Proglacial sediment dynamics from daily to seasonal scales in a glaciated Alpine catchment (Bossons glacier, Mont Blanc massif, France)

Abstract

The sediment yields of Alpine catchments are commonly determined from streamload measurements made some distance downstream from glaciers. However, this approach indiscriminately integrates erosion processes occurring in both the glacial and proglacial areas. A specific method is required to ascertain the respective inputs from (i) subglacial and supraglacial sediments, (ii) proglacial hillslopes and (iii) proglacial alluvial areas or sandurs. This issue is addressed here by combining high‐resolution monitoring (2 min) of suspended sediment concentrations at different locations within a catchment with discharge gauging and precipitation data. This methodological framework is applied to two proglacial streams draining the Bossons glacier (Mont Blanc massif, France): the Bossons and Crosette streams. For the Bossons stream, discharge and suspended load data were acquired from June to October 2013 at 1.15 and 1.5 km from the glacial terminus, respectively upstream and downstream from a small valley sandur. These hydro‐sedimentary data are compared with the Crosette stream dataset acquired at the outlet of the Bossons glacier subglacial drainage system. A fourfold analysis focusing on seasonal changes in streamload and discharge, multilinear regression modelling, evaluation of the sandur flux balance and probabilistic uncertainty assessment is used to determine the catchment sediment budget and to explain the proglacial sediment dynamics. The seasonal fluctuation of the sediment signal observed is related to the gradual closing of the subglacial drainage network and to the role of the proglacial area in the sediment cascade: the proglacial hillslopes appear to be disconnected from the main channel and the valley sandur acts as a hydrodynamic sediment buffer both daily and seasonally. Our findings show that an understanding of proglacial sediment dynamics can help in evaluating paraglacial adjustment and subglacial erosion processes. Copyright © 2017 John Wiley & Sons, Ltd.

Using Continuous Turbidity and Seismic Measurements to Unravel Sediment Provenance and Interaction Between Suspended and Bedload Transport in an Alpine Catchment

“…Measurements during the snowmelt period show that the relationship between turbidity and flow rate is highly variable through time. On one hand, Tu‐values show a well‐marked seasonal variation, with a Tu–Q relationships decreasing from April to June similar to observations in previous studies (Guillon et al., 2018; Mano et al., 2009; Mao & Carrillo, 2016; Navratil et al., 2011). On the other hand, despite some variability, the relationship between suspended load and bed mobility, inferred through the Tu–P b relationship, is much more stable through time.…”

Sidewall erosion: Insights from in situ‐produced 10Be concentrations measured on supraglacial clasts (Mont Blanc massif, France)

“…The present-day retreat rate was estimated to be 0.53 ± 0.24 mm year À1 for SZ1, and that is based on 4 years of stream sedimentary load measurements at the Bossons watershed outlet (Guillon et al, 2015b(Guillon et al, , 2018 and by taking the lithologic origin of the clasts (Godon et al, 2013) and their exposure history into account (Guillon et al, 2015a). The summation of the rockfalls from the rockfall catalogue also provides an estimate of the present-day erosion.…”

Quantifying bed‐related suspended load in gravel bed rivers through an analysis of the bedload‐suspended load relationship

“…This infiltration process was found to occur even for very low Rouse numbers (~0.01), especially when pore spaces were empty [Khullar, 2007;Mooneyham and Strom, 2018]. These alternative infiltration and bed mobilization processes could induce a buffering behavior for fine particle transport in the river bed [Guillon et al, 2018;Orwin and Smart, 2004]. However, the river bed could also be a zone in which fine particles are directly produced and not only temporarily stored.…”