Turkish J. Eng. Env. Sci. 28 (2004) , 207 – 221. c  T ¨ UB ˙ ITAK Numerical Study of Wind-Induced Currents in Enclosed Homogeneous Water Bodies M¨ usteyde Baduna KOC ¸Y ˙ I ˘ G ˙ IT, ¨ Onder KOC ¸Y ˙ I ˘ G ˙ IT Gazi University, Faculty of Engineering, Ankara-TURKEY e-mail: baduna@gazi.edu.tr Received 09.02.2004 Abstract Results of various circulation scenarios for wind-induced currents both in rectangular basins of constant depth and varying topography and in a small lake with a complex bathymetry are presented. The importance of some of the physical factors affecting the circulation pattern due to wind forcing in enclosed shallow homogeneous water bodies and the prediction of how physical changes might alter the circulation pattern were investigated. A 3-dimensional semi-implicit finite difference code was developed. The non-hydrostatic pressure component and the conventional sigma coordinate system in the vertical direction were incorporated into the model to take into account the effect of the vertical acceleration component and the bathymetric changes considered to be relatively important physical parameters for the circulation pattern. It was shown that the numerical model developed was capable of simulating wind-induced circulation in shallow enclosed water bodies and that the effect of topography and wind stress on the circulation pattern was of primary importance while the non-hydrostatic pressure component did not have much effect. Key words: Wind-induced circulation, Non-hydrostatic pressure distribution, Shallow water, Sigma coor- dinate. Introduction In recent decades, an increasing practical interest in water circulation in reservoirs and lakes has arisen due to the problems of water quality encountered in these water bodies from where water is supplied for either domestic or industrial use. This inter- est has led to the development of many numeri- cal models because of the unavailability of precise mathematical solutions to those problems of wa- ter quality. The formulation of the mathematical model in the coordinate system adapted is based on the physical properties of the flow domain and re- alistic assumptions (Koutitas and O’Connor, 1980). Hence, a large variety of numerical models have been developed over the years. In the early 1980s, 2- dimensional models which are computationally effi- cient and easily implemented were successfully used to predict the flow field and the distribution of pollu- tants (Falconer, 1986; Cheng et al., 1993; Hayter et al., 1997). However, it was soon recognised that the 2-dimensional models were not appropriate to simu- late wind-induced circulation due to their incapabil- ity of describing the detailed structure of velocity and thereby simulating the 3-dimensional effects. More- over, a bed stress calculation performed in 2-D mod- els is physically unrealistic since bed stress cannot be adequately parameterised in terms of depth-averaged velocity. Consequently 3-dimensional models such as multilayer models (Falconer, 1993) and quasi-3D models (Koutitas and Gousidou-Koutita, 1986) have been developed, thus including vertical variations in the overall solution accuracy and producing varia- tions in current and concentration through the ver- tical as well as in the horizontal. In order to in- crease the prediction capability of 3-D models, a large variety of numerical solution schemes (Simons, 1980; Sheng, 1994), orthogonal (Hamrick, 1994) 207