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Geomorphology and Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Giovanni Barrocu, Saeid Eslamian
Bank erosion is the wearing away of the banks of a watercourse, by the scouring of the moving water. The lowering of the river bed due to erosion increases the shear forces acting along the slope of the banks, which thus tend to slide and increase the stream load with their debris. Eventually, this process may unsettle the slope stability of steep valley sides. Valley or stream erosion is the process in which rushing streams, flowing downslope along rectilinear stretches, deepen them by wearing away their banks so that larger and larger valleys form. The Fish River Canyon, in southern Namibia, is the largest canyon in Africa and a product of valley erosion. Over millions of years, the Fish River wore away at the hard gneiss bedrock, carving a canyon about 160 kilometers (99 miles) in length, 27 kilometers (17 miles) wide, and 550 meters (1,084 feet) deep (Swart, 2008).
Proposing BEHI-NBS method for the estimation of river bank erosion on a river in Nepal
Published in Silke Wieprecht, Stefan Haun, Karolin Weber, Markus Noack, Kristina Terheiden, River Sedimentation, 2016
Stream bank erosion may be considered as either a hydraulic or a geotechnical process. In hydraulic process, individual soil particles at the bank surface are carried away by fluid flow (Crosato 2008a). Basically, there are wide varieties of processes that drive bank erosion, of which two major factors are characteristics of bank (erodibility potential) and hydraulic or gravitational force (Rosgen 1996). Hydraulic directly contribute to the bank erosion chiefly of non-cohesive bank by entraining sediments at or below the surface of water. Material erodibility is the susceptibility of bank to erosion by channel flow and shear strength is the ability of the bank to resist gravitational force that tends to cause bank failure (Throne 1981).
Bank Instability and Erosion Control Measures
Published in S.N. Ghosh, Tidal Hydraulic Engineering, 2017
Generally speaking, the instability of river bank is the cause of bank erosion. River bank may be damaged basically in two ways: (a) direct removal of material at the surface by scour; (b) internal shear failures resulting in sudden caving in or sloughing of large bodies of earth. Such shear failures may be caused by: (i) surface erosion at the toe of the slope, (ii) general bed deposition, (iii) excessive saturation of bank at low water, (iv) slope angle being too steep and earthquake effect.
Prediction of fluvial erosion rate in Jamuna River, Bangladesh
Published in International Journal of River Basin Management, 2022
Md. Shahidul Islam, Md. Abdul Matin
Two main mechanisms involved in riverbank erosion are fluvial erosion and mass failure (Couper & Maddock, 2001; Lawler et al., 1999; Zong et al., 2017). The most important mechanism controlling bank erosion is fluvial erosion (Kimiaghalam et al., 2015; Rinaldi & Nardi, 2013). Fluvial erosion is the direct removal of soil particles from the river bank by the erosive action of flowing water, while the collapse of the riverbank due to an unstable slope is known as mass failure (Lawler, 1995). Mass failures are usually initiated at the toe driven by hydrodynamic forces depending on the geotechnical load on the bank. Rinaldi and Darby (2007) reported that the long-term bank erosion rate is controlled by fluvial erosion near the bank toe. Therefore, the erosion process due to fluvial action needs to be modelled correctly before assessing the erosion caused by mass failure.
Morphological study of Upper Tapi river using remote sensing and GIS techniques
Published in ISH Journal of Hydraulic Engineering, 2019
S. R. Resmi, P. L. Patel, P. V. Timbadiya
The rivers are invariably posed to severe threats due to excessive erosion and deposition owing to the lateral migration of their either banks. The river tries to adjust its course to account for the lateral and vertical instability along its course (Rinaldi 2003). One of the major causes of such instability is the imbalance between sediment carrying capacity of the river and inflow of sediment, into the river (Garde and Raju 2000). While the rivers try to attain their equilibrium states, the external forces such as river regulations and enhanced land-use pressures degrade their flood plains (Hazarika et al. 2015). River bank erosion is an endemic and recurrent natural hazard, whose prolonged effects can cause serious damages to flood-plain dwellers, agricultural lands along the flood-plain, riparian vegetation, natural habitats, engineering structures like dams, bridges and embankments and grave consequences on the ground water table (Debnath et al. 2017). Identification of vulnerable locations/reaches along the river course in plan is extremely important to document the erosion hazard and to implement relevant management and stabilization measures. Leading studies undertaken in the past to identify the spatio-temporal pattern of the river planform and their bankline migration, with the aid of GIS and Remote Sensing tools, which will be useful to the reader for future reference are Das et al. (2012), Sarkar et al. (2012), Thakur et al. (2012), Florsheim et al. (2008), Heo et al. (2009) and Yang et al. (1981).
Simulation and control of sediment transport due to dam removal
Published in Journal of Applied Water Engineering and Research, 2018
The 1D model CONCEPTS developed by the USDA-ARS National Sedimentation Laboratory (Langendoen 2000, 2002) simulates unsteady flow, graded sediment transport, and bank erosion processes in stream corridors. Channel evolution is computed by tracking bed elevation changes and channel widening. Bank erosion is a combination of flow-induced basal scour and mass wasting (slab or planar and cantilever type bank failures). Streambanks may be composed of soil layers with different material properties. Transport of cohesive and cohesionless sediments, both in suspension and on the bed, are simulated selectively by size class. CONCEPTS is limited to straight channels or channels of low sinuosity, 14 pre-determined sediment particle size classes (0.01 mm < d < 128 mm), and homogeneous bed material across the channel. CONCEPTS uses a modification of the sediment transport capacity predictor SEDTRA, which calculates the total sediment transport by size fraction with a suitable transport equation for each size fraction: Laursen (1958) for silt size classes, Yang (1973) for sand size classes, and Meyer-Peter and Müller (1948) for gravel size classes. Numerical approaches to solve the governing equations of the 1D hydrodynamic and morphodynamic processes are similar to those used in CCHE1D. For example, the Preissmann’s scheme (1961) is used for discretizing the equations, but different from CCHE1D the linearized algebraic equations are solved by an optimized Gaussian elimination method. CONCEPTS has been successfully used in morphological studies of: (1) the advancement of head-cuts and knickpoints in James Creek and Yalobusha River, Mississippi (e.g. Langendoen et al. 2002; Simon et al. 2002); and (2) the effects of instream supercritical flow grade-control structures in Mississippi and Nebraska (e.g. Langendoen et al. 2000). It can predict the dynamic response of flow and sediment transport to in-stream structures. Its features are similar to those of the CCHE1D model, which was used in the previous section. Meanwhile, Manning’s n values also have to be calibrated based on observation data of water surface elevations.