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Optimal conditions for floodplain sedimentation and land aggradation in river deltas
Published in Wim Uijttewaal, Mário J. Franca, Daniel Valero, Victor Chavarrias, Clàudia Ylla Arbós, Ralph Schielen, Alessandra Crosato, River Flow 2020, 2020
W.J. Gerats, J.H. Nienhuis, H.J. Pierik
Currently it is hard to accurately determine dimensions of crevasse splays resulting from levee breaching. An important factor in determining the morphology and size of a crevasse splay is the D/E ratio (deposition/erosion) (Nienhuis et al., 2018), which can also be described as the balance between the amount of sediment entering the crevasse and the potential sediment capacity of the floodplain (Slingerland & Smith, 1998). Both hydrodynamics and floodplain properties impact this balance, which are variable along the river and between different river systems, thus causing a large variety in forms, shapes and sizes of crevasse splays. Millard et al. (2017) however showed that typical width/length scaling relationships of crevasse splays in the Columbia, Sandover - and Saskatchewan river systems are very similar and that floodplain drainage has a large effect on crevasse size, providing insight into the governing and size-limiting role of the floodplain on crevasse growth.
Sedimentary Environments and Facies
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
As a river debouches into a static body of water its competence decreases and the coarser sediment load is dropped at the fringe of the sea or lake in the form of spits, bars and islands. The distributary channels cutting through the alluvial plain are bordered by levees. When the proportion of suspended sediment carried by the stream is high, the river mouth is extended towards the sea by sedimentation. The deposits are oriented at a high angle to the coastline to form bar-finger or shoestring sand bodies, as in the bird-foot delta of the Mississippi River (Fig. 6.30A). The space between the distributary channels of such a delta is filled by marshes. At a high stage of flooding the distributary channels may be breached by crevasses. Crevasse splay deposits are formed when coarse sediments, pushed out of the crevasse, splay out on the adjoining marshes. Unstable conditions may arise when the rate of sediment deposition is exceptionally high in a delta. Frequent failures on the seaward side of the delta in such a case might result in faults contemporaneous with sedimentation. Such faults are called ‘growth faults’.
River action and control
Published in F.G. Bell, Geological Hazards, 1999
The alluvium of flood plains is made up of many kinds of deposit, laid down both in the channel and outside it (Marsland, 1986). Vertical accretion on a flood plain is accomplished by in-channel filling and the growth of overbank deposits during and immediately after floods. Gravels and coarse sands are moved chiefly at flood stages and deposited in the deeper parts of a river. As the river overtops its banks, its ability to transport material is lessened so that coarser particles are deposited near the banks to form levees. Levees therefore slope away from the channels into the flood basins, which are the lowest part of a flood plain. At high stages, low sections and breaks in levees may mean that there is a concentrated outflow of water from the channel into the flood plain. This outflow rapidly erodes a crevasse, leading to the deposition in the flood basin of a crevasse splay. Finer material is carried farther and laid down as backswamp deposits (Figure 6.5b). At this stage, a river sometimes aggrades its bed, eventually raising it above the level of the surrounding plain. In such a situation, when the levees are breached by flood water, hundreds of square kilometres may be inundated.
Postmortem analysis of safe-yield estimation of a heterogeneous aquifer for rural water supply
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2022
Elizabeth A. Munroe, Masaki Hayashi, Laurence R. Bentley
A large fraction of densely populated areas of Alberta is underlain by the Paleocene Paskapoo Formation (Figure 1a). The Paskapoo Formation is a fluvial complex that was created by deposition of sediments in a non-marine environment, consisting of both fine-grained and coarse-grained facies (Grasby et al. 2008). The fine-grained facies, which make up more than 50% of the formation, are composed of greenish sandy siltstone and mudstone. The coarse-grained facies comprise light grey sandstone that is well sorted and porous and appears as both thick and thin bodies. Reported hydraulic conductivities of sandstone facies range from 10−6 to 10−3 m s−1 (Grasby et al. 2008). The larger bodies are interpreted as the channels of the fluvial deposition and the thinner bodies as the crevasse splays. The channels consist of stacked stories that, individually, are 3–12 m thick. The stories can be stacked into units that are up to 50 m thick with horizontal extents of up to hundreds of metres, which produces a narrow, linear geometry (Grasby et al. 2008).
Lateral, longitudinal, and temporal variation in trench-slope basin fill: examples from the Neogene Akitio sub-basin, Hikurangi Margin, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2022
Adam D. McArthur, Julien Bailleul, Frank Chanier, Alan Clare, William D. McCaffrey
Interpretations: These laterally variable and often remobilised thin-beds, which occur adjacent to channel fills are interpreted as levees (sensu Kane and Hodgson 2011). The remobilisation, subsequent healing, and aggradation implies repeated incision, collapse, and regrowth of this association. The compound thickness, being hundreds of metres, implies channels were larger than their preserved fills. Furthermore, to build levees of this scale implies that substantial amounts of material must have passed through the parental channels. Small sandstone lenses representing scour fills within these intervals are inferred to be deposits of crevasse splays (Posamentier 2003).