2.6 Changes in Coastline

Indicator 2.6 - Changes in the Coastline of Héraðsflói bay

Kárahnjúkavirkjun power plant will cause less fluvial sediment transport through the two glacier rivers which can affect the coastline of Héraðsflói bay and vegetation next to the coast. Here we have findings from monitoring the coastline of Héraðsflói bay and vegetation next to the coast.


a. Location of shoreline measured by aerial photographs and cross-sectional bathymetric surveys.

According to Landsvirkjun's report on monitoring of Héraðsflói bay's coastline, it is roughly in balance, which means that it can potentially move forward  about 100 m and partly back decades later.

Baseline measurement was carried out in 2006 and next data collection planned 10-20 years later or in the period 2016 - 2026. Figure 1 is from Landsvirkjun's report and shows 60 years of development of the coast  based on a "balanced state". The river mouth can shift 3 km and the coastline move forward or retreat 100 - 200 m. Further information can be found in Landsvirkjun's report LV-2008/067 (only in Icelandic).


Figure 1. In the year 2014 the river mouth had moved 1.3 km compared to the location before Kárahnjúkavirkjun power plant and shifted about 3 km further north, than it has ever been since the middle of the last century. The new river mouth is now entrenched in new position and the old one has closed.

The coastline of Héraðsflói bay

Figure 2. The coastline of Héraðsflói bay. Image taken by drone, in the summer of 2016 by Svarmi ehf.

On an enlarged image (click on the image), the measurement from 2006 is in the Drona image which was taken 2016. Clearly, the northern part of the coast line has moved around 130 – 150 meters in 10 years. Then the location of the river mouth (which was diged in 2014) and the southern part of the coast line is unchanged or slightly further out.

Updated: June 6, 2019
Source: Landsvirkjun 2019

b. Vegetation cover, growth and species.

In 2006, vegetation and groundwater level monitoring began in Úthérað. The aim was to study the effect of changes in water volume of Lagarfljót and Jökulsá á Dal rivers on vegetation and groundwater level. These changes are related to establishment of Kárahnjúkar power plant. Initially, the monitoring was carried out by the Icelandic Institute of Natural History, but East Iceland Nature Research Centre took over the project in 2017.

There are 34 permanent plots in the research areas along the two the rivers. The plots are located in different vegetation types; in wetlands, heathland and sands. In addition to vegetation measurements, groundwater level was measured and signs of grazing were documented. In data analyses, Landsvirkjun's findings on water levels in the rivers and groundwater levels along the rivers were also used.

The results show that vegetation has changed, and it relates to the changing groundwater levels but is also shaped by other land conditions. These changes however vary by regions. Land has become wet and cover of wetland species has increased near Lagarfljót river but at Jökulsá á Dal river, the land has dried out to some extent and there has been a reduction in wetland species. Based on the results of this study, it can be assumed that vegetation will continue to change over time.

Map of the research area in Úthérað

Figure 3: Map of the research area in Úthérað. The study area, (green dots) vegetation monitoring sites and (orange square) water level monitoring sites. Image taken from Landsvirkjuns report ( LV-2018-096 ).

The level of groundwater has mostly followed changes in the water level of the rivers (LV-2012-099). In year 2013 vegetation study in the lowest areas indicated changes in vegetation (NÍ-13006). Based on that, transect for groundwater measurement was added in Kílamýri moor in the land of Húsey in autumn 2013. The groundwater level in Kílamýri is mainly correlated with the water level of the river, as is also the case in the lowest areas by the rivers (Minnisblað EA, 28.0115). However, water level in Torfulón reservoir responded immediately to the transfer of the river mouth. On average the highest water level of Torfulón reservoir is now 0.5 meter lower than before the transfer of the river mouth.

Updated: June 19, 2019
Source: Landsvirkjun 2019

Metrics, Targets and Monitoring Protocol

Metrics: What is measured?

  1. Location of shoreline as measured by aerial photographs and cross-sectional bathymetric surveys. (Project effect: indirect).
  2. Vegetation, both cover and vegetation index by Héraðsflói bay. (Project effect: indirect).

Monitoring Protocol

  1. Aerial photographs and cross-sectional bathymetric surveys.  Information gathered every 10 to 20 years.

  2. Satellite photos will be used to evaluate vegetation cover and growth (NDVI - Normalized Difference Vegetation index). The photos will be taken with 5-10 year intervals.

The NDVI (Normalised Difference Vegetation index) provides information about the growth and cover of vegetation in large areas.  Permanent plots have to be set up in order to gather information about vegetation cover and the species in the area.


  1. Location of shoreline will not change more than 280 m in one century as predicted by model.
  2. NDVI and number of species will not decrease.

Possible countermeasures

Not applicable, monitoring only.

Changes of indicator

In forth phase of the initiative the numbers of the sustainability were changed. This indicator was originally number 29.1 and is referenced as 29.1 in early documents of the project.


a. Location of Héradsflói coastline.

Strandlengja-Heradsfloa-1945-2006According to a report (LV-2008/067 - only available in Icelandic) on the monitoring of Héraðsflói coastline, it is relatively stable, which means that the coast can extend for about 100 m and then, decades later, retreat partly. The baseline study was performed in 2006 and the monitoring protocol plans the next data collection after 10-20 years, or in 2016-2026. The photo on the right, taken from the report, shows 60 years of evolution of the coastline based on "a stable condition." The mouth of the river can move for about 3 km and the coastline extend or retreat by 100-200 meters. (click for larger image)

2.6-yfirlitsmynd-breyting-a-strandlengju-vid-HeradsfloaAerial photographs and other photographs exist, showing the past changes of the coastline. In conjunction with the environmental impact assessment of the Kárahnjúkar project, geological and vegetation maps of the coastline have been produced and cross-sectional bathymetric surveys conducted. Onshore and offshore fauna, and human use of marine resources have been surveyed. In the fall of 2006 transect measurements on land were added as well as analysis of the coastline itself (click for larger picture).

b. Vegetation cover and NDVI (Normalized Difference Vegetation index). See a report made by Landsvirkjun on Vegetation Monitoring in Úthérad (only available in Icelandic).

Rationale for Indicator Selection

With the Fljótsdalur power plant, the two glacial rivers will carry much less sedimentation to the shore than before and this can affect the location of the shoreline and vegetation close to the shore.

The lowland of Úthérað area is largely formed by the two glacial rivers running there, Jökulsá á Dal river and Lagarfljót river. Of those, Jökulsá á Dal carries considerably more sediment,  estimated to be around 7–8 million tons per year. Most of this sediment is carried by the rivers to the sea.

The two rivers share the same river mouth at Héraðsflói bay. The coastline of the bay and position of the river mouth is affected by sediment transport of the two rivers and the erosive forces of the ocean waves. The river mouth has moved further north and it can be assumed that the beach is still moving further out.

With the harnessing of Jökulsá á Dal river, the bulk of the sediment, around 6.0 million tons on average per year, will settle in the Hálslón reservoir. With the sediment transport of the rivers so largely decreased, the present balance of the coastline will be disturbed and it is projected that the shoreline will retreat. Sea level rise due to global warming will add to and accelerate the erosion of the shoreline.

According to erosion models, it is predicted that the shoreline will retreat around 280 meters in the first 100 years of operation of Fljótsdalur Power Station, primarily driven by rough seas and surf during storms and other situations such as rise in sea level. Destruction of vegetation on the shoreline is expected to be proportionally less than the area of land that will be eroded.