The Responses Of Different Types Of Cave Dripping Water To Rainfall

Karst is widely distributed in China and has many types.It is one of karst most developed countries in the world.In Karst area,the complexity and particularity of aquifers increase the difficulty of Karst water research.However,the existence of drip water in the cave provides a convenient way to study the migration of groundwater in the vadose zone.This paper selects Laohuanglongdong cave of Aziying township in Kunming as the study area,13 drip points were selected and monitored for a hydrological year.Automatic recording instrument was set outside to record the rainfall at the same time.Smart and Friendrich classification system is used to divide drips by supply source,systematic cluster analysis is used to divide drips by the drip rate,the response curve is used to divide drips by the difference of responses to rainfall among different drips.Time series analysis is used to determine the response time of different types of drips to rainfall.Based on the response time,the existence of rainfall threshold effect is proposed,and the rainfall threshold of different types of drip water in different periods is analyzed.Finally,based on the characteristics of chemical parameters of different types of drips,the difference of them is analyzed with the conceptual model.The following conclusions are obtained:1.According to the difference of recharge source and supply way,13 drip points in the study area can be divided into three categories:I are stability drips,II are seasonal drips and III are sensitive drips.The responses of the three types of drips to rainfall are different.Drip rate of class I basically has no response to rainfall.Drip rate of class II has lagged response to rainfall and the lag time is about 35 to 98 days.Drip rate of class III has a fast response to rainfall,but there is also a lag time,and the lag time is about 28 to 63 days.The response characteristics of three kinds of drips to rainfall indicate that the difference between recharge source and pathway of supply will affect the lag time and duration,and the difference of response time also indicates the existence of rainfall threshold effect.2.Two points with obvious drip rate mutations of class II and III are choosed to analyse the rainfall threshold,that are S14,S17,S1 and S18 points.Based on the analysis of rainfall threshold in dry season to rainy season and rainy season,it is found that there are differences in rainfall thresholds between different types of drips and different periods.It shows that migration pathway of different types of drips are different.Because of the water deficit of the soil and the surface vadose zone,the responses characteristics to different rainfall and rainfall intensity are different.There is no sudden change of drip rate when the daily rainfall under 20mm.In the period from dry season to rainy season,the cumulative rainfall required by S14,S17,S1,and S18 points to the rainfall response respectively are 156mm,129.2mm,82.8mm and25mm;in the period of rainy season,the cumulative rainfall required for the drip rate mutation at each point respectively are 79.4mm,57mm,79.4mm and 79.4mm.3.The responses of hydrochemical parameters to rainfall are different.The chemical parameters of class I are more responsive to rainfall than the drip rate.The variation range of pH is 7.41⁷.50,the variation range of electrical conductivity is655¹094?s/cm,HCO₃^-concentration varies from 1.69 to 8.80mg/l,and the concentration range of Ca²⁺is 102¹99mg/l,because of the concentration of Br,the electrical conductivity and HCO₃^-concentration of S15,S16 points are obviously different from other points,it shows that electrical conductivity of them are both over1000?s/cm and the HCO₃^-concentration under 2.0mg/l.The concentration of Ca²⁺of class II has obvious response to the heavy rainfall,changes range is 66¹21mg/l.pH,HCO₃^-,electrical conductivity are only responses in the period of more rainfall.The range of pH is 7.52⁷.69,the HCO₃^-concentration range is 4.88⁹.12mg/l,the conductivity range is 365⁶51?s/cm.In the class III,the response of Ca²⁺concentration to rainfall is basically consistent with the drip rate and the range is81¹31mg/l.pH,HCO₃^-and electrical conductivity only have obvious response in the period of more rainfall.The range of variation respectively are 7.37⁷.59,5.91⁸.88mg/l and 442⁶25?s/cm.The response of hydrochmical parameters to rainfall is affected by the hydrodynamic conditions.The peak value of the Ca²⁺concentration of the three kind of drips are reached earlier than the peak value of the drop rate,indicating that the existence of the"piston effect".The response of electrical conductivities to rainfall of class II and III reflects the existence of"dilution effect".