Mr Schmid, you are a group leader in the Surface Waters department at Eawag and have been working on the effects of hydropower utilisation on water bodies for years. The pressure to generate even more energy from Swiss hydropower is currently very high. What are the consequences for our water bodies?

Martin Schmid: Hydropower has already led to major changes in many Swiss watercourses compared to their natural state and has thus severely impaired the basis for life of fish and other aquatic life. In residual water stretches, a large part of the natural run-off is missing, and downstream of the return lines from hydroelectric power plants, unnatural fluctuations in run-off cause organisms to become stranded or washed away. Weirs impede connectivity along the bodies of water. With the further expansion of hydropower, water bodies will be even more affected by such impacts.

Moreover, hydropower is not the only factor having an impact on water bodies. Structures for flood protection, chemical pollution and, increasingly, climate change are further stress factors. Numerous species have already become extinct in Swiss water bodies due to these stresses. Of the remaining fish species and the insects living in water bodies, more than half are considered to be endangered or potentially endangered. In view of these figures, one has to think very carefully about whether the living organisms in the water bodies can be expected to bear any further stress.

Martin Schmid: “One has to think very carefully
about whether the living organisms in the water bodies
can be expected to bear any further stress.”

However, with regard to residual water flows, there are efforts to relax the implementation of the minimum requirements of the Water Protection Act in order not to “lose” a single kilowatt-hour. Is there actually any room for manoeuvre from the point of view of water protection?

Adequate residual water is necessary for fish and other creatures to survive and reproduce in the water bodies. In addition, there are other functions that water bodies with insufficient residual water flows can no longer fulfil, such as feeding groundwater reserves or serving as recreational areas for the population. The ecology in residual water stretches is already severely impaired today and is coming under additional pressure due to climate change. From the point of view of water protection, it is therefore of great importance that at least the legally prescribed residual water flows are maintained. From a scientific point of view, it would also be desirable to have dynamic residual water flows whose variability corresponds to the natural dynamics of a body of water.

Another demand is to raise the dams of existing reservoirs so that more water and more electricity can be shifted from summer to winter. Is this a good solution from the point of view of water research?

In the case of most Swiss watercourses, climate change will mean that run-off will be significantly higher in winter and significantly lower in summer. The expansion of seasonal storage will further increase this effect. However, it has not yet been sufficiently studied how this will affect the ecosystems of the affected water bodies upstream and downstream of the dams.

Martin Schmid: “In the larger lakes, there is still
enormous potential for the use of heat without any
expected negative effects on the lake ecology."

A hitherto little-used possibility for energy generation is to extract heat from the lakes in winter and thus replace fossil fuels. Are there limits to this use, for example because it has a negative impact on the lake as a habitat?

In Switzerland, heat from lakes is increasingly being used for heating in heating networks. In the larger Swiss lakes, there is still enormous potential for this, which can be exploited without any expected negative effects on the lake ecology. It therefore certainly makes sense to further expand this regional and renewable energy source. Of course, the possible consequences for the water bodies must be assessed in each case as part of the concession procedure. On the one hand, the local effects caused by the construction of the required pipelines must be considered, and on the other hand, possible changes in the temperature and mixing behaviour of the lakes that may result from the heat extraction.

Could we not also utilise the rivers or groundwater much more as suppliers of heat?

Yes, the larger rivers in the Swiss plateau also have considerable potential for heat utilisation. However, the more time that goes by, the less suitable they are for cooling purposes, as climate change means that water temperatures in many places are increasingly above the tolerance limits of some species . Alpine streams, on the other hand, are less suitable for heating purposes because of their low flows and low temperatures in winter.

Groundwater is already used as a heat source in many places today. Care must certainly be taken to ensure that there are no excessive temperature changes in the long term, especially if the groundwater is used as a drinking water supply. Groundwater could also be an attractive seasonal heat reservoir, which is used for cooling in summer and heating in winter.