m deep No.107 well at Qipanjing Region, Otog Qi, Nei Mongol Autonomous Region (Fig.1), is on the northwest part of Mu Us Desert. Its potential yield is 10,000m3/D. Moreover, it contains some trace elements (Sr,Se etc.) which meet the National Standard of Mineral Water. The findings of deep karst water are highly praised by local residents. The Northwest China’s Special Program of Groundwater is still making Headway. According to tectonic background, hydrogeologists believe that it is also possible to find deep karst water in Ningxia Hui Autonomous Region and Gansu Province. Fig.3 Pumping test at Y1 well of Fuping county, Shaanxi Province
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