Articles | Volume 20, issue 5
Hydrol. Earth Syst. Sci., 20, 2035–2046, 2016
https://doi.org/10.5194/hess-20-2035-2016
Hydrol. Earth Syst. Sci., 20, 2035–2046, 2016
https://doi.org/10.5194/hess-20-2035-2016

Research article 23 May 2016

Research article | 23 May 2016

Subsurface flow mixing in coarse, braided river deposits

Emanuel Huber1 and Peter Huggenberger2 Emanuel Huber and Peter Huggenberger
  • 1Department of Geological Sciences, Stanford University, 367 Panama St, Stanford, CA 94305-2220, USA
  • 2Applied and Environmental Geology, University of Basel, Bernoullistrasse 32, 4056 Basel, Switzerland

Abstract. Coarse, braided river deposits show a large hydraulic heterogeneity on the metre scale. One of the main depositional elements found in such deposits is a trough structure filled with layers of bimodal gravel and open-framework gravel, the latter being highly permeable. However, the impact of such trough fills on subsurface flow and advective mixing has not drawn much attention. A geologically realistic model of trough fills is proposed and fitted to a limited number of ground-penetrating radar records surveyed on the river bed of the Tagliamento River (northeast Italy). A steady-state, saturated subsurface flow simulation is performed on the small-scale, high-resolution, synthetic model (size: 75 m  ×  80 m  ×  9 m). Advective mixing (i.e. streamline intertwining) is visualised and quantified based on particle tracking. The results indicate strong advective mixing as well as a large flow deviation induced by the asymmetry of the trough fills with regard to the main flow direction. The flow deviation induces a partial, large-scale rotational effect. These findings depict possible advective mixing found in natural environments and can guide the interpretation of ecological processes such as in the hyporheic zone.

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Short summary
This study puts the hydraulic heterogeneity of coarse, braided river deposits in concrete terms, combining geophysics and sedimentological observations; shows the possible impact of the heterogeneity on the three-dimensional flow field in terms of subsurface flow mixing; and demonstrates that not only the fast subsurface flow paths are important but also the hydraulic head field.