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Bank erosion

About: Bank erosion is a(n) research topic. Over the lifetime, 1631 publication(s) have been published within this topic receiving 45579 citation(s). The topic is also known as: riverbank erosion.
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Journal ArticleDOI
Emmanuel Partheniades1Institutions (1)
Abstract: The effects of shear stress, suspended sediment concentration, and shear strength of bed on the erosion rates of a cohesive bed in an open channel with salt water have been investigated. The deposition rates of suspended cohesive sediment and the patterns of bed erosion have been studied to a lesser extent. For the experimental range the erosion rates were found to be independent of the shear strength of the bed and the concentration of suspended sediment. They depend strongly on the bed shear stress. The minimum shear stresses for initiation of erosion were also found to be independent of the shear strength of bed. There seems to exist a critical velocity for the clay part of suspended sediment, above which all such sediment remains in suspension, whereas even for velocities slightly below this critical limit, the suspended clay deposits rapidly. Scouring occurred predominantly within a well defined narrow and relatively straight zone near the center of the flume.

995 citations

Journal ArticleDOI
Abstract: \ SUMMARY Stream channel development in forested areas is profoundly influenced by large organic debris (logs, limbs and rootwads greater than 10 cm in diameter) in the channels. In low gradient meandering streams large organic debris enters the channel through bank erosion , mass wasting, blowdown, and collapse of trees due to ice loading. In small streams large organic debris may locally influence channel morphology and sediment transport processes because the stream may not have the competency to redistribute the debris. In larger streams flowing water may move large organic debris, concentrating it into distinct accumulations . (debris jams). Organic debris may greatly affect channel form and process by: increasing or decreasing stabilty of stream banks; influencing development of midchannel bars and short braided reaches; and faciltating, with other favourable circumstances, development of meander cutoffs. In steep gradient mountain streams organic debris may enter the channel by all the processes mentioned for low gradient streams. In addition, considerable debris may also enter the channel by way of debris avalanches or debris torrents. In small to intermediate size mountain streams with steep valley walls and little or no floodplain or flat valley floor, the effects of large organic debris on the fluvial processes and channel form may be very significant. Debris jams may locally accelerate or retard channel bed and bank erosion and/or deposition; create sites for significant sediment storage; and produce a stepped channel profile, herein referred to as ' organic stepping , which provides for variable channel morphology and flow conditions. The effed of live or dead trees anchored by rootwads into the stream bank may not only greatly retard bank erosion but also influence channel width and the development of small scour holes along the channel beneath tree roots. Once trees fall into the stream , their influence on the channel form and process may be quite different than when they were defending the banks , and, depending on thesize of the debris , size of the stream , and many other factors, their effects range from insignificant to very important.

793 citations

Journal ArticleDOI
Joris de Vente1, Jean Poesen1Institutions (1)
Abstract: Basin sediment yield is the product of all sediment producing processes and sediment transport within a basin. Consequently, the prediction of basin sediment yield should take into consideration all different erosion and sediment transport processes. However, traditional physics-based, conceptual, and empirical or regression models have not been able to describe all these processes due to insufficient systems knowledge and unfeasible data requirements. Therefore, the applicability of these models at the basin scale is troublesome. This paper first illustrates the relation between basin area, dominant erosion processes, and sediment yield by a combination of measured sediment yield at different spatial scales in Mediterranean environments. This clearly reveals that soil erosion rates measured at one scale are not representative for sediment yield at another scale level. Second, the most important semi-quantitative models developed for erosion and sediment yield assessments at the basin scale are reviewed. Most of these models use environmental factors to characterise a drainage basin in terms of sensitivity to erosion and sediment transport. Six of the nine models discussed (PSIAC, FSM, VSD, Gavrilovic, CSSM, WSM) include sheet-, rill-, gully, bank erosion, landslides, and connectivity, at least partly, in the assessment of basin sediment yield. The low data requirements and the fact that practically all significant erosion processes are considered makes them especially suited for estimating off-site effects of soil erosion. The other three models (EHU, CORINE, FKSM) focus mainly on sheet and rill erosion and provide quantitative descriptions of the sensitivity to erosion at basin or even regional scales. These models thus focus mainly on on-site problems of soil erosion. Most of the semi-quantitative models might benefit from a more quantitative description of factors used to characterise the basin. Though an equilibrium should be found between the extra effort and increase in model performance, the increased availability of spatially distributed topographic data as well as high-resolution satellite imagery will probably make this feasible in the near future.

587 citations

Journal ArticleDOI
Abstract: The pattern (planform) of a river can be considered at vastly different scales, depending upon both the size of the river and the part of the fluvial system that is under consideration (Figure 1). For example, in the broadest sense, river patterns comprise a drainage network (dendritic, parallel, trellis, etc; Figure lA). The type of pattern is of interest to geomorphologists and geologists who interpret geologic conditions from aerial photographs. At another scale a river reach (which in Figure lB is meandering) is of interest to the geomorphologist who is interested in what that pattern reveals about river history and behavior, and to the engineer who is charged with maintaining navigation and preventing major instability. When a single meander is examined (Figure 1 C), the hydraulics offtow, the sediment transport, and the potential for bank erosion are of concern. In addition, the sedimentologist is interested in the distribution of sediment within the bend, bed forms within the channel (Figure lD), and sedimentary structures (Figure IE), which also establish a component of roughness for the hydraulic engineer. Finally, the individual grains (Figure IF) provide geologic information on the sediment sources, the nature of sediment loads, and the feasibility of dredging for gravel. There is an interaction of hydrology, hydraulics, geology, and geomorphology at all scales, which emphasizes the point that the fluvial system as a whole cannot be ignored, even though only a component of the system is to be studied. In this review only the patterns or planforms of alluvial rivers are discussed, although it is apparent that the hydrologic and sediment yield characteristics of the drainage basin (Figure lA), as well as its geologic history, cannot be ignored in the explanation of the pattern of any river

488 citations

Journal ArticleDOI
Abstract: Gravitational forces acting on in situ bank material act in concert with hydraulic forces at the bank toe to determine rates of bank erosion. The interaction of these forces control streambank mechanics. Hydraulic forces exerted by flowing water on in situ bank-toe material and failed cohesive material at the bank toe are often sufficient to entrain materials at relatively frequent flows and to maintain steep lower-bank profiles. Seepage forces exerted on in situ bank material by groundwater, downward infiltration of rainwater and lateral seepage of streamflow into and out of the bank are critical in determining bank strength. Data from a study site on Goodwin Creek, MS, USA clearly show the temporal variability of seepage forces and the lag time inherent in reductions in shear strength due to losses of matric suction and generation of positive pore-water pressures. Negative pore-water pressures (matric suction) have also been shown to increase the resistance of failed cohesive blocks to entrainment by fluid shear. A stable bank can be transformed into an unstable bank during periods of prolonged rainfall through: 1. increase in soil bulk unit (specific) weight, 2. decrease or complete loss of matric suction, and, therefore, apparent cohesion, 3. generation of positive pore-water pressures, and, therefore, reduction or loss of frictional strength, 4. entrainment of in situ and failed material at the bank toe, and 5. loss of confining pressure during recession of stormflow hydrographs. Relatively small frequent flows during the winter have the ability to erode failed bank materials, maintain oversteepened, unstable bank surfaces and promote prolonged periods of bank retreat, channel migration and high yields of fine-grained sediment. Confining pressures provided by stormflow are not as significant in maintaining bank stability as the counteracting force of fluid shear on the bank toe, which steepens the bank. For example, more than 2 m of bank retreat occurred during the study period at the research site on Goodwin Creek, northern Mississippi. The loss of matric suction (negative pore pressures) due to infiltrating precipitation has been found to be as significant as the development of excess pore pressures in contributing to mass bank instability. Apparent cohesion, friction angle, soil bulk unit weight and moisture content were measured in situ. Matric suction was measured continuously, in situ with a series of five pressure-transducer tensiometers. A bank-failure algorithm, which combines the Mohr–Coulomb approach, for saturated conditions and the Fredlund modification for unsaturated conditions was developed for layered cohesive streambanks. The resulting equation has been used successfully to investigate the role of matric suction, positive pore-water pressures and confining pressure for layered streambanks composed of cohesive materials.

459 citations

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