人工示踪技术在岩溶地区水文地质勘察中的应用

Application of tracer test techniques in hydrogeological survey in karst area

人工示踪技术用来验证地下水流动的方向和追溯地下水的来源,在水文地质勘察、水利工程防渗、地质工程涌水处理和查明矿井涌水来源方面有广泛的应用.相比于国际上示踪试验的应用,国内虽然在仪器设备上不相上下,但是在应用的广泛程度上差距很大.近年来示踪剂的自动化监测技术的进步使示踪试验在一些新的领域开展,例如研究平原地区岩溶含水层的流场,以及与天然示踪剂联用进行岩溶水系统的水文过程研究.由示踪试验计算得到平原地区岩溶含水层中地下水的视流速在数量级上为10~102 m·d-1,而地下河中的视流速为102~104 m·d-1.尽管从富水性上显示平原地区岩溶含水层的地下水赋存比较均匀,但是示踪剂的运移被严格限制在主径流通道中,很难发生侧向的弥散.相比于地下河系统,平原地区含水层中缓慢的流速和很好的富水性结合会产生强烈的稀释作用,这是开展此类示踪试验需要注意的重点.为此建议在平原地区开展示踪试验的最远距离一般不宜超过1km.鉴于示踪试验的重要性和南方大量地下河急需妥善管理,建议在水文地质普查中大量采用.

Tracer tests in karst area are used to indicate the flow direction and look for recharge.It widely helps to protect water engineering,stop flood at tunnels and wells.Comparing with the progress in the world,China has much less application of tracer test in karst hydrogeology.In recent years new progress in tracer test leads to two points of development in karst hydrogeological methodology.One achievement is the multi-tracer technique that combines natural tracers with artificial tracer used to judge flow regime in karst drainage system.Another new achievement is the first experience of tracer test in karst aquifer of peak forest area.The tests results show that the apparent velocity ofgroundwater with 10~102 m·d-1 in peak forest karst area,which is much lower than that in mountainous subterranean river in a range of 102~104 m·d-1.It is probably because of low hydraulic gradient and winding flow line in plain area.Especially the tracer is limited within a narrow belt called as concentrated flow zone there,which probably is related to fractures in stratum.In this case solute transport is still considered as one dimension character.Because tracer will be diluted by rich groundwater in the aquifer,the distance between injection points and monitoring points should be no longer than 1km for good test effect.Finally due to the increasing challenge of karst water protection from intensive pollution,tracer tests should be used widely and extensively.