Indicator 2.4 - Erosion of the River Banks
Erosion of the River Bank at Jökulsá in Fljótsdalur and Lagarfljót
The Kárahnjúkar dam may increase the flow of the rivers Jökulsá in Fljótsdalur and Lagarfljót which in turn can influence the potential for erosion of riverbanks. The increase in discharge is significantly less during floods. Flow velocity can also increase, which can lead to increased erosion of the riverbanks.
Considerable erosion of riverbanks already existed before the Kárahnjúkar Hydro project started, particularly in certain areas downstream from Lagarfoss in the Lagarfljót waterfall, but also to a certain degree in Jökulsá in Fljótsdalur.
See more under: Rationale for indicator selection
This photo was taken before Fljótsdalur Power Station was started.
Performance
Erosion of the banks of Lagarfljót river above Steinbogi towards Lagarfoss waterfall seems to be minimal and local. Downriver from Steinbogi, Lagarfljót flows in a winding channel. The nature of such channels it 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 of aerial photos show. Most erosion is visible by Hóll and in the curve of the east side river bank opposite to Grænanes.
Table 1: Erosion measurements by Lagarfljót river. Locations from Steinbogi down to Silungakíll in Kílamýri - 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.
* Erosion since 2009
Source: Landsvirkjun 2011.
Last updated 8 March 2012.
Metrics, Targets and Monitoring Protocol
Metrics: What is measured?
a. Location of riverbank in selected areas as measured by riverbank profiles. (Project effect: indirect).
Targets
a. To monitor possible erosion and if needed, to interfer with the development with riverbank protection.
Monitoring Protocol
a. Profiles are taken of the riverbank in selected places and marked on a map. Measurements taken very five years.
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. 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.
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 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 at Dagverdargerdi and Rangá River 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.
