A Shear Reynolds Number-Based Classification Method of the Nonuniform Bed Load Transport

Abstract

The aim of this study is to introduce a novel method which can separate sand- or gravel-dominated bed load transport in rivers with mixed-size bed material. When dealing with large rivers with complex hydrodynamics and morphodynamics, the bed load transport modes can indicate strong variation even locally, which requires a suitable approach to estimate the locally unique behavior of the sediment transport. However, the literature offers only few studies regarding this issue, and they are concerned with uniform bed load. In order to partly fill this gap, we suggest here a decision criteria which utilizes the shear Reynolds number. The method was verified with data from field and laboratory measurements, both performed at nonuniform bed material compositions. The comparative assessment of the results show that the shear Reynolds number-based method operates more reliably than the Shields–Parker diagram and it is expected to predict the sand or gravel transport domination with a <5% uncertainty. The results contribute to the improvement of numerical sediment transport modeling as well as to the field implementation of bed load transport measurements.

Validation of a Novel, Shear Reynolds Number Based Bed Load Transport Calculation Method for Mixed Sediments against Field Measurements

“…At these regions, more significant (~0.05 m) sedimentation was estimated. That is, at these less hydraulically rough parts of the river bed, the deposition of both the finer bed load and suspended load were expected, which areas can be detected by the Re * [22]. In turn, in the navigation channel, no considerable bed change happened.…”

“…Török and Baranya [22,26] pointed out a novel decision criterion, which is a suitable method for indicating whether the sand or rather the sand transport dominates locally. The herein presented combining method was based on this statement.…”

“…Many studies presented in the literature [13][14][15][16][17][18][19] that because of installations of many river regulation measures (e.g., groin fields, ripraps and hydropower plant at rkm 1819) in the last decades, intensive gravel formations [19], important bed level incision [20] and bed armoring processes [16,19] could be detectable, mainly in the main channel [21]. In contrast, the bed content is much finer in the groin fields, causing siltation and erosion of the finer sediments during flood waves [19,22]. The river reach can be characterized by the following parameters: the channel bed width at mean water-stage ranges between 150 m and 350 m [19] with the average water surface gradient of 0.0002-0.00025.…”

“…In turn, the middle Hungarian Danube (~200 km downstream) has a typical sandy bed with d 50 < 0.05 mm [25]. The complexity of the topography and bed content suggest spatially and temporally varied sediment transport nature [22]. That is in some places the gravel, elsewhere the sand transport dominates [26].…”

Modeling and Practice of Erosion and Sediment Transport under Change

“…In addition to sand-dominated sediment being transported within flow, gravel may also be transported in rivers with mixed-size bed material when dealing with large rivers with complex hydrodynamics and morphodynamics [56]. This is the collapse of the uniform sediment assumption, which then requires a suitable approach to estimate the nonuniform behavior of the sediment transport.…”