In karstic environments, it is not unusual for an underground river to split into two or more streams (diffluence) and merge back together downstream (confluence). This kind of behavior can generate multipeaked breakthrough curves (BTCs) in dye tracing at a sampling site located downstream of the confluence(s). It is also possible that such a phenomenon is difficult to highlight with dye tracing if the tracer clouds coming from the different streams reach the sampling locations at the same time. In this study, an attempt at quantifying the importance of different criteria in the occurrence of a multipeaked BTC is done by performing a dye tracing campaign in a two-tributaries diffluence-confluence (DC) system and using a one-dimensional solute transport model. The results from both field data and the solute transport model suggest that a double-peaked BTC occurs downstream of a DC system if the following conditions are met: (1) the injection is done close enough to the diffluence, (2) the sampling point is located not too far from the confluence, and (3) the two (or more) streams have sufficiently contrasted travel times from the diffluence to the confluence. The paper illustrates that, even if a diffluence occurs in a karstic river, multipeaked BTCs are not necessarily observed downstream of the confluence if these three conditions are not met. Therefore, characterizing a DC system using dye tracing is a real challenge. This could explain why publications that report studies involving multipeaked BTCs are quite rare.

在喀斯特环境中，地下河分裂成两条或多条溪流（分流）并在下游重新汇合（合流）的情况并不罕见。这种行为可以在位于汇合点下游的采样点处的染料示踪中生成多峰突破曲线 (BTC)。如果来自不同流的示踪剂云同时到达采样位置，则这种现象也可能难以通过染料示踪来突出显示。在本研究中，通过在两支流分流-合流 (DC) 系统中进行染料示踪活动并使用一维溶质传输模型，尝试量化不同标准在多峰 BTC 发生中的重要性。现场数据和溶质传输模型的结果表明，如果满足以下条件，则在直流系统下游会出现双峰 BTC：(1) 注射距离分流口足够近，(2) 采样点距离汇合点不太远，并且 (3) 两条（或更多条）河流从分流点到汇合点的行进时间具有足够的对比。该论文表明，即使在喀斯特河流中发生分流，如果不满足这三个条件，也不一定会在汇流下游观察到多峰BTC。因此，使用染料示踪表征 DC 系统是一个真正的挑战。这可以解释为什么报道涉及多峰 BTC 的研究的出版物非常罕见。