Morphodynamics of subaqueous levee formation: Insights into river mouth morphologies arising from experiments

Abstract

[1] Levee formation by deposition from sediment-laden flows debouching into open waters has been conceptually and analytically linked to jet hydrodynamics since the middle of the 20th century. Despite this long-standing association between jets and levees, the morphodynamics controlling subaqueous levee development remain largely unquantified and poorly understood. Here we report the results of physical experiments on subaqueous levee development modeled on floodplain tie channel processes. In the laboratory, we created subaqueous levees from a sediment-laden jet entering a basin of still water. Levee formation occurred where the local shear velocity of the jet declined below the critical shear velocity for entrainment of sediment into suspension. The rate of levee deposition depended on the rate of lateral sediment transfer to the jet margins and the settling velocity of suspended sediment. In our friction-dominated flows, lateral sediment flux to the levees was primarily due to dispersive lateral transport driven by turbulence. High rates of sediment transfer from the jet core to the margins led to levee growth that outpaced deposition along the flow centerline. Under hypopycnal conditions, we failed to produce levees. We observed distinct differences in levee morphology due to changes in the size and density of suspended sediment under identical hydrodynamic conditions. Our experimental results and review of published data on hypopycnal river mouths suggest that suspended sediment characteristics, relative magnitude of bed friction, and channel outlet aspect ratios may have a more significant influence on river mouth morphology than the buoyancy of discharging waters as envisioned in existing conceptual models.Citation: Rowland, J. C., W. E. Dietrich, and M. T. Stacey (2010), Morphodynamics of subaqueous levee formation: Insights into river mouth morphologies arising from experiments,

Effect of tides on mouth bar morphology and hydrodynamics

“…The transition from ZOFE to ZOEF marks the downstream location at which the turbulence generated by shearing along the margins of the jet affects the entire jet [Bates, 1953]. Jet theory has been largely used to describe rivers and inlets discharging into a standing water body [Bates, 1953;Wright and Coleman, 1974;€ Ozsoy and € Unl€ uata, 1982;Wright, 1977;Rowland et al, 2010;Falcini and Jerolmack, 2010;Nardin and Fagherazzi 2012;Nardin et al, 2013].…”

Establishing 3D Numerical Reservoir Analogues - Modelling the Formation of Sand Bodies in Deltaic Environments

“…However the total sand body extent will depend on the lateral connectivity between these sand rich features (Ravenne, et al 1989 (Ashworth, et al 2011), experimentally (Rowland, Dietrich and Stacey 2010) as well as numerically (Chatanantavet, Lamb and Nittrouer 2012;Nardin, et al 2013;Leonardi, et al 2013;Edmonds and Slingerland, 2007;Edmonds, et al 2010). Previous work on mouth bars, for example, includes their formation of river dominated delta networks (Edmonds and Slingerland, 2007) but there has also been studies focussed on sub-aqueous levee formation (Rowland, Dietrich and Stacey 2010). The effects of tides (Leonardi, et al 2013) and waves (Nardin, et al 2013) on the formation of deltaic mouth bars has been investigated.…”

Spillage sedimentation on large river floodplains

“…They may also extend erosively as dendritic networks draining surface waters or groundwaters (SLg). These convey sediment as much as contain them, producing elongate deposits in lakes (Rowland et al, 2009(Rowland et al, , 2010 and see Figure 1), though such channels may also silt up where not flushed by exiting mainstream flows (Rowland et al, 2005;Trigg et al, 2012).…”

“…Levees Smith, 1986;Cazanacli and Smith, 1998;Brierley et al, 1997;Ferguson and Brierley, 1999;Saucier, 1994;Adams et al, 2004;Klasz et al, 2014;Aalto et al, 2008;Park andLatrubesse, 2015 b. Bank-top splays Coleman, 1969;Alexander et al, 1999;Van de Lagerweg et al, 2013;Shen et al, 2015 c. Channel bars and islands Bristow, 1987;Gurnell et al, 2001;Mardhiah et al 2015;Rozo et al, 2014;Wintenberger et al, 2015 SL Secondary linear systems d. Accessory channels Dunne et al, 1998;Lewin and Ashworth, 2014a;Lewin and Ashworth, 2014b;Latrubesse, 2015 e. Crevasse splays O'Brien andWells, 1986;Smith et al, 1989;Smith and Pérez-Arlucea, 1994;Bristow et al, 1999;Farrell, 2001;Toonen et al, 2016 f. Crevasses with deltas Bogen, 1982;Tye and Coleman, 1989;Latrubesse and Franzinelli, 2002;Rowland et al, 2010;Olariu et al, 2012g. Drainage nets Day et al, 2008Trigg et al, 2012;Lewin and Ashworth, 2014b PF Prior-form following h. Cutoff and palaeochannel fills Dieras et al, 2013;Toonen et al, 2012;…”