Prosjekt | Nordre älv river estuary - Sweden west coast PERIODE | 2012 - 2015 LAND | GÖTEBORG, SWEDEN The pilot area, the Nordre älv estuary is located in the western part of Sweden, close to the second largest city Göteborg (Figure 1). The Göta älv river starts from the lake Värnen, which is the largest lake in Sweden. Figure 1. a) Sweden with the county Västra Götaland marked in read. The pilot area is indicated with a yellow ring b) the pilot
Transcript
Prosjekt | Nordre älv river estuary - Swedenwest coast
PERIODE | 2012 - 2015
LAND | GÖTEBORG, SWEDENThe pilot area, the Nordre älv estuary is located in thewestern part of Sweden, close to the second largest cityGöteborg (Figure 1). The Göta älv river starts from thelake Värnen, which is the largest lake in Sweden.
Figure 1. a) Sweden with the county Västra Götaland marked in read. The pilot area is indicated with a yellow ring b) the pilot
The length of the river system, from the lake to the sea Skagerrak is 93 km. The total riverruno time is between 1, 5 to 5 days. The fall height between the lake Vättern and the sea is 44m. Next to Kungälv city close to the sea, the Göta älv river is divided into a second branch, theNordre älv river. The two branches is separated from the mainland by the island Hisingen(which is a part of the city Göteborg) (Figure 1b). About 75% of the total water discharge owsthrough the Nordre älv river. See also Nordre Älv presentation poster.
Figure 1. a) Sweden with the county Västra Götaland marked in read. The pilot area is indicated with a yellow ring b) the pilot
area, Nordre älv estuary, and the surroundings with the rivers of Nordre älv and Göta älv.
Figure 2. Left map: The catchment area of the Göta älv river system, marked with light blue and the red rectangle is the pilot
area. Right map: Detailed information in the in the pilot area showing the Nordre älv estuary, the Nordre älv catchment area
The Göta älv river is a typical rift valley where the bedrock is dominated by gneiss. Thesediments in the Göta älv river valley are in many parts sensitive clay and silt soils whylandslides and gully formations are a natural part of the landscape formation. Consequently,this region is the most landslides hit regions in Sweden and there are historical notes of 15 largelandslides.
One of the most sever was in 1977 (at Tuve in Göteborg) when houses were destroyed andseveral people got injured and around 600 people became homeless (Figure 3).
Humans In this region there are several remaining's of human activities on the shore banks ofNordre älv river, such as burial grounds from Iron Age. The area have belonged to Norway andKungälv (or Kungahälla as it was called then), was, during the beginning of the 10th century,the largest and most southern town in Norway. At these times the water levels were about 2meter higher than today resulting in good transportation routes for ships.
At the 1200-1300 the Norwegian king Håkon Håkonsson, built a fortress at the southern shoreof Nordre älv river at Ranghildsholmen to protect the town and to have control of the rivernavigation. Later at the 12th century a bigger fortress were built, the fortress of Bohus, at thesplitting point of the Göta älv and the Nordre älv rivers, in the city of Kungälv (Figure 4). In thebackground of Figure 4 it possible to distinguish the relatively sharp morphology in the areadue to the river erosion through the former, rather at top surface forming 50-100 meter highriver shores.
area. Right map: Detailed information in the in the pilot area showing the Nordre älv estuary, the Nordre älv catchment area
and the limitations of the Natura 2000.
Figure 3. The Tuve landslide 1977, in Göteborg (Hisingen).
For centuries, Göta älv river has been a major transportation route, particularly since theconstruction of the Göta Canal in 1830, making it possible to transport goods al throughSweden to the eastern coast, just south from Stockholm. However, due to more shallowwaters in Nordre älv river and possibly also better marked waterways outside the river mothsthe shipping route is through the Göta älv river branch. Today, in the Nordre älv river there isonly leisure boats and smaller tourist touring boats using the river. However, there is a greatexploitation pressure from housing especially along the coast of the estuary.
Today the part of the river system that is located in the region of Västra Götaland County ishighly populated with 1,6 million inhabitants including the city Gothenburg, which is thesecond largest city in Sweden.
Since 1970 and up till today the shipping has increased and is now about 2500 ships/yearoperating the Göta älv river and in addition about 3000 leisure boats. The total shipped cargoon the Göta älv river is today approximately 3 million tons per year and about 25 % contains oiland chemicals. Further, the Port of Gothenburg is the largest port in Scandinavia, with over11,000 visits by ships each year. Almost 30 per cent of Swedish foreign trade passes throughthe port, and it is also the only port in Sweden with the capacity to receive the very largestocean-going container vessels. Thus, due to very high pressure on the Göta älv river every nowand then discussions occur of start using the Nordre älv river for ships too. If that becomesreal it would give an extremely large risk to the water environment in both the river and theestuary due to increased shipping and that large parts of the river have to be dredged.
ClimateThe southern Sweden is located in the so called west wind belt giving that the intra annualvariability can be very large. The recent climate of western Sweden is classi ed as a cool humidtemperate climate with a strong oceanic in uence. This means that the yearly amplitude of airtemperature is moderate. The winter and the winter temperature is strongly in uenced by thewarm Golf stream and the mean summer temperature is maximum 22 degrees Celsius.
Figure 4. The fortress of Kungälv (from the 12th century)
There is no speci c dry season even if the summertime is the driest but the driest month stillhas more than 30 mm of precipitation. According to global models the consequence on thewest coast from future climate change is primarily from a large increase of precipitation butalso a change in seasonality, meaning that the di erent seasons start later. Recent researchalso shows that the change has already started with twice the amount of total precipitationfrom the 60's with the greatest increase during the last 20 years from 650 mm/year to about1300 mm/yr. Also the intensity has increased during the same period.
NatureThe marine areas at the west coast are the most species rich and productive coastal regions inSweden, and provide habitat for a great variety of commercially important sh species. Themost important Swedish shing ports are in the Västra Götaland County which concentratesmost of the shing eet capacity in Sweden (86% of the gross tonnage, 2010).
The sh community includes many of the species found in the North Sea. Pelagic species likeherring, sprat and mackerel are shed in these regions, as are extermination species like cod,haddock and various at sh. Norway lobster and shrimp are also shed on a large-scale.Further, banks of Blue mussels and Oysters are found on hard bottom substrates, but duringthe last decade the density of these economically important mollusks has decline in someareas.
The range of di erent activities makes Västra Götaland County one of Sweden's mostimportant tourist regions. The archipelago area with beaches and rocky islands is well-knownfor the attractive outdoor life. During last years the boat tourism has increased and VästraGötaland accounts for almost half (46%, 2010) of all nights spent at guest marinas in Sweden.
Sport shing is also an important activity. Göta älv was once one of the country's best salmonshing rivers. To improve conditions for the salmon population, two salmon ladders has been
built at the Lilla Edet power station. Here, 30,000 smolt are released each year. Thanks to thesee orts, catches have increased considerably, much to the delight of anglers.
Figure 5. Marina and leisure boating in Nord älv estuary
Pilot areaFor the purposes of the Swedish case study area for the ARCH project we will focus on theNordre älv river catchment area (Figure 6) from where it separates from Göta älv river nearKungälv down to the estuary. This part of the river has a length of approximately 16 km. Thedrainage area of this part of the system covers 174 km2.
The tree municipalities connecting to the pilot area are Göteborg, Kungälv and Ökerö.Göteborg is the second largest municipalities in Sweden with over 52 0000 inhabitants,Kungälv has 41 000 inhabitants and Öckerö located in the archipelago on the outskirts of theestuary has 12 400 inhabitants, and is one of the smallest municipalities in Sweden.
In contrary to Göta älv river, the Nordre älv river area have been spared from major buildings,port facilities and industrial developments and it is one of the Västra Götaland county's mostvaluable natural area. The area has been classed as, "General areas of special important for theoutdoor life", on a Swedish national level.
The largest marina in northern Europe, Björnlanda Kile, which is with 2300 xed seats, issituated in the estuary near the mouth of Nordre älv (Figure7).
Figure 6. Typical surroundings of the Nordre älv river
The Nordre älv estuary has the typical estuarine quality with a strong mixing of freshwater andsea water. Also typical for an estuary is the reduced current ow in the shelter leading todeposition of ne sediments, forming intertidal sand and mud ats. Further, also the biologicalproduction is naturally high, creating good conditions for a rich biodiversity.
This estuary is the only one of its kind in Sweden because of the typical characteristic wherefreshwater species occur together with marine species. The area is also of regional importanceas a resting and wintering place for birds such as goldeneye, tufted duck and common eiderduck. Beach areas have large botanical values of both grazed meadows and wetlands.
Since 2005 a large part of Nordre Älv estuary is designated as Natura 2000 (Figure 8). There isseveral nature types protected in the large protected area of 7000 ha. The habitat type Estuary(1130) has the dominating distribution, but also terrestrial habitat types as for example"Perennial vegetation of stony banks" is protected. A part in Nordre älv estuary is alsoprotected according to RAMSAR. This site is a shallow marine bay on the west coast of theNordre älv river, were a large numbers of water birds are supported, especially waders andducks.
Figure 7. The marina Björlanda kile, located in the estuary of the Nordre älv river
According to local municipality, the Nordre älv river estuary has a good ecological status todaybased on phosphorus concentration. However, in next monitoring program nitrogen is alsogoing to be included and the municipality is unsure if the "good status" will be remained. Theincreased exploitation such as building houses and roads close to the shore line and most likelymore bridges crossing the rivers and more boating in the area has a negative impact on thequality status of the ecosystem .
Thus, even if the Nordre estuary can be seen as a well-protected area, further development ofmanagement of human activities is needed especially with focus on future stressors asincreased population and changing climate.
