Tracing suspended sediments in hydrosystems: a new methodological approach by Morphogranulometry

David Viennet (1) , Matthieu Fournier (1) , Maxime Debret (1) , Jean-Paul Dupont (1) , Yoann Copard (1)

1 M2C - Morphodynamique Continentale et Côtière

Source to sink is one of the main concepts in Earth Sciences for a better knowledge of hydrosystems dynamics. Regarding this issue, one challenge consists in the characterization by in-situ measurements of the sources of suspended sediment, or sediment source fingerprinting. Few methods can fully cover such requirements and among them, the methodology using the grain shape deserves to be developed. Indeed, morphometry of particles is widely used in sedimentology to identify different sedimentary stocks, source-to-sink transport and sedimentation mechanisms. Currently, most grain shape analyses are carried out with a scanning electron microscope coupled to image analysis to measure various size and shape descriptors on particles like elongation, circularity, bluntness or fractal dimension. However, complexity and time of analysis are the main limitations of this technique for a long-term monitoring of sediment transfers. Here we present an experimental morphometric approach using a morphogranulometer (a CCD camera coupled to a peristaltic pump). The camera takes pictures while the sample is circulating through a flow cell, leading to the analysis of numerous particles in a short time. The image analysis provides size and shape information discriminating various particles stocks according to their nature by statistical analyses. After lab calibrations, measurements were carried out on various field samples, from suspended sediments to core samples. Results shows that shape characterisation allows to identify the proportions of some sediment fractions, for examples charcoals levels in a sediment core or fine rootlets in suspended sediments. Some punctual multi-tracers tests were also conducted by injecting particles well defined by the morphogranulometer (colored silica sand) and chemical tracers at different hydrological conditions to compare with the previous chemical tracers tests made on site (Duran 2015) and statistical investigations of transport processes (Fournier 2008). These results show the promising ability of the morphogranulometer to trace sediment transfers on various hydrosystems.

Domaines: Interfaces continentales, environnement; Hydrologie

David Viennet, Matthieu Fournier, Maxime Debret, Jean-Paul Dupont, Yoann Copard. Tracing suspended sediments in hydrosystems: a new methodological approach by Morphogranulometry. American Geophysical Union, Dec 2018, Washington, United States. ⟨hal-03299850⟩