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Erosion can occur on the banks of reservoirs and in river channels as a result of water flow changes, changes in reservoir water levels, wind and water or wave erosion. Sediment transported by glacial rivers settles and accumulates in river waterways and reservoirs. Landsvirkjun monitors different aspects pertaining to erosion and sedimentation within the affected areas of the Company’s power stations. The aim is to map any changes to the river waterways and reservoirs in order to take action if and when the need arises.
Coastal erosion and sand encroachment by the Hálslón Storage Reservoir
Sand encroachment can be problematic in the Hálslón Storage Reservoir over the summer period when the reservoir water level is low. Landsvirkjun monitors the development of coastal erosion and any sand encroachment in the area surrounding the reservoir and the formation of sand fronts as a result of sand accumulation. Landsvirkjun has distributed fertiliser in the eastern end of the reservoir, since 2009, in an attempt to increase vegetation. The objective is to increase vegetation cover which could retain sand particles from the reservoir site.
The total size of the re-vegetated area by Hálslón is now approx. 680 hectares and the project has proved successful. Re-vegetation projects in the Hraunasvæði area (by Snæfell), previously disturbed by construction in the Keldár and Ufsalón area, have been ongoing. Grass seed has been distributed in the area alongside fertiliser.
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Erosion mitigation measures have mostly been executed on the east coast of the Hálslón Storage Reservoir where there is an increased risk of retaining sand particles (when there is a south-westerly wind direction). The Hálsvegur road runs alongside the eastern coast of the reservoir and provides some protection from erosion as it forms an erosion barrier. Trenches have been excavated below the road to retain sand particles from the reservoir site and so-called sand fences have been constructed. Landsvirkjun is also experimenting with sowing Lyme grass in the area to reduce the distribution of sand. Sand encroachment was observed for the first time in the reservoir area in the summer of 2013. The sand trenches successfully trapped substantial amounts of sand in certain areas. Sand trenches were constructed in the Jökulsá í Fljótsdal River, in 2013, to prevent erosion in the river channel.
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Coastal erosion and sand encroachment in the Blanda Storage Reservoir
Monitoring and research on sand encroachment has been conducted in the Blanda Storage Reservoir since 1993. Research has focused on monitoring erosion on the banks of the reservoir, sand encroachment from the reservoir site and monitoring fertiliser distribution, within sand encroachment areas, to support vegetation. Estimates suggest that the area affected by sand encroachment, since 1998, is approx. 52 hectares.
Meteorological conditions in the northwest of Iceland in 2012 were dry and warm whereas the conditions in 2013 were cold and wet. The main results from monitoring and research on erosion and sand encroachment by the Blanda Storage Reservoir can be seen below:
- Wave erosion levels were low on the banks of the Blanda Storage Reservoir between 2011 and 2012 or 0.08 m on average. Wave erosion levels were 0.12 m between 2012 and 2013. Wave erosion levels within this area have been low for four consecutive years. The average erosion rate between 2004 and 2012 was 0.42 m. Erosion levels rise during windy conditions and when the reservoir water level is high.
- Signs of sand encroachment were identified within new areas after the summer of 2012 and again in 2013. This could be due to unusually low water levels in the reservoir during this period.
- Fertiliser distribution in the sand encroachment area by the reservoir began in 2010 as a mitigation measure implemented to support vegetation in the area. Lyme grass sowing was one of the more successful measures implemented in the area. An assessment of the area in 2013 showed that fertilisation measures were taking effect and grass vegetation had increased. However, sheep and geese grazing in the area had an effect on the outcome.
