Investigating river-restoration-effects on riverbed-stability by physical modelling

This study shows how experimental results provide fundamental insights in the challenge of river revitalisation, and thus represent a powerful tool to guide engineers’ actions. Results concerns a study case, namely the “Wiese Vital” project, a restoration project in Basel area (Switzerland), with the objectives of safeguarding Basel's drinking water supply while revitalizing its watercourse and providing flood protection.

The planned revitalisation measures involve the reconstruction of the Wiese riverbed, the introduction of structures to improve its morphological variability and the replenishment of fine sediment to improve the spawning habitat of native fishes.

The new Wiese riverbed will consist of a coarser sediment layer, about 1.2 meters deep, overlaying a layer of finer sediments, meant to protect the underlaying aquifer from undesirable water infiltrations and thus to ensure Basel's drinking water supply safety. The stability of the coarser layer was investigated using a physical model in scale 1 to 20, built in the hydraulic hall of the University of Applied Sciences and Arts Northwestern Switzerland.

Experiments investigated the stability of the coarse protective layer in presence and in absences of revitalization measures: with and without “ecological” structures and before and after the addition of fine sediments.

Results revealed that wrong placement of “ecological” structures can cause local erosion and threaten the stability of the riverbed. Moreover, they provided useful insights on the response of a coarser riverbed to the input of fine sediments.