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Artificial floods revive the River Spöl

For the last 12 years, the Engadiner Kraftwerke AG has been creating artificial floods along the River Spöl, below the Livigno reservoir. These have restored some of the mountain stream’s original white water characteristics.

Greater dynamics for residual water stream

Since the Engadine hydroelectric power stations were put into operation in 1970, the Spöl is a residual water stream. The tamed watercourse lacked the essential characteristics of a mountain stream. In the course of a 12-year project, the operators of the power station tested a variety of floods. These floods developed into an internationally unique test series. In 2011, the new residual water regime was introduced permanently. This is how it works: In July, a flood with a peak outflow of 30 cubic metres per second is generated and in September a smaller one with 20 cubic metres per second. These two artificial floods have had a positive impact on the stream’s development. They have restored to the Spöl the dynamics that are necessary for it to develop back into a typical mountain stream. Minor floods with an outflow of just 10 cubic meters per second yield little ecological benefit, because they do not achieve a redistribution of the river bed. Very large floods are problematic, because too many living organisms are washed away.

New species in the River Spöl

The floods made a visible impact on the river bed: The cones of debris in the tributary streams were washed away; the bed was redistributed and loosened up. The growth of algae and moss decreased significantly. Since 2007, species were detected in the Spöl that could not be found previously. These most notably included rather rare stonefly and caddis fly species. The living conditions for fish also improved with the floods. The brown trout is the only species that lives continually in the Spöl. The number of spawning grounds as well the number of trout spawning pits per spawning ground has increased significantly since 2000.

Little water = low dynamics

From 1970, the six kilometres long, gorge-like residual water section developed into a watercourse with extensive shallow water areas and pools. On its way to the Ova Spin compensating reservoir, the nutrient-rich water from the Livigno reservoir stimulated the growth of algae and moss. The tributary streams deposited scree that was carried along with the water onto the river bed. The Spöl lacked the strength to carry the material further downstream. Fine sediments clogged the pores in the riverbed, which ceased functioning as a water filter. From the riverbanks, debris flows pushed into the riverbed and slowed down the water flow. The nature of the Spöl was transformed.

Idea resulted in a sustained improvement

Since 1990, a close cooperation exists between the operators of the Engadine power stations, the Swiss National Park and a working group of scientists. The initial purging of the reservoir exhibited a positive impact on the aquatic ecology. In 1995, the idea emerged to apply the experience to a sustainable development of the residual water stream. The first artificial floods roared down the Spöl in 2000. Since then a total of 24 floods, each lasting six to eight hours, have been initiated in the mountain stream. With the regime that has been introduced, the Spöl has regained some of its original character of a mountain stream. At the same time, the water is still used to generate energy.

Sources: Eawag information day on 22 June 2012, article in the NZZ newspaper on 9 January 2013, website of the Swiss National Park