Morphodynamics of Boulder?Bed Semi?Alluvial Streams in Northern Fennoscandia: A Flume Experiment to Determine Sediment Self?Organization

In northern Fennoscandia, semi-alluvial boulder-bed channels with coarse glacial legacy sediment are abundant, and due to widespread anthropogenic manipulation during timber-floating, unimpacted reference reaches rare. The landscape context of these rapids—with numerous mainstem lakes that buffer high flows connectivity in addition a regional low yield—contribute amounts fine incompetent transport boulders. To determine the morphodynamics rapids potential self-organization multiple flows, flume experiment was designed carried out mimic conditions Fennoscandia. Two slope setups (2% 5%) were used model range (Q1 (summer flow), Q2, Q10, Q50) 8 × 1.1 m distribution analogous field conditions; bed topography measured using structure-from-motion photogrammetry after each flow obtain DEMs. No classic steep coarse-bed channel bedforms (e.g., step-pools) developed. However, similarly relative submergence, at Q10 Q50 deposited upstream boulders scoured downstream. Because not able rework by disrupting grain-interlocking from preceding lower transporting boulders, or forming channel-spanning channel-forming discharge is larger than Q50. These results have implications for restoration gravel spawning beds Fennoscandia highlight importance large grains understanding morphodynamics.