Erosion and Deposition of Cohesive Soils
TL;DR: In this article, 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.
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.
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TL;DR: The DELFT3D-FLOW module as discussed by the authors is a 3D flow solver for modeling sediment transport patterns in the water column of the DELFT-3D flow model, which is used to model both suspended and bedload transport of noncohesive sediment.
1,641 citations
TL;DR: In this paper, the authors measured the size distribution of the removed component by repeated size measurement with intermediate steps of removal of components by dissolution, allowing inference of the size distributions of removed component as well as the residue.
Abstract: Fine sediment size (< 63 Ixm) is best measured by a sedimentation technique which records the whole size distribution. Repeated size measurement with intermediate steps of removal of components by dissolution, allows inference of the size distribution of the removed component as well as the residue. In this way, the size of the biogenic and lithogenic (noncarbonate) fractions can be determined. Observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 Ixm. The dynamics of sediment erosion, deposition, and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10-1xm grain size, .and noncohesive above that size. Thus silt coarser than 10 Ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed. Silt that is f'mer than 10 Ixm behaves in the same way as clay (< 2 !xm). Useful parameters of the distribution are the 10-63 Ixm mean size and the percentage 10-63 Ixm in the fine fraction. We cannot use size distributions to distinguish the nature of the currents. Therefore, to infer water mass advection speeds (i.e., the mean kinetic energy of the flow, Ku), regions of high eddy kinetic energy (KE) must be avoided. At the present, such abyssal regions lie under the high surface K E of major current systems: Gulf Stream, Kuroshio, Agulhas, Antarctic Circmpolar Current, and Brazil/Falldand currents in the Argenthe Basin. This is probably a satisfactory guide for the Pleistocene. With regard to the carbonate subfraction of the size spectrum, size modes due to both cocco!iths and foramlnlferal fragments can be recognized and analyzed, with the boundary between them again at about 10 lm. The flux of less than 10 lm carbonate, at pelagic sites above the lysocline, is another candidate for a productivity indicator.
593 citations
TL;DR: A broad overview of recent numerical models that quantify the formation and evolution of salt marshes under different physical and ecological drivers is presented in this article, focusing on the coupling between geomorphological and ecological processes and how these feedbacks are included in predictive models of landform evolution.
Abstract: Salt marshes are delicate landforms at the boundary between the sea and land. These ecosystems support a diverse biota that modifies the erosive characteristics of the substrate and mediates sediment transport processes. Here we present a broad overview of recent numerical models that quantify the formation and evolution of salt marshes under different physical and ecological drivers. In particular, we focus on the coupling between geomorphological and ecological processes and on how these feedbacks are included in predictive models of landform evolution. We describe in detail models that simulate fluxes of water, organic matter, and sediments in salt marshes. The interplay between biological and morphological processes often produces a distinct scarp between salt marshes and tidal flats. Numerical models can capture the dynamics of this boundary and the progradation or regression of the marsh in time. Tidal channels are also key features of the marsh landscape, flooding and draining the marsh platform and providing a source of sediments and nutrients to the marsh ecosystem. In recent years, several numerical models have been developed to describe the morphogenesis and long-term dynamics of salt marsh channels. Finally, salt marshes are highly sensitive to the effects of long-term climatic change. We therefore discuss in detail how numerical models have been used to determine salt marsh survival under different scenarios of sea level rise.
571 citations
TL;DR: In this article, the authors investigated the relationship between the erosional properties of combined mud and sand sediments, and found that adding sand to mud, or vice versa, increases the erosion resistance and reduces the erosion rates when the critical shear stress for erosion is exceeded.
500 citations
Cites background from "Erosion and Deposition of Cohesive ..."
...Conversely, small amounts of sand added to mud also increases the erosion resistance possibly due to changes in the micro-structure of the mud (McCave, 1984; Partheniades, 1965)....
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TL;DR: In this article, an experimental procedure involving layer by layer erosion under a range of bed shear stresses, τb, of successively increasing magnitude was utilized to investigate the erosion behavior of soft cohesive sediment deposits.
Abstract: Erosion behavior of soft cohesive sediment deposits has been investigated in laboratory experiments. Such deposits are representative of the top, active layer of estuarial beds. An experimental procedure involving layer by layer erosion under a range of bed shear stresses, τb, of successively increasing magnitude was utilized. Interpretation of the resulting concentrationtime data together with bed density profiles yielded a description of the variation of the bed shear strength, τs, with depth as well as an expression for the rate of surface erosion. In general, τs increased with depth and was also influenced by the type of sediment, bed consolidation period and salinity. The rate of erosion was found to vary exponentially with (τb-τs)1/2. In modeling estuarial bed erosion, it is essential to take these characteristics of τs and the rate of erosion into account.
471 citations