Hydraulic Modelling of Dynamics in Regulated Rivers

Sammanfattning: The Nordic countries hold a significant portion of the European hydropower production. One advantage of hydropower is its ability to store water in reservoirs in times when the energy demand is low.  The readjustment of energy production to renewable energy sources, as required by the Paris agreement, like wind power and solar power is likely going to change the role of Nordic hydropower production. Wind power and solar power are both dependent on the current weather conditions, in times when the weather is not favourable, hydropower can be used to stabilize the electricity grid. Since weather can change rapidly so will the discharge from the hydropower plants, causing hydropeaking events. Hydropeaking rapidly changes the flow conditions in proximity to the power plant. Such changes can be detrimental to the downstream habitats in and along the river.  The study reach in this work is the bypass reach in Stornorrfors in the Ume River. The open-source hydrodynamic solver Delft3D is used to numerically model the flow in the study reach. To validate the simulations water level measurements have been used.   The aim of the thesis is to investigate inherent damping properties in the river reach that can be used to mitigate the influence of hydropeaking scenarios. The influence of parameters such as upstream closing time, manning number distribution and hydropeaking frequency have been investigated.  It is shown that the closing time drastically affects the dynamics of the wetted area. The water surface elevation exhibits a hysteresis like behaviour. Inherent damping increases with the downstream coordinate. The frequency of the flow changes affects the areas upstream more than downstream. As a result, potential habitats in the downstream parts of the reach could become more stable if more frequent flow changes occur.