Multipeaked breakthrough curves in karstic rivers: effects of a diffluence-confluence system

Romain Deleu, Amaël Poulain, Gaëtan Rochez, Sandra Soares-Frazao, Guy Van Rentergem, Eli De Poorter, Vincent Hallet

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Abstract

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.

Translated title of the contributionCourbes de restitution multipics dans les rivières karstiques: effets d’un système de diffluence-confluence
Original languageEnglish
Pages (from-to)433-451
Number of pages19
JournalHydrogeology Journal
Volume32
Issue number2
DOIs
Publication statusPublished - 31 Oct 2023

Keywords

  • Breakthrough curve
  • Dye tracing
  • Karst
  • Numerical modelling
  • Solute transport

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