| Karst groundwater account for 1/4 of the total groundwater resources in China,and play an important role in socio-economic development.Karst groundwater is transported and stored in karst aquifer media.The heterogeneity of karst aquifer media and the anisotropy of hydraulic connection are prominent due to material migration and differential dissolution of carbonate rocks.The morphological combination of conduit,fissure and pore media has multiplicity and complexity.Further more,the topography of karst area is rugged,and the characteristics of aquifer media in groundwater system can not be observed on the surface,so hydrological survey is difficult.This makes its research methods different from surface water.It is difficult for a single method to obtain a systematic understanding of aquifer media,which requires a variety of methods to verify each other.This paper takes Shuifangquan watershed in Jinfo Mountain as the research object,and on the basis of grasping the climate,hydrogeology,geomorphology and human activities of the watershed,obtains high-resolution data of meteorological and groundwater physical and chemical indicators such as temperature,rainfall,discharge and conductivity through automatic monitoring.At the same time,field tracer test were carried out and combine on-line monitoring with quantitative interpretation.Furthermore,water samples of Shuifang Spring under rainfall conditions were collected daily to analyze the cations and anions.Methods of discharge exponential recesion equation,tracer test,conductance frequency distributions（CFDs）and hydrochemical analysis were employed to investigate the karst aquifer media of study area.Result of the flow curve analysis showed that the curve shape is asymmetrical peak with steep ascending wing and gentle descending wing,which indicates that karst conduit are developed,and there are considerable karst fissures and pore development,which have certain regulating and storing functions for groundwater.The discharge growth curve shows that the average flow velocity of groundwater is 41.52 m/h and the basic reservoir capacity of groundwater is 117-145m3.In the stage of flow recession,the curve under heavy rainfall can be divided into three distinct sub-dynamics.The first sub-dynamic performance is not obvious under weak rainfall.Cave-conduit media water accounts for 7.6%of the total water storage,while fissure-pore media accounts for 92.36%of the total water storage.Fissure-porous media play an important role in the storage and regulation of water resources.Tracer tests show that there is a direct hydraulic connection between No.1 sinkhole and Shuifang Spring.The low recovery rate of Tinopal CBS-X is perhaps attributed to its non-conservative nature.The groundwater flow path is smooth,the maximum velocity is 1431 m/d,and the Reynolds number is more than 4000,which is a typical turbulent flow pattern.The karst aquifer media is very uneven,two conduits are developed,with main pipeline parallel cracks without underground lakes.Conduit shape can be divided into three types:branch in series,first branch in series and then confluence,and first confluence and then in series and then branch.Based on the application of Qtracer2 software,the geometric parameters of karst conduit such as flow channel volume,cross-sectional area,average diameter and Reynolds number are 2244-4317m3,2.84-5.47m3,1.9-2.64m,4518-5374,respectively.Conductance frequency distributions（CFDs）analysis shows that there are four water source components in the basin,which can be classified into two categories:The P1 component stored in karst fissures and porous media,which belongs to the matrix or fissure gravity water.P2,P3 and P4components from surface rainwater,soil and hotel sewage are mainly transported by conduit media.The coexistence of fissure and conduit media in the study area explains the multi-peak phenomenon of CFDs and verifies the applicability of this method.The results of hydrochemistry also show that there are many sources of groundwater chemical components in the study area.HCO3-,Ca2+,Mg2+,Sr2+produced by water-rock interaction have a small coefficient of variation.They are stored in karst unsaturated zone media such as pore and karst fissures.During rainfall,they are affected by piston effect and recharge underground rivers with diffusion flow.The chemical components such as NO3-,Cl-,Fe and Al3+from hotel sewage and soil erosion have not been regulated and stored in the karst unsaturated zone,and the coefficient of variation is large.They are mainly directly poured into underground rivers through sinkhole to transport rapidly in the form of conduit flow.In conclusion,composition of different aquifer media can be defined by the equation of discharge recession,supplemented with tracer test for the calculation of the diameter of the karst conduit and the relevent hydrogelogical parameters,and the identification of the watershed boundary.At the same time,CFDs and geochemical methods are used to identify the differences of migration paths of different groundwater components,so as to verify the fact that different aquifer media coexist. |
