Effect of tides on mouth bar morphology and hydrodynamics

Abstract

[1] Mouth bars are morphological units important for deltas, estuaries, or rivers debouching into the sea. Several processes affect the formation of these deposits. This paper focuses on the role of tides on shaping mouth bars, presenting both hydrodynamic and morphodynamic results. The effect of tides is analyzed in two end-member configurations: a river with a small tidal discharge compared to the fluvial discharge (fluvial dominated) and a river with a very large tidal discharge (tidal dominated). Mouth bar formation is analyzed using the coupled hydrodynamic and morphodynamic model Delft3D. The presence of tides influences the hydrodynamics of the jet exiting the river mouth and causes an increase in the averaged jet spreading. At low tide the lower water depth in the basin promotes a drawdown water profile in the river and an accelerated flow near the mouth. The resulting velocity field is characterized by residual currents affecting growth and final shape of the mouth bar. Simulations indicate that mouth deposits are characterized by the presence of two channels for negligible tidal discharge, whereas three principal channels are present in the tidal-dominated case, with a central channel typical of tidal inlets. On the basis of our numerical analyses, we present a robust criterion for the occurrence of mouth deposits with three channels. Trifurcations form when the tidal discharge is large with respect to the fluvial one and the tidal amplitude is small compared to the water depth. Finally, predicted mouth bar morphologies are compared with good agreement to river mouths in the Gulf of Mexico, USA.

Tidal controls on river delta morphology

“…Despite the active morphological processes in distributaries and mouth bar regions in tidal deltas 15,32 , recent research suggests that tides may act to stabilize the delta planform, provided that near-equilibrium conditions are prevalent at the landscape scale. The rates of meander migration in tidally-influenced distributary channels are relatively low 87 , which can be explained from the reversing flow reducing the point bar push effect 90 held responsible for meander migration 91 .…”

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).…”

“…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. There has also been work considering the effect of different sediment types on delta deposits (Edmonds, et al 2010), but this study did not look at the influence on 3 dimensional distribution of facies in the resultant system.…”

Measuring Subaqueous Progradation of the Wax Lake Delta with a Model of Flow Direction Divergence

“…These deltas can be qualitatively classified as river-dominated (Galloway, 1975), both by their large fluvial sources and relatively small winds and tides. Strong waves and tides can significantly alter this morphology (Leonardi et al, 2013;Nardin and Fagherazzi, 2012). Hence, we limit ourselves to river-dominated conditions here.…”