Long term evolution of self-formed estuarine channels

ABSTRACT: The aim of this paper is to investigate the long term configuration attained by a tidal channel, namely its longitudinal bed profile and shape. Channel evolution is simulated through a one-dimensional numer-ical model, where the role of intertidal areas is neglected. The channel has a rectangular cross section and it is closed at one end. The major novelty of the work is that the width of the channel is allowed to change in time: in the present model lateral erosion is computed as a function of bed shear stress, provided it exceeds a threshold value within the cross section.The system, forced by a prescribed free surface oscillation at the seaward boundary, reaches an equilibrium profile of both bottom elevation and channel bank. The equilibrium geometry of the channel is determined for different initial and boundary conditions. Furthermore, the spatial variations of the cross section at equilibrium are analyzed in order to identify those conditions under which the commonly used exponential law of channel width variation is reproduced. Finally, a comparison is pursued between model predictions and bathymetries of real estuaries.