Changes to the water flow in rivers and the water levels in reservoirs as well as the effects of wind, water and tide can lead to the erosion of river channels and river banks. Bed load transport from glacial rivers can accumulate in the reservoirs. Landsvirkjun monitors erosion and sedimentation within the Company’s operational areas and mitigation measures are implemented when and if they are needed.
This chapter will discuss two projects pertaining to erosion and sedimentation. The first is a monitoring and research project on erosion on the coastline of the Blanda Reservoir in the northwest of Iceland and the second is a research project on the shifting channels of the Lagarfljót and Jökla estuary, within the affected area of the Fljótsdalur Hydropower Station.
Landsvirkjun has conducted research and monitoring in the Kárahnjúkar Hydropower Project area since construction began in 2003 to assess the need for mitigation measures. The results are shared with the municipal councils and stakeholders and are also made available digitally via websites such as Sustainability.is. The website also shares information on sedimentation levels in the Hálslón Reservoir, changes to the Héraðsflóa coastline, sand encroachment by Hálslón and further information on Landsvirkjun‘s many different monitoring projects in the east of Iceland.
The shift in the Lagarfljót and Jökla estuary in the Héraðsflóa area
It is a well-known fact that the location of estuaries in river streams on the coastline can change. The Markarfljót (a river in the south side of Iceland) estuary is a good example of this as the location of the estuary can, amongst other things, depend on the weather, coastline tides and ice blockages. The shared estuary of the Lagarfljót and Jökla Rivers share these traits.
The estuary has shifted 1.3 km northward between 2007 and 2014 or since operations began at the Kárahnjúkar Hydropower Station. The estuary has shifted 3.2 km further to the north than it has for the large part of the last century. The cause is unclear but the shift to the north cannot be solely attributed to water transport, pertaining to the Station, as it began before the Station became operational.
In 2013, landowners to the north of Jökla became worried about the ongoing movement of the estuary. They pointed out that an ongoing shift northwards would result in the estuary merging with the Fögruhlíðar River. Landsvirkjun consulted the various stakeholders in the area (angling societies, land owners, institutions and municipalities within the Fljótsdalur County) and subsequently decided to attempt to excavate a new estuary, an estuary approx. 3 km to the south of the current estuary and where the estuary had been located previously between 1945 and 2000.
A 10 m wide canal was excavated in February, 2014, traversing the coastline ridge. The river would then take over and carve the new estuary as the tide would close off the older estuary. The new estuary channel also shortened the distance between the river and the sea.
The project used methodology which predicted that the river would naturally create a new estuary in the channel excavated by Landsvirkjun and that the decreased stream in the old estuary would ensure that the tide would rapidly shut it off.
Photograph of the Héraðsflóa coastline taken on the 7th of October, 2013. The river channels flowing towards the sea can be seen to the left of the picture and the circle shows the location of the new estuary.
The new estuary shortly after it was excavated on the 8th of June, 2014. A five metre wide channel was excavated.
The water rapidly created a new estuary. The channel was already 100 m wide, only 24 hours later.
The new estuary on the 15the of June, 2014. The channel is now 200 m wide. Lagarfljót and the southernmost branches of Jökla clearly follow the new channel.
The new estuary was rapidly shut off by the strong tide. A decision was made to make a second attempt in the autumn, thus avoiding the salmon migration period. Landowners and local residents requested that Landsvirkjun open the new estuary the following June. Landsvirkjun then made a second attempt to open the new estuary on the 8th of June, 2014, after consulting the Institute of Freshwater Fisheries and receiving permission from the Directorate of Fisheries.
This attempt was successful and the water rapidly created a new estuary channel and Lagarfljót and the southernmost branches of Jökla merged with the estuary a week later. The tide finally closed the older estuary in January, 2015.
Relocating the Lagarfljót and Jöklu Estuary
Two attempts were made to move the Lagarfljót and Jöklu estuary. The tide shut off the first attempt but the second attempt was successful.
The water created a 200 m wide channel within a week of the second attempt and the Lagarfljót and the southernmost branches of Jöklu merged with the estuary.
The Blanda Reservoir shoreline
Research on the Blanda Reservoir shoreline began in 1993 or two years after it was constructed. Research includes monitoring on groundwater level and changes to vegetation by the reservoir, erosion on the banks of the reservoir and the shape of the shoreline. Sand encroachment and the formation of sand fronts (aeolian sand deposits) in a number of areas by the shoreline of the reservoir became obvious after the expansion of the Blanda Reservoir in 1997. Sand encroachment generally occurs when reservoir levels are low during the spring period.
In 2009, sand fronts covered an area of 30 hectares in the Blanda Reservoir and mitigation measures were clearly needed.
Monitoring began on the formation and spread of these sand fronts and research on the issue, alongside necessary measures to bind sand from the reservoir, became the primary task in the area. The development of vegetation has been monitored in the area and experiments have been conducted with fertiliser to strengthen vegetation. Vegetation was mostly affected by the increase in groundwater levels in the first few years after the reservoir was constructed and before the reservoir water level was increased to its current level.
Erosion levels have reached 1.55 m per year but the average for the period 2004 to 2014 is 0.35 m per year.
Wave erosion is active when the Reservoir spillover is active and when waves are formed during volatile weather conditions during the autumn. The wind direction during these storms steers these erosion sites of which some have been identified in the peninsulas and steep land areas to the north and west of the Reservoir. Wave erosion separates fine sand particles from the soil, shifting it into shallows and creeks. The sand can drift inland in windy conditions, if reservoir levels remain low during the summer. Low-growing vegetation is sensitive to sand encroachment but coarser vegetation and long grass species are more resilient.
Monitoring on shoreline erosion and sand encroachment was continued as a result of the increased strain on vegetation. Fertiliser was distributed in sand encroachment areas as this type of experimentation has proven quite successful in the past.
Olga Kolbrún VilmundardóttirSand encroachment in the heathland area to the north of the Blanda Reservoir in 2008.
Borgþór MagnússonA sand area to the north of the Reservoir was fenced off in 2003 and experiments were conducted with fertiliser. Fertilised land was then compared with unfertilised land to assess the outcome.
Sigmar MetúsalemssonThe fence in Sandvík (in 2012) after 11 years of protection. Sand has increased in the area but the woody willow species has thrived in sand-rich areas.
Borgþór MagnússonFertiliser has been distributed in the main sand encroachment areas around the Reservoir since 2010 in an attempt to assist the spread of vegetation. The photograph shows fertiliser distribution in the area to the south of Áfangafell.
Borgþór MagnússonThe same area to the south of Áfangafell in 2013. The effect of fertiliser distribution is obvious but the land is used for grazing by sheep and geese.
Borgþór MagnússonIn 2013, the sand encroachment area in Lambavík, to the north of the Reservoir, was fenced off. Blue Lyme grass seed was sown into the loose sand and formed lines in the sand when it grew that summer.
The distribution of fertiliser and grass seed sowing has been quite successful but varied depending on conditions. Sheep and goose grazing has also slowed progress. In 2012, sand encroachment became problematic in the area to the north of the Reservoir. A decision was made to fence off the Lambavík area in 2013. Blue Lyme grass seed was sown in the area and fertiliser was distributed. These measures could be promising as the woolly willow species currently grows in sand fronts, binding sand blown in from the Reservoir.
Research and experimentation with fertiliser between 2010 and 2014 and erosion monitoring data since 1997 are now used as the basis for ongoing and future measures. The main objectives for the coming years include fencing off more areas where sand fronts have formed as well as increasing fertiliser distribution and sowing measures.