Flood in Buochs (2005)

Boards and sand bags can be used as a protective device to prevent a flood from spreading. During the storm of 2005 a sand bag barrier was erected in Buochs so to prevent the rising lake water from spreading in the direction of the village. Picture: Sandsacksperre in Buochs, Kanton NW 2005
During a log jam, a channel becomes blocked with driftwood, bed load and other material. These driftwood blockages at bridges and weirs often exacerbated the flood situation during the storm events. Many bridges were damaged by driftwood colliding with them. Picture: Clogging Engelberger Aa, Luther Kanton NW 2005
During the storm of 2005, the water level in Lake Lucerne rose and flooded the village of Buochs in the canton of Nidwalden. Wooden pedestrian bridges were installed throughout the village as an immediate temporary measure. Picture: Fussgängerbrücke in Buochs, Kanton NW 2005
During the storm of 2005, Buochs outdoor swimming pool was covered with thick layers of fine sand, dirt and driftwood. The widespread areas covered with sediment, fine sand, dirt and driftwood had to be cleared using an excavator. Picture: Feinsandablagerung im Freibad in Buochs, Kanton NW 2005
Despite the discharge measures carried out on the Engelberger Aa, the river still generated torrential volumes of water in Buochs. It was possible to contain this water in the riverbed as, thanks to the four discharge corridors, the water flowed at a maximum rate of 150 m³/s below the Ambauen weir into Lake Lucerne. The peak flow of the Engelberger Aa during the flood of August 2005 was 230 m³/s (see images: Engelberger Aa discharge corridor). Picture: Hochwasser in Buochs, Kanton NW 2005
Due to the flood peaks of the river Sarner Aa from the canton of Obwalden and the Engelberger Aa from the canton of Nidwalden, Lake Lucerne almost reached its maximum water level. The maximum level of 435.23 m for the storm period in August 2005 arose on the afternoon of 24 August. As a result the lake was 165 cm over its average water level of 433.58 metres above sea level and just 2 cm below the previous maximum of June 1910. The lake's peak level caused static flooding in areas close to the lakeshore. Picture: Seehochstand des Vierwaldstättersees in Buochs, Kanton NW 2005
During the flood of August 2005, in addition to the water and bed load, many mountain and valley rivers also transported large volumes of driftwood. In some cases the driftwood was carried over long distances, for example into lakes. In others it jammed at bottlenecks such as bridge and weirs and, as a result, caused the water courses to break their banks and flood. Picture: Schwemmholz im Vierwaldstättersee, Kanton NW 2005
When the flood subsided, the driftwood accumulated at flat embankments, in the forelands of the water courses or directly in the channels. Such deposits need to be cleared as quickly as possible as otherwise they will be mobilised again during the next flood event. Picture: Schwemmholzablagerung in der Badi Buochs, Kanton NW 2005
All of the landslides in the canton of Nidwalden occurred within a 24-hour period. The Blatti landslide is located on a steep south-sloping meadow. The area was already known as an area prone to landslides before the storm of 2005. The landslide was triggered on the morning of 22 August 2005. The slope slid suddenly on a clayey sliding surface. The sliding surface had formed on the rock slab from the slope seepage water. The water-saturated soil slid on the rock slab. The agricultural land at the bottom of the slope was also affected by overland sedimentation. The rupture width of the landslide was around 50 m and the rupture area was approximately 3,000 m2. The fracture depth of the landslide was between 2 m and 4 m. Picture: Mittelgründige Rutschung in der Blatti in Ennetbürgen, 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. In addition, the water level in Lake Lucerne exceeded the damage limit for around eight days and the rising groundwater level caused numerous floods in the cellars and ground floors of buildings.

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