China
Africa
Explore chapters and articles related to this topic
Suspended load monitoring for sustainable hydropower development
Published in Silke Wieprecht, Stefan Haun, Karolin Weber, Markus Noack, Kristina Terheiden, River Sedimentation, 2016
M. Guerrero, A. Antonini, N. Rüther, S. Stokseth
The suspended-load may be further subdivided into suspended bed-material load, which is the coarse portion of the suspended-load for which the transport rate is governed by the transport capacity of the flow, and that is generally transported close to the riverbed, and wash-load: the fine portion of the suspended-load for which transport rate is governed by upstream supply. The wash-load is homogenously distributed through the water column because it does not exchange with the riverbed in contrast to suspended bed-material load. The wash-load, usually containing silt and clay, often represents the majority of sediment volume that deposit for very low water velocity such as in reservoirs. Sand, forming the riverbed, is usually transported fully suspended or close to the bottom. The suspended-load is generally referred to the transport mode of fine to fine-middle sand that occurs in full suspension, whereas coarser particles (i.e., middle-coarse sand and gravel), form the heavily laden flux that is transported close to the riverbed (i.e., the bed-load transport).
Sediment Sampling and Transport
Published in Sandeep Samantaray, Abinash Sahoo, Dillip K. Ghose, Watershed Management and Applications of AI, 2021
Sandeep Samantaray, Abinash Sahoo, Dillip K. Ghose
The above illustration, which is typical of many streams, shows that the amount of wash load carried by a stream may not be related to the discharge. Wash load originates from caving of the banks of the main stream or its tributaries, erosion of the gullies, and sheet erosion. This material washes through the reach without appreciable deposition. One of the reasons why the amount of wash load carried by the stream cannot be predicted is that this amount is dependent on the availability of the material in the watershed. On the other hand, the quantity of bed material load transported depends on the hydraulic conditions and the characteristics of the bed material.
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).
Sediment transport capacity of low sediment-laden flows
Published in Journal of Hydraulic Research, 2022
Meirong Zhou, Junqiang Xia, Shanshan Deng, Zhiwei Li
In the current study, Zhang’s STC formula needs to be calibrated using the measurements of suspended bed-material load. Therefore, the concentration of wash load should be excluded from the total suspended sediment . The division between suspended bed-material load and wash load is achieved using the grain-size distributions of suspended sediment and bed material (B. S. Wu et al., 2008). The specific principle is as follows: (i) on the grain-size distribution curve of bed material, the diameter corresponding to the inflection point in the range of Pb < 10% is usually regarded as the critical grain size (dc) to distinguish bed-material load from wash load. This indicates that the sediment with the grain size larger than dc is abundant on the riverbed surface, which belongs to the category of suspended bed-material load. However, the sediment with the grain size smaller than dc is rare or nearly absent on the riverbed and it is usually classified as the category of wash load (B. S. Wu et al., 2008). In order to simplify the calculation process, the critical grain size (dc) is set as the diameter corresponding to Pb= 5% on the grain-size distribution curve of bed material (B. S. Wu et al., 2008), as shown in Fig. 3a; (ii) then the percentage with the particle diameter smaller than dc is the portion of wash load (PWD), while the remaining is the part of suspended bed-material load (Fig. 3b).
Assessing heuristic models through k-fold testing approach for estimating scour characteristics in environmental friendly structures
Published in ISH Journal of Hydraulic Engineering, 2019
Milad Abdollahpour, Ali Hosseinzadeh Dalir, Davoud Farsadizadeh, Jalal Shiri
Sediment transport, particularly of bed material load, is key to the development and maintenance of natural alluvial channels. Stable channel morphology and associated habitat features reflect the nature of transport processes. Erosion in the river bend causes loss of agricultural lands, adjacent facilities, and fish habitat.
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 7 shows the general behaviour of the proposed sediment mixture transport relation, as implemented for a case based on parameters for the LYR. The bed shear stress is computed for fixed values of channel slope, channel resistance and channel width, and over a range of values for water discharge. More specifically, down-channel slope is 0.00015, dimensionless Chezy resistance coefficient is 30, channel width is 500 m, and water discharge varies from 100 to 10000 m3 s−1. With the use of the bed material GSD at the Lijin gauging station, total bed material load, as well as bed material load for each grain size range is computed over a range of values of bed shear stress corresponding to varying water discharge. Figure 7a shows the total bed material load qT, as well as the bed material load for the three grain size ranges with characteristic sizes 0.354 mm (coarse), 0.158 mm (middle), and 0.035 mm (fine). It is seen that both total bed material load qT and the bed material load for each grain size range qi increase with increasing bed shear stress . Unlike gravel bed rivers where the GSD of the bed material load approaches that of the bed surface as the bed shear stress increases (Parker, 2008), in the case of the LYR the GSD of the load diverges from that of bed material and becomes finer as the bed shear stress increases (Fig. 7b). This fining of the load is associated with the negative correlation of the exponent Bi with Di/Dg seen in Fig. 6 (Eq. (16)). Figure 7c and 7d show the GSDs of the bed material and the load for low bed shear stress () and high bed shear stress (), respectively, for a set bed slope of 0.00015. Figure 7 also demonstrates that the fraction of fine material increases with increasing bed shear stress, causing overall fining of the bed material load.