Tracing sediment sources during floods using Diffuse Reflectance Infrared Fourier Transform Spectrometry (DRIFTS): A case study in a highly erosive mountainous catchment (Southern French Alps)

Abstract

en ligne : http://www.sciencedirect.com/science/article/pii/S0022169411008079International audienceIn mountainous catchments, large quantities of sediment are exported within very short periods leading to numerous environmental problems (e.g. reservoir siltation). The origin of suspended sediment during two distinct floods was determined by conducting an original fingerprinting method coupling Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and a chemometric technique (i.e. Partial Least Squares - PLS-analysis). Samples of the potential sediment sources were collected in badland areas developed on various substrates (i.e. molasse, marly limestones, black marls and gypsum) in the Galabre 20 km2-catchment located in the French Southern Alps. DRIFTS spectra provided a way to discriminate between the different potential sediment sources. Furthermore, the use of mid-infrared spectra allowed the direct quantification of the gypsum proportion in sediment. This contribution was systematically null at the catchment outlet because of the rapid dissolution of gypsum in the river. A PLS model was then constructed to estimate the contribution of the three other potential sources to the sediment flux during the floods. This model was developed and validated using a set of 45 ''experimental'' samples that were prepared in the laboratory in order to contain various proportions of the three remaining sources. By introducing DRIFTS spectra into the PLS model, we could predict the proportions of those sources in the mixed 'experimental' samples with a confidence interval of ca. ±10%. The model was then applied to the sediment collected during the two selected floods in order to outline their origin. Black marls provided the highest contribution of sediment during both events, but the analysis also revealed a significant contribution of molasse. Results also showed the remobilisation of sediment originated from molassic substrates that deposited on the riverbed during a preceding event. Opportunities for improvement and further use of this method as an alternative or rapid complementary sediment fingerprinting technique are finally discussed

Suspended sediment transport dynamics in rivers: Multi-scale drivers of temporal variation

“…Finally, traditional sediment fingerprinting approaches based on geochemical analysis techniques are very time-and cost-consuming, limiting the use of the technique at a high temporal resolution (Brosinsky et al, 2014a;Cooper et al, 2014a;Poulenard et al, 2012). Recently, studies have demonstrated the promise of spectral reflectance-based (visible and (near) infrared) fingerprinting methods as a quicker and less costly alternative for sediment source apportionment, with considerable potential to expand the temporal resolution of sediment fingerprinting analyses during high-flow events (e.g.…”

“…The amount of SS transport by rivers depends on the interaction of multiple drivers acting on different spatial and temporal scales (Bracken et al, 2015;Fryirs, 2013;Onderka et al, 2012;Poulenard et al, 2012;Rickson, 2014;Sear et al, 2003). In this section, we provide a concise summary of the main processes of fine sediment generation and transport on land (Section 2.1), and the factors driving spatial (Section 2.2) and temporal (Section 2.3) variability in SS transport within rivers.…”

“…Furthermore, erosion hotspots such as gullies can form on fields during storm events, causing an increased contribution of sediment from from a specific source. Finally, during individual precipitation events, the sediment supply from a particular source can become exhausted or diluted during persistent high discharges, or other sediment sources might become more connected to the river over time (Fan et al, 2012;Francke et al, 2014;Martínez-Carreras et al, 2010;Poulenard et al, 2012).…”

“…Belmont et al, 2011;Chen et al, 2016) and during individual events (e.g. Cooper et al, 2014a;Evrard et al, 2013;Poulenard et al, 2012). Therefore, applying sediment fingerprinting on multiple timescales can provide information on possible variations and shifts in the dominant sediment source over short to long term timescales, which can help to better understand the interactions between the factors underlying SS transport.…”

“…Over the last few decades, a wide range of empirical approaches have been developed and applied, from single sediment rating curves to complex multivariate analysis techniques (Asselman, 2000;Francke et al, 2014;Onderka et al, 2012;Poulenard et al, 2012).…”