• Researcher: Ariel do Prado
• Host institution: University of Bern
• Supervisor: Fritz Schlunegger

Objectives: In mountainous environments, human impact upon the transport of coarse-grained material through the construction of check dams. The anticipated consequences are an inferred increase in the timescale of effective sediment transport and the evacuation of material supplied from hillslopes. However, the impact of these constructions on the energy gradient of mountain streams, the channel widths, the grain size distribution and overall sediment flux and timescale thereof has not been explored. We plan to address this question through the focus on two mountain steams situated in the Gurnigel area (46°44’43N/7°30’32E) at the northern border of the Swiss Alps. While the stream on the western slope of this mountain range has been managed through >50 check dams (the Gürbe River), the stream on the opposite slope (the Sense River; 46°43101N/7°19’15E) has still maintained its natural character. We will measure, from the headwaters down to the valley bottom: channel widths, energy gradients and grain sizes, with collaboration of Castelltort (UNIGE) during field campaigns. We will repeatedly measure these variables twice a year to detect possible temporal variations of these variables. In addition, we will determine patterns of long-term sediment flux using in-situ 10Be. We will combine these results and estimate patterns of bedload and suspension load in an Anthropogenically and natural stream on both margins of the Gurnigel mountain range. We will map the processes on the adjacent hillslopes to identify the mechanisms of sediment supply. We will model sediment transport, sediment flux and grain size distribution for both streams using the Bagnold equation for bedload transport. The comparison of the results from a nonmanaged and an Anthropogenically managed stream will allow us to quantify the human impact on bedload transport.

Expected Results:

• High-resolution characterization of grain size patterns,
• Geomorphic map, 10Be-based basin-averaged denudation rates in an Anthropogenically managed and in an natural Alpine catchment,
• Model of sediment transport, denudation and sediment flux in natural and Anthropogenically managed systems.

Secondments:

• Stiftung Landschaft and Kies (R. Lötcher) - Sedimentary architecture of the deposits, analyzing the provenance of the material and estimating the volumes of the deposited gravel (2 months)
• Georesources Switzerland (S. Heuberger) – gravel mines datas – Sedimentology and analyzing the provenance of the sediment (2 months)
• Imperial (A. Whittaker) - Grain size analysis and sediment transport modelling (3 months)