Abstract We conducted lab-scale experiments to investigate the mechanism of dual-peaked breakthrough curves (BTCs) in karst tracer tests. Three groups of dual conduit structures were constructed by varying: (1) the length ratio between the two conduits for a fixed length of the shorter conduit, (2) the total length of the conduits for a fixed length ratio, (3) the connection angle between the conduits. The BTCs generated by the tracing experiments were fitted by a Dual-Region Advection Dispersion (DRAD) model to derive effective transport parameters. Our results confirm that the dual conduit structure triggers the double-peaked BTCs. Increasing the conduit length for a fixed length ratio or increasing the length ratio increases peak separation. The connection angles between the two conduits θ1 and θ2 also influence the BTCs: increasing θ1 and decreasing θ2 causes the first peak to get smaller and the second peak to get larger. The DRAD model can reproduce the dual-peaked BTCs while its application to the case of single-peaked BTCs may be problematic due to strong interaction between model parameters. A method is proposed for estimating underground karstic conduit lengths from experimental dual-peaked BTCs.

中文翻译：

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双通道结构对岩溶示踪剂测试中溶质运移的影响：实验室研究

摘要 我们进行了实验室规模的实验，以研究岩溶示踪剂测试中双峰突破曲线 (BTC) 的机制。三组双导管结构通过改变：（1）较短导管固定长度的两个导管之间的长度比，（2）固定长度比的导管总长度，（3）连接导管之间的夹角。追踪实验生成的 BTC 由双区域平流分散 (DRAD) 模型拟合，以推导出有效的传输参数。我们的结果证实双导管结构触发了双峰 BTC。为固定长度比率增加导管长度或增加长度比率会增加峰分离。两个管道 θ1 和 θ2 之间的连接角度也会影响 BTC：增大 θ1 和减小 θ2 会导致第一个峰值变小，第二个峰值变大。DRAD 模型可以重现双峰 BTC，但由于模型参数之间的强相互作用，将其应用于单峰 BTC 的情况可能存在问题。提出了一种从实验双峰 BTC 估算地下岩溶管道长度的方法。