Artificial floods are jointly responsible for deficits
December 20th, 2005
So-called «hydropeaking» is becoming a problem for water ecology in Swiss rivers and streams, particularly for fish. Of Switzerland 's larger rivers, one in four is influenced by such water surges on a daily and weekly basis. Together with the widespread river training and channelisation, such intermittent flow is one of the main causes for the biological deficits that can be observed, for example, in the valleys of the Rhone or the alpine Rhine. In those sections subject to surges, researchers examining the Rhone have noted much lower levels of colonisation and lower biodiversity among fish and other water organisms than would be expected in non-affected sections. Typical effects of hydropeaking also include increased turbidity during the winter and short-term fluctuations in temperature. Water organisms are drifted away by rapidly increasing water levels during hydropeaking. When the water level drops again, they may ground in locations that quickly dry out .
Up to now, no legal regulations on hydropeaking exist either in Switzerland or in other countries in which rivers and streams are influenced by hydropeaking. Both operational as well as structural measures can be taken into consideration to provide attenuation of peak flows. The investigations made in the Rhone-Thur-project show that, when taking the economic viability of hydropower into account, the building of retention pools or underground storage systems is often the most sensible solution.
Hydropeaking alone can not be made responsible for many of the ecological deficits found. The impoverished and monotonous morphology of the river and other anthropogenic influences contribute to these deficits to a great extent. On the other hand, however, hydropeaking complicates the matter and poses an additional, limiting condition on the revitalisation of rivers and streams. This means, for instance, that when widening riverbeds, it must be assured that sufficient structural elements - gravel banks, deadwood etc. - are available and not only those areas are extended that always dry out after peak flow has sunk once more. Recommended or threshold values that would permit a hydro-ecological assessment of the effects of hydropeaking are still missing to a large extent and too little is known about the interdependencies between hydropeaking and other deficits concerning rivers and streams.
Media release [pdf]
Synthesis reports: www.rivermanagement.ch