Flood prevention and revitalisation of the Kleine Emme

The canton of Lucerne was hit by extensive flooding in August 2005, with the Kleine Emme catchment area affected in particular. Built structures suffered damaged to the tune of more than 200 million francs. With this project, the canton of Lucerne aims to ensure improved flood protection for both the population and the infrastructure along the Kleine Emme while simultaneously enhancing the ecological value and condition of the waterway. Where space permits, the channel will be widened to the “regime width”, thus ensuring sufficient discharge capacity for the future and restoring the river to its natural shape and morphology. The hydraulic engineers at Basler & Hofmann led the development of the construction and approval project in an engineering consortium. The Stägmättli section near Malters is one of the two sections the team has also worked on and supervised during execution. Two innovative concepts were also implemented during this process.

Deadwood and “sawteeth” for ecological enhancement

These ideas included bank cuts in the form of “sawteeth” (see figure below), which stimulate the natural widening of the Kleine Emme. The goal is to have these teeth gradually shape and widen a portion of the river area, rather than use mechanical means to widen the channel cross-section all at once. The second innovative concept involved using various deadwood structures and “engineered log jams”, which were positioned in the riverbed and at the foot of the embankment. These riverbed and shoreline structures provide valuable aquatic habitat, especially for fish. The natural erosion banks in the area of the sawteeth are also a delight for kingfishers and other species that thrive in such habitats. The protective measures were put to the test soon after the construction was complete. When five-year flooding events occurred in both November and December 2023, the Kleine Emme handled these episodes with ease. There was not much to be seen of the sawteeth afterwards. As intended, the flowing water mounted a frontal attack on the cuts in the riverbank, resulting in the formation of a natural erosion embankment.