Thesis defence in the University of Oulu

Doctoral Candidate

Master of Science (Tech) Faisal Bin Ashraf

Faculty and research unit

University of Oulu Graduate School, Faculty of Technology, Water, Energy and Environmental Engineering Research Unit

Field of study

Water Resources and Environmental Engineering

Date and time of the thesis defence

29.5.2020 12:00

Place of the thesis defence

Remote connection: https://oulu.zoom.us/j/64916397323

Topic of the dissertation

Changing river regimes: River regimes and energy demand interactions in Nordic rivers

Opponent

Associate Professor Miroslav Marence, Institute for Water Education, Delft, The Netherlands

Custos

Professor Bjørn Kløve, University of Oulu

River regimes and energy demand interactions in Nordic rivers

River regimes in Nordic rivers are changing, mainly due to climate change and river regulation. As renewables penetrate the power market, the conventional role of hydropower in energy markets is also changing. These factors are altering river flows in ways that are not fully understood. This thesis addressed these information inadequacies in the ecologically sensitive Nordic region.

To assess the relative effect of regulation practices and climate change, a spatio-temporal study of two adjacent rivers in Northern Europe, the Kemijoki (regulated) and Tornionjoki (pristine), with similar climate and catchment conditions, was performed. Degree of hydrologic alteration on Kemijoki was twice than at Tornionjoki, while regulation and climate change seemed to have similar degrees of effect on flow alteration in the Kemijoki (50% each). This was confirmed by analyzing data from Ounasjoki, a pristine tributary of the Kemijoki.

Short-term changes in Nordic rivers were quantified using discharge datasets from 150 sites with hourly time-step. The results revealed high levels of hydropeaking in Nordic rivers, with increases especially in recent few years. This indicates that expanding for renewable energy, increasing the need for load balancing in the energy market, may increase hydropeaking in Nordic rivers.

A method based on wavelet analysis was developed to characterize variability in hydrologic time series data in different periods. It was found that, in winter, sub-daily variations in some large regulated rivers were up to 20 times higher than in free-flowing rivers. For smaller regulated rivers with lower levels of regulation, the variation was highest in summer.

We have assessed the impact of intra-day power demand variation on regulated rivers flow and potential to comply with instant energy demand, by quantifying the impact of reservoir volume and hydropower capacity constraints using two new metrics, power market impact and system efficiency ratio. The metrics were tested for the Kemijoki, with defined thresholds based on the natural flow regime (Ounasjoki) and hourly energy price in Finland in 2017, to estimate the impact of regulation on hourly flow regime at Taivalkoski station. Annual flow regime impact in 2013, 2014, and 2015 was estimated to be 74%, 84% and 61%, respectively, while monthly impact varied from 27% to 100%.

 

Dissertation

Last updated: 27.5.2020