明月峡背斜南部张关—排花洞岩溶水系统地下水径流模式解析

川东明月峡背斜地下岩溶发育的强烈非均质性造就了独特的地下水径流模式，孕育出区域复杂的岩溶工程水文地质问题，查明明月峡背斜南段地下水径流模式对指导区内隧道工程选址及建设具有重要意义。文章在已有研究基础上，以“张关—排花洞”岩溶水系统为研究区，通过系统厘清区内水文地质条件，深入剖析区内地下水水文地球化学特征及水动力条件，明确区内岩溶含水介质不均一性控制下的地下水小尺度径流规律。结果显示：研究区地下水在平面上表现为形似“扫帚状”的径流模式：在补给、径流区，三叠系下统嘉陵江组一段（T₁j¹）、嘉陵江组三段(T₁j³)地层（强岩溶化）与嘉陵江组二段（T₁j²）、嘉陵江组四段 （T₁j⁴）地层（弱岩溶化）呈间互状分布的特点导致相邻地层之间水力联系较弱，以地层为单位形成多个相对独立的岩溶水子系统；在研究区排泄区，受控于势汇最强的T₁j³内部管道流对其他地层地下水持续的袭夺效应，地下水统一汇聚至排花洞暗河出口向御临河排泄，各岩溶水子系统最终整合为一个岩溶水系统。

Analysis of groundwater runoff patterns in Zhangguan-Paihuadong karst water system in the south of the Mingyue gorge anticline

The long-term interaction between groundwater and karst development in eastern Sichuan has created a unique groundwater runoff pattern and caused a complex hydrogeological problem of karst engineering. Hence, finding out the groundwater runoff pattern in the southern section of Mingyue gorge anticline is of great significance for guiding the site selection and construction of tunnel engineering in this area.Based on previous studies, hydrogeological conditions of the study area are systematically sorted out. Mingyue gorge anticline is a typical closed one in eastern Sichuan, and there is no fault in the area. Atmospheric rainfall is the main recharge source in the water system. Controlled by the boundary of the non-soluble rock formation on the two sides of anticline and topographic relief, groundwater converges and is recharged through the karst structures such as depressions and sinkholes, flowing toward the river runoff at the lowest discharge datum along the tectonic line within the region. The outlet of S05 (Paihuadong), exposed on the bank slope of Yulin river, is a main discharge point of groundwater in the system. The discharge is about 365 L·s-1 in the dry season, accounting for 95.94% of the total discharge of all natural groundwater outcrops in the study area. Main aquifers in the area are composed of carbonate rocks of Jialingjiang formation and Leikoupo formation. The lithology of T₁j1 and T₁j3 is mainly limestone, while the lithology of T₁j2 , T₁j4 and T₂l is mainly dolomite. The difference of rock solubility results in different karst development in each aquifer. From the perspective of surface karst phenomenon, the area of depression and the number of falling holes developed in T₁j1 and T₁j3 strata respectively account for 67.38% and 69.84% of the total amount of the system. From the perspective of underground karst phenomenon, 121 karst caves have been revealed by 22 boreholes in the study area. The number of karst caves distributed in T₁j1 and T₁j3 strata accounts for 75.8% of the total. Statistical results of surface and underground karst phenomenon reflect that the degrees of karst in T₁j1 and T₁j3 strata is significantly higher than those in T₁j2 , T₁j4 and T₂l strata. Because aquifers with different degrees of karstic distribution are intersectional in the plane, the heterogeneity of water-bearing media leads to relatively weak hydraulic connection in adjacent strata, and the groundwater level revealed by boreholes and spring points is obviously different in different layers.Results of hydrochemical analysis of 18 groups of water samples in the study area further illustrate the discontinuity of groundwater in each aquifer. HCO₃-Ca type water mainly exists in T₁j1 and T₁j3 strata. Their conventional hydrochemical and isotope characteristics indicate that the water-rock interaction time is relatively short. Hydrochemical types of T₁j2, T₁j4and T₂l strata are mainly HCO₃·SO₄-Ca and HCO₃·SO₄-Ca·Mg. Their conventional hydrochemical and isotope characteristics indicate that the water-rock interaction time is relatively long, and the hydrochemical characteristics of groundwater outcrop in strong and weak karstified strata are obviously different. From the hydrogeological profile of S01 (Zhangjiadong) to S05 (Bahuadong), the hydrochemical types of water samples S01 and ZK07 in the recharge and runoff area of the system are HCO₃-Ca type, and the hydrochemical characteristics of the two are very similar. When sampling sites are located within a drainage area of the system, the hydrochemical type of groundwater near sampling sites ZK10 and S05 is changed to HCO₃·SO₄-Ca type, and corresponding TDS values are significantly higher than those of recharge and runoff area, indicating that groundwater in different aquifers is mixed in the system discharge area.Based on the analysis of karst hydrogeological conditions and hydrogeochemical characteristics in the study area, a runoff law of groundwater in Zhangguan-Paihuadong karst water system is summarized (groundwater in the study area generally shows a broom-like runoff pattern). In system recharge and runoff areas, a hydraulic connection between aquifers is not strong. Multiple groundwater flow systems have formed with the stratum as a unit, and groundwater carries out relatively independent bedding runoff in each layer. In the drainage area of the system, the mutual capture of each water flow system is increasingly strong. Hence, these water flow systems gradually merge into one, discharging to Yulin river through the drainage hole. In addition, according to previous research, groundwater inside the system vertically presents a multi-order nested flow system. Controlled by the discharge datum of different cutting depths, this system is successively developed into local flow system, intermediate flow system and regional flow system from the shallow part to the deep.