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Meiringen
1
Alpbach
2
Milibach
Conjunct ion of
Alpbach/Milibach
3
2%
3%
3%
>20%
4
Milibac h (old)
5
Aare
12%
>20%
Fig. 1 Model perimeter of the physical scale model Meiringen. The numbers in percentage
correspond to the slope
Table 1 Characteristics of Milibach and Alpbach above the conjunction
Type of rainfall
Flood event Milibach
Alpbach above conjunction
Discharge
(m 3 /s)
Bed load
(kg/s)
Discharge
(m 3 /s)
Bed load
(kg/s)
Persistent precipitation
HQ 100
4
190
20
300
EHQ
6
280
30
2,000
Thunderstorm
HQ 100
15
610
34
1,140
EHQ
22
1,850
51
3,280
the middle of the village and subsequently flowing together into the river Aare
(Fig. 1 ). It is assumed that the flood in 2005 corresponded to a return period of 100
years (Table 1 ). Persistent precipitation induced a mobilization of the unstable
subsurface of the mountainous catchment area, leading to a high sediment input
into the streams. While the sediment was transported in the steep, upper part of the
catchment area, the transport capacity was too small in the flat and populated area
of Meiringen. Sediments deposited in the channel and reduced the flow section,
causing an overbank flow. Deposition initially took place mainly at the slope
changes and bridges. The Milibach (Fig. 1 ) got blocked with boulders of diameters
larger than 1 m. As Meiringen is located on the alluvial fan of the two channels, the
overtopped water and sediment went directly down through the village. Sediment
was deposited everywhere, even inside houses.
In order to protect Meiringen from future flooding, a flood mitigation project was
proposed by local engineers and tested at the Laboratory of Hydraulics, Hydrology
and Glaciology (VAW) in Zurich. The project includes sediment traps installed in
the upper part of the catchment area to reduce the sediment input into the populated
area. In spite of these measures, a lot of sediment will reach the channels in
Meiringen during exceptional floods (Table 1 ). Therefore, the sediment transport
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