On Strong Nearshore Wind-Induced Currents in Flow-Through Gulfs: Variations on a Theme by Csanady

Georgios Horsch,Nikolaos Fourniotis

doi:10.3390/w10050652

Georgios Horsch, Nikolaos Fourniotis

Open Access

https://doi.org/10.3390/w10050652

Copy DOI

Abstract

Csanady’s (1973) model, used to explain the development of strong, wind-induced nearshore currents in long lakes, has been extended to explain the same phenomenon in flow-through semi-enclosed gulfs. As in the original theory, it is predicted that the depth-averaged velocities move with the wind in regions shallower than the characteristic depth and upwind in deeper parts of the basin. The characteristic depth in the modified theory, however, is shown to be larger than the characteristic depth of the original theory, which is the basin mean depth, by a parameter λ, which can be calculated using the wind stress, the cross-section area and the volumetric inflow into the gulf. The theory is further used to examine in detail the scaling of the flow and identify the dimensional parameters underlying the formulation of the Csanady model. By expanding in an appropriately-defined inverse, Rossby number, which can be made arbitrarily large for small times, it is shown that under the influence of the Coriolis force, the free surface assumes a characteristic S-like shape and the shorewise volume flux an M-like shape. It is suggested that the shorewise flux might be of interest in environmental applications. The predictions of both variations of the original model of Csanady have been illustrated by numerical simulations, in pertinent idealized geometries, and have been also used to explain salient features of the wind-induced circulation in the Gulf of Patras in Western Greece.

Highlights

A ubiquitous feature in simulations of wind-induced circulation in lakes of variable bathymetry is the strong nearshore currents that develop soon after the application of wind shear on the lake’s surface.This phenomenon is accompanied by a weak return flow, which seems to have been first reported by [1] and has been observed in many simulations ever since, up to recent ones
Our goal is not to present a quantitative comparison of simulations with the respective theories, which, if attempted, would have been hampered by the omnipresent wind-induced flows, seiches, but rather to show how to properly interpret flow features appearing in complete numerical simulations that could have remained, otherwise, obscure
Flow-through long gulfs share with long lakes the development, under wind forcing, of strong nearshore currents and a return flow, in the depth-integrated sense, at the deeper regions

Summary

Introduction

A ubiquitous feature in simulations of wind-induced circulation in lakes of variable bathymetry is the strong nearshore currents that develop soon after the application of wind shear on the lake’s surface. This phenomenon is accompanied by a weak return flow (in the depth integrated sense), which seems to have been first reported by [1] and has been observed in many simulations ever since, up to recent ones. Csanady’s original model was developed for lakes, but the same phenomenon has been observed by [5] to occur in simulations of wind-induced circulation in a flow-through, semi-enclosed gulf, namely the Gulf of Patras, in Western Greece.

Objectives

Results

Conclusion