摘要
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.关键词
岩溶包气带/室内试验/衰减曲线/调蓄系数Key words
karst vadose zone/laboratory test/attenuation curve/regulating coefficient分类
天文与地球科学
