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Landslide risk assessment in the Göta river valley: effect of climate changes
L'évaluation des risques de glissement de terrain dans la vallée de la rivière Göta :
effet des changements climatiques
Tremblay M., Svahn V., Lundström K.
Swedish Geotechnical Institute, Linköping and Gothenburg, Sweden
ABSTRACT: The predicted effects of the ongoing climate change such as increased precipitation and longer dry periods are expected
to result in an increased frequency of landslides in Sweden. In order to meet this challenge, the Swedish Government commissioned
the Swedish Geotechnical Institute (SGI) to investigate and assess the landslide risk in the Göta river valley, which is one of the
Swedish valleys with the highest landslide frequency and where consequences of a landslide could be severe due to the number of
large industrial sites as well as residential areas and infrastructure. A mapping of the landslide risk considering both present
conditions and the effects of a future climate change has been performed. The investigation shows that climate change will increase
the risk of landslides in the valley. However, it also shows that high level of risk is already estimated in many areas which can be
affected even in today’s climate.
RÉSUMÉ : Les effets prévus du changement climatique en cours, comme l'augmentation des précipitations et des périodes sèches
plus longues devraient se traduire par une augmentation de la fréquence des glissements de terrain en Suède. Afin de relever ce défi,
le gouvernement suédois a chargé l'Institut suédois de géotechnique (SGI) d’étudier et d’évaluer le risque de glissement de terrain
dans la vallée de la rivière Göta, qui est une zone à haute fréquence de glissement de terrain et une zone particulièrement vulnérable
en raison du nombre de grands sites industriels ainsi que des zones résidentielles et des infrastructures. Une étude des risques de
glissement de terrain considérant à la fois les conditions actuelles et les effets d'un changement climatique à venir a été effectuée.
L'étude montre que le changement climatique augmente les risques de glissements de terrain dans la vallée, mais elle montre aussi que
le niveau de risque est déjà élevé dans de nombreuses parties de la vallée, même dans le climat actuel.
KEYWORDS: lanslides, risk assessment, climatic changes, mapping.
1 INTRODUCTION
The
Göta river valley is situated in the southwest of Sweden and
runs from Lake Vänern in the north to Gothenburg in the south,
Figure 1
. It
is one of the areas in Sweden which is most
frequently affected by landslides. Each
year, several landslides
of various size and character occur in this region. The landslides
are generally small and shallow, however, a number of large
landslides have occurred during the past century, some of them
with human casualties and extensive property damages (e.g.
Alén et al. 2000; Hultén et al. 2007). One reason for the high
frequency of landslides in the Göta river valley is its geological
history. The deep clay layers were formed during and after the
latest glaciation period and in some parts reach a thickness up to
100 meters. The Göta river has overtime cut deep into the clay,
forming the prerequisites for landslides. As the clays were
mainly deposited in a marine environment, quick clay is
therefore widespread in the area. The total length of the river is
about 100 km.
The valley has a long history of human activities resulting in
settlements, industries, shipping and harbours. Roads and
railroads of national importance follow the river bank for
kilometres, and environmentally hazardous activities and
contaminated sites are common. More than 100,000 people live
in the valley and the river is also the fresh water source for
about 700,000 people. Due to the relatively high exploitation of
the area, the consequences of a landslide in the Göta river valley
can therefore be very severe.
The Göta river has suffered from many landslides over the
years that have been documented.
Parts of the most populated
areas in the valley have earlier been investigated for mapping
the risk of landslides, but in order to predict the effect of climate
changes, the Swedish Government has commissioned the
Swedish Geotechnical Institute to investigate and map landslide
risks in the whole valley.
Figure 1. Location of the Göta river
2 METHODOLOGY OF RISK MAPPING
The concept of risk used in these investigations refers to a
combination of the
probability
that an event might happen in a
given area and the
consequence
of this event occurring.
Risk is defined as a combination of these two parameters:
Risk = Probability x Consequence
