Showing papers by "Giovanni Seminara published in 1998"
TL;DR: In this article, the problem of one-dimensional tide propagation in convergent estuaries was revisited, and a nonlinear parabolic approximation of the full de Saint Venant equations was developed to describe this behaviour.
Abstract: We revisit the problem of one-dimensional tide propagation in convergent estuaries considering four limiting cases defined by the relative intensity of dissipation versus local inertia in the momentum equation and by the role of channel convergence in the mass balance. In weakly dissipative estuaries, tide propagation is essentially a weakly nonlinear phenomenon where overtides are generated in a cascade process such that higher harmonics have increasingly smaller amplitudes. Furthermore, nonlinearity gives rise to a seaward directed residual current. As channel convergence increases, the distortion of the tidal wave is enhanced and both tidal wave speed and wave lenght increase. The solution loses its wavy character when the estuary reaches its “critical convergence”; above such convergence the weakly dissipative limit becomes meaningless. Finally, when channel convergence is strong or moderate, weakly dissipative estuaries turn out to be ebb dominated. In strongly dissipative estuaries, tide propagation becomes a strongly nonlinear phenomenon that displays peaking and sharp distortion of the current profile, and that invariably leads to flood dominance. As the role of channel convergence is increasingly counteracted by the diffusive effect of spatial variations of the current velocity on flow continuity, tidal amplitude experiences a progressively decreasing amplification while tidal wave speed increases. We develop a nonlinear parabolic approximation of the full de Saint Venant equations able to describe this behaviour. Finally, strongly convergent and moderately dissipative estuaries enhance wave peaking as the effect of local inertia is increased. The full de Saint Venant equations are the appropriate model to treat this case.
195 citations
TL;DR: Linear and nonlinear aspects of the development of morphodynamical features of fluvial and coastal environments are reviewed in this article, where it is emphasized that, in spite of the as yet incomplete understanding of the mechanics of sediment transport, some essential mechanisms operating in morphodynamics have been recently clarified by employing classical tools of linear and weakly nonlinear stability theory.
Abstract: Linear and nonlinear aspects of the development of morphodynamical features of fluvial and coastal environments are reviewed. It is emphasized that, in spite of the as yet incomplete understanding of the mechanics of sediment transport, some essential mechanisms operating in morphodynamics have been recently clarified by employing classical tools of linear and weakly nonlinear stability theory.
86 citations
TL;DR: In this article, the authors developed an analytic approach able to predict flow and bed topography in curved cohesionless wide channels, which is applied to the case of constant curvature channels and can be extended, in principle, to channels with variable curvature.
Abstract: We develop an analytic approach able to predict flow and bed topography in curved cohesionless wide channels. The novel feature of the present theory, compared with previous analytic approaches, is its ability to treat bottom perturbations of finite amplitude and situations such that sediment transport does not occur within the whole cross section. The theory is presently applied to the case of constant curvature channels though it can be extended, in principle, to channels with variable curvature. Results show that the dominant mechanism controlling the establishment of bed profile is the topographic feedback of bottom deformations on the flow field, while the role of the dispersive transverse transport of longitudinal momentum and of the metrically induced transverse variations of longitudinal slope is usually relatively small. The theory extends previous linear analyses which are shown to underpredict deeping of the cross section close to the outer bank. Also, unlike linear theories, the present approach predicts a transverse slope of the bed profile increasing towards the outer bend in agreement with experimental observations. The maximum depth is found to depend on the friction coefficient Cu of the undisturbed uniform stream and on the parameter v(θu)1/2/Cu where v is curvature ratio, that is, the ratio between channel half width and radius of curvature of the centerline, while θu is the Shields stress of the undisturbed uniform stream. Comparison with experimental observations is fairly satisfactory. The shape of the cross section is then determined also for values of θu close enough to the critical values not to allow bedload transport within the whole cross section. The threshold value of θu separating the total transport from the partial transport regime is finally determined as a function of the curvature ratio v.
30 citations