Geomorphic and particle attributes influence on entrainment and sediment transport in semi-alluvial streams

Abstract: Streams around the world are shaped by physical processes between water and sediment transport which generates unique geomorphic structures for each stream. This study aimed to evaluated how geomorphic structures and grain attributes would influence entrainment frequency and transport distance of traced clasts. The morphologic structures observed were the clasts morphologic setting in the surface bed, constrainment type, clasts location and distance to immobile boulders, slope, dimensionless critical shear stress and bankfull shear stress. The grain attributes consisted of the length of the longest(L), intermediate(I) and shortest(S) axis and the ratio between I/L and S/I to classify the shape of the clasts. To observe this, passive integrated transponders (PIT) were inserted into 558 clasts and then implemented into a stream in northern Sweden. The study was set up with 15 transects with 10 meters apart in the summer of 2017. The clasts new position, morphologic setting and constrainment type were resurveyed in the summer of 2018 and 2019. The entrainment frequency was higher at 74% during 2017-2018 compared to 54% during 2018-2019 and the mean transport distance was 0.59m and 0.19m respectively. The results show that 7 out of 14 variables had a significant effect (α=0.05) on entrainment and transport distance during 2017-2018 and 5 out of 14 during 2018-2019. The explanatory value (R2) for each significant variable, however, was low between 0.01-0.04. The major difference in entrainment frequency and transport distance during 2017-2018 compared to 2018-2019 and low R2-value show complex relationship between stream characteristics and grain attributes in streams.