As part of the development of the Grand-Saconnex motorway junction and the Vengeron interchange, a drainage and treatment station for roadway water, known as the SETEC basins, was built.

The SETEC basins collect and treat pavement water, and include a technical room, a reception structure acting as a scourer, an OPAM reservoir, two “Splitt”-type coarse filtration basins, and two finer filtration basins with vegetated sand.

The concept consists in creating a system that does away with the usual mechanical constraints. Filtration is provided naturally by two types of filter: coarse “Splitt” filters and fine sand filters, stabilized by reeds. The proposed system meets the high treatment requirements for this type of structure, and the treated water is returned with a high quality (pollutant treatment efficiency of over 90%).

The landscape integration of the basins into the site was approached by playing on their significance. The “magical” aspect of the reed ponds, which treat the water from the freeway’s pavements, has been incorporated into the architectural concept. The shape of the basins is rounded off to form an aggregation of organically shaped cells, expressing their function as containers. Rounding off the corners of the basins enables the pre-stressing cables required to limit cracking to be routed through them. The basins are partially buried so that only the crown is visible, enhancing the value of the reed planting. Peripheral landscaping accompanies the installation, creating a gentle transition between the ponds and the forest, with lean grassland and shrubs.

The SETEC ponds are built on a general reinforced concrete base. The walls are made of prestressed concrete, and are built over the ponds in stages to limit cracking. Perimeter walls act as retaining walls for the ground. The interior walls separate the basins.

The project is being developed using BIM, enabling coordination between the various specialists (civil engineering, hydraulic engineering, BSA engineering) right from the start.