Risk Assessment and Decision Making on Mitigation Measures

Abstract

The proliferation of hydropower development to meet obligations under the Renewable Energy Directive has also seen the emergence of conflict between the hydropower developers and the fisheries and conservation sectors. To address this trade-off between hydroelectricity supply and its environmental costs, this chapter introduces a series of tools and guidance to assess environmental hazards of hydropower in particular on fishes, to enhance assessing cumulative effects from several hydropower schemes and to enable informed decisions on planning, development and mitigation of new and refurbished hydropower schemes. The newly developed European Fish Hazard Index is introduced as objective, comparable, and standardized screening tool for assessing the impacts on fishes at existing and planned hydropower schemes, while explicitly considering the ecological status and consecration value of the ambient fish assemblage. In addition, guidance is provided on assessing the environmental impacts of consecutive hydropower schemes in a river system. This guidance separates between cumulative impacts on habitats and species and thus, considers cumulative length of all impoundments in a river system, total fragmentation by barriers (barrier density), but also different migratory life history traits of species and their encounter probability with hydropower schemes and sensitivity to mortality. Finally, a decision support scheme is provided to balance the environmental risk with appropriate, site-specific mitigation planning and implementation at new and existing hydropower schemes.

Prioritisation of Barriers According to Their Impact on Migratory Fish in the Lowland River Basin District

“…One of these is the possibility to separately assess the importance of river sections currently flooded by dams and the river network above the reservoir. A separate assessment of the flooded river sections and the upstream areas showed that ponds cover almost 19% of the area of habitat suitable for migratory fish in the lowland rivers, which is already equivalent to a medium cumulative impact in terms of habitat loss due to barriers [43]. This aspect cannot be ignored when choosing between several alternatives, such as removing dams or installing fishways.…”