Management of vegetation encroachment by natural and induced channel avulsions: A physical model

Abstract

Flow regulation and water abstractions may change the complex relationship between river hydraulics, morphology, and riparian vegetation. As a result, rivers are likely to decrease their dynamics, increase the amount of vegetation, and modify their habitat structure. Flood events provide a natural mechanism for removal of invasive vegetation and recreation of natural floodplain habitats. This work aims at evaluating and quantifying how gravel‐bed braided rivers naturally control vegetation encroachment through morphological processes and the impact of both naturally occurring and induced avulsions. Flume experiments were conducted in a 24‐m‐long x 1.6‐m‐wide channel filled with well‐sorted sand and constant longitudinal gradient at 0.01 m/m. Once a braided network developed, the flume was seeded with Eruca sativa at a density of 1.5 seeds/cm2 and grown until an approximate height of 1.1 cm. Experiments evaluated low‐, medium‐, and large‐flood events and documented morphological changes and impacts to vegetation at four intervals during the experiments. High‐resolution images captured approximately 3 m above the flume were used to produce accurate Structure‐from‐Motion‐derived topography and orthoimagery (average errors 2 mm). Vegetation dynamics were observed to be highly variable and depend on local morphological changes and bank erosion. Discharge is the first‐order control on vegetation removal, but our results show that occurrence of avulsions significantly increases vegetation removal. The experiments highlight that a relatively small amount of sediment relocation can be an effective tool to induce avulsions and reduce vegetation encroachment on regulated rivers.

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

“…It also supports biodiversity as it provides habitat and food for the growth of aquatic life (Stoesser, Neary, & Wilson, 2005;Wu & He, 2009). The influence of riparian vegetation on flow as well as ecological processes in rivers has become progressively significant in flood risks, river restoration, and aquatic ecological management (Bauer, Harzer, Strobl, & Kollmann, 2018;Javernick & Bertoldi, 2019;Seer, Brunke, & Schrautzer, 2018) (Nezu & Onitsuka, 2001;Rominger & Nepf, 2011;White & Nepf, 2008). However, the flow structures of such natural rivers (having partly placed vegetation) are strongly influenced and become more complex.…”

“…It also supports biodiversity as it provides habitat and food for the growth of aquatic life (Stoesser, Neary, & Wilson, 2005; Wu & He, 2009). The influence of riparian vegetation on flow as well as ecological processes in rivers has become progressively significant in flood risks, river restoration, and aquatic ecological management (Bauer, Harzer, Strobl, & Kollmann, 2018; Javernick & Bertoldi, 2019; Seer, Brunke, & Schrautzer, 2018). Among the hydraulic characteristics of flows with vegetation in open channels, the velocity dissemination has been widely studied, since it is pertinent to simulate flow patterns and discharge.…”

Professor Geoffrey Petts (1953–2018): An outstanding interdisciplinary river scientist

“…Rodríguez et al () also consider interactions between plants and sediments that give rise to patterns of overbank sedimentation within the lower Orinoco floodplain. Finally, Javernick and Bertoldi () present the results of experimental flume research designed to investigate how gravel‐bed braided rivers naturally control vegetation encroachment through morphological processes and the impact of both naturally‐occurring and induced avulsions on those processes.…”

Numerical Modelling of Turbulence Kinetic Energy in Open Channel Flows with Mixed-Layer Vegetation

“…Riparian vegetation influences flood management, channel design, and ecological river management [8,9]. Velocity distribution has been widely studied in open channel flows with macro-roughness-like vegetations, influencing zonal and stage discharge [10].…”