The Szczecin Lagoon is an inshore water close to the Baltic Sea which can be subdivided into two major basins — the Kleines Haff in the western part of the lagoon and the Zalew Wielki (Großes Haff) in the eastern part. The lagoon has an area ofA ≈ 685 km2 and an average depthD of ≈ 3.8 m. It drains into the Baltic Sea via three outlets — Peenestrom, Swina Strait and Dziwna.
In summer 1997 one of the most severe floods ever recorded was running down the river. When this flood reached the lagoon, a monitoring network consisting of three fixed platforms already established delivered continous data recordings about environmental and water quality parameters. In addition, the research vesselLudwig Prandtl was on a permanent cruise within the Zalew Wielki in order to complete the information delivered by the fixed measurement platforms. Recordings of conductivity taken by the fixed stations indicate a different behaviour of the two parts of the lagoon regarding water quality parameters. Whereas the flood water spread very quickly throughout the Zalew Wielki, the Kleines Haff was affected only with a remarkable time delay. Differences in water quality could be observed even by eye, showing clearly distinguishable colors in the different parts of the lagoon. ADCP measurements along different transects recorded by a ship-mounted current profiler gave valuable information about water exchange rates. For instance, the Odra river inflow had maximum discharge rates of aboutQ = 3000 m3/s. Discharge rates of the Swina Strait and Old Swina were also obtained.
A three-dimensional hydrodynamical model (TRIM3D) was run in order to investigate the impact of the flood on the lagoon. The model was implemented on a grid with a spatial resolution ýx = 250 m giving a total number of 85000 grid points. Numerical simulations reproduced water level time series within the lagoon and gave good agreement between modelled and measured discharge rates. Transport paths and impact of the flood water body could be traced by use of this model.