水箱-管道系统溶质运移实验研究及其岩溶水文地质意义

为了研究岩溶管道中溶潭对溶质运移的影响,在实验室内构建水箱-管道系统,在不同管道结构和水流条件下进行定量示踪实验并得到相应的穿透曲线(BTCs);采用Qtracer2软件分析溶质运移参数,采用滞后系数R分析实验结果与一维经典对流弥散方程解析解之间的差别。实验结果显示:随着水箱数量的增加,示踪剂(NaCl)峰值质量浓度逐渐降低,弥散系数和弥散度逐渐增加,穿透曲线拖尾逐渐增长,表明水箱的瞬态存储使溶质运移滞后;与不对称水箱相比,对称水箱BTC拖尾较长;峰现时间随着不对称水箱数量的增多明显滞后;出口流量增加时,弥散度减小,BTC拖尾变短。一维经典对流弥散方程解析解仅对单管道最大流量条件下的BTC拟合较好,对流量较小的单管道和水箱-管道系统的BTC拟合较差,需研究适用的模型解释其拖尾现象。

Experimental Study of Solute Transport in Pool-Pipe System and Its Significance on Karst Hydrogeology

In order to investigate the effect of pools on solute transport in the conduit, a pool-pipe system was built in the laboratory and the breakthrough curves (BTCs) were generated through quantitative tracer tests under different conditions.The Qtracer2 program was used to obtain solute transport parameters.We use retardation coefficient R to characterize the difference between the 1-D analytical solution of classical advection-dispersion equation and the experimental results.The experimental results reveal that the peak concentration decreases with more pools in series whereas the dispersion and the dispersivity increase gradually.Adding transient storage increases retardation as tailing of the BTC grows with more pools.This demonstrates that transient storage within pools is transformed to retardation.The symmetrical pool has longer tails compared to the asymmetrical pool.The peak concentration lags behind significantly due to the asymmetrical pools.As the flow rate increases, the amount of tailing and the dispersivity decrease in any case.The 1-D analytical solution of classical advection-dispersion equation can fit BTC of the single pipe in maximum discharge well but cannot fit other BTCs with appreciable tails.Therefore, it requires an appropriate model to explain the tailing of BTC.