The transport of large wood (LW) has been a focus of research in the last decades because of its importance for river ecosystems, fluvial dynamics and flood protection.Riverine processes connected with the presence of LW have largely been based on laboratory experiments carried out in straight or weakly bended channels. The dynamics of LW in sharp river bends has received less attention, so there exist many open questions regarding how LW is transported through such channel parts. For this reason, this paper presents results of unique laboratory experiments designed to study the trajectories of single wooden dowels in sharp bends. Dowel trajectories were determined for four dowel sizes, two initial dowel orientations with respect to the main channel axis and three inlet positions. Information about the 3D velocity field in the bend were obtained from a previous study that used the same channel with identical hydraulic boundary conditions. Furthermore, a force-balance analysis was developed for interpreting the dowel trajectory and drag coefficient of LW in sharp river bends. The experimental results show that the dowel length is the main parameter controlling dowel trajectory in a sharp bend, and indicate the role of inertial effects that drive the dowel drift along the bend. The obtained drag coefficients ranged between 0.35 and 1, which is in agreement with previous values for submerged, or semi-submerged, fixed pieces of wood in straight river reaches.

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Restoration works on an 11 km long reach of the Spree River near Cottbus in Germany were accomplished in 2014. The overall objective was to improve the biodiversity, changing the morphological structure from a straight single-thread river to a braiding one with reshaped thalweg, and creating zones with varying flow velocities required for fish spawning. Several interventions were made, among which also two types of groynes were constructed along the reach: impermeable stone groynes, with an inclined crest so that only the tip is typically submerged during normal flow conditions, and wooden groynes made of several large trunks, which are mainly submerged at normal flow conditions. To compare local morphodynamic effects caused by the different types, flow velocities and bed topography were measured at distances of 12 m upstream and 16 m downstream of two selected groynes. The vertical profile was captured by measuring at five levels above the bed. Bed material was sampled at several locations around the groynes. The analysis of the measurements showed the effect of each groyne type on the flow velocity, bed topography and bed material. Furthermore, the differences in the effects of each groyne type on the flow, bed topography and bed material were highlighted.