Discarge corridor Ennetbürgen-Buochs (2005)

Due to the fact that the flood protection project along the Engelberger Aa river had not been completed, it was not possible to protect Ennetbürgen against flooding in summer 2005. Thanks to the measures that had already been completed it was possible, however, to minimise the scale of the flooding and damage considerably. Picture: Überschwemmung in Ennetbürgen, Schweizer Luftwaffe 2005
During the flood of August 2006 the measures already carried out as part of the Engelberger Aa flood protection project proved worthwhile. Thanks to investments totalling CHF 26 million, damage in excess of CHF 100 million could be prevented. The four discharge corridors constitute the main component of the flood protection project. In the case of excess load, the excess water flowing in the river channel is channelled into the discharge corridor. This guarantees that the volume of water remaining in the channel at each discharge location corresponds to the capacity of the next section of the river. Picture: Discharge corridors of the Engelberger Aa (1), Kanton NW 2005
The excess water in the river Engelberger Aa leaves the riverbed at the planned discharge locations and flows through the discharge corridor between Ennetbürgen and Buochs into Lake Lucerne. The four discharge corridors at Dallenwil, Ennerberg und Buochs airfield constitute the main component of the Engelberger Aa flood protection project. Once the river has passed the fourth discharge area, a maximum of 150 m³/s of water remains in the riverbed which can be channelled without causing any damage into the lake in Buochs. The purpose of flood protection concepts like that of the Engelberger Aa discharge corridors is to provide robust protection in the case of extreme flood events. These concepts must not fail suddenly in the case of excess load and increase the amount of damage arising from the flood but must provide space for extraordinary volumes of discharge or bed load. Picture: Discharge corridors of the Engelberger Aa (2), Kanton NW 2005
The implementation of the Engelberger Aa flood protection project was motivated by the flood in Uri in 1987. The measures that have been completed up to now were able to prevent major damage during the storm of 2005. The four discharge corridors constitute the main component of the flood protection project. In the case of excess load, the excess water flowing in the river channel is channelled into the discharge corridor. This guarantees that the volume of water remaining in the channel at each discharge location corresponds to the capacity of the next section of the river. Picture: Discharge corridors of the Engelberger Aa (3), Kanton NW 2005

The intensive precipitation in summer 2005 transformed both the river Engelberger Aa and nearby streams into raging torrents that transported large volumes of bedload, debris and wood into the valley and burst their banks in places. Because the implementation of flood protection project measures had not been completed, the water from the Aa flooded into the low-lying settlement area of Ennetbürgen.

Differentiated flood protection

The canton of Nidwalden adopted the concept of differentiated flood protection for its flood protection project on the river Engelberger Aa. Based on this concept, flooding is not prevented at any cost. Instead, the focus is on the protection of valuable structures and properties. Hence, in August 2005, the Engelberger Aa was allowed to flood in a controlled way at two points on the plain between Ennetbürgen and Buochs. It was possible to prevent extensive damage in more vulnerable locations in this way.

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