Sediment dredged from the port of Hamburg is treated and stored upland in a storage facility. The site is covered by a system of topsoil above a sand drainage layer and a barrier layer made of processed harbour sludge in order to minimize the input of water after completion of the site. In 1995 in-situ investigations have started to study the hydraulic properties, the water balance and the water quality of the cover system of the storage site Francop in Hamburg. Two lysimeters (500 m(2) each) were constructed. During the first dry year after the construction of the lysimeters discharge rates <0.05 mm/d were measured below the sludge barrier. The hydraulic gradients indicate downward water movement in the sludge barrier during the summer and the winter of 1996. The chemical composition of the discharge below the barrier is typical for sludge pore water. An increase of the discharge above the sludge barrier neither led to an increase of discharges nor to changes in the concentration of the water compounds below the barrier. We assume that up to now there is no preferential flow through the sludge barrier. The cover system including the sludge barrier performs very well. The monitoring of the lysimeters is continued. (C) 1998 IAWQ. Published by Elsevier Science Ltd.