Determination of the bedload transport rate in a small proglacial High Arctic stream using direct, semi-continuous measurement

Abstract

The article presents the results of a 34-day series of direct semi-continuous measurements of the bedload transport, performed during the melt season 2013 in the Scott River catchment (NW part of the Wedel-Jarlsberg Land, Spitsbergen). The daily variability of the bedload transport rates and its relation to the dissolved and suspended load were analysed in two cross-sections located in the lower course of a proglacial gravel-bed river. The bedload flux was measured by means of two 4-module sets of River Bedload Traps (RBT). In the research period, a total of 34 day-long samples of bedload and 34 water samples for the determination of the dissolved and suspended load were collected in each of the two cross-sections, 200m apart. The measurements showed longitudinal and temporal variability of bedload flux and the remaining components (solutions, suspensions) corresponding with changes in water discharge. The mean daily bedload flux QB in consecutive measurement cross-sections XS amounted to 124kgd−1XS I and 59kgd−1XS II, respectively, and showed high variability and an evident relationship with temperature. The unequal bedload flux of the two measuring stations XS I and XS II suggests aggradation within the alluvial fan that separates the two reaches. The volume and rate of bedload flux were determined by the frequency of the occurrence of flood flows during which approximately from 59% XS I to 77% XS II of total bedload was discharged. The highest recorded daily values constituted 12% of total bedload flux. Through the cross-section below the alluvial fan, the river discharged approximately 6 million cubic meters (Mm3) of water, 3t of bedload Lb, 2238t of suspended load Ls, and 613t of dissolved load Ld. The relationships between the three components of the load suggest a 500-fold excess of suspended load, and a 100-fold excess of dissolved load in relation to bedload flux. High temporal and latitudinal variability of the bedload transport rate resulted in changes in the channel morphology, and during floods — also the floodplain.