The Göta Älv (Göta River) is the largest river in Sweden. The Göta River area runs from Lake Vänern in the north to Göteborg in the south. In the south, two third of the river flow is in the Nordre älv and one third runs through Göteborg, i.e. the Göta River estuary.
The Göta River valley, and the city of Gothenburg, has a long history of anthropogenic activities such as settlements, shipping, harbours, industry, activities causing contaminated soil and infrastructure including large roads and railroads. The river is used by many different actors with various interests. The archipelago is highly populated with commuters (ferries) and in summer season the population is increased due to tourism. In the estuary of Göta River the Gothenburg harbour, Scandinavia's largest and most important port, is located. Consequently the sea outside Göteborg is very busy.
Nordre älv and the Göta River estuaries are characterized by low-lying areas with deep clay deposits. Along the coastlines in the Göta River estuary there are also fillings and the western parts are dominated by rocks. The clays are mainly glacial and post glacial deposits. Already today flooding occurs with mainly material damages and infrastructure failures. The infrastructure damages have had some serious impacts such as "knock out" of the regions SOS alarm central, which was not manageable because of its flooded computer and IT-system central. Also the storm and sewage water systems have difficulties functioning under flood and storm events. Under such events the pollutant load to the Göta älv estuary is increased
Due to the first flush not passing the water treatment plant and that the contaminated land upstream, highly polluted roads and urban areas are flooded. In the area, flood events are caused both by high precipitation and high sea water levels. The high sea water levels are caused by low pressure situations with westerly and high winds.
Climate change is expected to result in a sea level rise. Based on the latest IPCC report (IPCC, 2013) and previous estimates from SMHI (Bergström et al., 2007) the sea level might increase by one meter until year 2100. Furthermore, extreme weather situations including storms and heavy rainfall will increase with an increased frequency of flooding events as a result.
One proposal to reduce the probability of flooding in the central parts of Gothenburg is to build barriers in Göta Älv, i.e. one barrier upstream the river south of the branching to Nordre Älv and one barrier downstream, west of Älvsborgsbron. Both the sea level rise alone, increased extreme weather events and measures taken to reduce the risk may have a non-wanted impact on the environment and economic and social consequences are expected. The Gothenburg City is currently performing cost benefit analyses of the suggested barriers. The assessment focuses, however, only on the inner Gotheburg parts and not the impacts on the Nordre älv. Within EMOVE a brief assessment of the impacts on the natural environment in Nordre älv has been performed.
Increased precipitation will increase the contamination load in the Göta Älv estuary unless the capacity of the storm water system and the water treatment plant is increased. As part of the EMOVE some potential solutions are investigated. In addition there are major infrastructural activities in progress that will affect the Gothenburg estuary such as the infrastructure project called the West Link project including several tunneling projects and discussions about expanding port activities.
The West link (and related infrastructure projects) impacts on the estuary
Tunnel constructions, such as those in the West Link project, involve great excavations. This may affect the estuary in several ways. Excavated material must be moved and placed somewhere. This can be done in several ways:
- Dumping at Sea
- Fillings (after stabilization and solidification of the masses) in the estuary to support central densification and/or to expand the port activities
- Use the masses for other purposes (e.g. tiles) which may demand large areas for drying
Using any of the above suggestions, the process will affect the environment and may also affect the picture of the city and the estuary. To be able to handle these masses, efficient infrastructure both on land and in the estuary is required. How the masses are transported also affect the environment and it is therefore highly important to find the most optimal system for transport and to have an infrastructural system that will increase the availability and contribute to a sustainable development of the estuary.
In EMOVE we look at the impacts of dumping the masses as well as using them for expanding parts of the port and the other alternatives and its impacts on the estuary. This work is done in cooperation with the Swedish Transport Administration (Trafikverket).