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Sediment transport
Published in Arved J. Raudkivi, Loose Boundary Hydraulics, 2020
The bed load is usually the major component of transport in gravel-bed rivers. The transport formulae imply a steady state transport that occurs only if the bed shear stress is higher than that for the limiting armour layer, i.e. when all sizes are indiscriminantly in transport. At lower shear stresses the transport rate is a function of time and can vary substantially. Generally, the transport rate is approximately constant initially, followed by a rapid decrease. The rate of decrease is function of the bed materia] grading. If the bed material has a broad grain-size distribution the initial phase is longer, particularly if the distribution is also skewed towards the finer particles. The initial phase is short and the decline in transport rate is rapid if the grain size distribution of the bed material is strongly skewed towards the larger sizes and these constitute the bulk of the sample. The decrease in transport rate has a ‘wavy’ pattern affected by the making and breaking of the armour clusters. In time the transport rate approaches a ‘steady’ low rate that is quite low for sediment gradings skewed to coarse fractions but higher if the bed material has a broad grading. The time required for the transport rate to reach the new asymptotic equilibrium may range from few hours to few days.
Water Drop Algorithm
Published in Nazmul Siddique, Hojjat Adeli, Nature-Inspired Computing, 2017
The specific characteristics of the sediment load are another key factor influencing channel form and process. The load is the total amount of sediment being transported. There are three types of sediment load in the river: dissolved, suspended, and bed load, as shown in Figure 6.3. The dissolved load is made up of the solutes that are generally derived from chemical weathering of bedrock and soils. Fine sands, clay, and silt are typically transported as suspended load. The suspended load is held up in the water column by turbulence. The bed load is made up of sands, gravel, cobbles, and boulders. Bed load is transported by rolling, sliding, and bouncing along the bed of the channel (Allan, 1995). While dissolved and suspended loads are important components of the total sediment load, in most river systems, the bed load is what influences the channel morphology and stability (Kondolf et al., 2002).
Effect of proportion of wash load to suspended load on river erosion and deposition
Published in Silke Wieprecht, Stefan Haun, Karolin Weber, Markus Noack, Kristina Terheiden, River Sedimentation, 2016
C.T. Liao, K.C. Yeh, G.H. Liu, K.W. Wu
Steep slope, huge sediment discharge and severe bed changes are the characteristics of Taiwan’s rivers. These characteristics often cause erosion and deposition significantly, then it results a large amount of property damage and threats to the safety of hydraulic structures. In natural rivers, sediment transport includes wash load, suspended load, and bed load (Fig 1) Wash load is the portion of sediment that is carried by a fluid flow, such that it always remains close to the free surface (near the top of the flow in a river). It is in near-permanent suspension and is transported without deposition, essentially passing straight through the stream. Suspended load is the portion of the sediment that is carried by a fluid flow which settles slowly enough such that it almost never touches the bed. It is maintained in suspension by the turbulence in the flowing water and consists of particles generally of the fine sand, silt and clay size. Bed load describes particles in a flowing fluid that are transported along the bed by rolling, sliding, and saltating.
Analysis of the riverbed backscattered signal registered by ADCPs in different bedload transport conditions – field application
Published in Journal of Hydraulic Research, 2023
Slaven Conevski, Massimo Guerrero, Axel Winterscheid, Doreen Faltis, Colin D. Rennie, Nils Ruther
Sediment particles transported in flowing water, rolling or saltating, along a river bottom, are denoted as bedload (Bagnold, 1956). The riverbed surface consists of the sediment particles that are mobile, the bedload, as well as particles that are immobile, which collectively form the rough surface (Conevski et al., 2020b). The active bedload layer most often refers to the layer of mobile sediment at the riverbed (Church & Haschenburger, 2017). Compared to the suspended sediment transport, sediment particles transported in the water column, the bedload is characterized by much slower dynamics, but is crucial for shaping the river morphology. As such, a thorough understanding of bedload transport is essential for effective and sustainable sediment management, especially in large and heavily exploited, navigable rivers. Information about the bedload transport quantities and spatial distribution could significantly influence the dredging of the rivers, the definition of shipping routes, and the operation of hydraulic gates or any other man-made structures in the rivers.
Evaluation of bed load equations using field measured bed load and bed material load
Published in ISH Journal of Hydraulic Engineering, 2021
Sanjaykumar Madhusudan Yadav, Vipin Kumar Yadav, Anurag Gilitwala
Movement of bed load due to the flow of water in a river is very crucial as the trapping efficiency of bed load is comparatively higher than the suspended load. Reservoirs built across such high bedload carrying rivers experience capacity loss at a very high rate (Fan and Morris 1992). Worldwide, the storage capacity of the reservoirs is in declination, with present storage capacity being on the same order as it later was in 1950 (Annandale et al. 2018; Sumi and Kantoush 2018). The impacts of suspended sediment transport on larger dams have been extensively studied and are therefore comparatively well known as compared to unmeasured (bed) load (Salas and Shin 1999; Kondolf et al. 2014; Tadesse and Dai 2018). Measured bed load and variation in model predictions, presented in the study, may help to make uncertainty bounds to the bed load estimates and will guide practising field engineers to understand the importance of bed load size distribution for prediction of bed load. Hence, the research presented may guide field engineers/dam operators for sediment management across a hydraulic structure.
Bedload transport: a walk between randomness and determinism. Part 1. The state of the art
Published in Journal of Hydraulic Research, 2020
Bedload transport is a specific form of sediment transport, which involves coarse particles (sand, gravel or coarser particles) rolling or saltating along the streambed. In Europe, the increased construction of navigation channels in the eighteenth century gave impetus to the creation of hydraulics – the science of water flow (Levi, 1995). The issue of bed erosion and stability had become progressively more problematic as more channels were built across Europe. The first qualitative description of the erosive action of rivers appeared in 1697 in the book “Della natura de' fiumi” (On the nature of rivers) by the Italian polymath, Doménico Guglielmini. Today it is largely forgotten, but its influence was significant in the eighteenth century (Simons & Şentük, 1992). At the end of the Little Ice Age, in the nineteenth century, many European countries faced major flooding. For the first time in European history, nationwide mitigation strategies based on river engineering and reforestation were implemented to control water flow on a large scale (Ford, 2016; Vischer, 2003). Rivers and mountain streams mobilizing coarse sediment posed their own specific problems, and these pushed engineers to make the distinction between bedload and suspension. Indeed, bedload transport theory appeared at that time, with the earliest quantitative formulation of a bedload equation usually being attributed to Paul du Boys, a young French engineer studying the Rhone (du Boys, 1879; Hager,2005, 2009).