Indicator 2.2 - Changes in Hydrology
This indicator applies only to Landsvirkjun.
With the construction of Kárahnjúkar power station, the river Jokulsá in Dal was diverted from Hálslón Reservoir into Jokulsa in Fljótsdal and Lagarfljót. Water from Jokulsa in Fljótsdal and from rivers in the Hraun area were also diverted to the power plant. This may have caused substantial changes in the hydrology of the area. Water discharge could increase in some areas but decrease in others. Water level changes, which in turn can affect ground water level, sediment transport, changes in erosion and so on, would also occur.
See more about this indicator under "Rationale for Indicator Selection."
When Hálslón Reservoir has reached its maximum water level (625 m above sea level), water is discharged by an overflow into Jökulsá in Dal, and the flow of that river increases. When the water is discharged, this remarkable waterfall called Hverfandi (which means "disappearing" or "fading away") comes into being.
Performance
a. Water levels and discharge at gauging stations in rivers.
Measurements of surface water levels and discharge at gauging stations and ground water levels exist, but from different time periods at different locations. Ever since Lagarfoss Power Station was started in 1975, the water level of Lagarfljót river has been kept higher than it used to be, by almost 0.5 m from October to March each year.
The graphs below show the flow and water level as it was before Fljótsdalur Power Station was started. Each graph shows the highest and lowest flow/water level which has been measured in that period, as well as the average flow. The difference between these is the span of flow (light gray shadow).
The graph showing the water level span in Lagarfljót River by Egilsstadir also shows the probability of deviation from the average flow. A deviation from such probability distribution is the best metric for seeing changes, but that kind of an analysis can not be done until the power station has been in operation for at least 5-10 years.
Location 1: Jökusá in Dal river by Hjardarhagi
1963-2006 (dark grey line) and 2007 (blue). Shadow: annual fluctuation 1963-2006.
Table 1.2: Performance 2008-2010
1963-2006 (dark grey line), 2008 (blue), 2009 (red) and 2010 (green). Shadow: annual fluctuation 1963-2006.
Location 2: Jökulsá in Fljótsdalur river by Hóll
1963-2006 (dark grey line) and 2007 (blue). Shadow: annual fluctuation 1963-2006
Table 2.2: Performance 2008-2011
1963-2006 (dark grey line), 2008 (blue), 2009 (red), 2010 (green) and 2011 (violet). Shadow: annual fluctuation 1963-2006.
Location 3: Lagarfljót River by Lagarfoss
1977-2006 (dark grey line) and 2007 (blue). Shadow: annual fluctuation 1977-2006.
Table 3.2: Performance 2008-2010
1977-2006 (dark grey line), 2008 (blue), 2009 (red) and 2010 (green). Shadow: annual fluctuation 1977-2006.
Location 4: Lagarfljót river by Egilsstadir (Lagarfell)
1977-2006 (dark grey line) and 2007 (blue). Shadow: annual fluctuation 1977-2006
Table 4.2: Performance 2008-2010
1977-2006 (dark grey line), 2008 (blue), 2009 (red) and 2010 (green). Shadow: annual fluctuation 1977-2006.
b. Ground water levels in holes
Four measuring stations have been set up to measure ground water levels in some holes close to rivers. The span of all measurements in the rivers concerned, and the water level, is used as a comparison basis for measuring after the reservoir and power station have been set up.
No outcomes of measurements of ground water levels are available, but these will be published after data processing after 2011.
Baseline condition
Measurements on groundwater levels in two measuring stations at Jökulsá in Fljótsdalur, one by Jökulsá river in Dal and one by Lagarfljót river. Measurements started in 2000 and were performed every week unntil end of 2001 by the local people. Repeat gauges were placed in a few groundwater holes in 2003-2004. Local people started measuring again in the all of 2005 and 2006 in holes which do not have repeat gauges. Measurements have been repeated now and then in 2009-2011.
Click on the URLs below to see a larger picture.
Graph 1: Groundwater level by Valthjófsstaðanes 2004-2007
Graph 2: Groundwater level by Bessastadagerdi 2004-2007
Graph 3: Groundwater level by Lagarfljót in Úthérad, Hóll 2004-2007
Graph 4: Groundwater level by Jökulsá in Dal, in Úthérad, Hólmatunga 2004-2007.
Last updated 7 March 2012
Metrics, Targets, Monitoring Protocol
Metrics: What is measured?
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Water levels and discharge at gauging stations in rivers. (Project effect: indirect).
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Ground water levels in holes. (Project effect: indirect). Measurements repeated at regular intervals in 2009-2011.
Targets
- Changes in water levels will not be more than what predicted in baseline models.
- Changes in water levels will not be more than what predicted in baseline models.
Monitoring Protocol
- Ever since Fljótsdalur Power Station started operation, many gauges have been set up and monitored to determine the flow into the station. The gauges measure the water level at the location, and this data is calculated into flow with so-called flow keys. A number of these gauges are now operated in order to monitor changes in flow.
- Four stations to measure groundwater have been located in wells close to the rivers. Two are in Fljótsdalur and two in Úthérad. In each gauging station there is digital equipment, a groundwater station and a water level station, that measure and register the water level every hour. A report is piled every year for each station. Groundwater level is also measured manually in other groundwater holes with regular intervals
The three maps below show the measuring stations.
Map 1: Measuring stations set up to measure flow
This map shows the locations of measuring stations in two rivers: Jökulsá in Dal and Lagarfljót. These were set up before the dam was built and utilised to estimate flow to the power station. These same gauges are still working, except for V336 in Reykjará river and V205 in Kelduá River by Kidafellstunga. Gauge in Kelduá (V454) has been moved above Kelduárlón.
Map 2: Location of measuring stations in Fljótsdalur
This map shows water level gauges in Jökulsá river in Fljótsdalur, used for measuring groundwater in flatlands by the river. The blue dots mean constantly measuring gauges in groundwater holes, and the black dots indicate groundwater holes that are measured manually.
Map 3: Location of water level measuring stations in Úthérað
Map three (right) shows water level gauges in Úthérad.
Water level gauges in Jökulsá river in Dal and Lagarfljót river (triangles crossed with a blue line) are associated with measurements on groundwater levels in flatlands by the rivers.
Click here to see a larger version of the map.
Rationale for Selection
With the construction of Karahnjukar power station, the river Jokulsa in Dal will be diverted from Halslon Reservoir into Jokulsá in Fljótsdal and Lagarfljot. Water from Jokulsá in Fljótsdal and from rivers in the Hraun area will also be diverted to the power plant. This has caused substantial changes in the hydrology of the area. Water discharge would increase in some areas but decrease in others. Water level changes, which in turn can affect ground water level, sediment transport, changes in erosion and so on, can also occur.
The discharge of the rivers Jokulsá in Fljótsdal, downstream of the tailrace canal, and Lagarfljot will increase considerably, on average just less than 90 m3/s. The mean annual discharge at Egilsstadir will increase by about half with the construction of the power plant.
The increase in discharge differs within the year. It is highest in winter (around 100 m3/s increase), but much less during the period of maximum discharge in summer when the power plant is mainly utilizing water from Jokulsá in Fljótsdal and rivers in the Hraun area. Increased discharge in floods will be proportionally much less.
At worst case scenarios in floods (all reservoirs full), the discharge of Jokulsá in Fljótsdal and Lagarfljot will increase by about 60 m3/s. In the largest recorded floods in Lagarfljót (October and November 2002), the maximum discharge was estimated about 1,650 – 1,700 m3/s. Maximum discharge at the Lagarfoss waterfall in the same floods was measured at 950 m3/s. The increase in maximum discharge into Lagarfljot and the flow by Lagarfoss waterfall is caused by dissemination effects of the lake by Egilsstadir. The Fljótsdalur Power Station therefore increases the flow to Lagarfljót river in floods by around 3-4%, and after the water has levelled in Lagarfljót river, the level by Lagarfoss increases by 30 m3/s (goes from around 950 to around 980 m3/s).
Just as discharge increases in the rivers Jokulsá in Fljótsdal and Lagarfljót, it is considerably reduced in the river Jokulsá in Dal. The mean discharge is reduced for most of the year, although least during summer and into the autumn when it is likely that water will be discharged over the spillway of Kárahnjukar dam. Floods due to glacial melt during summer are significantly reduced until August when the Halslón Reservoir fills up. Typical autumn-, winter- and spring-floods in the lower part of the river are only minimally reduced, as these originate mainly from the river catchment's area below Kárahnjúkar dam. The same applies to the Jokulsa in Fljótsdal upstream of the tailrace canal.
