| In the mountainous southwest China karst terrain, there are numerous basins scattered on the rolling plateau karst surface (planation surface). Many of these basins are inhabited by tens of thousands or even over one million people and with tens of thousands ha arable land. The river levels in these areas are much lower than the farmland, human settlement areas and economic districts, which gives rise to the problem of disharmony between the uses of land and water. Meanwhile, in these areas the karst water resources, in particular the underground karst water reserves, are valuable natural reservoirs. To scientifically carry out exploration, planning, exploiting and make rational use of these karst water resources will greatly ease the problems of water shortage and the disharmony between land and water. In a karst basin and along the whole drainage area, i.e. from the recharge area to the runoff area and to the discharge area, not only the geological conditions but also the characteristics of water source, water storage and flow change drastically from place to place. Accordingly, different water exploration and exploitation techniques are needed for different areas. What techniques should be adopted can only be determined by many experimental studies and engineering practice on typical karst areas. In this respect, the successful study and karst water exploration and exploitation practice in Luxi basin and Xiaojiang drainage area provides a good example for many water-stricken karst areas. It will be of great significance for many other karst areas to adopt the Luxi model of karst water exploration so as to effectively make use of karst water and control rock desertification.Covering a total of 1,009.28 km~2, the Xiaojiang drainage area of Luxi County is located in eastern Yunnan Province. Carbonate rock, particularly the limestone and dolomite (Gejiu Formation) of the Middle Triassic period account for more than 70 % of the drainage area. The Luxi basin is a NE-SW stretching, oval-shaped karst basin positioned in the middle-upper reaches of the Xiaojiang drainage area. The flat basin bottom area, 78.1km~2 and 1700m above sea level, serves as the erosion base of the higher regions. Surrounding the basin is the carbonate mountain area that characterized by well-developed various karst landforms between 1,800-2,459m elevation range. To the south of the basin is the Xiaojiang River valley which located in the lower reaches of the drainage area. As the discharge base of the lower regions, the Xiaojiang River valley is in "V" shape and with the lowest elevation at 820m, its down-cutting depth ranges from 500m to 1639m. The karst geological and ecological environments along the Xiaojiang drainage area are diverse and complex. The whole drainage area features uneven karstification processes, from the recharge area to the discharge area there are Karst mountain, valleys, hills, peak cluster-depressions, plain and canyon, etc. In many ways the Xiaojiang drainage area is a typical area in the southwest karst terrain of China.This study has accomplished the hydrogeological and environmental geological surveys of the whole Xiaojiang drainage area including the physiographic and geological backgrounds, hydrogeological conditions, and evaluations on geological environment and hydrogeologic zonation; This study has also systematically analyzed the transfer and equilibrium among different waters, redefined the meaning of "karst water source field" and put forward a new category of "karst water source field"; The new category first classifies, based on the bury state of aquifer and water exposure on surface, the "karst water source field" into two broad types: "natural exposed karst water source field" and "buried karst water source field"; Further, based on water-bearing medium, water conduit and storage place and structure, water dynamic feature, the "natural exposed karst water source field" is subdivided into three subtypes: "subterranean stream", "karst spring" and "epikarst spring"; The "buried karst water source field" is subdivided into "water-rich block in water-saturated zone " and "water-rich block in epikarst zone"; This study has carried out research and appraisal on the concentration patterns of different karst waters, their sources and dynamic features, their exploitative technical conditions and vulnerability; Based on thorough study of previous karst water prospecting and exploiting practice and helped with latest engineering techniques, this study has reviewed past experiences and, in particular, made some improvements to the previous successful karst water prospecting and exploitation techniques; During the research process, experimental study of karst water exploration and and exploitation was conducted on selected sites where the water source and the geological environment were different; Finally, a comprehensive karst water exploration and exploitation plan was worked out and an integrated water exploitation model of karst basin and drainage area was achieved. In order to find out the effective karst water probing techniques, seven sites, which located in different geological conditions such as large karst springs, epikarst springs, buried water-rich blocks in the water-saturated zones., have been chosen for experimental test. Adopted methods include electrical-resistivity method, induced activity polarization method, nuclear magnetic resonance method, geologic radar method, high-density resistivity method and so on. Some combined methods have also been tested. These tests have examined the effectiveness of the adopted methods and brought about needed parameters which were later integrated into the effective water probing techniques.For the water-rich block in water-saturated zone, firstly use the electrical-resistivity method to outline the size and preliminary ascertain the water-rich section, then, based on the results of geological survey and electrical-resistivity probing, select several candidate borehole locations; Secondly, use the nuclear magnetic resonance method to examine the water concentration extent of each unit that encircled by probing antenna, find out the unit with highest water concentration; Finally, use induced activity polarization method at 10m interval or high density electrical-resistivity method to locate the the underground location of karst water-storing void. This water probing procedure has greatly enhanced the accuracy of borehole design, all five wells drilled succeeded in water exploration.In order to investigate the epikarst development and provide data for drilling shallow well, geologic radar was adopted to probe the strata profile. Four boreholes have been drilled and all of them were successful. It demonstrates that the geological radar is an effective means for examining lithological layering and karst fracture zone.Large spring experimental exploration was conducted at Pijiazhai and high-density resistivity method was used to probe the structure, stability and karst aquifer of the capping bed. It was proved by boreholes that the thickness of the top clay layer is very close to that of the estimated, and water conduits were also found at the speculated karst locations. It shows that the high-density resistivity method is an efficient means for locating the underground karst and its burial depth by shallow borehole (less than 60m deep). For karst water exploitation experiment, nine pilot engineering projects have been conduced at different karst water source fields, each field has different geological conditions:Two epikarst water diverting and storing projects were conducted respectively at Wanbankong and Liziqing, Santang Town, which is the mountainous recharge area adjacent to the basin; For the exploitation of water-rich block in the water-saturated zone of the exposed karst area, two deep well projects were carried out respectively at the Dayicun and Wanmuguoyuan, an water recharge area and a karst hill-valley- peak cluster-depressions terrain located at the upper part of the basin; One restricted fluid-control hydraulic pressure-raised big karst spring water exploitation project was conducted at Pijiazhai, a karst hill-valley area by the upper part of the basin where the upper karst water discharged; One shallow well demonstration project was conducted at Nabao Village, an area located at the karst hill-platform by the middle-upper part of the basin, to exploit the epikarst water-rich block and provide water for family use; Tow deep well demonstration projects were carried out respectively at the runoff area - Sanjia Village and the runoff transitional area-Daxingbao Village, both located at the hill-platform by the lower part of the basin, to exploit the water-rich block in the water-saturated zone of buried karst; One deep well project was conducted at the flat basin-eastern Dinghe Village to exploit the water-rich block in the water-saturated zone of buried karst. All these pilot projects have brought about fruitful results. To date, seven step hydropower stations have been built in the Xiaojiang River with a total of installed capacity of 35.38MW.Based on plentiful engineering practice, an integrated water exploitation model of karst basin and drainage area has been accomplished. This model can be summarized as follows: Take into consideration of the karst water process in the water course from the recharge area to the runoff area and to the discharge area, combine conventional techniques with latest techniques, to find out the karst water resource, water source field type, water concentration pattern and exploitative technical conditions along the whole drainage area; According to the local geological conditions, water exploitation purpose, and take into account of the karst water source area type, water occurrence state of different karst bio-geological sections in the whole drainage area, to plan and design water exploitation projects; In the recharge area, i.e. the exposed karst mountain area surrounding the basin, mainly carry out epikarst water diverting and storing projects; In the peripheral area of the basin, i.e. the karst hill-valley-peak cluster-depressions-platform area, mainly carry out diverting, pumping, embanking projects of subterranean streams and springs, and also exploit the water-rich blocks in the water-saturated zone; In the flat basin area, mainly carry out borehole drilling projects to exploit the water-rich blocks in the water-saturated and epikarst zones, also conduct diverting, pumping, embanking projects of subterranean streams and springs; In the lower reach valley area, mainly carry out step water reservoir and hydropower station construction so as to make full use of the water resource.The karst water exploitation model of Luxi Xiaojiang karst basin embodies the principle of adopting appropriate engineering techniques to the local physical conditions, and exploiting different karst water source fields for different water needs. The karst water exploitation projects have resulted in significant economic, social and environmental benefits. These pilot projects have realized, their expected goals.Now, in the study area the annual water production rate is 22.39×10~6 m~3. It meets the water needs of 30,326 people, 3,670 livestock and 2,146.67 ha. farmland. It brings about 2.87 million yuan direct income and 6.75 million yuan indirect benefits. The spring season of 2005 was the driest season since 1980, but all the demonstration projects functioned very well. Their drought-against role manifested perfectly.
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