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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 annual flow rate before Kárahnjúkar (Power Plant) (1963 – 2006) and figures on the right for the annual flow after Kárahnjúkar (Power Plant).

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

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 2019.

 

Figure 2: Annual discharge fluctuation in Jökulsá á Dal river by Hjarðarhagi (vhm 110) after construction of Kárahjúkavirkjun power plant 2008 - 2017and measured discharge 2019

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 2019.

Figure 2: Annual discharge fluctuation in Jökulsá á Dal river by Hjarðarhagi (vhm 110) after construction of Kárahjúkavirkjun power plant 2008 - 2017and measured discharge 2019
 
Labels: Y-axis: Average daily discharge (m3/s). Gray shadow - annual fluctuation 1963-2006, dark grey line – average 1963-2006, light grey line - quartile, brown line - measurements in the year 2018. Click for larger images.

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

Figure 3: Annual discharge fluctuation in Jökulsá í Fljótsdal river by Hóll (vhm 109) before construction of Kárahnjúkavirkjun power plant 1963 - 2006 and measured discharge 2019

 

Figure 4: Annual discharge fluctuation in Jökulsá í Fljótsdal river by Hóll (vhm 109) after construction of Kárahjúkavirkjun power plant 2008 - 2017 and measured discharge 2019

Figure 3: Annual discharge fluctuation in Jökulsá í Fljótsdal river by Hóll (vhm 109) before construction of Kárahnjúkavirkjun power plant 1963 - 2006 and measured discharge 2019
Figure 4: Annual discharge fluctuation in Jökulsá í Fljótsdal river by Hóll (vhm 109) after construction of Kárahjúkavirkjun power plant 2008 - 2017 and measured discharge 2019
 
 
 
 
Labels: Y-axis: Average daily discharge (m3/s). Gray shadow - annual fluctuation 1963-2006, dark grey line – average 1963-2006, light grey line - quartile, brown line - measurements in the year 2018.Click for larger images.

 


Location 3: Lagarfljót River by Lagarfoss

Figure 5: Annual discharge fluctuation in Lagarfljóts river by Lagarfoss (vhm 325/V325) before construction of Kárahnjúkavirkjun power plant 1975 - 2006 and measured discharge 2019.

 

 
FIgure 6: Annual discharge fluctuation in Lagarfljót river by Lagarfoss (vhm325/V325) after construction of Kárahnjúkavirkjun power plant 2008 - 2017 and measured discharge 2019.
Figure 5: Annual discharge fluctuation in Lagarfljóts river by Lagarfoss (vhm 325/V325) before construction of Kárahnjúkavirkjun power plant 1975 - 2006 and measured discharge 2019.
 
FIgure 6: Annual discharge fluctuation in Lagarfljót river by Lagarfoss (vhm325/V325) after construction of Kárahnjúkavirkjun power plant 2008 - 2017 and measured discharge 2019.
Labels: Y-axis: Average daily discharge (m3/s). Gray shadow - annual fluctuation 1963-2006, dark grey line – average 1963-2006, light grey line - quartile, brown line - measurements in the year 2018.Click for larger images.
 

 

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 2019.

 

Figure 8: Annual water level fluctuations in Lagarfljót river by Lagarfoss (vhm 17/V505) after construction of Kárahnjúkavirkjun power plant 2008 - 2017 and measured water level 2019.

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 2019.

Figure 8: Annual water level fluctuations in Lagarfljót river by Lagarfoss (vhm 17/V505) after construction of Kárahnjúkavirkjun power plant 2008 - 2017 and measured water level 2019.
 
Labels: Y-axis: Average daily discharge (m3/s). Gray shadow - annual fluctuation 1963-2006, dark grey line – average 1963-2006, light grey line - quartile, brown line - measurements in the year 2018. Click for larger images.

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

 

 

Figure 9: Annual water level fluctuation in Lagarfljót river by Egilsstaðir (Lagarfell, vhm7/V7) before construction of Kárahnjúkavirkjun power plant 1977 - 2006 and water level measurements 2019.

Figure 10: Annual water level fluctuations in Lagarfljót river by Egilsstaðir (Lagarfell, vhm7/V7) after construction of Kárahnjúkavirkjun power plant 2008 - 2017 and water level measurements 2019.
 
Labels: Average daily discharge (m3/s). Gray shadow - annual fluctuation 1963-2006, dark grey line – average 1963-2006, light grey line - quartile, brown line - measurements in the year 2018. Click for larger images.
 

Updated: April 17, 2020
Source: Landsvirkjun 2020

Metrics, Targets and Monitoring Protocol

What is measured?

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

The purpose of measurements is i.a. to analyze the effects of the operation of the power plant from natural fluctuations.

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.

Figure 11. Overview map of flowable meters in East Iceland, meters in operation and discontinued meters.

Click to download larger image

Updated: April 17th, 2020

Changes of indicator

This indicator was originally number 25.1. It was then named Changes in Hydrology 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 2.1.3 Ground water levels in holes
2007 2.2b Changes in Hydrology

Baseline

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 12 – 14 show a grey shaded area between the recorded min and max discharge/water level as well as average discharge/water level.

In figure 15 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 12.  Annual fluctuation of discharge in Jökusá á Dal river by Hjarðarhagi, vhm 110, before Kárahnjúkavirkjun power plant, 1963-2006

Figure 12.  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.

Mynd 2: Árssveifla rennslis í Lagarfljóti við Lagarfoss 1975-2006

Figure 13. 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 14. Annual fluctuation of water level in Lagarfljót river by Lagarfoss 1977 – 2006

Figure 14. 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.).

Figure 15. Annual fluctuation of water level in Lagarfljót river by Egilsstaðir 1977 - 2006.
Figure 15. 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.)

Rationale for Indicator 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) a.

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.

a: Updated from original terms

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

Further reading

LV-2017-024 Kárahnjúkavirkjun - Framkvæmd skilyrða fyrir virkjunarleyfi

LV-2017-024 Kárahnjúkavirkjun - Framkvæmd skilyrða fyrir virkjunarleyfi

2017

Eftir 10 ára rekstur Kárahnjúkavirkjunar þykir tímabært að fara yfir það hvernig Landsvirkjun hefur höndlað ýmis skilyrði sem sett voru fyrir leyfi til virkjunar. Þessi skilyrði eru aðallega þrennskonar; skilyrði sem umhverfisráðherra setti í tengslum við úrskurð sinn um mat á umhverfisáhrifum, fyrirheit Landsvirkjunar í matsskýrslu og viðbótarskilyrði iðnaðarráherra í virkjunarleyfi. Skilyrðunum má skipta í rannsóknir og vöktun og aðgerðir til að vinna gegn ætluðum umhverfisáhrifum. Í meginatriðum er markmið rannsókna og vöktunar að ganga úr skugga um hver umhverfisáhrifin eru í raun og hvort þau eru í samræmi við það sem álitið var eða meiri eða minni? Í þeim tilfellum þar sem mögulegt er að draga úr áhrifum er því lýst hvernig það hefur verið gert, í öðrum tilvikum hvernig aðferðir hafa verið þróaðar til að fást við áhrif svo sem af áfoki, sem frá upphafi var helsta áhyggjuefni um illviðráðanleg umhverfisáhrif. Mótvægisaðgerðir hafa gefið góða raun svo langt sem þær ná, en ekki hefur í öllum tilvikum reynt á þær, svo sem við firnamikið áfok.

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