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

The eight Swiss Competence Centers for Energy Research (SSCERs), financed by the Commision for Technology and Innovation, 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 2.4 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 2.4

  • 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.

According to the Swiss energy strategy 2050 a maximum additional yearly production of 2200 GWh of electricity should be provided by small run-of-river hydropower plants (<10 MW). Such small plants are perceived to have a smaller ecological impact. However, there is evidence that the network-scale impacts of small hydropower plants may be more far-reaching than expected so far. Studies assessing local and network-scale impacts of small hydropower plants are rare. There is a need for tools assessing the overall impact of multiple hydropower plants within a river network, both locally and network-wide.

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. Optimal positioning of multiple hydropower plants within the river network

Small hydropower may have a significant impact on riverine ecosystems, especially in the Alpine region where depleted flow reaches tend to be long. Increased hydropower exploitation within a river basin can cause cumulative impacts, such as habitat fragmentation, loss of suitable habitats, interruption of migration dynamics due to altered flow regimes and the disruption of the river continuum by weirs or dams. When selecting suitable locations for new hydropower plants, such network-scale effects have been mainly neglected. This is partly due to the lack of tools allowing to evaluate the interdependency of river network topology, migration dynamics and biodiversity.

We are developing a framework for Pareto-optimal positioning of small hydropower plants. This is done by evaluating the influence of multiple configurations of power plants within a river network on the extinction probability of migratory species by combining metapopulation capacity (a measure for the viability of a species within a network of habitable patches) and discharge dynamics.

So far, we could show that including a network perspective into the planning process, offers optimal configurations which differ from solutions that were only based on local ecological impacts.

Related projects

  • FLEXSTOR WP1: Assessing the performance of hydro-peaking remediation measures under future scenarios – Performance of Innertkirchen compensation basin with operation of Trift dam
  • Participation in NRP 70 projects (HyApp, HydroEnv).