Sea outlet of the Saâne river (France)

Restoring the estuarine character of the lower Saâne valley

Client: Syndicat des Bassins Versants Saâne, Vienne et Scie - Scale: 1:80

Background

The Saâne is a small coastal river that flows into the sea via a conduit crossing the dike supporting the coast road, against which there is a pebble beach.

The discharge capacity of this system is insufficient when the river is in flood, and the lower valley upstream of the mouth is subject to frequent flooding.

A physical movable-bed model was used to study a new outlet that would also help to restore the estuarine character of the lower part of the valley, restore functional natural habitats and reinstate free passage for migrating fish. The model simulated the movement of pebbles under wave action with a view to examining and defining development works to stabilise the river mouth and limit tidal ingress upstream of the estuarine section to be restored.

Model characteristics and contributions

• Undistorted model of the pebbled coastline
• Pebble ridge represented by fine sand
• Representation of changes in the pebble ridge under the action of waves and ebb currents in the Saâne
• Testing of several scenarios offering alternatives to a conduit fitted with a non-return valve, including a free-surface outlet
• Testing of tidal ingress in the restored estuary.