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Blog | Better Hydro: reducing sedimentation and erosion at Blanda, Iceland

Better Hydro: reducing sedimentation and erosion at Blanda, Iceland

This case study is featured in Better Hydro: Compendium of Case Studies 2017, which highlights examples of good practice in hydropower sustainability across all aspects of project development. You can download the full compendium here.


Key project features

Project stage: operation
Developer/operator: Landsvirkjun
Capacity: 150 MW (3 x 50 MW units)
Annual generation: 800 GWh 
Reservoir area: 56 km2 (Blöndulón) and 5 km2 (Gilsárlón) 
Head: 287 m
Purpose: power generation
Commissioning: 1991


The Blanda project carried out one of the largest revegetation and erosion control programmes in Iceland's history. This case study demonstrates how the project's efforts to reduce sedimentation and erosion have benefited local communities and biodiversity. 

Blanda lies on the fringe of the central highland plateau, with gentle hills and heathland on shallow soils. The climate in the area is dry, cold and windy, with a mean annual precipitation of 400 mm and a mean annual temperature of 0.6 °C.

Blöndulón reservoir is formed by two dams, on the Blanda river and the Kolkukvísl river, and water is diverted through 9,800 m of diversion canals and four lakes to an intake reservoir (Gilsárlón). From Gilsárlón, water runs through a 1,300 m canal and a 347 m headrace tunnel, before dropping vertically through a 236 m penstock to the underground power station. From the turbines, the water flows through a 1,700 m tailrace tunnel into the Blanda river.

The Blanda river used to be a highly turbid glacial river. It presents an interesting example of a system that has, in the view of affected communities, largely benefited from trapping sediment in an upstream reservoir. River banks have stabilised, primary productivity has increased due to greater light penetration, abundance of aquatic life has increased, and the opportunities for angling have improved. 

The project’s development had few adverse environmental and social impacts. One of the most significant impacts, the loss of vegetation and sheep grazing lands to create the reservoir, has been compensated by a large-scale revegetation programme. The area that was inundated was once an area with high-quality soils, the best land for sheep grazing in the region. The absence of vegetative and soil cover is a national environmental problem in Iceland, so the loss of these fertile soils prompted widespread concerns. This resulted in one of the largest revegetation and erosion control programmes in the country’s history. Extensive revegetation efforts have been and are being undertaken to compensate for and extend well beyond the loss of the grazing area.

Watershed-wide research allows in-depth understanding of geomorphology

Landsvirkjun and researchers have studied the geomorphology of the Blanda river system in depth. Any changes to erosion and sedimentation that would positively or negatively affect power generation or other river uses will be identified through a broad array of monitoring initiatives: 

  • long-term suspended sediment sampling was undertaken at the Langamýri gauge downstream of the power station from 1965 to 2011; this data was used in baseline geomorphology studies and pre- and post-project sediment rating curves;

  • samples of suspended and bedload sediments have been taken regularly across the basin;

  • glaciological research has been established upstream;

  • aerial pictures and site visits of the downstream river reach and the river mouth were used to monitor channel stabilisation; and

  • data and studies have either been published or are accessible in the Iceland Meteorological Office database.

Shoreline erosion and sediment accumulation in the Blanda reservoir are monitored. For example, a bathymetric survey using echo sounders was conducted in 2012 as part of a Landsvirkjun programme to survey all reservoirs, which will be repeated every five to 10 years.

Partnerships with habitat restoration experts maximise success in catchment revegetation

The revegetation programme around the reservoir compensated for the loss of grazing land and avoided displacing grazing pressure onto soils susceptible to erosion. Farmers with lands in the valley floor are benefiting from improved grazing and even some grain production. 

Since 1975, more than 20 studies have been carried out to assess land use change and the impact of grazing and land reclamation in the region. Numerous grazing experiments were undertaken by the Soil Conservation Service of Iceland between 1975 and 1989 to find effective ways of meeting grazing requirements without damaging vegetation.

The Soil Conservation Service runs the revegetation programme in partnership with Landsvirkjun and a farmers’ cooperative. There are two formal meetings a year to discuss the programme’s direction and any issues arising. 
The programme also brings benefits for biodiversity. This is notable in an area to the west of the river where native vegetation is developing in place of grass cover, made possible by the soil depth and land cover created by the former cultivated grassland. The Institute of Natural

History believe that a decrease in grazing pressure from sheep and horses, and a change in climate, have contributed to the success of the revegetation programme. 

The fertilisation of some areas, creating good grazing land, has enabled the movement of animals, allowing overgrazed areas to recover. 

The revegetation programme around the reservoir compensated for the loss of grazing land and avoided displacing grazing pressure onto soils susceptible to erosion."

Silt or dust storms are typical in Iceland, where much of the landscape is not covered by vegetation due to harsh natural conditions and centuries of overgrazing and wood harvesting. At low water levels and high winds, sediment from the exposed area can be windblown. Sand then settles close to the reservoir, threatening to cover the low vegetation, whilst finer silt is blown further and can be a nuisance.

In partnership with the Icelandic Institute of Natural History, Landsvirkjun has established measures to stabilise areas of land around the reservoir affected by windblown sand. This includes the application of fertiliser to encourage plant growth, and fencing to prevent grazing. If dust storms were to become a more regular occurrence, there is an intention to replicate Landsvirkjun’s ongoing monitoring programme from the Kárahnjúkar project.

In-river geomorphological changes can also deliver benefits for communities

As a glacial river, the Blanda river was carrying high sediment loads of around 570,000 tonnes per year. Damming the river has substantially reduced sediment load downstream to about 63,000 tonnes per year. However, the erosive capacity of the river is also reduced as spring floods are curtailed. The river has changed from a dynamic braided system with frequently changing channels to a largely static one, and gravel banks in the channel have become vegetated. 

The project also had unanticipated benefits for local communities, arising from altered river geomorphology. The effects of the project on erosion and sedimentation are generally seen as positive by the local population. Angling – in particular for salmon – has significantly increased, both because the river provides a better habitat and because of increased visibility. It was also possible to relocate the national road from Blönduós to Akureyri as the river was stabilised and flooding reduced.


This case study is based on an official assessment of the Blanda project using the operation stage tool of the Hydropower Sustainability Assessment Protocol. The assessment was conducted in 2013, with an on-site assessment in September 2013. 

The case study is featured in Better Hydro: Compendium of Case Studies 2017, which highlights examples of good practice in hydropower sustainability across all aspects of project development. You can download the full compendium here.

The Blanda project was the winner of the 2017 IHA Blue Planet Prize; click here to view our short documentary about the project.