Abstract
As part of the investigation of a new and optimized environmental flow regime in a regulated
river (Mandalselva, Norway), a modeling study was conducted on the trade-offs between the
production of Atlantic salmon (Salmo salar) smolts and the production of hydropower. Impacts
of alternative flow regimes on smolt production were examined under different physical
mitigation scenarios using the minimum flow regime recently proposed by the Norwegian
Water Resources and Energy Directorate (NVE) as a baseline. Different combinations of
hydropower operational strategies and/or physical mitigation measures were examined together
with changes in the minimum discharge using a series of linked simulation models with the
objective of finding combinations that both increased smolt production and maintained power
production. This methodology provided a toolbox for predicting both the potential tradeoffs
between smolt production and power production and therefore the evaluation of the most costeffective
environmental flow regime. The main finding was that it was possible to achieve a
similar smolt production with a lower hydropower plant flow release (with consequent lower
power loss) than the flow regime proposed by the NVE. Introducing habitat modification
measures further reduced the need for release of water in relation to the proposed minimum
flow, while increasing the smolt production. In an economic cost-benefit analysis perspective,
benefits per smolt from recreational fishing were small compared to hydropower costs per smolt,
with hydropower losses determining optimal flow. This study concludes that the use of a
modeling-based methodology to define a targeted environmental flow can be used to successfully
balance the sometimes conflicting requirements of effective management of salmon populations
while maintaining hydropower production.
Energy production
Atlantic salmon production
Mitigation measures
Cost-effectiveness comparison
Fish benefit
Trade-offs analysis
river (Mandalselva, Norway), a modeling study was conducted on the trade-offs between the
production of Atlantic salmon (Salmo salar) smolts and the production of hydropower. Impacts
of alternative flow regimes on smolt production were examined under different physical
mitigation scenarios using the minimum flow regime recently proposed by the Norwegian
Water Resources and Energy Directorate (NVE) as a baseline. Different combinations of
hydropower operational strategies and/or physical mitigation measures were examined together
with changes in the minimum discharge using a series of linked simulation models with the
objective of finding combinations that both increased smolt production and maintained power
production. This methodology provided a toolbox for predicting both the potential tradeoffs
between smolt production and power production and therefore the evaluation of the most costeffective
environmental flow regime. The main finding was that it was possible to achieve a
similar smolt production with a lower hydropower plant flow release (with consequent lower
power loss) than the flow regime proposed by the NVE. Introducing habitat modification
measures further reduced the need for release of water in relation to the proposed minimum
flow, while increasing the smolt production. In an economic cost-benefit analysis perspective,
benefits per smolt from recreational fishing were small compared to hydropower costs per smolt,
with hydropower losses determining optimal flow. This study concludes that the use of a
modeling-based methodology to define a targeted environmental flow can be used to successfully
balance the sometimes conflicting requirements of effective management of salmon populations
while maintaining hydropower production.
Energy production
Atlantic salmon production
Mitigation measures
Cost-effectiveness comparison
Fish benefit
Trade-offs analysis