Aare, Interlaken (BE): Scour protection downstream of a weir

After the rehabilitation of a weir in the river Aare near Interlaken in 1993, bed erosion downstream of the weir produced damages at the river banks. Both, physical model tests and numerical simulations (2-D) showed that bed erosion was induced by asymmetrical flow conditions.

Within the model tests several rehabilitation concepts were investigated. The best solution implies an open armour layer, which protects the scour hole filled with fine material. It could be shown that a cover of 41 % of the surface area by coarse armour elements is sufficient to protect the underlying material. In the vicinity of the banks an additional protection is required by placing several layers of rough elements.

An alternative solution with bed ribs was assessed more negatively, because a protection of the underlying material would have required small distances between the ribs. Realizing larger distances between the ribs an additional protection in the spaces is needed.