This report is to describe the application of a previously developed two-dimensional hydrodynamic numerical model (W.Wilmot 1976) to Öresund between Sweden and Denmark. The purpose of this application is to investigate the effect of a proposed tunnel connecting Helsingborg in Sweden and Helsingör in Denmark on the circulation and salinity content of the Sound.

The model resul t is first compared with synoptic field data from the Sound. The effects of the proposed tunnel are investigated by comparing model results with and without the tunnel.

The tunnel between Helsingör and Helsingborg is planned to be built partly below the bottom, but partly on an artificial bank across the deeper part of the Sound. The exact position of the tunnel has not yet been decided . Among the different proposals given, this report concerns only the situation which gives the maximum change in the sectional area compared to the natural case.

Three alternative depths are given for the tunnel. The main proposal is a distance from the free surface to the roof of the tunnel of 24 m. Also the depths 28 m and 20 m can be considered.

The sill depth through Öresund into the Baltic Sea is about 8 m and the  unnel is therefore not considered to change the water exchange between the Baltic and the North Sea. However, south of the planned tunnel (see fig 1) there are areas with depths of 30 m and more. The circulation and salinity of these areas are studied in the model with various external conditons.

The same study has also been carried out in a two-layer numerical model (Danish Hydraulic Institute 1977) and to a limited extent in a channel model including an advanced turbulence description (Technical High School, Lund 1976). The ultimate result from the hydrodynamic model studies has been the basi sof an ecological model and other ecological considerations (Vandkvalitetsinstitutet 1976).