典型岩溶包气带洞穴滴水水文过程研究——以桂林硝盐洞为例

Research on Hydrological Processes of Cave Dripping Water in a Typical Karst Vadose Zone:A Case Study of Xiaoyan Cave,Guilin

选取桂林丫吉试验场硝盐洞为研究对象,通过示踪试验和高分辨率水文水化学监测,确定滴水补给来源,研究典型岩溶包气带洞穴滴水对降雨响应的水文过程。研究结果表明,硝盐洞XY5滴水主要受到两种径流成分补给,即集中补给的管道流和弥散流。硝盐洞上部包气带中可能存在表层岩溶带含水层,长期维持滴水流量。滴水流量、电导率和示踪剂浓度的峰值均出现在强降雨时段,表现出快速响应的管道流特征,存在降雨阈值引起硝盐洞滴水降雨响应。降雨前岩溶含水层水分条件是包气带水文响应差异的主要原因,雨季滴水对降雨响应迅速,XY5滴水对降雨响应的滞后时间为10 h;而旱季对降雨的响应滞后明显,滞后时间达9.8天,体现了土壤和表层岩溶带的调蓄作用。74.4 mm降雨量是旱季转雨季滴水响应的降雨阈值。借助于洞穴滴水的水文动态变化和示踪试验技术对于研究包气带水文过程,深入了解岩溶含水层结构及特征,揭示岩溶区降雨入渗补给机制具有重要作用。

The high resolution monitoring of hydrochemistry and tracing test were conducted to determine recharge sources and study hydrological response processes of cave dripping water to precipitation in Xiaoyan Cave.The results indicate that the dripping water of Xiaoyan Cave is mainly recharged by two different flow components,i.e.,conduit flow characterized by concentrated recharge and diffuse flow.The epikarst aquifer probably exists in the upper vadose zone of Xiaoyan Cave,which continuously maintains the drip flow.The peak of drip flow,electrical conductivity and tracer concentration all show a rapid response with conduit flow during the intensive precipitation events,and there is a threshold arousing the dripping water response to the precipitation in Xiaoyan Cave.The pre-even karst aquifer hydrological conditions are main factors that cause hydrological response differences of karst vadose zones.Two response modes of dripwater to infiltration event was identified as the retention function of soil and epikarst,with the result of a10-hour rapid response in wet season and a9.8-day lagged-time response in dry season.74.4mm rainfall is the threshold for precipitation response from dry to rainy season.The integration of cave dripwater hydrodynamic variation and tracer test technology proves to have a significant influence on studying hydrological processes in vadose zone,acquiring the structure and characteristics of karst aquifer and revealing the mechanism of precipitation infiltration recharge in karst area.