The most common reasons to dam failure is a combination of high water flows and technical problems with spillway gates, caused by bad condition and deficient maintenance. Depending on the type of plant and the dam flow class, the outcomes for the society may differ considerably.

The purpose of this study is to investigate the spillway gates on plants located in the chosen river system, inform about potential problems and what improvements that can be made on gates. This have been done by evaluating the condition of several gates and their spillway capacity and evaluate what can be done to increase dam safety.

In order to develop a model for this, the thesis project started with a literature study, to see what RIDAS recommend and what intention it has on high dam safety. Interviews were made with experts within Fortum, in order to get a picture of what outcome they want of the thesis work. Interviews and field tests have been carried out with Bilfinger, in order to make an understanding of how the gates are maintained.

Using information from interviews and data collection within Fortum, recommendations and improvements have been suggested to Fortum in order to maintain high dam safety.

The results showed that there are less spillway gates on plants in flow class I, than there are in class II and it’s a relation between the number of spillway gates and backup systems that can be applied at the plants. The plants that have more gates can be equipped with more backup systems, even if the gates are of the same type at both flow classes. Plants in flow class I have less gates and lower access for backup system, even if a dam break in class I have larger effect on society. Plants in flow class I and II should be equipped with two backup system independently of each other to form redundancy. It can be enough with two backup systems that can be applied to the same gate to form redundancy. There are plants found in the study that do not meet the redundancy requirements.