Landsvirkjun operates 14 hydroelectric power stations across the country. Electricity generation involves channelling the water flow from the Company’s main reservoirs to the power stations, creating energy and maximising the utilisation of this water reserve.
Steering water discharge within an isolated hydropower system
The electricity system in Iceland is isolated and the optimum utilisation of the water reserve in reservoirs is integral to the safety of operations. The water cycle is inherently subject to weather conditions at any given time. During the summer, the snow melt and water from melting glaciers is collected in reservoirs and this water is then used during the winter. The electricity generation at hydropower stations involves channelling the water flow from the main reservoirs to create energy, thus maximising the utilisation of the water reserve. More detailed information on electricity generation in an isolated hydropower system can be found in the Annual Report from 2014 in the chapter on the water reserve.
Water steering via water channels and reservoirs reduces fluctuations in water flow generally associated with rapid snow melt, ablation or flooding. Fluctuations in water flow can have a negative effect on the ecosystem, soil and society.
Landsvirkjun seeks to reduce fluctuation and rapid changes in water levels below the power stations in cooperation with experts and local residents within the various operational areas of the Company. Water management at all of Landsvirkjun’s power stations is subject to the framework outlined in working procedures pertaining to restrictions on water flow. Temporary restrictions are also placed on water flow in the case of salmon fishing or waterfall water flow.
The water year 2013-2014
Landsvirkjun’s water year begins on the 1st of October and concludes on the 30th of September in the following year.
Generally, the water year commences during the autumn when the reservoirs have reached their highest level. The water is then released to the power stations over the winter period reaching their lowest level in the spring before the spring melting period and ablation fills the reservoirs once again.
Total amount of energy generated by hydropower in 2014.
The inflow to Landsvirkjun’s operational areas in the water years 2013- 2014 was 7% below the average for the last ten water years. The year is therefore categorised as below average without being categorised as dry. The hydrology status this year is the result of a combination of a very dry year between 2012 and 2013 and a low inflow rate from October, 2013 and up until April 2014.
The autumn period in 2013 in the water catchment areas in Þjórsá, Tungnaá and Blanda was rather dry and cold. Inflow rates to the reservoirs were less than that of the previous year and remained below average into the winter period. The groundwater level in the Þjórsá and Tungnaá area was the lowest recorded in a decade. Þórisvatn reached its lowest recorded level since the Þórisvatn Reservoir was constructed (560.3 m.a.s.l). The water flow showed signs of recovery in the spring and remained average for the rest of the water year. Ablation from the northern part of the Hofsjökull Glacier was substantial and the Blanda Reservoir had filled by the beginning of September. The year 2014 is thus considered to be a dry year in the Þjórsá, Tungnaá and Blanda area.
Snow accumulation was above average in the east of Iceland and the area experienced a cold winter. The inflow to reservoirs was significantly below average well into the winter period and there were no winter floods. There was a rapid increase in temperature at the end of May and the air temperature on the Brúarjökull Glacier was above freezing until the end of the water year. The inflow at the Hálslón Reservoir during the spring and most of the summer was the highest on record (for the same period) in the last decade. The Hálslón Reservoir was full by the end of August and the spillover was utilised until mid- October. The water flow to the Fljótsdalur Hydropower Station was therefore above average.
Increased capacity of the Hálslón Reservoir
The Brúarjökul terminus after the surge in 1964 (red line) and how the terminus has retreated. Data collected from the Institute of Earth Sciences at the University of Iceland.
Landsvirkjun monitors various aspects which could affect sediment accumulation within the affected areas of power stations. The objective is to map any changes to the reservoirs and waterways so that mitigation measures can be implemented if and when needed.
The Hálslón reservoir is the largest manmade central reservoir in Iceland, measuring approx. 62 km2 with a volume of approx. 2100 Gl. The Hálslón Reservoir is formed by three dams: Kárahnjúkastífla, Desjárstífla and Sauðárdalsstífla and the water supply for the reservoir is mostly sourced from the Brúarjökull Glacier. The water from the reservoir is channelled over a distance of 40 km via a tunnel and into the turbines at the Fljótsdalsur Hydropower Station.
The construction of the Fljótsdalsur Hydropower Station resulted in substantial changes to the sediment load in water streams within the affected area. The greatest changes were detected in the Jökulsá á Dal River where sediment levels increased significantly. The construction of the Kárahnjúkar Dam resulted in the transport of sediment from the river and into the Hálslón Reservoir where it settles and accumulates. This can reduce the capacity of the reservoir.
Sedimentation and the decrease in the capacity of the Hálslón reservoir can affect the lifetime of the reservoir and generation capacity. Monitoring reservoir levels and capacity is therefore important to operations as well as any changes to the Brúarjökull Glacier and the potential effects of this on the Hálslón reservoir.
The volume of the Hálslón reservoir has increased by 110 GL since 2001. The change can be attributed to the fact that the Brúarjökull Glacier has retreated by 4.5 km during the same period.
A traverse survey of Hálslón was completed in the summer of 2013. The results show that the volume of the reservoir has increased by 110 Gl since the last survey was conducted in 2001. The change can be attributed to the fact that the Brúarjökull Glacier has retreated by 4.5 km during the same period.
Changes to the glacier terminus mean that reservoir surveys are not comparable between years. A comprehensive assessment of the sediment levels deposited in the reservoir between 2008 and 2013 is therefore difficult. However, the actual increased volume of reservoir due to the retreat of Brúarjökull glacier may be higher than recorded as mud and river bed materials have settled in the reservoir due to sediment deposition. According to an estimate, around 25 – 35 Gl of reservoir volume should be lost due to sedimentation during the reservoir’s operation. It may therefore be estimated that the increase in reservoir volume due to the retreat of the Brúarjökull Glacier may in fact amount to 135 – 145 Gl.
Glacier mass balance
Landsvirkjun operates an extensive research and monitoring program for glaciers, assessing long-term changes and runoff from the glaciers that are important for hydropower operations. Research is conducted in cooperation with the Institute of Earth Sciences at the University of Iceland, the Glacier Research Society of Iceland (JÖRFI) and the Icelandic Meteorological Office.
A 300 km distance is driven across Langjökull and a 1000 km distance is driven across Vatnajökull, on an annual basis to collect accurate elevation profile data using a GPS navigation system.
The glacier year 2013- 2014 marked the twentieth year in a row where the mass balance for the Vatnajökull Glacier was negative. Glacier mass balance, the product of glacier accumulation plus ablation, is expressed in water equivalents, i.e. the amount of water bound within snow and ice. The average winter mass balance for the entire glacier was 10% above the average for the last twenty years (1.7 m water equivalents) and the average summer mass balance (ablation) was 20% above the average (-2,45 m water equivalents).
The net mass balance for the glacier year 2013-2014 was therefore close to the long-term average or approx. -0.75 m water equivalents. The long-term mass balance average at the Vatnajökull Glacier, calculated from the glacier year 1995- 1996 to the present day, is approx. -0.76 m water equivalents which is equal to 130 km3 of ice or approx. 4% of the entire ice mass of the glacier.
Winter and summer mass balances are measured at 23 monitoring stations on the Langjökull Glacier and at 50-60 stations on the Vatnajökull Glacier. Glacial ablation monitoring has been carried out for over twenty years.
The run-off to rivers was satisfactory overall. The run-off to the Tungnaá River was close to average. Run-off to the Hálslón Reservoir (Jökulsá á Brú) and to the Hágöngulón Reservoir (Kaldakvísl) was approx. 5–6% above the average. The run-off to the Jökulsá diversion (Jökulsá í Fljótsdal) was 4% below the average. The glacier year 2013 to 2014 is therefore considered an average year.
Cooperation with the various tour operators
Landsvirkjun cooperates closely with tour operators within the affected area of the Fljótsdalur Hydropower Station. The objective is to minimise the impact of the altered flow regimes in rivers and waterfalls on the experience of tourists in the region. Landsvirkjun utilises the spillover from the Jökulsá diversion during the summer period to minimise the impact of the station on waterfall water flow rates and to achieve the average water flow ratel in the Jökulsár í Fljótsdal and Kelduár River channels.
More detailed information on Landsvirkjun‘s cooperation with the various tour operators in the east of Iceland can be found on the website: sjalfbaerni.is. The website also provides information on the water flow levels in waterfalls and changes in hydrology.