TO MY LATE PARENTS, FAMILY AND FRIENDSii ACKNOWLEDGEMENTS I would never have been able to finish my dissertation without the guidance of my committee members, help from friends and support from my family members.First and foremost, my utmost gratitude goes to my advisor, Dr. Ranjith P.Udawatta, for awarding the assistantship for my research study and generously sharing his hard earned research data without which this dissertation would not have been a realization. I am also grateful for his dedicated guidance and support provided for this project to make it a completion. I cannot find words to thank him for constantly pushing and persuading me for an early start for publication and presentation of the research and also making me participate in many conferences and training workshops. His strong reviews and criticisms made my writing stronger and I am very much thankful for his patient and prompt corrections of my written work. I also wish to thank him for withstanding all the tough times I underwent in both professional and personal life.It is with deep pleasure I acknowledge the support and help of my co-adviser, Dr.Stephen H. Anderson had it not been for his constant monitoring and keeping me up to date on both of my course work and research requirements, the completion of this project would have possible. He gave his best suggestions whenever I was faced with dilemmas in both course work and research work and his long experience with students as a professor was an asset to me in getting the correct advice.I wish to express my deep appreciation to Dr. Claire Baffaut as this dissertation iii would not have been possible without her support as well. Her strong criticisms and reviews based on her knowledge and experience in hydrologic modeling immensely helped me to improve and sharpen both my research work and writings. Her interest in my work made her surpass as the capacity of a committee member in her contributions to this project.I also wish to sincerely thank Dr. Allen L. Thompson for agreeing to be my external committee member and also for all the support given to me in time and advice during the examinations, research work and publications. I am also grateful for the assistance provided to me by Dr. Verel Benson to help me out from the initial obstacles I faced in learning the model. My great appreciation goes to my friend Nakini Thushar Kanta Das for his invaluable help in MATLAB programming offered generously by spending his most invaluable time and energy.