Abstract
Structures like blunt-nosed chevrons, log deflectors and double-winged log frames help in modifying the flow regime in the channel by concentrating the flow and increasing navigability. Moreover, they create scour pools in the downstream stilling basin, which can be used either as fish refuge or as an in-stream storage site for previously dredged material. In this respect, the use of wood debris in the channel in the form of wood bundles has gained attention for the ability of these structures to integrate into the surrounding fluvial habitat and to divert the flow partially towards the central part of the channel when placed in curves. Considering the absence of studies dealing with wood bundles as a restoration structure, the aim of this paper is to analyse the scour mechanism and equilibrium scour morphology of wood bundles in straight and curved channels. In doing so, a wide range of hydraulic conditions, structure positions and configurations were tested. Thereafter, dimensional analysis was carried out to derive useful empirical relationships to predict the maximum scour depth and length as well as the maximum dune height based on a novel, equivalent Froude number, which accounts for the effects of channel curvature and structure position. Moreover, the various resulting scour morphology types were classified, and conditions of their existence were determined depending on the abovementioned Froude number and other key hydraulic parameters.
Highlights
IntroductionDue to overwhelming anthropogenic activity and climate change, most of the world’s rivers have undergone degradation in terms of sediment-carrying potential and channel stability
River systems are a crucial component of the fresh water resources of the world
The emphasis of hydraulic engineers has been on the use of eco-friendly structures, which can modify the sediment-carrying potential of the rivers and create low- velocity localised scour zones to be used by fish and other organisms as resting spots in their migration path
Summary
Due to overwhelming anthropogenic activity and climate change, most of the world’s rivers have undergone degradation in terms of sediment-carrying potential and channel stability. The restoration of such rivers can be done either passively by promoting proper land use and irrigation [1] or more actively by installing low-head river restoration structures to enhance grade control and aquatic habitat [2]. The flow is asymmetric in nature because of the centrifugal force acting on it, and this increases the scour along the outer channel bank. Some of these structures (such as J-Hook vanes) can be placed in the vicinity of the outer bank to divert the high flow gradients towards the centre of the channel and thereby protect the outer bank from failure
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