Physical modelling of the combined effect of vegetation and wood on river morphology

Abstract

The research reported in this paper employs flume experiments to investigate the potential effects of living vegetation and large wood on river morphology, specifically aiming to explore how different wood input and vegetation scenarios impact channel patterns and dynamics.We used a mobile bed laboratory flume, divided into three parallel channels (1.7 m wide, 10 m long) filled with uniform sand to reproduce braided networks subject to a series of cycles of flooding, wood input, and vegetation growth. Temporal evolution of river configuration (in terms of the braiding index), vegetation establishment and erosion, and wood deposition amount and pattern was recorded in a series of vertical images. The experiments reproduced many forms and processes that have been observed in the field, from scattered logs in unvegetated, dynamic braided channels, to large wood jams associated with river bars and bends in vegetated, stable, single thread rivers. Results showed that the inclusion of vegetation in the experiments changes wood dynamics, in terms of both the quantity that is stored and the depositional patterns that develop. Vegetated banks increased channel stability, reducing lateral erosion and the number of active channels. This promoted the formation of stable wood jams, where logs accumulated continuously at the same locations during subsequent floods, reinforcing their effect on river morphology. The feasibility of studying these processes in a controlled environment opens new possibilities for disentangling the complex linkages in the biogeomorphological evolution of the fluvial system and thus for promoting improved scientific understanding.

Recent advances quantifying the large wood dynamics in river basins: New methods and remaining challenges

“…A recent, pioneer experiment investigated the coupled effects of living vegetation and large wood dynamics on river morphology [Figure ; Bertoldi et al ., , Figure ]. The experiments confirmed that vegetation increases bank stability, reducing erosion, and the number of active channels [ Tal and Paola , ; Van Dijk et al ., ] and also showed how this affects large wood dynamics, promoting the formation of stable wood jams where logs accumulated constantly during sequences of floods, further increasing the effect on river morphology.…”

“…Comparisons between (a) flume‐scale and (b) field‐scale (Tagliamento River, Italy) wood deposition patterns in a braided morphology [from Bertoldi et al , , Figure ; Used with the permission of Elsevier].…”

Assessing and mitigating large wood‐related hazards in mountain streams: recent approaches

“…Schmocker and Hager, ; Gschnitzer et al ., ). More recently, the interactions between wood and morphodynamics (Bertoldi et al ., ) and wood, vegetation, and morphodynamics (Bertoldi et al ., ) were analysed. Figure illustrates the laboratory flume at the University of Innsbruck, which has been used for experiments on LW clogging at bridges (Gschnitzer et al ., , , ).…”

Assessment and Research of River Restoration Processes in Regulated Streams of Southeastern Lithuania

“…We chose to research 17 regulated streams in Lithuania: Vaišvilė (1), Dūkšta (2), Vilnoja (3), Gnesvianka (4), Ž-2 (5), Girija (6), Žalesa (7), Ž-3 (8), R-55 (9), Riešė (10), G-1 (11), Nemėža (12), Mažasis (13), Rudamina (14), N-2 (15), Asdrė (16), and Bezdonė (17 (Fig. 1).…”

“…Thus, the streams with no overgrown woody vegetation and steeper slopes have higher probability for tides and destroying slopes. Bertoldi et al [16] agree that ensuring the stability of stream slopes and an increase in hydraulic conductivity are the two main factors that help woody vegetation make an impact on the morphometric parameters of the stream.…”