珠江流域岩溶地下河分布特征与影响因素研究

珠江流域岩溶地下河枯季流量约4 738.69万m³·d⁻¹，赋存丰富的地下水资源，探讨地下河分布和发育特征对我国南方岩溶水资源的开发利用具有重要的指导意义。文章以西南岩溶区大量的野外调查工作为基础，结合珠江流域内1∶20万水文地质普查报告，选择348组岩石样品和1 036条岩溶地下河，从岩性、地形地貌、构造、水动力条件和新构造运动等角度总结分析珠江流域地下河发育规律、分布特征及其影响因素。结果表明：地下河在比溶解度介于0.84~1.2的细粒−鲕粒生物碎屑纯灰岩中最为发育，在比溶解度介于0.43~0.61的泥质灰岩中发育较弱。根据地下河形态及水循环演化条件，将地下河分为发育初期单管型、发育多期羽毛型、新构造控制网络型、发育成熟期树枝型4种类型。地形地貌和地表河网决定岩溶地下河运动的趋势和方向；构造控制地下河发育的空间格局，其中构造反接复合部位、压扭性断裂两侧破碎带、与非可溶岩接触带、褶皱弯曲最大部位、背斜轴部破碎带和向斜轴部地下河发育尤为明显；水动力特征影响地下河发育规模和发育深度；新构造运动促进地下河发育向深性、继承性、新生性发展。

Distribution and influencing factors of karst underground rivers in the Pearl River Basin

The Pearl River Basin is the area of first-class water resources at the southernmost end of China. Its geographical location is 102°14′-115°57′ E and 21°35′-26°50′N. The main stream of the Pearl River, with a total length of 2,214 km, flows through Yunnan, Guizhou, Guangxi and Guangdong. The total area of the Pearl River Basin is about 438,100 km2, including Nanbeipan river, Hongliu river, Yujiang river, Xijiang river, Beijiang river, the Pearl River Delta and the dongjiang river basin. The water-bearing rocks in the Pearl River Basin are divided into karst water of carbonate rock, fissure water of clastic rock, pore water of loose rock and fissure water of magmatic rock. The distribution area of exposed carbonate rocks is about 149,500 km2, and that of buried carbonate rocks is about 39,600 km2, accounting for 43.16% of the total area. Because there are 1,036 karst underground rivers, and the discharge of karst underground rivers of the Pearl River Basin in the dry season is about 47.39 million m3·d−1. the basin is rich in groundwater resources. Therefore, it is of great significance to explore the distribution and karstification characteristics of underground rivers for the exploitation and utilization of karst water resources in southern China. Based on a large number of field investigations in the southwest karst area, 200,000 hydrogeological survey reports and the 1∶250,000 and 1∶50,000 karst hydrogeological surveys conducted from 2003 to 2016 in the Pearl River Basin, we selected 348 groups of rock samples and 1,036 karst underground rivers as study objects. Then, taking Dalongtan and Sanqiutian underground rivers in Yunnan Province, Sixiaojing, Tianshengqiao and Huachu underground rivers in Guizhou Province, and Disu, Zhaidi and Dizhou underground rivers in Guangxi as examples, we analyzed and summarized the development law, distribution characteristics and influencing factors of underground rivers in the Pearl River Basin from the perspectives of lithology, landform, structure, hydrodynamic conditions and neotectonic movement. According to the analysis, the outlets of 310 underground river are at an elevation between 200-400 m, accounting for the largest proportion. Among them, more than 30 underground rivers, mainly located in the river basins of Hongliu river, Yuhe river, South Panjiang river and north Panjiang river, respectively cover a catchment area greater than 200 km2. Their discharge in the dry season is greater than 1,000 L·s−1 and the length of main pipeline is greater than 10 km. The study result shows that the underground river is most developed in fine-grained oolitic bioclastic pure limestone with a specific solubility of 0.84-1.2, moderately developed in dolomite with a specific solubility of 0.62-0.83, and weakly developed in argillaceous limestone with a specific solubility of 0.43-0.61. Landform and surface river network determine the trend and direction of karst underground river movement. The structure controls the spatial pattern of underground river development. The development of underground river is particularly obvious in the reverse composite part of the structure, the fracture zone on both sides of the compressional torsional fault, the contact zone with the non-soluble rock, the part with the largest fold bending, and the fracture zone in the anticline axis and the syncline axis. Hydrodynamic characteristics affect the development scale and depth of underground rivers. The neotectonic movement facilitates the constant changes of cycle and alternation conditions of groundwater, as well as the deep, inherited and new development of underground rivers. Finally, according to the morphology of underground river and the evolution conditions of water circulation, the underground river can be divided into four types: single conduit type at the initial stage of development, multi-stage feather type, neotectonic control network type and mature dendritic type. All in all, this study is expected to provide data support for the exploitation and utilization of karst underground rivers, monitoring and evaluation of water resources, and the selection of backup water sources to meet urban emergency in the Pearl River Basin.