Secutex® H needle-punched nonwoven geotextiles significantly enhance system performance when two soil layers with dissimilar or non filter-stable grain structures are used as well as when a revetment is installed. Even where only hydro static loads are anticipated it is generally recommended to follow the requirements of the MAG (Instructions for the use of geotextile filters in waterways, Federal Institute for Hydraulic Engineering (BAW), Karlsruhe, Germany 1993). In filter applications for soil types 1 to 3, Secutex® H 609 with a minimum thickness of 4.5 mm is well suited (for further details please refer to the chapter «Filtration», pages 6-7), whereas for soil types 1 to 4, Secutex® H 813 with a minimum thickness of 6.0 mm would be appropriate. The installation instructions for different current velocities described in the chapter «Filtration» should be observed during common underwater installations. In the case of deeper water and higher current velocities, the use of Secutex® H sand mats or Secutex® Soft Rock sand containers is recommended as they provide excellent stability. The three-dimensional fibre structure of Secutex® H nonwoven geo textiles exhibit high elongation capacity and robustness. With these characteristics, they easily accommodate irregular or soft subgrades and are capable of withstanding installation loads when covered with stone, without loss of their filtration performance. The large effective pore space of the Secutex® H nonwoven geotextile structure offers an excellent environment for the establishment or continued propagation of local flora and fauna.