| Located in the northwest region of Guizhou Province, Caohai in Weining County,with agriculture being its pillar industry, is a first-class national reserve area as well asthe major agricultural and tourism base of this place. It’s of great significance to havea good understanding of the local hydrogeological conditions and a sound assessmentof local water resources for such an understanding and assessment can be instrumentalin reasonable development and utilization of water resources, working out feasiblelayout of industrial and agricultural production as well as tourism development andachieving sustainable use of water resources. On the basis of preliminary datacollection, field investigations and analysis of groundwater samples, conclusions thatthis paper draws are as follows:(1) Weining County enjoys a subtropical humid monsoon climate bearing no coldwinter or hot summer. It has abundant rainfalls and a hot rainy season. This place alsobears the characteristics of low-latitude western plateau monsoon climate, havingapparent differences despite its small land area. The annual average temperature is11.1℃, with extreme maximum temperature being30.7℃and extreme minimumtemperature being-10.3℃. Its annual average rainfall is903.5mm and the periodfrom May to September is the wet reason, rainfalls in this period accounting to70%of the year’s total precipitation. Surface streams on the west side largely flow intoCaohai.(2) With an overall terrain of high west and low east, the study area is located inthe Yunnan-Guizhou Plateau, the northern section of Wumeng Mountains. Thealtitude of most areas is2180~2500m and it’s a hilly area with a maximum relativeelevation of359.0m. Major landforms of the study region include corrosion landformand lacustrine accumulation landform, and the former is divided into such microlandforms as erosion gentle hills, karst gullies, dissolution depressions, funnel andsinkholes.(3) There are a total of three sets of outcropping strata in study area,namelyCarboniferous (C), Permian (P) and Quaternary loose sediment layer (Q).Main fractures in this area are Kongjiashan Fracture (F2) and Mengjiashan Fracture (F3) which stretch in a direction of310°, and the southern segment of Erpu Fracturewhich distributes on the northwest side of the study region. Weishui anticline is thearea’s main fold and Datang Formation is the main core strata whose axis stretchesnorthward in a curve.(4) Carbonate karst fissure water is the major karst water in this region and can be divided into two sub-categories: karst water and karst fissure water.The main aquifers are the lower Permian Qixia formation (P1q) as well as limestone and dolomites between Carboniferous System’s Maping group (C3mp) and Datang Formation’s Jiusi section (C1d1). Carboniferous System’s Liangshan group (P1l) is the main aquiclude and middle sandstones, siltstone interbedded with shales and coal seams are the main exposed rocks.There are five main hydro chemical types of groundwater, namely HCO3-Ca·Mg, HCO3-Ca, HCO3+SO4-Ca·Mg, HCO3+SO4-Ca, and SO4-Ca·Mg with HCO3+SO4-Ca being the main one.Compared with dolomite area, karst of pure limestone area in this region hasa much stronger development and karst in tectonic belt has a strong development scale and depth. Erosion gullies with large scales usually develop along fractures and depressions, funnels as well as sinkholes with karst shapes, mainlydeveloping between Baizuo group (C1b) and Maping group (C3mp), largely grow along advantageous crack directions. Kongjiashan fault and Mengjiashan fault in the northwest study area play aapparently control role in the recharging, runoff and drainage of karst water.(5) The supply of natural karst water resources are calculated as follows: when Pequals95%, it’s21,047,500m3/a; when P equals75%, it’s25.8808millionm3/a; whenP equals50%, it’s29.4261millionm3/a; and the total volume of exploitablegroundwater resources is6.1861millionm3/a. The quality of karst water is in a soundoverall situation, basically reaching the secondary groundwater quality standard.(6) Water in this area is mainly for agricultural application and daily life use. Themajor ways of developing and utilizing karst water include direct use throughunderground rivers and karst springs, indirect use through establishing diversionchannels and reservoirs. Besides, very few regions utilize atmospheric precipitationby taking advantage of natural gullies and reservoirs. The four major protection areasof karst water are mainly for protecting karst spring, water quality, water volume andcoal seam belt. |
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