), Scotland, UK, which has a long history of hydropower generation that is supported by a complex network of inter- and intra-catchment water transfers and river impoundments. There are concerns that these are affecting high conservation freshwater populations of Atlantic Salmon (Salmo salar), highlighting the need for a good understanding of present impacts and the extent to which flow variables can be modified without major degradation to the river's ecosystem. The model was used to explore the spatio-temporal dynamics in water allocation for hydropower operations and environmental flows, and thereby characterise the natural flow regime, assess the regulation impacts, and explore sensitivities to allocation changes in water management.
The results for the River Lyon application showed that generally, changes following regulation include decreases in inter-and intra-annual variability of all aspects of the flow regime. Effects are most marked for mid-range events and hydropower water allocation results in major shifts in the spatio-temporal dynamics of natural water balances. The impacts on flow regimes extend to large scales, several kilometres downstream of the river regulation infrastructure. Various life stages of Atlantic salmon have different flow requirements. Considering that the regulation moderates the variability of most aspects of the flow regime, these are most likely all affected. Although we cannot directly link the regulation impacts on the flow regime to effects on salmon populations, the results can be used as a first approximation to assess the degree of flow alterations and inform consideration of alternative environmental flows in regulated, montane rivers. Sensitivity tests showed that a more variable release regime, as opposed to changes in the efficiency of the present regulation regime, could be most beneficial for the ecological status of the Lyon, while still maintaining viable hydropower generation.
Overall, the results demonstrated that the simple, conceptual modelling approach developed here can capture the dominant catchment and regulation processes well, especially at the time scale at which operation rules apply. Consequentially, the approach is data undemanding, flexible, and able to provide a basis for assessing impacts on flow regimes and informing hydropower operations and environmental flows in other (data sparse) regions with heavily regulated mountain river ecosystems. Furthermore, its results are easily communicated to stakeholders, and can therefore offer a basis for discussing the development of new adaptive management strategies that explore the trade-offs between the different water users.
Birkel, C., Soulsby, C., Ali, GA. & Tetzlaff, D. (2014). 'Assessing the cumulative impacts of hydropower regulation on the flow characteristics of a large atlantic salmon river system'. River Research and Applications, vol 30, no. 4, pp. 456-475. DOI: 10.1002/rra.2656
Geris, J., Tetzlaff, D., Seibert, J., Vis, M. & Soulsby, C. (2014). 'Conceptual modelling to assess hydrological impacts and evaluate environmental flow scenarios in montane river systems regulated for hydropower'. River Research and Applications. In Press DOI: 10.1002/rra.2813
Soulsby, C., Birkel, C., Geris, J. & Tetzlaff, D. (2014). 'The isotope hydrology of a large river system regulated for hydropower'. River Research and Applications. In Press DOI: 10.1002/rra.2740