Swiss Competence Centre for Energy Research – Supply of Electricity (SCCER-SoE)

The eight Swiss Competence Centers for Energy Research (SSCERs), financed by the Innosuisse, are research networks created to increase the research capacity in the energy domain. Their aim is to support the development of innovative solutions to address the technical, social, and political challenges resulting from the aims of the Swiss Energy Strategy 2050.

The SCCER Supply of Electricity (SCCER-SoE) focuses on the domains of hydropower and geoenergies (deep geothermal energy and CO2 sequestration). Eawag leads task 2.3 of the SCCER-SoE, which aims at assessing the environmental impacts caused by an expected increase in hydropower production in Switzerland, and at developing strategies for reducing these.

Objectives of Task 2.3

  • Ecological effects of small-scale hydropower plants
    What are the ecological impacts on the river network due to the large number of new small hydropower plants that are expected to be constructed to fulfil the aims of the energy strategy, and how can these impacts be reduced?

  • Environmental flows
    What are the best strategies for environmental flow releases downstream of dams in order to both optimize hydropower production and maintain healthy and dynamic ecosystems in the residual flow reaches?

  • Hydro- and thermopeaking
    Hydro- and thermopeaking are strong sub-daily fluctuations of discharge and temperature in rivers caused by intermittent power production from hydropower plants. How will the dynamics of hydro- and thermopeaking be modified by future changes in energy demand and by a changing climate?

    What can be done to reduce the ecological impact of future hydro- and thermopeaking patterns?

Activities at Eawag focus mainly on the trade-off between electricity production from small run-of-river hydropower plants, biodiversity and ecosystem services, and on the effects of hydro- and thermopeaking.

Research goals

  • Developing methods which, based on a detailed understanding of local and network-scale impacts, provide hydropower operators and local authorities with information on the suitability of potential sites for small hydropower plants.
    While most tools for hydropower planning have been based on local ecological impacts, the complex nature of riverine ecosystems requires a tool that considers multiple objectives to assess suitable locations within a river network. These objectives should include fish biomass related to habitat availability and diversity, requirements for organism movements related to the local fish population, protection of locally adapted species, and ecosystem functions. The long-term goal is maintaining a high genetic variation and a high evolutionary potential which allows species to adapt to a changing environment. Longitudinal barriers, interrupting gene flow across the landscape, might compromise this evolutionary potential.
  • Provide methods for determining suitable ecological flow releases from small run-of-river hydropower plants.
    Most management tools were developed for the operation of large storage hydropower plants. But small-scale run-of-river hydropower plants are usually not operated actively. So far, the main goal for small hydropower plants was the implementation of ecological flow requirements, which have to be considered at the design stage; e.g. implementation of proportional flow release structures.

Research activities

1. Local impacts of small-scale hydropower on ecosystem functioning

The impacts of small hydropower plants are most obvious in the depleted river reaches, from the point of abstraction to return, which experience reduced flows and sediment inputs. The resulting deterioration of the in-stream habitat has been shown to impact on fish density and condition, fish community composition and ecosystem functioning, such as organic matter breakdown and nutrient retention. But we currently lack an understanding of the underlying mechanisms affecting food-web structure and dynamics.

We are therefore investigating in-stream conditions and the structure and functioning of food-webs along the river reaches impacted by small run-of-river hydropower plants. First results show that the deterioration of the in-stream habitat reduces trout body condition, which is partially explained by decreased prey availability and the feeding behaviour. The knowledge we gain will then help designing efficient mitigation measures.

2. Impacts of hydropower plants on river temperatures

Storage hydropower plants affect the thermal properties of the downstream rivers by releasing water from reservoirs with a different temperature. This results both in short-term temperature fluctuations, so-called thermopeaking, and in a seasonal shift in temperature, typically with higher winter and lower summer temperatures. We investigate these effects and their ecological consequences in two sister projects. In the first proejct, the effects of thermopeaking on the spatial variability of temperature in the downstream river is investigated using an extended version of the numerical model BASEMENT. In the second project, conducted by the FishEc department, the effects of seasonal temperature changes on the early life stages of brown trout are investigated.