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Sediment transport
Published in Arved J. Raudkivi, Loose Boundary Hydraulics, 2020
Wash load arises primarily from the soil and dust brought into the stream by overland flow and consists of fine material. The amount depends on catchment conditions. Some wash load may also be produced by wear of sediment in transport, particularly of greywacke origin. Wash load, although a suspended load, is not in a functional relationship with flow rate like the suspended load except that rain washes the material into the stream and rain also leads to an increase in stream flow. If a suspended load sample is analyzed, it will be found that fractions greater than a given size can be related to flow rate according to suspended load concepts but not the finer fractions, usually finer than ca 30 µm or ca 10% finer by weight of the bed material size distribution. Heavy concentrations of wash and suspended load reduce the flow resistance and the height of bed features, but increase the bulk density of flow. Gradually, an increasing concentration of colloidal material leads to a change in flow properties of the fluid-grain medium, hyperconcentrated flow (Section 7.4). Some of the wash load may at times settle on the stream bed, but the amounts are small compared to the total wash load.
Introduction
Published in Jamie Bartram, Richard Ballance, Water Quality Monitoring, 1996
Jamie Bartram, Richard Ballance
Suspended load comprises sand + silt + clay-sized particles that are held in suspension because of the turbulence of the water. The suspended load is further divided into the wash load which is generally considered to be the silt + clay-sized material (< 62 μm in particle diameter) and is often referred to as “fine-grained sediment”. The wash load is mainly controlled by the supply of this material (usually by means of erosion) to the river. The amount of sand ( >62μm in particle size) in the suspended load is directly proportional to the turbulence and mainly originates from erosion of the bed and banks of the river. In many rivers, suspended sediment (i.e. the mineral fraction) forms most of the transported load. Bedload is stony material, such as gravel and cobbles, that moves by rolling along the bed of a river because it is too heavy to be lifted into suspension by the current of the river. Bedload is especially important during periods of extremely high discharge and in landscapes of large topographical relief, where the river gradient is steep (such as in mountains). It is rarely important in low-lying areas.
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
The main source of wash load is the sediment eroded and washed from upstream reach, soil and earth of watershed with water to the downstream along the river to estuary. Grain size, material composition, and fluvial conditions could be used to classify the wash load. Table 1 shows the general empirical methods for the classification of wash load.
Improving spate flow diversions in spate irrigation intake structures
Published in ISH Journal of Hydraulic Engineering, 2022
Hintsa Libsekal Gebremariam, Abraham Mehari Haile
Transported sediment particles in the spate system include bed and suspended loads. The bed load comprises sands, gravels, and boulders, and this can be transported during medium, high, and extreme flood events. The suspended load comprises wash load (silt and clay) and can be transported during flood events. The sediment transport can be affected by catchment characteristics such as slope, soil type, land use, and rainfall intensity. Ratsey (2011) state that, 5–10% of spate flood discharge comprises sediments. Lawrence et al. (2001) state that the Engelund and Hansen method is the best sediment transport predictor in areas that do not have enough data of sediment concentrations. Hence, the sand transport prediction was made using the Engelund and Hansen`s sediment transport predictor method to obtain the sediment load concentration (Qs) of the river in parts per million (ppm).
Extended Engelund–Hansen type sediment transport relation for mixtures based on the sand-silt-bed Lower Yellow River, China
Published in Journal of Hydraulic Research, 2019
Kensuke Naito, Hongbo Ma, Jeffrey A. Nittrouer, Yuanfeng Zhang, Baosheng Wu, Yuanjian Wang, Xudong Fu, Gary Parker
Figure 3 shows the GSDs of bed material and suspended load at the Lijin gauging station. The GSDs of bed material and suspended load of the Mississippi River at St. Louis, USA, which is considered as a typical sand-bed river, are also plotted for comparison. It is seen that the bed of the LYR contains a large fraction of silty sediment that is finer than 62 µm, a range that is typically considered to be wash load in most sand-bed rivers (e.g. Woo, Julien, & Richardson, 1986), such as the Mississippi River, as can be seen in Fig. 3. Wash load is defined as the sediment that is being transported, but is too fine to be found in easily measurable quantities in the bed (Bettess, 1994). For the LYR, we select 15 µm (0.015 mm) to be the cut-off size for wash load (Ma et al., 2017). Sediment finer than 15 µm is considered to be wash load, and hence is excluded in the development of the sediment transport relation herein.
A total load approach to predict bed load transport of Indian alluvial river
Published in ISH Journal of Hydraulic Engineering, 2018
Sahita Ibopishak Waikhom, Sanjaykumar Madhusudan Yadav
Sediment transport in natural rivers has been widely studied in the past few decades. The subcommittee on Sediment Terminology of the American Geophysical Union has defined various loads (sediments) carried by a stream as bed load, suspended load, wash load, etc., and stated that the total load is the sum of the bed load, suspended load and wash load (Vanoni 1975).The wash load is material sourced from erosion of cohesive river banks and surface erosion in the catchment and usually is finer than 0.062 mm (Knighton 1998). Sediment in the wash load is transported in suspension by turbulent eddies in the flow and generally moves at the same rate as the flow (Edwards and Glysson 1999). These particles pass through the river system relatively unrelated to the hydraulic condition in a given reach and are independent of the discharge in stream (Roger, 2008). Thus, the total load carried by the stream is considered as the sum of suspended load and bed load transported per unit time per unit width of channel, not including wash load. The partitioning of the total sediment load of a river into suspended load and bed load is a key factor in fluvial geomorphology, sedimentation engineering and sedimentology. An appropriate assessment of the partitioning requires both short- and long-term measurements (Turowski et.al 2010). In a fluvial system, the analysis of short- (single flood event) and long-term (year of decade) evolution of total load and its partitioning may be a valuable support for applications such as hazard assessment, infrastructure design, reservoir management, environmental engineering and planning for climate or land use changes (Rainato 2016).