2.4 Erosion of the River Banks

Indicator 2.4 - Riverbank Erosion at Jökulsá í Fljótsdal and Lagarfljót rivers

2.4-toppmynd-rof-i-arbakka

Here you can find results from measurements on riverbank erosion at Jökulsá in Fljótsdalur and Lagarfljót rivers.


Results


Riverbank erosion at Lagarfljót river above Steinbogi, rock arch, towards Lagarfoss waterfall seems to be limited and local. Downriver from Steinbogi, Lagarfljót flows in a winding channel. The nature of such channels is that while erosion takes place in the outer banks of a curve, land formation takes place in the inner banks. Erosion has therefore always been ongoing in this area, as the comparison to aerial photos show. Most erosion is visible by Hóll, farm, and in the curve of the east side river bank opposite to Grænanes, point.

An appraisal was made in August 2012 on the condition of the banks of rivers Lagarfljót and Jökulsá in Fljótsdalur. Employees of the Soil Conservation Service of Iceland conducted the appraisal and focused on type, height and inclination of the riverbanks and land erosion. The total length of riverbanks examined was 211.5 km. The results of the appraisal are available by clicking here.

The table below shows the results of measurements of bank erosion at several sites along the river Lagarfljót, the progression of erosion in areas around the river is examined annually. Last year, most erosion was in area 8, south of Hóll.

Table 1: Erosion measurements by Lagarfljót river. Locations from Steinbogi down to Silungakíll, back water, in Kílamýri, swamp, - distance (m) from stake to riverbank edge.

You can click on any of the areas below to see an aerial photo, with markings, of the area in question.

Area / Year
Erosion from 2005-2016 Erosion 2015-2016
Area 7: Vatnavik Steinboga – Profile 1 6.4
 0.8
Area 7: Vatnavik Steinboga – Profile 2 5.7 0.9
Area 7: Vatnavik Steinboga – Profile 3 3.4 0.5
Area 8: Hóll - Profile 1 9.3a 1.3
Area 8: Hóll - Profile 2 12.6b
 1.1
Area 8: Hóll - Profile 3 6.4 0.1
Area 8: Hóll - Profile 4 3.8 0.1
Area 9: West bank by Hóll – Priofile 1 0.3 0.2
Area 9: West bank by Hóll – Profile 2 0.2 0
Area 9: West bank by Hóll – Profile 3 0.3c 0
Area 10: East bank by Grænanes - Profile 1 7.3
 0
Area 10: East bank by Grænanes – Profile 2 5.8
 0.1
Area 10: East bank by Grænanes - Profile 3 6.7
 0
Area 10: East bank by Grænanes - Profile 4 8.0
 0.1
Area 11: By Silungakíl in Kílamýri - Profile 1 1.0
 0.1
Area 11: By Silungakíl in Kílamýri – Profile 2 6.1
 0.1
Area 11: By Silungakíl in Kílamýri – Profile 3 2.3
 0.1

a Erosion since 2011
b Stake could not be found in 2014, measurement from 2013.
c Erosion since 2009

Updated: August 2017
Source: Landsvirkjun (2016-2017)




Metrics, Targets and Monitoring Protocol


Metrics: What is measured?

Location of riverbank in selected areas as measured by riverbank profiles. (Project effect: indirect).

Monitoring Protocol

Profiles are taken of the riverbank in selected places and marked on a map. Measurements taken very five years.

Targets

To monitor possible erosion and if needed, to interfere with the development with riverbank protection.

Possible countermeasures

If erosion is found in river banks, interfere with riverbank protection. 


Changes of indicator

In forth phase of the initiative the numbers of the sustainability were changed. This indicator was originally number 18.1 and is referenced as 18.1 in early documents of the project.

Baseline


In a few places along Lagarfljót, upriver from Lagarfoss, erosion of the riverbanks has been monitored by RARIK since the construction of Lagarfoss Hydroelectric Plant. This has been done as a part of monitoring of vegetation. Thus, some knowledge exists about baseline in this area. This monitoring has been taken place by measuring the distance between the riverbank and 13 vegetation study plots that are located in 7 areas by the river Lagarfljót. Erosion differs considerably between areas and it is heaviest north of Egilsstadir, especially close to the farms at Dagverdargerdi and Rangá 1.

In 2005 baseline was measured in the places along Lagarfljót, downriver from Lagarfoss, where there is some erosion danger. These measurements will be repeated in the spring of 2009 to compare with measurements from 2005 and decide if action is needed.


Rationale for Indicator Selection


The Kárahnjúkar dam will increase the flow of the rivers Jökulsá in Fljótsdalur and Lagarfljót which in turn can influence the potential for erosion of riverbanks. The mean annual discharge of the two rivers will increase by slightly less than 90 m3/s. This increase will roughly double the mean annual discharge at Egilsstadir. The increase in discharge will be significantly less during floods. Flow velocity will increase, which can lead to increased erosion of the riverbanks.

This erosion will mainly take place during floods, when the impact of the Kárahnjúkar project is relatively small and flow speeds are only slightly increased. Considerable erosion of riverbanks already exists, particularly in certain areas downstream from Lagarfoss waterfall, but also to a certain degree in Jökulsá in Fljótsdalur.

Increased discharge will cause a rise in the water level, which also can cause increased erosion, especially where the flow velocity is low and erosion due to waves becomes the dominating factor. This is the case in Lagarfljót, upstream from Egilsstadir, and to a certain amount downstream from Lagarfoss waterfall. Erosion due to waves is already taking place along Lagarfljót.

Ice can also cause riverbank erosion. The Kárahnjúkar project is not expected to have much impact on formation of ice on Lagarfljót. The potential impact of the power station will indirectly affect ice-related riverbank erosion due to the rise in the water level during winter, which can cause erosion by the presence of ice higher on the river banks. This only applies to the area downriver from Lagarfoss. Conversely, the water level will be lower in the area between Lagarfoss and Egilsstadir, so the effect there will be opposite.