Field-based analysis of fluvial bedload transport and its response to climatic changes in the cold-climate and mountainous upper Driva drainage basin in central Norway

In cold-climate environments, climate change can cause changes in the precipitation, hydrological and ground frost regimes which affect the activation of sediment sources and sediment transfers.

The upper Driva drainage basin in central Norway (Oppdal-Hjerkinn) is situated in a cold-climate and mountainous environment and ranges with a total drainage basin area of 1630 km² from 220 to 2286 m a.s.l. The mean annual air temperature at Oppdal (545 m a.s.l.) is 4.3°C, and mean annual precipitation amounts to 532 mm. The lithology in the drainage basin is complex and varied, and is dominated by metamorphic rocks, mostly gneisses and schists. Vegetation cover varies between tundra vegetation in the high and rather flat areas of the uppermost drainage basin area, tree vegetation in the lower parts of the incised tributary valleys of the Driva main river and grasslands in the agriculturally used areas along the main river valley of the Driva. Relevant geomorphological processes include chemical and mechanical weathering, rockfalls, snow avalanches, debris flows, slides, wash processes, fluvial erosion, fluvial stream bank erosion and down-cutting,  and fluvial solute, suspended sediment and bedload transport.

This ongoing GFL research on sediment sources, controls and spatiotemporal variability, and future trends of fluvial bedload transport includes detailed field-based studies with extensive granulometric and shape analyses of bedload material, and high-resolution bedload transport measurements applying different tracer techniques, Helley-Smith samplings, and underwater video filming together with impact sensor measurements. Specific focus is on selected stream channel stretches in the six tributary systems Svone, Kaldvella, Stølåa, Tronda, Vinstra and Ålma, and on three selected stream channel stretches of the Driva main river in the upper Driva drainage basin system. Stationary hydrological stations are monitoring runoff continuously as discharge occurs in all tributary systems year-round. The runoff regime is nival with mean annual runoff amounting to 576 mm for the entire upper Driva drainage basin.

The activation of sediment sources and the temporal variability of fluvial bedload transport are largely controlled by thermally and, to a lower degree, by pluvially determined events. The selected tributary systems display varying intensities of bedload transport and varying particle-size compositions and shape characteristics of the bed surface material. These detected spatial variations are explained by different lithologies, different levels of sediment connectivity and spatially varying sediment availabilities in the different tributary systems. The clearly highest share of annual bedload transport occurs during the snowmelt period in spring. Continuing climate change might lead to less distinct spring snowmelt generated peak discharge events associated with reduced fluvial bedload transport during these events. Continuing climate change also affects processes like debris flows, snow avalanches and permafrost degradation having variable implications for sediment supply into these stream channels.