Study About A Typical Karst Water System In The Karst Feng Lin Plain Area Of South China

The natural resource of groundwater in karst areas of southern China is huge but unevenly distributed.Ecological systems in this area are fragile with significant functions.Population density is high but economy is underdeveloped.In order to ensure the coordinated development of economic development and ecological environment protection,it is necessary to study the typical karst water system in southern China.The ancient human cultural relic of Zengpiyan in Guilin is threatened by water hazards.However,the distribution of karst passage and fissures are not clear.Moreover,the understanding of hydrodynamic processes such as runoff and discharge is also divergent.By means of field investigation,tracer test,drilling,geophysics and other basic data analysis,hydrochemistry,isotope analysis,water level dynamic analysis,time series analysis and neural network,the medium field,hydrodynamic field and hydrochemical field of karst water system in typical peak forest plain of Zengpiyan are comprehensively analyzed.The results show that:?1?The medium of karst water system is mainly karst cave and NS,NE,NW fissures.The directions of maximum permeability are NE-SW and NW-SE.Karst development is characterized by horizontal and vertical zoning.Karst is weakly developed to the west of the P1-P2-P3 axis,which is the local water-proof boundary of the system,and strongly developed to the east of the P1-P2-P3 axis.Vertically,it is divided into two strong karst development zones,and deep karst is not developed.Lithology,geological structure and hydrodynamic conditions are the decisive factors of zonation.The caves are distributed in a three-storey attic,and their formation and evolution are controlled by geological structure.?2?Karst water system is divided into NS and NW-SE runoff systems.Karst springs in P2 are caused by that the horizontal runoff of groundwater is blocked by confining bed,and then it turns into vertical runoff,and confined water emerges in the karst strong development area.?3?HCO₃-Ca is the main hydrochemical type.The high content of Na⁺,Mg ²⁺,SO₄^2-in the karst water system is due to the input of C₁₂H₂₅SO₃Na and silicates.SO₄^2-in ZK10 is reduced to SO₃^2-,and Ca²⁺are exported in the form of CaSO₃precipitation,which leads the concentration of Ca²⁺and SO₄^2-are low.?4?Atmospheric precipitation is the main source of karst water in this system.The upper level of recharge elevation is 155 m.The Huang-cun fault is the recharge boundary in the northwest of the study area.Using a method of combining neural network with WTF the recharge coefficient of effective rainfall in 2017 is calculated to be 18.33%,and the recharge amount is 1.325×10⁴ m³/a.Based on time series analysis,a dynamic prediction model of karst groundwater level in Zengpiyan is established with a high accuracy and reliability.?5?In terms of the response to rainfall,the spatial variation is decided by the degree of karst development,the media of water containing and conducting and the connectivity among the media.As to the temporal variation,it represents the variation of groundwater level changes to the precipitation,which is decided by the cumulative rainfall,antecedent rainfall,water level and the media of water conducting.The features of spatial and temporal variation is the water level of aquifers with a high degree of karst development and diffusion flow for water diversion rises and falls slowly,featuring a strong autocorrelation in water level,and the water level of aquifers developed with karst conduits rises and falls rapidly,with a fast decay rate of water level autocorrelation coefficient,a short lag time in response to rainfall,and a multimodal cross-correlation function graph.