2.2 Changes in Hydrology

Indicator 2.2 - Changes in Hydrology


2_2_Fljótsdalsstöð

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.

Progress


a. Water levels and discharge at gauging stations in rivers.

It is important to determine a baseline for hydrological measurements to be able to assess the impact of the plant.  Annual fluctuation in water level and discharge is shown for Jökulsá á Dal river (flow by Hjarðarhagi) and in Jökulsá í Fljótsdal river and Lagarfljót river.

The “Baseline” section contains figures that show all possible water positions of flow in a specified period before Kárahnjúkar Power Plant started. It also shows annual variation and average water level and flow before the major rivers were affected by the construction of the power station.  The same figures are used as the basis of the corresponding measurements from year to year after the construction of the power plan.

The figures to the left represent the last five years (2012-2016), while the ones on the right represent baseline plus  2008 - 2011. .


Location 1: Annual  discharge fluctuation in Jökusá á Dal river by Hjarðarhagi, VHM 110

Discharge of Jökulsá á Dal river by  Hjarðarhagi
   
 Annual  discharge fluctuation in Jökulsá  á Dal river by Hjarðarhagi (vhm 110) before construction of  Kárahjúkavirkjun power plant 1963 - 2006 and measured discharge 2012 - 2016
   Annual discharge fluctuation in Jökulsá  á Dal river by Hjarðarhagi (vhm 110) before construction of  Kárahjúkavirkjun power plant 1963 - 2006 and measured discharge 2008 - 2011
Figure 1: Annual discharge fluctuation in Jökulsá á Dal river by Hjarðarhagi (vhm 110) before construction of Kárahjúkavirkjun power plant 1963 - 2006 and measured discharge 2012 - 2016
  Figure 2Annual discharge fluctuation in Jökulsá  á Dal river by Hjarðarhagi (vhm 110) before construction of  Kárahjúkavirkjun power plant 1963 - 2006 and measured discharge 2008 - 2011

Labels: Y-axis:  Average daily discharge (m3/s). Gray shadow - annual fluctuation 1963-2006, dark grey line – average 1963-2006, colored lines:  measurements in the years 2008 - 2016.




Location 2:  Annual discharge fluctuation in  Jökulsá í Fljótsdal river by Hóll

 Discharge of Jökulsá í Fljótsdal river by Hóll
   
 Annual discharge fluctuation in Jökulsá í Fljótsdal river by Hóll (vhm 109) before construction of Kárahnjúkavirkjun power plant 1963 - 2006 and measured discharge 2012-2016
   Annual discharge fluctuation in Jökulsá í Fljótsdal river by Hóll (vhm 109) before construction of Kárahjúkavirkjun power plant 1963 - 2006 and measured discharge 2008 - 2011
Figure 3Annual discharge fluctuation in Jökulsá í Fljótsdal river by Hóll (vhm 109) before construction of Kárahnjúkavirkjun power plant 1963 - 2006 and measured discharge 2012-2016   Figure 4Annual discharge fluctuation in Jökulsá í Fljótsdal river by Hóll (vhm 109) before construction of Kárahjúkavirkjun power plant 1963 - 2006 and measured discharge 2008 - 2011
Labels

: Y-axis:  Average daily discharge (m3/s). Gray shadow - annual fluctuation 1963-2006, dark grey line – average 1963-2006, colored lines:  measurements in the years 2008 - 2016.





Location 3: Lagarfljót River by Lagarfoss


Discharge of Lagarfljót river by Lagarfoss
   
Annual discharge fluctuation in  Lagarfljóts river by Lagarfoss (vhm 325/V325) before construction of  Kárahnjúkavirkjun power plant 1975 - 2006 and measured discharge 2012- 2016
   Annual discharge fluctuation in Lagarfljót river by Lagarfoss (vhm325/V325) before construction of Kárahnjúkavirkjun power plant 1975 - 2006 and measured discharge  2008 - 2011
Figure 5:  Annual discharge fluctuation in Lagarfljóts river by Lagarfoss (vhm 325/V325) before construction of Kárahnjúkavirkjun power plant 1975 - 2006 and measured discharge 2012- 2016
  FIgure 6Annual discharge fluctuation in Lagarfljót river by Lagarfoss (vhm325/V325) before construction of Kárahnjúkavirkjun power plant 1975 - 2006 and measured discharge 2008 - 2011

Labels: Y-axis:  Average daily discharge (m3/s). Gray shadow - annual fluctuation 1975-2006, dark grey line – average 1975-2006, colored lines:  measurements in the years 2008 - 2016.


Water level in Lagarfljót river by Lagarfoss     
Annual water level fluctuations in  Lagarfljót river by Lagarfoss (vhm 17/V505) before construction of Kárahnjúkavirkjun power plant 1977 - 2006 and measured water level in  2012-2016
   Annual water level fluctuations in Lagarfljót river by Lagarfoss (vhm 17/V505) before construction of  Kárahnjúkavirkjun power plant1977 - 2006 and measured water level 2008 - 2011
Figure 7:  Annual water level fluctuations in Lagarfljót river by Lagarfoss (vhm 17/V505) before construction of Kárahnjúkavirkjun power plant 1977 - 2006 and measured water level in 2012-2016   Figure 8: Annual water level fluctuations in Lagarfljót river by Lagarfoss (vhm 17/V505) before construction of Kárahnjúkavirkjun power plant1977 - 2006 and measured water level 2008 - 2011

Labels: Y-axis:  Average daily water level (m.a.s.). Gray shadow - annual fluctuation 1977-2006, dark grey line - average 1977-2006, colored lines:  measurements in the years 2008 - 2016.




Location 4: Water level fluctuations in Lagarfljót river by Egilsstaðir (Lagarfell)


Water level in Lagarfljót by Egilsstaðir

   
 Annual water level fluctuation in  Lagarfljót river by Egilsstaðir (Lagarfell, vhm7/V7) before construction of Kárahnjúkavirkjun power plant  1977 - 2006 and water level measurements  2012-2016
   Annual water level fluctuations in Lagarfljót river by Egilsstaðir (Lagarfell, vhm7/V7) before construction of Kárahnjúkavirkjun power plant 1977 - 2006 and water level measurements 2008 - 2011
Figure 9Annual water level fluctuation in Lagarfljót river by Egilsstaðir (Lagarfell, vhm7/V7) before construction of Kárahnjúkavirkjun power plant 1977 - 2006 and water level measurements 2012-2016   Figure 10Annual water level fluctuations in Lagarfljót river by Egilsstaðir (Lagarfell, vhm7/V7) before construction of Kárahnjúkavirkjun power plant 1977 - 2006 and water level measurements 2008 - 2011
Labels:

Y-axis:  Average daily water level (m.a.s.). Gray shadow - annual fluctuation 1977 - 2006, dark grey line – average 1977-2006, colored lines:  measurements in the years 2008 - 2016


Map of the gauging stations can be seen in the chapter Metrics, Targets, Monitoring Protocol.

Data on water level and discharge by Lagarfoss courtesy of Orkusalan.

Updated:  September 2017
Source:   Landsvirkjun (2014 and 2017)


b. Ground water levels in holes

Four gauging stations were established to measure ground water levels in holes close to rivers. Comparison basis for measuring ground water level is based on data from 2000 - 2007 before the power plant and the data after the power plant, from 2008, the years 2010-2011 and 2015-2016.

Measurements will be repeted, at least the year 2017.

Location 1: Valþjófsstaðanes

Figure 11: Individual weekly observations over four periods of time, two before and two after construction of the power plant compared to continuous observations on water level of the river. The classic representattion of the average measurements in each hole (Figure 12) and for Bessastaðanes and Hóll (Figures 13 and 14). These figures have not been updated, nor a picture of measurements at Hólmatunga.


2.2b-Mynd2017


Figure 12: Average water level observed in holes before (blue) and after (red) construction of power plant compared to ground level (black line) in holes  FLJ1-2.

Labels: Y-axis: Groundwater level (m.a.s.l.), x- axis: Distance (m). Vegur - road, Farvegur - river channel.

2.2.b. Meðaltal mælinga í hverri holu 1

Location 2: Bessastaðanes

Figure 13: Average water level observed in three holes before (2000-2007, blue) and after (2010-2011, red) construction of power plant compared to ground level (black line) in holes BES 1-3.

Labels: Y-axis:  groundwater level (m.a.s.l.), x- axis: Distance (m). Farvegur = river channel.

2.2.b. Meðaltal mælinga í hverri holu 2

Location 3: Hóll in Úthérað

Figure 14: Average water level observed in five holes before (2000-2007, blue) and after (2010-2011, red) construction of power plant compared to ground level (black line).

Labels: Y-axis:  groundwater level (m.a.s.l.), x- axis: Distance (m). Farvegur = river channel.

2.2.b.-mynd4


Location 4: Hólmatunga

Results from groundwater level analysis  at Hólmatunga are shown in two graphs. The upper graph shows Individual weekly observations over two periods before and after construction of Kárahnjúkavirkjun power plant compared to continuous observations on water level of the Jökulsá á Dal river. (Graph 4.I)

Observations were made during the summer when the water level in Jökulsá á Dal river is lowest.  During summer the ground water level falls about 40 - 60 cm at 600 - 1300 m distance from the river, compared to 30-35 cm average value for the whole period. (Graph 4.II)

Figure 15:  Individual observations over two periods 

Labels: Y-axis:  groundwater level (m.a.s.l.). Blue line average 2000-2006, red line average 2006 -2011

2.2.b.-mynd5

Figure 16:  Ground water level by Hólmatunga before (2000-2007, blue) and after (2010-2011, red) construction of power plant compared to ground level (black line).

Labels: Y-axis:  groundwater level (m.a.s.l.), x- axis: Distance (m). Farvegur = river channel.

2.2.b.-mynd6

Updated:  September 2017
Source:   Landsvirkjun (2014 and 2017)

Results

Measurements generally are based on both recording gauge in specific holes and weekly measurements during specific periods in other holes on same Gauging stations. This provides information about the relationship between ground water levels on flat land, discharge in the closest river and precipitation.

  1. On the flat vegetated land water level, adjacent river has a major impact on the groundwater table. This can refer to at least 700-800 m from the river.

  2. In a slope end close to the foot a-of a slope the groundwater table is more influenced by rainfall. This has not changed after construction of the power plant.

  3. As expected the ground water table in both Jökulá í Fljótsdal river and Lagarfljót river has risen but subsided in Jökulsá á Dal river.

 It was assumed that the plant could cause up to 25 cm rise in groundwater in Valþjófsstaðanes. Given the topography and the depth of groundwater in areas adjacent to Jökulsá í Fljótsdal river it was expected that the ground would get wetter if nothing was done. To counteract this the drainage canals were cleared and deepened and water pumped from them to Jökulsá í Fljótsda river. If nothing had been done the ground water table would probably now be about 1 m higher in Valþjófsstaður peninsula and probably the lowest areas under water.


Baseline

a. Water levels and discharge at gauging stations in rivers before Kárahnjúkavirkjun power plant.

Information on water level and discharge at monitoring stations in rivers is available for different periods.  Since Lagarfoss power plant began operation in 1975, the water level in Lagarfljót river has been kept up to 0.5 m higher   from October to March each year.

Figures in this section show discharge and water level as it was before onset of Kárahnjúkavirkjun power plant.  Figures 1 – 3 show a grey shaded area between the recorded min and max discharge/water level as well as average discharge/water level.

In figure 4 probability of deviation from mean is also reported.  Deviation from such probability distribution is the best criterion to pick up change but cannot be employed until the plant has been operating for at least 5 – 10 years.


Figure 1. Annual fluctuation of discharge in Jökusá á Dal river by Hjarðarhagi, vhm 110, before Kárahnjúkavirkjun power plant, 1963-2006Figure 1. Annual fluctuation of discharge in Jökusá á Dal river by Hjarðarhagi, vhm 110, before Kárahnjúkavirkjun power plant,  1963-2006

Labels:  Shaded area:  Annual fluctuation of discharge 1963 - 2006; Grey line:  Average 1963 – 2006; Blue line:  Measurements in 2007; Comment:  Ice in riverbeds often interferes with discharge during winter.  Winter measurements are only from 1998 - 2006.


Figure 2. Annual fluctuation of discharge in Lagarfljót river by Lagarfoss 1975 – 2006

Figure 2.  Annual fluctuation of discharge in Lagarfljót river by Lagarfoss 1975 – 2006

Labels: Shaded area:  Annual fluctuation in discharge:  1975 – 2006; Grey line:  Average discharge:  1975-2006;  Y-Axes:  Average 24 hour discharge (m3/s).




Figure 3. Annual fluctuation of water level in Lagarfljót river by Lagarfoss 1977 – 2006Figure 3.  Annual fluctuation of water level in Lagarfljót river by Lagarfoss 1977 – 2006

Labels:  Shaded area:  Annual fluctuation in water level 1977-2006; Grey line: Average water level; Y-Axes:  Average 24  hour water level (m.a.s.l.).




visir-2.2-mynd-3-arssveifla-vatnshaedar-lagarinsFigure 4. Annual fluctuation of water level in Lagarfljót river by Egilsstaðir 1977 - 2006.

Labels:  Shaded area:  Annual fluctuation in water level 1977 - 2006.  Red line:  median; Y-Axes:  Average 24 hour water level (m.a.s.l.)




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.

visir-2.2-mynd-5-grunnvatnshaed-vid-Valthjofsstadanes  Figure 5: Groundwater level by Valthjófsstaðanes 2004-2007

visir-2.2-mynd-6-grunnvatnshaed-vid-Bessastadagerdi  Figure 6: Groundwater level by Bessastadagerdi 2004-2007

visir--2.2-mynd-7-grunnvatnshaed-vid-Hol Figure 7: Groundwater level by Lagarfljót in Úthérad, Hóll 2004-2007

visir-2.2-mynd-8-grunnvatnshaed-vid-Holmatungu Figure 8: Groundwater level by Jökulsá in Dal, in Úthérad, Hólmatunga 2004-2007.


Last updated November 25 2015

Metrics, Targets, Monitoring Protocol


Metrics: What is measured?

  1. Water levels and discharge at gauging stations in rivers. (Project effect: indirect).

  2. Ground water levels in holes. (Project effect: indirect). Measurements repeated at regular intervals in 2009-2011.

Targets
  1. Changes in water levels will not be more than what predicted in baseline models.
  2. Changes in water levels will not be more than what predicted in baseline models.


Monitoring Protocol



  1. 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.
  2. 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

2.1-kort_maelistador_rennsli_500px

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

2.2-mynd-Stadsetning-maelistada-i-Fljotsdal

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.


2.2-Utherad_Maelistadir_grunnvatns-mynd

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.



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 25.1 and is referenced as 25.1 in early documents of the project.



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.