Abstract
In a natural gravel-bed stream, the bed that has an organized roughness structure created by the streamflow is called the water-worked gravel bed (WGB). Such a bed is entirely different from that created in a laboratory by depositing and spreading gravels in the experimental flume, called the screeded gravel bed (SGB). In this paper, a review on the state-of-the-art research on WGBs is presented, highlighting the role of water-work in determining the bed topographical structures and the turbulence characteristics in the flow. In doing so, various methods used to analyze the bed topographical structures are described. Besides, the effects of the water-work on the turbulent flow characteristics, such as streamwise velocity, Reynolds and form-induced stresses, conditional turbulent events and secondary currents in WGBs are discussed. Further, the results form WGBs and SGBs are compared critically. The comparative study infers that a WGB exhibits a higher roughness than an SGB. Consequently, the former has a higher magnitude of turbulence parameters than the latter. Finally, as a future scope of research, laboratory experiments should be conducted in WGBs rather than in SGBs to have an appropriate representation of the flow field close to a natural stream.
Highlights
The topic of natural gravel-bed streams remains a continued research interest for several decades owing to its practical importance
By analyzing the higher-order structure functions in worked gravel bed (WGB) for different armoring discharge structures possess multiscaling behavioral features, which is in conformity with the findings of conditions (0.012–0.025 m3 s−1 ), Aberle and Nikora [10] found that the WGB roughness structures
The water-work causes a difference in bed topography between a WGB and an screeded gravel bed (SGB), even for an identical particle-size distribution in both the beds
Summary
The topic of natural gravel-bed streams remains a continued research interest for several decades owing to its practical importance. The bed surface topography in a natural gravel-bed stream possesses a spatially multifaceted, but coherently organized bed structure, because it is created by the natural erosion and deposition processes governed by continual flood cycles. In this process, a water-worked gravel bed (WGB) is developed in a natural gravel-bed stream (Figure 1). In laboratory experimental studies, manmade gravel-bed is prepared by depositing and spreading gravels into the flume for a given thickness Such a bed is called a screeded gravel bed (SGB) (Figure 2).
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