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The report, on environmental impact assessment of Kárahnjúkar power plant, states that it is important to establish a monitoring system along all edges of Hálslón reservoir since considerable erosion is to be expected in the first years/decades after its formation with the associated risk of aeolian deposits reaching vegetated areas. In accordance, Landsvirkjun has monitored erosion proceedings at Hálslón reservoir in various ways. Coastal areas have been walked and mapped to include erosion areas and mineral composition of the reservoir coast, erosion at the highest reservoir level has been monitored and aerial photos have been taken regularly. Also, the coast has been geodetically measured in several transects which helps to monitor the long-term development of the coast. Simultaneously, aeolian deposition is monitored above coastal areas. In addition to closely observing the progress of the coastal areas, erosion and encroachment defences have been installed (see pictures above) and the vegetation strengthened east of Hálslón reservoir so that it can better survive the blowing sand. A method to clean sand of grown land has been developed. In 2014 the Soil Conservation Service of Iceland (Landgræðsla ríkisins) was asked to do assess aeolian deposits at Hálslón reservoir and at the same time design a system to monitor long term aeolian depositions. Concurrently three measuring stations were set up at Kringilsárrani area to monitor and measure aeolian deposition.

Further information on countermeasures and observations at Hálslón reservoir can be found in reports under the "Further reading" tab (only in Icelandic).

Findings from inspection 2019:
Inspection of aeolian deposition 2018, was performed on July 1.–3. As in previous years, the coastal area in Kringilsárrani from Kringilsá to Syðri Hraukar was explored. The east coast of Hálslón, along the coast from Sauðá north to Desjarárstífla, was also explored.

Unfavorable weather conditions, ie. dry westerly wind directions while the water level in the lagoon was low and large sources of aeolian deposition in the reservoir area on the east coast of Hálslón caused a lot ofaeolian deposition in both Lindabunga and Kofaölda and does the aeolian deposition cover larger area than before but is rarely continuous. The thickness of the material is usually less than 1 cm, most close to Hálslónsvegur but decreases rapidly from it.

Preventive measures that have been taken in the area (sand pits below the road and revegetation) seem to be able to limit the distribution of aeolian deposition into the vegetation above Hálslónsvegur.

The effect of increased aeolian deposition on the east coast is not noticeable south of Sauðá to Jökulkvísl.

In Kringilsárrani, there were relatively few traces of new aeolian deposition, except in the north, where there was considerable aeolian deposition, but there are large sources of aeolian deposition material.

Two pulse meters were measured with the automatic measuring stations in Kringilsárrani in the summer of 2017. Measuring station 2, which was located north of Hraukur, was taken down and moved to Kofaölda on the east coast of Hálslón.

Figure 1. Hálslón and surroundings. The black line shows the area covered by the monitoring and the yellow line shows the areas along the coastline that are measured. Blue crosses indicate the location of automatic measuring instruments that measure the aeolian deposition.

Figure 1. Hálslón and surroundings. The black line shows the area covered by the monitoring and the yellow line shows the areas along the coastline that are measured. Blue crosses indicate the location of automatic measuring instruments that measure the aeolian deposition.

Updated: March 2, 2020
Source: Landsvirkjun (2020)

Metrics, Targets and Monitoring Protocol

What is measured?

Coastal areas of Hálslón reservoir in spring and autumn. Areas where sand has drifted from the coast are recorded, their size estimated/measured as well as sand thickness (project effect: direct).

Monitoring Protocol

Visual monitoring. Data gathered after the reservoir is filled. Regular visits will be made to the area following storms.


No aeolian deposition east of the reservoir

Possible countermeasures

Landsvirkjun initiates countermeasures to prevent aeolian deposition.

Updated: January, 6th, 2016

Changes of indicator

At the annual meeting of the initiative on May 6 2015 the following proposed amendment was passed.

Table 1. Changes accepted in annual general meeting 2015
Original text Changed text
Volume of aeolian deposition
from the east coast of the reservoir.
Coastal areas of Hálslón reservoir in spring and autumn. Areas where sand has drifted from the coast are recorded, their size estimated/measured as well as sand thickness (project effect: direct).

Rationale for changes: The monitoring protocol states analysis of volume of aeolian deposition east of the reservoir. It is technically difficult and not realistic to measure volume but possible to estimate area. In addition, the protocol only mentioned the East coast of the reservoir but Kringilsárrani area is also monitored and should be included in the monitoring protocol.

This indicator was originally number 26.2. It was then named Blowing Sand from Halslon Reservoir and can be found under that number in documents of the project from 2005 and 2006.

The indicator number has been changed twice.

Table 2. Changes to name and number of indicator
Year Nr. Indicator name
2020 2.2.4 Sand Encroachment by Hálslón
2007 2.29 Sand Encroachment by Hálslón Reservoir


Figure 2.  The status of the reservoir in the average year at the beginning of June

The map to the right is a rendering of the reservoir in beginning of June on an average year. The water level is then 580 meters above sea level or 45 meters under the highest water level. During this period 16 km2, of the reservoir bed, are above water level on the east side of the reservoir. The right side of the map, shows the reservoir in early August during an average year. The water level is then 615 meters above sea level or 10 meters below the highest water level. During this period 4 km2 of the reservoir bed are above water level east of the reservoir and the potential for wind erosion has decreased. The thickness of the soil is estimated to be in average about 2-2.5 meters east of the reservoir. The area will be categorized according to land slope in order to evaluate beforehand where it is most likely that sand piles will form.

Research are ongoing on the stamina of the vegetation in the eastern part against aeolian deposition and how to react to possible deposition of minerals.

Rationale for Indicator Selection

Part of the reservoir shoreline area or approximately 15 km2 is covered with around 2.5 m thick soil coated with thin layer of vegetation. With time this volcanic soil can wash into the reservoir through water erosion and wave action, but also drift to surrounding area causing soil thickening and even vegetation loss.

With time wave erosion removes soil from Hálslón reservoir shoreline. The erosion rate is dependent on the slope of the shore area and the intensity of wave action. The erosion rate is highest on steeply sloping shore areas and slowest on flat plains on the shore.

On these gentle sloping planes the vegetation might disappear after a few years of reservoir operation, leaving only soil. On steeper shoreline areas erosion slumps can form in the soil before it is removed by wave erosion. These conditions may prevail during the first one or two decades of reservoir operation.

During dry storms from the south and southwest the exposed dry soil may be picked up by the wind and the largest particles drift onto adjacent vegetated area forming sand piles above the highest water level. In wetlands this risk is however greatly reduced. The east side of the reservoir is specially prone to aeolian deposition. On the west shoreline, windblown sand drifts chiefly to the reservoir during strong wind from South or South-West and therefore no sand piles are formed.

While soil prone to erosion remains, various operations are planned to prevent aeolian deposition to damage vegetated areas in Vesturöræfi wilderness. Sand traps were setup along vegetated areas by the east shoreline of the reservoir. Irrigation, dust binding and sand fences are planned as means to control drift of soil.

Measures to strengthen vegetation east of the reservoir, are also being considered.

Original Rationale for Indicator Selection

The area that will be inundated once Halslon Reservoir is created has relatively thick volcanic soil beneath the vegetation. With time, the vegetation by the reservoir shoreline will disappear and this will leave the soil unprotected from wind and wave erosion. The soil could be flushed into the reservoir or blown to surrounding areas, causing the thickening of the soil or even destruction of vegetation. The smallest particles create dust but do not have negative effect on vegetation. The larger particles that move on the surface in sand piles pose a greater threat since they can suffocate vegetation closest to the reservoir.

When wind is strong, it usually blows from the southwest. Soil from west of the reservoir will therefore blow into the water but soil from the east side could blow over the vegetation on Vesturoraefi if no mitigation measures are taken. This danger is greatest in the first half of summer once the surface has dried up from spring thaws and the reservoir has not yet filled. Wetlands are less affected by wind erosion since groundwater keeps the soil wet.

Part of the soil that creates the wind erosion threat will slide into the reservoir with time. This will happen first in areas where slopes are greater than seven percent. Landsvirkjun plans to remove the soil from the flattest areas by pumping it into the deepest part of the reservoir. If those plans succeed, the soil on the east shoreline of the reservoir should be gone about 10 or 15 years after the dam starts to operate because of erosion or pumping

During the time soil erosion and creation of sand piles are still an issue, several mitigation measures are planned to prevent sand from piling up and destroying vegetated areas on Vesturoreafi. These measures include special protection walls, sand traps, fences, and sand erosion banks. Measures to strengthen vegetation east of the reservoir, in case of damage, are also being considered.

From phase I/II report on indicators and baseline from April 2005

Further reading

LV-2020-039 - Úttekt og mælingar á áfoki við strönd Hálslóns. Áfangaskýrsla 2020

LV-2020-039 - Úttekt og mælingar á áfoki við strönd Hálslóns. Áfangaskýrsla 2020


Landgræðslan hefur séð um vöktun og mælingar á áfoki við austurströnd Hálslóns og í norðurhluta Kringilsárrana frá 2014 að beiðni Landsvirkjunar. Vettvangsferð var farin 6.-8. júlí 2020 þar sem mælireitir voru ljósmyndaðir og þykkt og útbreiðsla áfoks mæld. Jafnframt voru sjálfvirk mælitæki tekin

Við austurströnd Hálslóns hafði lítið sem ekkert nýtt áfoksefni borist inn á svæðin og virku áfokssvæðin minnkað umtalsvert þ.e. úr 14,6 ha 2019 í 0,9 ha 2020 á Lindabungu og á Kofaöldu úr 16,7 ha 2019 í 11,3 ha 2020. Í Kringilsárrana sýndu niðurstöður frá sjálfvirku mælistöðvunum fram á lítið sem ekkert áfok. Almennt var ekki að sjá nein ný áfoksefni og samkvæmt mælingum á útbreiðslu áfokssvæðanna var stærð þeirra svipuð eða heldur minni eins og nyrst í Rananum þar sem áfokssvæðið hafði minnkað úr 1,8 ha 2019 í 0,9 ha 2020. Áfokssvæði inn með Kringilsá sem er neðan fokgirðinga sem teknar voru niður 2017, hefur þó stækkað lítillega úr 0,9 ha 2019 í 1,1 ha 2020. 

You can view more material related to the indicator by clicking on the link above.