Potential of a Hypothetical Multi-Purpose Reservoir in the Upper Catchment Area of the Alptal
Creators: name: Kummer, Céline
Publisher: name: Zenodo
Year: 2022
Subjects: hydrology, multi-purpose reservoir, water management, Alps,

description: Msc thesis under the direction of Prof. Dr. B. Schaefli (University of Bern) and the co-supervision of Dr. M. Stähli, (WSL). Abstract: Multi-purpose reservoirs have recently been discussed as an adaptation measure to mitigate the effects of climate change. The management of multi-purpose reservoirs, however, is challenging as trade-offs between compromising water uses need to be accounted for. A lot of studies elaborated optimizing reservoir operation rules by applying meta-heuristic techniques, whereas non-algorithmic approaches are currently missing in the literature. In addition, the potential and management of small reservoirs are rarely addressed. Thus, this Master’s thesis has developed a simple methodology for the assessment of the potential of small multi-purpose reservoirs in pre-alpine catchments and applied it to a hypothetical reservoir in the Alptal. The main objective consisted in the proposal of an optimal reservoir design and management strategies considering all potential purposes of the reservoir. These purposes include (i) improving streamflow conditions for brown trout populations in the Alp, (ii) snowmaking, (iii) artificial flood experiments for research related to the morphology and control of torrents, (iv) flood retention and (v) tourism. The methodology implied the simulation of the reservoir as a component of the streamflow network of the catchment area. Reservoir filling and water release was simulated in the “Water Evaluation And Planning” system (abbr. WEAP) by using an area-based approach to downscale high resolution discharge data (years 2009-2019). A specific water demand was assumed for every purpose, allowing their integration into the model and thus the evaluation of benefits. The results show a great potential of a small reservoir (&lt;30’000 m3) for snowmaking under current climate conditions, for the conduction of artificial flood experiments and for the augmentation of streamflow during low flow periods. With respect to the latter, the reservoir’s potential is limited during long periods of low flow for all analyzed reservoir sizes (&lt; 100’000 m3). Thus, an intermittent streamflow augmentation may be considered, although studies providing evidence for stress reduction in brown trout have yet to be undertaken. Regarding management strategies, trade-offs were analyzed by comparing the benefits of each purpose in both a single-purpose and multi-purpose reservoir system. This analysis allowed the formulation of adequate prioritization rules of different purposes throughout the year. In general, intermittent water uses such as snowmaking and tourism are prioritized over the continuous purpose of streamflow augmentation for brown trout. Furthermore, adequate management allows negative effects of summer tourism on streamflow augmentation to be compensated. Thus, this Master’s thesis concludes that there is a striking potential of a multi-purpose use of small reservoirs in pre alpine areas if adequate operation rules are applied.