Hydraulic geometry describes the relations between stable channel characteristics and discharge and adjustments made by a stream in response to changes in river discharge and sediment load. This book introduces hydraulic geometry and discusses different theories and their applications in river engineering, thus providing a comprehensive summary for hydraulic engineers, as well as graduate students and researchers in fluvial geomorphology and hydraulic and environmental engineering. Topics covered include the basis of power form of hydraulic geometry relations, validity and stability of power relations, state and assumption of equilibrium, variability of exponents, variation of channel width and velocity, and the effect of stream size and river channel patterns.