Generation Mechanism of an Alongshore Bar
on a Sandy Beach Slope

I. O. Leont’yev

Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia

E-mail: leontev@ocean.ru

Received August 15, 2007

Abstract—A model explaining the mechanism of alongshore bar formation from the point of view of the sed-
iment balance in the surf zone is considered. A cloud of suspended matter that appears during wave breaking is
transported shoreward and simultaneously sediments forming a vertical material flux directed to the bottom (S).
Simultaneously, an undertow generates a horizontal offshore flux of suspended matter q_x. Under these condi-
tions, the sediment balance is determined by the equality of the flux –S and the gradient dq_x/dx. The bottom pro-
file satisfying the balance equation is a bar profile with the crest at the point of the flux maximum –S. The model
predicts a concave profile of the seaside slope and a concave–convex profile of the slope in the trough. A con-
clusion is reached on the basis of the calibration and verification of the model based on the field data that the
suggested mechanism manifests itself differently in the outer and inner zones of the coastal zone. In the inner
zone, the horizontal size of the bar is determined by the length of short wind waves, while, in the outer one, it
is determined by the length of the infragravity waves related to the groups of short waves. It is shown that the
model can be applied to estimate the parameters of the largest bar in the inner part of the coastal zone.

DOI: 10.1134/S000143700902012X

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