The build-up of this thesis has been a long effort. During the course of it, a large number of friends and colleagues have supported and encouraged me and given me strength. I wish to address my gratitude to all of them for their patience and kindness. They have helped me to remember that life is much more than just flowing water.
In addition, I wish to thank the following Finnish foundations for their financial support: the RES Foundation (Promotional Foundation of Civil Engineering Field), the OLVI Foundation, Maa- ja Vesitekniikan Tuki r.y. (the Land and Water Technology Foundation), the Tauno Tönning Foundation, the Ympäristöinstituutti Foundation (Environmental Institute Foundation), the Thule Institute, and the Academy of Finland, the Research Programme on Ecological Construction.
I owe my deepest thanks to Professor Jussi Hooli of the Water Resources and Environmental Engineering Laboratory for his never-ending trust in me. Special thanks are also due to Tech.Lic. Lauri Eskelinen for his valuable advice. In addition, Phil.Lic. Anne Laine deserves my deepest gratitude for her friendship and valuable assistance with the mental life of fish. My humble thanks are due to the whole staff of the Water Resources and Environmental Engineering Laboratory for stimulating working atmosphere. Especially, the inspiring discussions with Dr. Jyrki Röpelinen and M.Sc. Jarmo Sallanko have been of special value. In the practical accomplishment of the studies, the assistance of Technicians Antti Aitto-oja and Viljo Peltoniemi has been indispensable. I also want to express my thanks to Cindy Ruuskanen for revising the language.
The kindness and advice of Professors N. Rajaratnam of the University of Alberta and Chris Katopodis of the Freshwater Institute during my six-month visit in Edmonton, Canada are also worth mentioning, as well as the far reaching assistance of Technician Sheldon Lovell of the T. Blench Hydraulic Laboratory of the University of Alberta.
Finally, I wish to address my love and gratitude to my family for their support: my husband, who has also helped me to carry out some of the studies, and my daughters Riikka and Siru.
Oulu, April 2001 Riitta Kamula