Observations of the transport through the belt sea and an investigation of the momentum balance

The Fehmarn Belt is a main channel in the Belt Sea and plays an important role in the exchange of water between the Baltic Sea and the North Sea. This article deals with the discharge through the Fehmarn Belt. Data given by seven stations measuring water level, salinity, temperature, wind speed and direction, and currents over the period 15 October 1996 – 15 October 1997 are used. The discharge based on these measurements is calculated using two methods: the first uses the measured currents and the second uses water level differences assuming geostrophic balance. The discharge time series enables an investigation of the one-dimensional momentum equation and of the discharge distribution between the Belt Sea and the Sound. The one-dimensional momentum equation is a simple tool as can be used in many different straits. The water level difference and the head loss term appear to be the most important terms in the momentum equation, but the coefficients of the momentum equation depend on the halocline position and the seasonal variations. The estimated blocking by a construction (a potential Fehmarn Belt link) on the basis of the momentum equation is also given. The comparison with the discharge through the Sound confirms the previous ratio of 3 : 8, but not more recent investigations suggesting 2 : 8.