The Göta River Commission
To respond to future climate changes and deal with increased flows through the Göta river we need better knowledge of the stability conditions. The Government has therefore given the Swedish Geotechnical Institut (SGI) the commission to map the lanslide risk for the Göta River valley. SGI started the mission in 2009 and it will be completed in 2011.
For the past ten years, the frequency of natural hazards has doubled and from what we know, they will continue to increase. Higher temperatures and the increased occurrence of sudden and heavy rainfalls, floods and landslides are some effects of climate change in Sweden. Some regions are particularly vulnerable; for instance, if Lake Mälaren floods it will seriously affect infrastructure and residential areas for 2.5 million people in the Mälardalen region. In order to prevent future catastrophes, future settlements and infrastructure should be developed to withstand increased natural hazards. More knowledge and improved preparedness are required in order to prevent life, environment and property from being endangered.
The river Göta Älv
In the first report from the Swedish Commission on Climate and Vulnerability (“Threats of flooding, risks and measures for Lake Mälaren, Hjälmaren and Vänern,” First report from the Swedish Commission on the Climate and Vulnerability, SOU 2006:94), increasing flows in the Lake Vänern region was addressed. To prevent extensive floodings and damages, it is necessary to allow controlled overflow from Lake Vänern through the river Göta Älv (River), which in turn leads to an increased risk for landslides in the Göta Älv valley. Careful geotechnical investigations and risk analyses will be required along the entire river Göta Älv.
Government commission to SGI
In order to meet the upcoming climate changes and to handle the increasing flows through the Göta Älv, we need to improve the knowledge of the stability of the entire river bank in the Göta Älv valley. The Government has commissioned SGI to investigate the landslide potential of the Göta Älv valley, taking the predicted climate changes into consideration. The commission provides SGI with MSEK 35 a year, for three years.
Area of investigation
The investigated area includes the parts of Göta Älv that could be affected by increased flows from Lake Vänern. Areas where the increased flow will affect stability and where landslides will affect the could cause damming of the river. The area to be investigated is mainly restricted to the banks of Göta Älv from the outlet at the island Vargön in Vänersborg, to the bridge Marieholmsbron in Göteborg, plus along the river Nordre Älv including Ytterby in the municipality of Kungälv. The area of investigation also includes the tributaries in connection to Göta Älv. Below Marieholmsbron, the sea level affects the water level; at high sea water levels, the limits of investigation are shifted further north. Climate adaptation within the city settlement of Göteborg, below Marieholmsbron, will require special measures against flooding, which lies outside the SGI commission.
Landslide risk analysis
In the landslide risk analyses developed for Göta Älv, the likelihood of landslides and estimation of the subsequent consequences are included. The methodology involves a judgement of the extent of the risk area on the basis of a risk matrix, which has been used in previous landslide risk analyses. The landslide risk analysis allows for an assessment of where geotechnical reinforcements would be necessary. A cost estimation for the required reinforcement measures will also be provided.
In areas where the estimated risk for a landslide is low, a stability mapping in accordance with the model used by the Swedish Civil Contingencies Agency (MSB) will be developed; however, the new mapping will also extend beyond residential areas.
There is a foreseeable need for improving the mapping methods of the river. Improved mapping methodology would include data gathering and risk estimation. The outer and inner erosion potential of the Göta Älv is not fully known and more information regarding the river floor and shores is required.
In the short and long run
The most recent major investigation including the entire river stretch was completed in 1962. With modern methods, landslide risk analyses were made in the mid-1990s for about 43 km of the total 200 km shoreline. Stability mappings have been developed by the former Swedish Rescue Services (now MSB) within residential areas in Vänersborg and the Trollhättan municipalities.
The new commission will provide updated analyses with regards to future climate changes and the effects on increased pore pressures and erosion. Analysis and measures of erosion and sediment transportation, combined with the bathymetric and topographic conditions, will be performed. New methods for landslide risk analyses may be evaluated and possibly used within certain sections. However, the work performed within this commission will mainly use existing methodology.
Dialogue and collaboration
The commission will affect a number of operators and interested parties along Göta Älv, such as municipalities, the county administrative board, private landowners, the Swedish Maritime Administration, Vattenfall and other authorities. SGI will seek to find broad collaboration with involved parties. We will also seek collaboration with institutes of technology and universities.