Research on water flow attenuation process and regulating capacity in karst vadose zone
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摘要: 我国岩溶水资源丰富，是岩溶地区重要的生产生活用水来源。岩溶包气带对地下水起着涵养调蓄作用，为定量评价岩溶包气带水流衰减过程和调蓄能力影响因素，通过搭建实验室尺度的岩溶包气带物理模型，分析衰减曲线与调蓄系数，探究降雨强度、传输带裂隙发育程度、传输带厚度对岩溶包气带水流过程与调蓄能力的影响。试验结果表明，降雨强度的增大将引起岩溶包气带水流衰减系数的增大与调蓄系数的减小，降雨强度对结构一定的岩溶包气带调蓄能力的影响有一定限度；随着传输带裂隙增加，快速流衰减系数呈增大趋势，慢速流衰减系数呈减小趋势，调蓄系数呈减小趋势；传输带厚度的增加引起衰减系数的减小与调蓄系数的增大，但对调蓄系数的影响不明显。Abstract:
The karst area in China accounts for about 20% of the total land area. The karst groundwater is rich in resources and is an important source of production and living water in karst areas. The annual average rainfall in karst areas of Southwest China exceeds 1,200 mm, but the time distribution of rainfall is extremely uneven, which is likely to cause drought and flood disasters, and hence will seriously restrict the production and life of local people. The karst vadose zone has the function of conserving and regulating groundwater. Therefore, it is of great significance to study the influence mechanism of water flow attenuation process and regulating capacity in the karst vadose zone for rational development and utilization of karst water resources. The high heterogeneity and the anistropy of the karst aquifer system often make the karst vadose zone form a drainage network and become a channel for groundwater. A karst vadose zone is mainly composed of soil zone, epikarst zone and transfer zone, of which the soil zone and the epikarst zone are main water storage space. The water storage function of karst vadose zone is related to the dynamic regulation of groundwater resources in the epikarst zone. Rainfall infiltration is transferred from the transfer zone to the phreatic aquifer through the regulating and diversion of the epikarst zone. In the karst vadose zone, the low flow velocity in diagenetic pores, micro fissures and carbonate rock matrix shows its feature of slow flow, while the fast flow velocity in large fissures and sinkholes is characterized by rapid flow. Therefore, the heterogeneity of karst aquifer system and the complexity of runoff path in karst vadose zone increase the difficulty of the study on groundwater flow process. In previous laboratory tests on water flow attenuation process and regulating capacity in karst areas, a two-dimensional fissure-conduit model built of polymethyl methacrylate was mostly used. Although it can simplify the structure of aqueous medium, it is quite different from the actual structure, and the soil zone is not considered. Meanwhile, the current studies on the regulating capacity of karst areas are mainly focused on the epikarst zone, and the studies on the influence of the transfer zone on the regulating capacity are very few. In this study, a laboratory-scale three-dimensional model of karst vadose zone was built with limestones. The attenuation curve was analyzed by superposed exponential decay equation, and the regulating coefficient was calculated by formula. The influence of rainfall intensity, fissure development degree and thickness of transfer zone on the attenuation process and regulating capacity of water flow in karst vadose zone were explored. In this study, three tests were set up to explore the influence of the above factors on the attenuation process of water flow and the regulating capacity in karst vadose zone. In Test 1, five control groups with different rainfall intensities were designed, including 5 mm·h−1, 10 mm·h−1, 20 mm·h−1, 30 mm·h−1 and 50 mm·h−1, and the attenuation coefficient and regulating coefficient under the corresponding rainfall intensity were obtained respectively. The analysis of test data shows that the greater the rainfall intensity is, the faster the attenuation speed is, and the influence on the attenuation coefficient of fast flow is greater than that on the attenuation coefficient of slow flow. When the structure of karst vadose zone is fixed, the regulating capacity gradually decreases with the increase of rainfall intensity, but this effect is limited: when the intensity increases to a certain extent, the regulating coefficient is basically unchanged. In Test 2, the number of fissures in the transfer zone is designed as 1, 2, 3, 4 and full fissures. It is concluded that the attenuation speed of fast flow accelerates and the attenuation speed of slow flow slows down with the increase of fissure development in the transfer zone. The data also demonstrates that the higher the fissure development is, the weaker the regulating capacity of the aquifer system is. In Test 3, five groups of control tests with different thicknesses of transfer zone were designed, and the thickness increased from 40 cm to 120 cm, with a difference of 20 cm between each group. Results indicate that the increase of the thickness will lead to the decrease of the attenuation coefficient and the increase of the regulating coefficient, but the influence of thickness on the latter is not very obvious. -
Key words:
- karst vadose zone /
- laboratory test /
- attenuation curve /
- regulating coefficient
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图 1 岩溶包气带概念模型和物理模型图
Figure 1. Conceptual and physical model diagrams of karst aeration zone
图 4 不同降雨强度下水流衰减系数与调蓄系数变化
Figure 4. Variation of attenuation coefficient and regulating coefficient of water flow under different precipitation intensities
图 5 不同裂隙发育程度下水流衰减系数和调蓄系数变化
Figure 5. Variation of attenuation coefficient and regulating coefficient of water flow under different fissure development degrees
图 6 不同传输带厚度下水流衰减系数和调蓄系数变化
Figure 6. Variation of attenuation coefficient and regulating coefficient of water flow under different thicknesses of transfer zone
表 1 降雨强度影响试验试验条件
Table 1. Test conditions for influence of precipitation intensity
对照组编号 有无落水洞 传输带厚度/cm 地面坡度/° 降雨强度/mm·h−1 裂隙/条 1-a 有 80 15 5 2 1-b 有 80 15 10 2 1-c 有 80 15 20 2 1-d 有 80 15 30 2 1-e 有 80 15 50 2 
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表 2 传输带裂隙发育程度影响试验试验条件
Table 2. Test conditions for influence of fissure development degree of transfer zone
对照组编号 有无落水洞 传输带厚度/cm 地面坡度/° 降雨强度/mm·h−1 裂隙/条 2-a 无 80 0 20 1 2-b 无 80 0 20 2 2-c 无 80 0 20 3 2-d 无 80 0 20 4 2-e 无 80 0 20 全裂隙
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表 3 传输带厚度影响试验试验条件
Table 3. Test conditions for thickness influence of transfer zone
对照组编号 有无落水洞 传输带厚度/cm 地面坡度/° 降雨强度/mm·h−1 裂隙/条 3-a 无 40 0 20 2 3-b 无 60 0 20 2 3-c 无 80 0 20 2 3-d 无 100 0 20 2 3-e 无 120 0 20 2
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