Is river avulsion style controlled by floodplain morphodynamics?

Hajek, Elizabeth; Edmonds, D. A.

doi:10.1130/g35045.1

Cited by 91 publications

(95 citation statements)

References 17 publications

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“…Having two water level boundary conditions as the driving force, as opposed to an upstream discharge boundary condition, is critical as it results in a floodplain-dependent discharge and sediment supply that enables levee breaches to close or to expand into an avulsion. Other morphodynamic models of crevasse splays (e.g., Hajek & Edmonds, 2014;Millard et al, 2017;Sandén et al, 2016) simulate autogenic breach discharge by including the trunk channel itself into the model domain. However, simulating the trunk channel is computationally expensive and numerically challenging, so here we simplify the channel boundary in order to focus deliberately on the role of floodplain conditions.…”

Section: à4mentioning

confidence: 99%

“…Their model, as well as other "bifurcation stability" models (e.g., Bolla Pittaluga et al, 2003;Kleinhans et al, 2008), are commonly able to distinguish between unstable and stable breaches or bifurcations but do not take into account any distal floodplain effects on their stability, such as whether or not the floodplain is properly drained (e.g., Hajek & Edmonds, 2014;Mohrig et al, 2000). Channel bifurcation models also cannot predict crevasse splay morphology.…”

Section: Introductionmentioning

confidence: 99%

“…Inspired by Hajek and Edmonds (2014), we hypothesize that crevasse splay morphology is controlled by the relative dominance of floodplain erosion versus deposition. To scale the relative importance of various external controls on levee breach evolution, we therefore developed a predictive metric that compares the potential floodplain deposition rate (D, kg m À2 s…”

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confidence: 99%

See 2 more Smart Citations

Crevasse Splays Versus Avulsions: A Recipe for Land Building With Levee Breaches

Nienhuis

Törnqvist

Esposito

2018

Geophysical Research Letters

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Natural-levee breaches can not only initiate an avulsion but also, under the right circumstances, lead to crevasse splay formation and overbank sedimentation. The formative conditions for crevasse splays are not well understood, yet such river sediment diversions form an integral part of billion-dollar coastal restoration projects. Here we use Delft3D to investigate the influence of vegetation and soil consolidation on the evolution of a natural-levee breach. Model simulations show that crevasse splays heal because floodplain aggradation reduces the water surface slope, decreasing water discharge into the flood basin. Easily erodible and unvegetated floodplains increase the likelihood for channel avulsions. Denser vegetation and less potential for soil consolidation result in small crevasse splays that are not only efficient sediment traps but also short-lived. Successful crevasse splays that generate the largest land area gain for the imported sediment require a delicate balance between water and sediment discharge, vegetation root strength, and soil consolidation. Plain Language Summary Man-made sediment diversions from the Mississippi River into adjacentwetlands are an ambitious and novel concept to form new land, replicating how large portions of the Mississippi River Delta have kept pace with sea level rise over the last thousands of years. However, the geomorphic evolution of diversions remains uncertain. How much new land will be formed, and is that dependent on vegetation type or soil consolidation rates? Will its channels silt in and close the diversion? Here we show with a numerical model that successful diversions generating the largest land area gain require a delicate balance between water and sediment discharge, vegetation root strength, and substrate erodibility. Diversions enhance local subsidence rates, but this can, counterintuitively, enhance land-building by allowing more sediment to flow into the diversion. Based on our model experiments, we have also found that diversions into easily erodible substrates can initiate a river avulsion and form a new river delta lobe, shedding light on the origin of river delta shapes we find on Earth today.

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Section: à4mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Crevasse Splays Versus Avulsions: A Recipe for Land Building With Levee Breaches

Nienhuis

Törnqvist

Esposito

2018

Geophysical Research Letters

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“…In particular, river avulsions take place when the main channel becomes infilled with sediments, triggering the diversion of the river into a new course (Slingerland and Smith, 2004;Buehler et al, 2011). River avulsions are the main mechanism behind the formation of distributary fluvial systems (DFS), which fill alluvial basins (Hajek and Edmonds, 2014;Weissmann et al, 2010;Hartley et al, 2010). High aggradation rates in the main river channel can result from a variety of causes such as (i) an increase in the sedimentary load of the river; (ii) an increase in the peak water discharge of the river or (iii) a decrease in the channel gradient, which can be caused by a rise of the base level or downstream tectonic uplift (Slingerland and Smith, 2004).…”

Section: Rivers and Palaeoriversmentioning

confidence: 99%

Neotectonics, flooding patterns and landscape evolution in southern Amazonia

Lombardo

2014

Earth Surf. Dynam.

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Abstract. The paper examines the role of neotectonic activity in the evolution of the landscape in southern Amazonia during the Holocene. It uses both new and published data based on the analysis of remote sensing imagery and extensive field work in the Llanos de Moxos, Bolivian Amazon. The study of the region's modern and palaeorivers, ria lakes, palaeosols and topography provides a strong case in favour of the thesis that the northern part of the Llanos de Moxos constitutes the southern margin of the Fitzcarrald Arch and that it has experienced uplift during the Holocene. The paper assesses the extent and timing of the neotectonic activity in light of the new data and reconstructs the evolution of the landscape since the late Pleistocene. The evidence suggests that at least two uplift events took place: a first uplift in the late Pleistocene, which caused the formation of Lake Oceano, and a second uplift during the mid-Holocene, which formed Lake Rogaguado. These two uplifts appear to be linked to the knickpoints observed close to the towns of Guayaramerín and Puerto Siles respectively. The backwater effect due to these uplifts transformed the region's major rivers in seasonal ria lakes, causing the deposition of thick organic clay layers along the Beni, Mamoré and Madre de Dios river banks. I argue that neotectonic episodes could have dramatically changed the drainage of the Llanos de Moxos, determining its flooding regime, soil properties and forest-savannah ecotone. These results stress the need for geomorphologists, palaeo-ecologists and archaeologists to take into account neotectonics when reconstructing the region's past.

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“…Despite a large body of studies, the exact mechanisms controlling crevasse splays and river avulsions are not entirely understood (Hajek and Edmonds, 2014;Stouthamer and Berendsen, 2007; Ash- , 2004). When the various processes that push the river towards the avulsion threshold proceed at a faster pace than those that act as triggers, the latter control the frequency of crevasses and, eventually, avulsions (Jones and Schumm, 1999).…”

Section: Discussionmentioning

confidence: 99%

Alluvial plain dynamics in the southern Amazonian foreland basin

Lombardo¹

2016

Earth Syst. Dynam.

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Abstract. Alluvial plains are formed with sediments that rivers deposit on the adjacent flood-basin, mainly through crevasse splays and avulsions. These result from a combination of processes, some of which push the river towards the crevasse threshold, while others act as triggers. Based on the floodplain sedimentation patterns of large rivers in the southern Amazonian foreland basin, it has been suggested that alluvial plain sediment accumulation is primarily the result of river crevasse splays and sheet sands triggered by above-normal precipitation events due to La Niña. However, more than 90 % of the Amazonian river network is made of small rivers and it is unknown whether small river floodplain sedimentation is influenced by the ENSO cycle as well. Using Landsat images from 1984 to 2014, here I analyse the behaviour of all 12 tributaries of the Río Mamoré with a catchment in the Andes. I show that these are very active rivers and that the frequency of crevasses is not linked to ENSO activity. The data suggest that most of the sediments eroded from the Andes by the tributaries of the Mamoré are deposited in the alluvial plains, before reaching the parent river. The mid-to-late Holocene paleo-channels of these rivers are located tens of kilometres further away from the Andes than the modern crevasses. I conclude that the frequency of crevasses is controlled by intrabasinal processes that act on a yearly to decadal timescale, while the average location of the crevasses is controlled by climatic or neo-tectonic events that act on a millennial scale. Finally, I discuss the implications of river dynamics on rural livelihoods and biodiversity in the Llanos de Moxos, a seasonally flooded savannah covering most of the southern Amazonian foreland basin and the world's largest RAMSAR site.

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Is river avulsion style controlled by floodplain morphodynamics?

Cited by 91 publications

References 17 publications

Crevasse Splays Versus Avulsions: A Recipe for Land Building With Levee Breaches

Crevasse Splays Versus Avulsions: A Recipe for Land Building With Levee Breaches

Neotectonics, flooding patterns and landscape evolution in southern Amazonia

Alluvial plain dynamics in the southern Amazonian foreland basin

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