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Modelling Spatio-temporal Dynamics In Water Allocation For Hydropower Operations And Environmental Flows In Data Scarce Mountain River Ecosystems

Congress: 2015
Author(s): Josie Geris, Bas Buddendorf, Iain Malcolm, Mark Wilkinson, Chris Soulsby
University of Aberdeen1, Marine Scotland Freshwater Laboratory2, James Hutton Institute3

Keyword(s): Sub-theme 9: Water allocation among competing uses and users,
AbstractMountain rivers in many parts of the world provide important services, e.g. in terms of energy, the provision of high quality downstream water supply, and the maintenance of in-stream habitats. In Scotland, rivers are increasingly exploited for hydropower production in order to meet pressing renewable energy targets. Although this provides a safe and low-cost source of renewable energy, the river regulation that is involved with these practices has widespread effects on the timing and volume of flows (Birkel et al., 2014; Soulsby et al., 2014), and there are concerns about the impacts on in-stream aquatic ecology as users of water. To be able to address these conflicts between ecosystem and hydropower generation needs for water, and provide the scientific evidence to underpin sustainable water management, a good understanding of the impacts and the resilience of hydropower regimes within the context of the wider ecosystem is important, in particular as both future supply and demand of water resources are likely to be impacted by environmental change. However, determining the specific needs for these two water users is often limited by inadequate data, both on pre-regulation and current regimes. In such cases, where complex models with high data demands are inappropriate, there is a need for simple conceptual modelling approaches that can still capture the dominant natural runoff generation and artificial regulation processes.

The main aim was to develop and apply a modelling to assess hydropower effects on natural flow regimes, predict water availability, and test system resilience for present and future hydropower production schemes in data sparse mountain river ecosystems (Geris et al., 2014). Model routines for simulation of runoff regulation (reservoirs and water transfers) were implemented into the HBV rainfall-runoff model, allowing for situations where regulation amounts are known and those where regulation amounts have to be estimated based on simple regulation rules. The new model was applied to the heavily regulated River Lyon (391 km2), 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

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