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River Delta Processes and Shapes
Published in Yeqiao Wang, Wetlands and Habitats, 2020
Douglas A. Edmonds, Rebecca L. Caldwell
Deltas are also influenced by the process of channel avulsion. Avulsion occurs when flow is diverted out of an existing river channel and establishes a new channel on the adjacent floodplain (Figure 8.3).[20,21] Deltaic avulsions are probable if there is a more attractive flow path down the delta, due to a steeper slope or superelevation of the channel. Superelevation occurs when channels perch themselves above their floodplain by sedimentation on the channel bed and levees. In some sense, avulsions are an inevitable outcome of delta growth. Differential progradation of the delta front will create more attractive, steeper paths on other parts of the delta.[22,23] Also, as deltas prograde their channels must aggrade lest their bed slopes decrease. Maintaining a constant slope requires aggradation which will lead to superelevation of the channel.
Process-based approach on tidal inlet evolution – Part 1
Published in C. Marjolein Dohmen-Janssen, Suzanne J.M.H. Hulscher, River, Coastal and Estuarine Morphodynamics: RCEM 2007, 2019
D.M.P.K. Dissanayake, J.A. Roelvink
Rivers depositing their sediment in deltas and coastal areas frequently change course, a process that is called avulsion. As a part of the process, a splay develops where the river diverts out of the old course, and in favourable conditions a new river develops from the channels feeding the splay (e.g. Smith et al., 1989; Stouthamer and Berendsen, 2000; Slingerland and Smith, 2004). The avulsion is (at least temporarily) a river channel bifurcation (Kleinhans et al., 2006). Its evolution is partly determined by downstream boundary conditions and partly by morphodynamics at the node. We study a deltaic avulsion site along the river Merwede (The Netherlands) that was initiated about 600 years ago by a series of catastrophic storm surges and river floods. The avulsion splay formed a shallow water delta in an area now known as the Biesbosch (Fig. 1) (Weerts et al., 2005).
Fluvial depositional landforms
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
The most detailed study of a river that has undergone periodic avulsion on a grand scale has been carried out on the Mississippi River, by Fisk and his colleagues (1944, 1952), using vast quantities of information provided by the US Army Corps of Engineers, which provides a fairly clear picture of the response of the Mississippi River to delta growth through time. Two types of avulsion have taken place, in one of which a major diversion of the river hundreds of kilometres from the sea results in it forming a new delta, and the other when the avulsion occurs on the delta itself to form a new delta lobe. When the river shifted from construction of the Teche delta to the beginning of the construction of the St Bernard and LaFourche deltas (Figure 14.31), the Mississippi River, at a position approximately 240 kilometres from the sea, shifted from the west to the east side of its valley. This abruptly shortened the course of the river. The river remained in this position, with progressive growth of the LaFourche delta. When the LaFourche delta had grown to essentially its maximum extent, the river was approximately 2146 kilometres long. There was then a shift in the position of the river upstream to its present position along the east bluff below Vicksburg, and the LaFourche delta was abandoned. Both of these events dramatically shortened the course of the river.
Sedimentation and erosion at Majuli Island, Assam, India: analysis of paleo-depositional environment
Published in International Journal of River Basin Management, 2022
Sangram Mishra, Dipika Dutta, Ananda Badekar, Anil Kumar Misra
The river mechanics are analysed very well through their important principles and laws operating in actions of erosion, transportation and deposition (Morisawa, 1985). The alluvial rivers have been grouped into braided, straight and meandering by Leopold and Wolman (1957) based on their characteristics and depending upon the platform. The flood plains and river banks are a staple source of inhabitation as well as an important part of the ecosystem. So any change in the river system not only modifies the landscape but also influences and/or affects the lives dependent on it. Therefore, studies on river processes and landforms are important to understand the river system. The avulsion of the channel is the most common fluvial process that need to investigate about the shifting of the river course. The avulsion and associated changes can be attributed to tectonic activities, large sediment influx and heavy discharge as well as floods. To keep track of the subsequent changes, and to counter any associated hazards such as bank line erosion, proper geomorphological, sedimentological and stratigraphic studies have become very important (Gohain & Prakash, 1990; Schumm, 1977).
Locating the channel and other tales from the river bank: constants and change in river boundary delimitation
Published in Water International, 2022
So Plumer commissioned the Colonial Office to conduct a survey of other river boundaries in an effort to establish whether it was the norm in such instances for the old channel course to be maintained as the boundary or for the new shifted course to be adopted. On 27 July 1927, the Colonial Office reported back as follows: It will be observed from this memorandum that according to a general rule of International Law, the gradual shifting of the thalweg from one side of the river to the other by reason of imperceptible erosion of accretion of its banks, has the effect of changing the boundary to a corresponding degree. If, however, the river should, by a process known as avulsion, suddenly become diverted from its regular channel, the boundary line remains where it was before the change. (Oliphant, TNA, 1927, CO 733/142/1)