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Progress

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).

70 ára þróun strandar og óss. Árið 2014 hafði ósinn færst um 1,3 km frá því sem hann var fyrir virkjun og var komin um 3 km norðar en hann hafði oftast verið um og eftir miðja síðustu öld (sjá  gagn og gaman á forsíðu).  Ósinn var færður 2014 og hefur nú fest sig í sessi á nýja staðnum og sá gamli hefur lokast.

Figure 1. 70 years of development of the coastline. In the year 2014 the river mouth had moved (Icelandic only) 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.

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

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: April 6, 2020
Source: Landsvirkjun 2020

Metrics, Targets and Monitoring Protocol

What is measured?

Location of shoreline as measured by aerial photographs and cross-sectional bathymetric surveys. (Project effect: indirect).

Monitoring Protocol

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

Targets

Location of shoreline will not change more than 280 m in one century as predicted by model.

Possible countermeasures

Not applicable, monitoring only.

Changes of indicator

This indicator was originally number 29.1. It was then named Movement of Coastline and can be found under that number in documents of the project from 2005 and 2006.

The indicator number has been changed twice.

Table 1. Changes to name and number of indicator
Year Nr. Indicator name
2020 2.2.2 Coastline of Héraðsflói bay
2007 2.6 Changes in the Coastline of Héraðsflói bay

Baseline

Staðsetning strandlínu Héraðsflóa.

Figure 3. Shoreline by Héraðsflói bay. Measured shoreline 2006 and shoreline prepared from aerial photographs and maps from 1945-6. The aerial photo in the background is from August 2006

According to a report LV-2008/067 (Icelandic only) 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.

 Figure 4. Overview of a change in the coastline at Héraðsflói bay.


Aerial 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.

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.

Updated: February 18, 2015


Original Rationale for Indicator Selection

With the Kárahnjúkar power plant, the two glacial rivers will carry much less sedimentation to the shore than under current conditions and this could influence the location of the shoreline and vegetation composition and cover close to the shoreline. The lowlands of Utherad are largely formed by the two glacial rivers running there, Jokulsá in Dal and Lagarfljot. Of those, Jokulsá in Dal carries considerably more sediment and the sediment transport is conservatively estimated to be around 7 – 8 million tons per year. The sediment transport of Lagarfljot is much less. Most of this sediment is carried by the rivers to the sea. The two rivers share the same river mouth at the shore of Herdasfloi Bay. The shoreline of the bay is affected by the sediment transport of the two rivers and the erosive forces of the ocean waves. At present, it can be assumed that the shoreline is advancing.

With the harnessing of Jokulsá in Dal, the bulk of the sediment, around 6.5 – 7.0 million tons per year, will settle in the Halslon 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. Global sea level rise 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 the dam, 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

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

Further reading

LV-2018/096 - Gróðurbreytingar 2006-2017 við Lagarfljót og Jökulsá á Dal á Úthéraði

LV-2018/096 - Gróðurbreytingar 2006-2017 við Lagarfljót og Jökulsá á Dal á Úthéraði

2018

Árið 2006 hófst vöktun á gróðri og grunnvatnsstöðu á Úthéraði. Markmiðið var að rannsaka áhrif breytinga á vatnafari Lagarfljóts og Jökulsár á Dal í kjölfar Kárahnjúkavirkjunar á fyrrnefnda þætti. Í upphafi var vöktunin unnin af Náttúrufræðistofnun Íslands en Náttúrustofa Austurlands tók við umsjón verkefnisins árið 2017. Niðurstöður sýna að breytingar hafa orðið á gróðri. Breytingarnar eru mismunandi eftir svæðum, tengjast breyttri grunnvatnsstöðu en mótast einnig að aðstæðum. Á svæðum við Lagarfljót hefur land blotnað og þekja votlendistegunda hefur aukist. Við Jökulsá á Dal bendir til að land hafi þornað að einhverju leyti og þar hefur dregið úr þekju votlendistegunda.

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

A film about the transfer of the Lagarljót and Jökla estuary (expected).