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.

Updated: February 25 2016  (reviewed March 9 2016)
Source: Landsvirkjun 2015

b. Vegetation cover, growth and species.

Changes in groundwater and vegetation in 25 permanent plots in Úthérað area have been monitored since 2008 (Figure 2). Visual assessment is made to evaluate the condition of vegetation and groundwater depth is measured in pipes. Whereas groundwater level has risen in some permanent plots, it has lowered in others. Changes in vegetation cover and species composition are very slow and may take decades to be detected. The permanent plots will be revisited every 5-10 years, next in 2015-2020.  Assessment of Normalized Difference Vegetation index (NDVI) based on satellite images, as has been done in Vesturöræfi highlands has not been performed. Satellite images from before the project are available for comparison purposes and  new images will be taken in 2016-2018 when an overall assessment will be made.


Figure 2: Map of the research area in Úthérað. Locations of monitoring areas and permanent plots are marked.

Groundwater has mostly followed changes in the water level of the rivers (LV-2012-099). Estimating state of vegetation in the lowland, indicated changes in vegetation (NÍ-13006). Based on that, groundwater measurement section was added in Kílamýri moor in the land of Húsey from the autumn of 2013. Progress of groundwater level is essentially the same  as is typical in the lowland by the rivers; the water level correlates to the river some hundred meters from the coastline and further away precipitation and ablation (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: February 25 2016  (reviewed March 9 2016)
Source: Landsvirkjun 2015

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.