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Hydraulics, Sediment Transportation and Structures of Mechanical Origin
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
A suspension (suspended) load is defined as one in which the weight of the suspended particles is continuously supported by the fluid. The force necessary to keep the particles heavier than water or wind in suspension is provided by the vertical component of turbulence. As this is a fluctuating phenomenon, attempts to compute in absolute terms the amount of suspension load in a turbulent flow have led to extraordinarily complex exercises. On the other hand, equations have been developed for estimation of relative concentration of suspended loads in open channel flows (Rouse 1938, p. 341): Cy/Ca=[{(d−y)/y}⋅{a/(d−a)}]z,
Introduction
Published in Jamie Bartram, Richard Ballance, Water Quality Monitoring, 1996
Jamie Bartram, Richard Ballance
The amount and nature of suspended load in a water body is affected by the availability of sediment as well as by the turbulent forces in the water. The sand component of the suspended load in a river originates mainly from the river bed. As discharge increases, so do the turbulent forces that cause the sand to be taken into suspension. Sand particles tend to settle quite rapidly because of their shape, density and size. Therefore, the concentration of sand is highest near the bed of a river and lowest near the surface. The curves for medium and coarse sand in Figure 13.1 show this variation of concentration with depth. In lakes, coarser material is deposited rapidly at the point where the river enters the lake and is only resuspended and redeposited under highly turbulent conditions (such as generated by high winds).
Sedimentation in Reservoir and Measurement
Published in Kumkum Bhattacharyya, Vijay P. Singh, Reservoir Sedimentation, 2019
Kumkum Bhattacharyya, Vijay P. Singh
The total quantity of sediment load in rivers is the sum of bed load, suspended load, and wash load. Bed load comprises coarse sediment particles located on a river bed, which is dragged along by the flowing water. The bed load movement takes place by the processes of rolling, sliding, and saltation. Suspended load is a constituent of the total sediment load made up of particles moving in continuous or semi-continuous suspension within the water column. Bed-material load is the portion of the total sediment load comprised of grain sizes that are found in considerable quantities in the river bed. Leopold et al. (1964) considered the Bagnold definition which states better than any other the difference between bed load and suspended load. Bagnold (1954) “defines ‘bedload’ as that portion of the total load whose immersed weight is carried by the solid bed—that is, borne by the bed grains. ‘Suspended load’ is that part whose immersed weight is carried by the fluid and thus finally by the interstitial fluid between the bed grains.” Wash load usually consists of very fine particles, such as clay particles or silt, usually finer than 0.062 mm in diameter, having vanishingly low rates of settling; hence these particles move through the river reach system relatively unconnected to the hydraulic conditions of a given reach (Leopold et al. 1964). Measured load is the portion of total sediment load that is sampled by suspended load samplers. The sediment sampled in obtaining the measured load comprises a large portion of the suspended load but eliminates that portion of the suspended sediment load moving very near the riverbed that is below the sample nozzle and the entire bed load. Unmeasured load comprises the portion of the total sediment load that passes beneath the nozzle of a conventional suspended load sampler, flowing in near-bed suspension and as bed load (Biedenharn et al. 2008) (Table 3.1).
Towards an evaluation of bedload transport characteristics by using Doppler and backscatter outputs from ADCPs
Published in Journal of Hydraulic Research, 2021
Slaven Conevski, Massimo Guerrero, Colin D. Rennie, Nils Ruther
For reliable bedload measurements, it is crucial to understand and characterize the sediment transport mechanisms. The suspended load refers to sediment particles that are transported by the turbulent eddies of the flow and thus are suspended into the water column and follow the water velocity streamlines (Parker, 2004). Conversely, bedload transport involves larger particles with high particle Reynolds number (Rep) that slide, roll, or saltate on the riverbed. They tend to stay close to the riverbed, and the transport mechanism involves collisions and friction of moving particles with the immobile sediment bed that significantly reduces their velocity (Parker, 2004). The bedload transport mechanism is extremely complicated and, therefore, it is challenging to perform accurate and precise measurements of its characteristics and dynamics.
Analysis of sediment transport in sewer pipes using a coupled CFD-DEM model and experimental work
Published in Urban Water Journal, 2019
Maryam Alihosseini, Paul Uwe Thamsen
Sediments in sewers vary from very fine particles (less than 0.063 mm), which are commonly described as cohesive-like particles (Banasiak and Verhoeven 2008), to very coarse particles (up to 50 mm). In sewers, solids may travel either in suspension or as bedload, depending on the bed and flow conditions. The suspended load includes solids, which are in suspension as a result of turbulence. Mostly, particles of very small sizes or low densities remain in suspension and thus do not have a significant effect on the hydraulic performance of the sewer systems. In contrast, heavier and larger particles are more likely to settle down and form deposits on the bottom of the channels. Solids in the bedload have different movement modes depending on the value of bed shear stress: rolling, jumping or sliding. When the value of the bed shear stress slightly exceeds the critical value for the initiation of motion, the particles will be rolling, sliding or both combined. When the bed shear stress increases further, the particles will be jumping. Deposits in the inverts of pipes are predominantly caused by coarse minerals such as sand and gravels with sizes ranging from 0.063 to 50 mm (Crabtree 1989). Ab Ghani et al. (2000) determined the sediment size distribution in five cities in Malaysia from sediment deposition data collection. The samples were mostly made up of non-cohesive materials, also sand and gravel. They concluded that the average size of sediment for these five cities ranges between 0.6 and 0.9 mm. Gebhard (2009) characterized a range of 0.2 mm to 6 mm as a relevant range for inorganic particle sizes, which are accumulated in sewer systems by the environment and deposited as a bed.
Field investigation of suspended sediment transport study in the Kandla creek, Gujarat, India
Published in ISH Journal of Hydraulic Engineering, 2023
D. Nandhini, J. Sriganesh, K. Murali, V. Sundar
Further, sediment load estimation is a fundamental practice for understanding the physics behind the process of bed evolution over time (Tsai et al. 2010). Sediment transport, in general, occurs in two modes as bed load and suspended load. The bed load is part of the total load that moves directly over or near the bed, mainly transporting coarser materials or fine materials on plane beds, whereas the suspended load transports the finest materials along with the flow. The quantity of these modes of transport is governed by the grain size of the sediments and the flow velocity, which, in turn, dictates the settling velocity responsible for the bed load and sedimentation.