Pressure fluctuation is one of the important factors in causing hydraulic destruction phenomena such as cavitation. In this book, pressure fluctuations, its process and cavitation phenomenon in area of emergency gate slot have been investigated and analyzed by two hydraulic models. These experiments were conducted at the different openings gate and in different heads in region of gate slot. The necessity of this is study lies in the numerous damages inflicted so far on such parts of hydraulic structures as the bottom outlet gates by pressure fluctuations and, as a result, cavitation phenomenon, causing strong problems and, at times, a drastic failure. This book can be used by MS and PhD students and engineers. I hope this research to be able to add a drop to the ocean of knowledge. Amirfarid Hashemi