基于MODFLOW-CFP的贵州大井流域岩溶地下水数值模拟

贵州大井流域岩溶分布广泛,岩溶水是当地人民生产和生活的主要来源。由于对岩溶水资源的不合理开发利用,水资源短缺现象经常发生。大井流域水文地质条件复杂,管道-多孔介质双重介质特征明显。文章采用MODFLOW-CFP耦合模型对大井流域展开数值模拟,进而掌握大井流域地下水运动规律、准确评价岩溶水资源,促进其合理开发利用。结果表明:大井流域管道与多孔介质交换量为6 719.1 m³·a^-1,主要集中在上游和中游;总补给水量为10 977.3×10⁴m³·a^-1,补给模数为133.495m³·km^-2·a^-1,其中降雨汇入量和降雨入渗量占总补给量的81.35%,而总排泄量为10 813.47×10⁴m³·a^-1,主要在地下河出口排泄。

Numerical simulation of karst groundwater in Dajing basin of Guizhou Province based on MODFLOW-CFP

China is a country with the most widely distributed karst, and the karst is extensively developed in its southwesten part where 2,836 underground rivers are distributed with about 1,847.8×108 m3·a−1 of karst groundwater resources and a total discharge of 479.7×108 m3·a−1 in the dry season. These underground rivers become the main water source for people's life as well as the development of industry and agriculture in Southwest China. However, water shortage has often occurred in recent years, due to the unreasonable development and utilization of karst water resources. How to make scientific, reasonable and effective use of karst water resources has become a difficult problem in tackling water resource crisis. In this paper, we have studied the hydrological process and numerical simulation of groundwater in karst areas from the perspective of groundwater science, which is of great significance to the accurate evaluation, and rational development and utilzation of karst water resources.In this study, we take Dajing basin, a typical karst peak-cluster depression area in southern Guizhou Province, as the study area. Water-bearing media in karst areas often include karst pipelines with high permeability and dissolved gaps with low permeability. The flow mechanism of groundwater in these two media is quite different. The groundwater in the gap mainly accords with Darcy’s law and the laminar flow mechanism, while the groundwater in the karst pipeline is mostly in the turbulent state due to the large flow rate. In the actual situation, the two media are independent of each other, but there is an interrelated process of hydraulic exchange on the boundary. Based on this, we adopt MODFLOW-CFP coupling model to carry out a numerical simulation of Dajing basin. MODFLOW-CFP is a dual-system coupling model based on dual structure theory. MODFLOW-CFP model contains three groundwater flow simulation methods. In this study, CFPM1, the most basic model, is adopted. In this pattern, the traditional groundwater flowing model is coupled with a specific pipeline model. The main purpose is to depict caves, cracks in interstitial space and basaltic aquifer pipes in karst aquifers, where groundwater can be fully or partially filled and flow patterns can be laminar or turbulent. Therefore, a complete simulation of the hydrological process of karst groundwater may help us to grasp the law of groundwater movement in Dajing basin, accurately evaluate karst water resources, and thus promote the rational development and utilization of the resources.The process of using MODFLOW-CFP to establish a mathematical model of groundwater in Dajing basin includes the establishment of porous media model in MODFLOW and pipeline model in CFP. Subsequently, the two models are combined together to identify the model and analyze the water balance, based on the coupling model. Finally, the water resources are evaluated and the mechanism of groundwater migration is studied. In this study, it is found that Dajing basin is a groundwater system with complete recharge, runoff and drainage conditions, and the North-South and the Northeast-Southwest trending structures control the distribution of regional karst aquifers and the development of karst. According to the buried conditions of groundwater and the practical significance of water supply, the main source of recharge in this area is atmospheric rainfall, and the main discharge is the outflow from the southern Dajing basin. Meanwhile, the simulation results show that the exchange capacity between pipes and porous media is 6,719.1 m3·a−1, mainly in the upper and middle reaches of Dajing basin. The total recharge water in the study area is 10,977.3×104 m3·a−1, and the recharge module is 133.495 m3·km−2·a−1. The rainfall inflow and infiltration accounts for 81.35% of the total recharge, and the total discharge is 10,813.47×104 m3·a−1, mainly from the outlet of the underground river. Based on the research findings, the migration mechanism of groundwater in Dajing basin is clarified, and new development and utilization of water resources are put forward to address the shortage of local water resources.