AUTHOR=Zăinescu Florin , Anthony Edward , Vespremeanu-Stroe Alfred 

TITLE=River Jets Versus Wave-Driven Longshore Currents at River Mouths

JOURNAL=Frontiers in Marine Science

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.708258

DOI=10.3389/fmars.2021.708258

ISSN=2296-7745

ABSTRACT=<p>At river mouths, fluvial jets and longshore currents (LSCs) generated by waves interact hydrodynamically. This idealized numerical modeling study simulates a large number of hydro-morphodynamic conditions (650) to explore the emergent hydrodynamics determined by different mouth bar volumes and geometries, river discharge, wave heights, and directions and their potential stress on river-mouth development. We find that in the absence of a river-mouth bar (RMB), interactions are driven by momentum balances, expressed either as the balance of wave momentum flux (<italic>Mw</italic>) and jet momentum flux (<italic>Mj</italic>), or the balance of river jet discharge (<italic>Q</italic><sub><italic>Jet</italic></sub>) and longshore current discharge (<italic>Q</italic><sub><italic>LSC</italic></sub>). When a RMB is present, the topography modifies the structure of the jet by spreading it, and we quantify this mechanism through the lateral jet transfer rate (<italic>LJT</italic>). Secondly, topography generates complex longshore wave-driven circulation as a result of the protruding shoreface which serves as a platform on which counter LSCs develop. The balance in <italic>Q</italic><sub><italic>Jet</italic></sub>/<italic>Q</italic><sub><italic>LSC</italic></sub> may be used as an indication of the type of circulation. High and oblique waves favor longshore circulation and RMB bypass, whereas low waves and normal-to-coast angles generate diverging LSCs on the mouth bar crest which interrupts the longshore circulation. A quantification of the dynamic diversion is proposed in the form of the non-dimensional Dynamic diversion index (<italic>DyD</italic>), which scales with the product of <italic>Mj</italic> and <italic>Mw</italic>, and can account for the absolute strength of hydrodynamic interactions occurring at river mouths. RMB morphology can affect <italic>DyD</italic> in multiple ways by strengthening or by weakening the interactions. The <italic>DyD</italic> effect seems to increase with increasing RMB size, indicating that the RMB scale regulates the interplay of the wave-driven circulation and the river jet which further controls the adjacent topography changes.</p>