西南岩溶峰丛洼地地区二元补给过程与分布式水文模型研究

Due to the complex hydrogeological characteristics of Southwest karst in China, the development of distributed hydrological model suitable for these areas has always been the research hotspot and challenge. Although the double-medium model, such as MODFLOW-CFP, could simulate the hydrological process in the dual structure of karst consisting of the conduit and fissured matrix, this model can hardly consider the dual recharge processes occurring in the unsaturated zone of peak cluster-depression area, which is very important for the simulation of hydrological process in the saturated zone and spring discharge. In this study, the Yaji karst experimental site is chosen as the research area. The cave dripping and epikarst spring in the depression is selected as the representative points of diffuse and concentrated recharge respectively. The methods of discharge curve analysis, hydrological chemistry and tracer test are used to study the dual runoff process and hydrodynamic characteristic of the unsaturated zone. Based on the analysis result, the physical conceptual model of the unsaturated zone is explored, and then is used to couple with the dual-medium model to establish the suitable distributed hydrological model for the cluster depression region. Finally, this new model is used to simulate the spring catchment of S31 to verify its feasibility. This research could further improve the understanding of hydrological process of unsaturated zone and promote the development of distributed hydrological model in the karst region.

由于西南岩溶地区复杂的水文地质条件，建立适合该地区的分布式水文模型一直是研究热点和难点。尽管目前提出的双重介质模型（例如MODFLOW-CFP）能较好地模拟含水层饱水带内管道-裂隙二元结构的径流过程，但该模型很难考虑峰丛洼地地区的二元补给过程（分散和集中补给过程），而这种二元补给过程对该地区水文过程和岩溶出口流量的模拟十分重要。本课题拟以桂林丫吉岩溶试验场为例，选取洞穴滴水和表层岩溶泉作为分散补给和集中补给的研究点，通过流量曲线分析、水化学和示踪试验等手段详细研究岩溶峰丛洼地地区包气带内的二元补给过程和水动力特征，在此基础上建立适合研究区包气带物理概念模型，并将该物理概念模型与双重介质模型耦合，建立既能反映峰丛洼地地区二元补给过程，同时也能模拟饱水带管道-裂隙二元结构的分布式水文模型。本项目的研究将进一步完善峰丛洼地地区补给过程的研究，同时也推动西南岩溶地区分布式水文模型的发展和应用。

本项目以桂林丫吉试验场为例，通过对表层岩溶带泉和洞穴滴水长时间监测详细调查了包气带内水文过程，基于多模型对比手段进一步分析了S31泉域内的主要水文过程，最后建立了适合峰丛洼地地区的分布式水文模型，并将该模型用于S31泉域流量和一次管道示踪试验模拟，取得了良好的模拟结果，该模型也极易用于我国其它岩溶峰丛洼地地区。野外监测结果显示该场地内包气带存在明显的二元补给过程（快速流和慢速流），其中快速流仅当场区内降雨量达到一定阈值时才产生，表层岩溶带泉或滴水流量出现陡涨陡落，这也是暴雨条件下S31泉流量陡涨的主要原因；而在小降雨条件下，包气带内仅存在慢速流，表层岩溶泉或滴水流量变幅相对较小。基于此，本项目在MODFLOW-CFP模型基础上采用一个表层岩溶带水箱来反映不同降雨条件下包气带的补给过程，MODFLOW-CFP模型用于模拟含水层饱水带内的水文过程，最后将两者耦合模拟整个泉域的水文过程和一次管道内溶质运移过程。对比不考虑包气带内二元补给过程的模型，该模型能更好模拟不同降雨条件下的泉流量过程和管道溶质运移结果。