Quantifying reservoir impacts on river flows across Great Britain through large-sample hydrology and large-scale hydrological modelling

Abstract

Reservoirs are essential components of many water supply systems and reservoir operations have wide-reaching impacts on the downstream river flow regime. Consequently, incorporating reservoirs into hydrological modelling is essential for accurately simulating past, present and future flow. However, there is still no clear consensus on the best way to model reservoir operations within hydrological modelling and their impacts on the flow regime are not fully understood. This thesis focuses on developing new methods for quantifying and understanding the impacts of reservoirs on river flows across Great Britain (GB). Specifically, it investigates (1) how and where reservoirs are impacting the flow regime, (2) where and when the integration of reservoir representation into large-scale hydrological modelling can improve streamflow simulations and (3) whether reservoirs (or additional catchment storage) can be used to mitigate the impacts of climate change on the flow regime. First, we collate a suite of hydrological signatures to locate and quantify the impacts of reservoirs on the flow regime across GB and infer upstream reservoir operations. We find that abstractions from reservoirs induce deficits in the water balance, and that pre-defined flow releases reduce variability in the downstream flow duration curve. Second, we use this understanding to develop a set of simple operating rules, designed to simulate flow downstream of water supply reservoirs. Our operating rules significantly increase model performance in a large sample of reservoir-impacted catchments with only two calibrated parameters. Third, we evaluate the effectiveness of additional catchment storage in mitigating the impacts of climate change on the flow regime. We find that only very large storage solutions can protect the baseline flow regime under a worst case emissions scenario. Finally, we discuss several overarching questions and future research opportunities that will be important for advancing our understanding of the large-scale interactions between reservoirs and river flow.

Date of Award	1 Oct 2024
Original language	English
Awarding Institution	University of Bristol
Sponsors	Wessex Water Ltd.
Supervisor	Gemma Coxon (Supervisor), Francesca Pianosi (Supervisor), Michael Bliss Singer (Supervisor) & Christopher Hutton (Supervisor)