岩溶山区坡面一孔多层地下水监测试验及科学意义

郭芳; 姜光辉; 刘凡; 李志杰

doi:10.11932/karst20240301

岩溶山区坡面一孔多层地下水监测试验及科学意义

doi: 10.11932/karst20240301

郭芳^{1, 3,},
姜光辉^{2, 4, ,},
刘凡^{1, 3},
李志杰¹

1.
中国地质科学院岩溶地质研究所/自然资源部、广西岩溶动力学重点实验室/联合国教科文组织国际岩溶研究中心, 广西桂林 541004
2.
广西大学土木建筑工程学院, 广西南宁 530004
3.
广西平果喀斯特生态系统国家野外科学观测研究站, 广西平果 531406
4.
广西大学广西岩溶区水安全与智慧调控工程研究中心, 广西南宁 530004

基金项目: 国家自然科学基金资助项目（42172287，42272303）；广西自然科学基金(2020GXNSFDA238013)；桂林岩溶地质广西野外科学观测研究站（科研能力建设）(桂科23-026-274)；国家自然科学基金（41472239）

详细信息

作者简介:
郭芳（1978－），女，博士，研究员，主要从事岩溶水文地质研究。E-mail：gfkarst@126.com

通讯作者:
姜光辉（1977－），男，博士，教授，主要从事岩溶水文地质研究。E-mail：bmnxz@126.com。

中图分类号: P641
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出版历程
- 收稿日期: 2024-01-10
- 录用日期: 2024-04-29
- 修回日期: 2024-04-26
- 网络出版日期: 2024-08-15
- 刊出日期: 2024-06-25

Experiment of monitoring multi-layer groundwater at a karst hill slope and its scientific significance

GUO Fang^{1, 3
,},
JIANG Guanghui^{2, 4
, ,},
LIU Fan^{1, 3},
LI Zhijie¹

1.
Institute of Karst Geology, CAGS/ Key Laboratory of Karst Dynamics, MNR & GZAR/International Research Centre on Karst under the Auspices of UNESCO, Guilin, Guangxi 541004, China
2.
College of Civil Engineering and Architecture, Guangxi University, Nanning, Guangxi 530004 China
3.
Pingguo Guangxi, Karst Ecosystem, National Observation and Research Station, Pingguo, Guangxi 531406 China
4.
Guangxi Provincial Engineering Research Center of Water Security and Intelligent Control for Karst Region, Guangxi University, Nanning, Guangxi 530004 China

摘要

摘要: 钻孔是揭露含水层结构和开展地下水监测的重要载体。在场地地下水监测中，不分层的丛式钻孔存在成本高、代表性不全等缺陷。“一孔多层”分层监测对水头或溶质分布的区分度高，在孔隙和裂隙含水层应用广泛，但岩溶介质因结构复杂，极少有案例研究。文章对丫吉试验场西坡径流小区的一个钻孔(ZK6)进行分层并开展监测。依据钻孔岩芯编录资料、抽水试验以及水化学与温度测孔的结果，判断岩溶发育的特征，确定将ZK6孔划分为四层，实施了钻孔封隔。对四个层位的水文观测发现，四个层位的水位动态对降雨的响应有较大差异。其中，第一层一个水文年中无水和充水状态时长分别占79%和21%，说明该层的岩溶介质处于充水和无水交替，且更多时间处于无水状态；第二层水位响应滞后明显；第三层和第四层水头差异表现出地下水排泄区的水头垂直分布特征。ZK6孔四个层位的水化学存在差异，表明岩溶介质结构的差异不仅影响了水文过程也影响水化学特征。第四层的电导率基本稳定在450 μS·cm⁻¹，而第二层因表层元素积累和水更新速率慢，电导率是第四层的2倍，第一层电导率的剧烈变化则反映表层岩溶带受到降雨补给影响最为强烈。综合钻孔分层的水文和水化学特征，认为第一至第四层分别代表表层岩溶带、裂隙基质带、上部饱水带和下部饱水带。岩溶山坡的“一孔多层”分层技术难度大，但一旦实现不仅可以认识岩溶垂向分带的水动力机制，也为地下水分层开发利用技术突破提供了可能。
- 坡面水文 /
- 钻孔多层监测技术 /
- 表层岩溶带 /
- 岩溶水 /
- 丫吉试验场
Abstract: The heterogeneity of karst aquifers and the complexity of karst hydrogeological conditions pose significant challenges to groundwater observation compared to the groundwater in pore and fissure aquifers. In the areas of springs or underground rivers in which lack natural groundwater outcrops, borehole drilling is crucial for us to reveal aquifer structures and monitor groundwater. Clustered single-hole drilling inadequacies are pronounced in karst regions, because we need numerous times of single-hole drillings to comprehensively reveal different aquifer conditions, which may in turn result in land occupation and high costs. Besides, the difficulty in accurately locating karst conduits or fractures, due to complex hydrogeological conditions, may contribute to potential incompleteness of single-hole representativeness. Finally, drilling for groundwater monitoring may traverse multiple geological layers, causing interconnection of groundwater, thereby making it impossible for us to distinguish water quality conditions in different layers or channels during groundwater quality monitoring.The drilling of one shaft with multi-layer borehole refers to the technique that can achieve segmentation of multiple layers within a single borehole drilling operation. This technique, also known as Continuous Multichannel Tubing (CMT), is an internationally recognized method for layered drilling monitoring, is widely utilized in North America but seldom used in China. Because the technique of one shaft with multi-layer monitoring demonstrates its high ability in differentiating water head or solute distribution, it has been extensively applied in monitoring in pore and fissure aquifers, but seldom in karst media because of its complex structure. Therefore, there are no reported cases of application of this technique in karst regions, and its feasibility needs to be confirmed.The Yaji karst hydrogeological experimental site (hereinafter referred to the Yaji experimental site) represents a typical bared karst aquifer system in Southern China. The aquifer comprises three parts: the upper vadose zone, lower vadose zone, and saturated zone, playing the role of rainfall storage and regulation. Eighteen clustered-distributed boreholes established at the experimental site can reflect the heterogeneity of karst development or water level changes on a planar scale, yet they can hardly reveal the vertical groundwater movement. It is difficult for us to use open boreholes in defining how the differences in karst development vertically affect hydrodynamics. Therefore, this study selected one borehole (ZK6) from the runoff area on the western slope of the Yaji experimental site to implement the one shaft with multi-layer drilling experiment, aiming to explore the application of layered drilling monitoring technique in karst aquifers. The study result can provide conditions for understanding groundwater stratification, vertical distribution of water heads, and layered pumping, and more importantly, provide experience in applying borehole layering techniques and schemes in highly heterogeneous karst water-bearing media.Firstly, based on the data of borehole core, pumping tests, and results from hydrochemical and temperature logging, ZK6 was divided into four layers, with karst development characteristics as the main basis for division. Secondly, hydrological and hydrochemical characteristics of the four layers were compared and analyzed. Significant differences were found in the water level dynamics of the four layers in response to rainfall. The first layer predominantly alternates between being dry and being filled with water throughout a hydrological year, occupying 79% and 21% of the time respectively, which indicates alternating dry and wet conditions in the karst media, with a tendency towards dryness. The second layer exhibits significant lags in water level response. Differences in water heads between the third and fourth layers reflect the vertical distribution characteristics of groundwater discharge zones. Differences in hydrochemical characteristics among the four layers suggest that discrepancies in karst media structures affect both hydrological processes and hydrochemical characteristics. The electrical conductivity in the fourth layer remains relatively stable at 450 μS·cm⁻¹, while in the second layer, due to surface element accumulation and slow water renewal rates, the electrical conductivity is twice that of the fourth layer. The drastic changes in electrical conductivity in the first layer reflect the strong influence of rainfall recharge in the surface karst zone. Finally, based on the hydrological and hydrochemical characteristics of borehole layers, it is concluded that the first to fourth layers respectively represent the epikarst zone, fissure-matrix zone, upper saturated zone and lower saturated zone. Although the technique of one shaft with multi-layer poses operating challenges in karst mountain slopes, once achieved, it will not only facilitate our understanding of the vertical hydrodynamic mechanisms of karst stratification, but will also achieve possible breakthroughs in technology for layering development and utilization of groundwater in heterogeneous karst aquifers. The use of borehole layering monitoring technique enables the measurement of vertical distribution of water heads within boreholes, thereby providing the potential for utilizing layering isolation techniques to facilitate runoff utilization from epikarst zones and vadose zones.
- hillside hydrology /
- technique of multi-layer monitoring /
- epikarst /
- karst water /
- Yaji experimental site

HTML

图 1 丫吉试验场S31泉域系统与钻孔分布图

1. 泉水及编号 2. 钻孔及编号 3. 洼地及编号 4. 系统边界 5. 断层 6. 地下水流向 7.峰丛洼地与峰林平原界线 8. 公路 9. 第四系 10.融县组灰岩

Figure 1. S31 spring system and borehole distribution in the Yaji experimental site

1. Springs and numbers 2. Boreholes and numbers 3. Karst depressions and numbers 4. Water system boundary 5. Fault 6. Groundwater flow direction 7. Boundary of peak cluster-depression and peak forest-plain 8. Road 9. Quaternary 10. Limestone in Rongxian Formation

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图 2 ZK6钻孔分层示意图

Figure 2. Schematic diagram of borehole layers(ZK6)

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图 3 ZK6水化学测孔剖面与岩溶带的划分

Figure 3. Profile of hydrochemistry logging and the division of karst zones

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图 4 ZK6(孔口标高：156.45 m)和ZK7(孔口标高：160.35 m)水文动态变化

Figure 4. Variation of hydrological processes in boreholes ZK6 (orifice elevation: 156.45 m) and ZK7(orifice elevation: 160.35 m)

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图 5 ZK6分层水化学对比(2018年7月)

Figure 5. Comparison of hydrochemistry among different layers at ZK6

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图 6 钻孔ZK6的三个层位水温和电导率监测结果

Figure 6. Online monitoring results of water temperature and conductivity at three layers of borehole ZK6

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表 1 钻孔ZK6的分层方案

Table 1. Layering scheme of borehole ZK6

层位	通道	分层位置	岩溶特征	分层目标
第一层	ZK6-1	岩石表面至洞穴下方。深度为地面以下6.5 m（156.45~149.95 m）	发育0.7 m高的洞穴	洞穴可能为表层岩溶水季节性的排泄通道，需要独立观测水位
第二层	ZK6-2	第一止水位置（6.5 m）至表层岩溶带的下界，第二止水位置为地面以下10 m（149.95~146.45 m）	疑似岩溶管道一处	水化学与温度变化趋势发生变化，需要独立观测
第三层	ZK6-3	第二止水位置至变径处，止水位置为地面以下28 m（146.45~128.45 m）	岩溶裂隙发育的迹象	岩溶裂隙水流导致水化学变化，推测可能是坡面下部径流的主要排泄区
第四层	ZK6-4、ZK6-5 ZK6-6、ZK6-7	第三止水位置以下至孔底（128.45~95.45 m）	具有弱岩溶现象的裂隙	水流微弱，可能是地下缓流层

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表 2 ZK6分层之前与其他坡面钻孔的水的物理－化学性质对比

Table 2. Comparison of physicochemical properties of ZK6 before layering and other boreholes at the slopes

钻孔编号	水深 /m	Ca²⁺	${\rm{HCO}}_3^{-}$	温度 /℃	pH	电导率 /μS·cm⁻¹
钻孔编号	水深 /m	/mg·L⁻¹		温度 /℃	pH	电导率 /μS·cm⁻¹
ZK1	9.63	138	378	26.6	7.13	580
ZK2	8.84	137	317	27.3	7.38	456
ZK3	7.91	98	268	24.4	7.57	409
ZK4	2.72	108	329	25.1	7.30	498
ZK5	7.57	130	397	27.8	7.20	531
ZK6	6.50	136	397	21.1	7.15	590
ZK7	6.19	82	238	20.3	7.58	391
ZK8	4.57	131	354	20.5	7.25	549
ZK9	3.65	148	433	25.3	7.10	665

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