Sealing materials are of major importance in hydraulic engineering applications. They ensure the stability of hydraulic structures and prevent or reduce seepage losses out of the waterway. In waterways, mainly natural liners have been used. In the new turnout Eberswaldes, Germanu, a needlepunched geosynthetic clay liner(GCL) was installed in a navigated waterway as a canal liner by order of the Federal Water and Shipping Administration (Fleischer and Schreier, 1998). GCLs are thin composite materials combinning bentonite clay(usually natural sodium bentonite) and geosynthetics (usually geotextiles) and are generally used to replace or augment compacted liners. To avoid the closure of the waterway for ship traffic, an installation method was chosen which allowed continuous ship traffic. The GCLs were installed in two segments, both halfway under water, and a sand ballast mat provided the necessary confining stress prior to the rock ballast covering, and acted mainly as a protection layer for installation stress due to the placement of the rock rip rap. Continuous monitoring was carried out to prove the efficiency of the sealing system.(C)2000 Elsevier Science Ltd. All right reserved.