EGU2020-21513
https://doi.org/10.5194/egusphere-egu2020-21513
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Solute transport in dual conduit structure: experiment and modelling

Chaoqi Wang, Xiaoguang Wang, Samer Majdalani, Vincent Guinot, and Hervé Jourde
Chaoqi Wang et al.
  • Laboratoire HydroSciences Montpellier, Le Centre national de la recherche scientifique, France (chaoqi.wang@etu.umontpellier.fr)

An important phenomenon often encountered when interpreting tracer tests in karst aquifers is the occurrence of dual-peaked breakthrough curves (BTCs). The dual-peaked BTCs are usually attributed to tracer transport through a conduit system consisting of a dual-conduit structure: an auxiliary conduit that deviates from the main conduit at the upstream and converges back at the downstream. In order to understand how the geometric configuration of the dual-conduit structure influences the BTCs, laboratory experiments utilizing plastic tubes were conducted. The physical models were constructed by varying: 1) the total length of the conduits, while fixing the length ratio; 2) length ratio between the two conduits, while fixing the length of the main conduit; and 3) conduits connection angle. The tracer experiments are then fitted by a Multi-Region Advection Dispersion model and a Transfer Function model to derive effective transport parameters. This allows us to quantitatively compare the experimental results, and thus to analyse the conduit geometry effects on solute transport and to compare the performance of the two models.

Results show that the dual-conduit structure causes the double peaks of BTCs. Keeping the length ratio of the two conduits and increasing their total length leads to a larger separation of the two peaks of the BTCs. Keeping the length of main conduit while increasing the length of the secondary conduit causes similar effects. As (θ12) increases, the first peak concentration value decreases, the second peak concentration value increases.

Keywords: karst, lab experiment, dual-peaked BTCs, modelling

How to cite: Wang, C., Wang, X., Majdalani, S., Guinot, V., and Jourde, H.: Solute transport in dual conduit structure: experiment and modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21513, https://doi.org/10.5194/egusphere-egu2020-21513, 2020

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Presentation version 1 – uploaded on 07 May 2020
  • AC1: Comment on EGU2020-21513, Chaoqi Wang, 07 May 2020

    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 the geometry of the dual-conduit structures. 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 length ratio or total conduit length causes a larger separation of dual peaks of BTCs.  The DRAD model can reproduce the dual-peaked BTCs. A method is proposed for estimating underground karstic conduit lengths from the dual-peaked BTCs in field tracer tests.