The contents of this chapter can be divided into (1) solving problems in natural or irregular channels and (2) structures used to control and measure channel ¢ows, including the design of transitions. The subject of ¢ow in natural channels will be dealt with ’rst and thereafter controls and other topics will be covered as they are used in both man-made and natural channels. Currently the program HEC-2 “Water Surface Pro’les” developed by the U.S. Army Corps of Engineers, Hydrologic Engineering Center, is quite widely used in practice in solving open channel ¢ows in natural channel. Therefore, after describing the principles and techniques that are applicable to irregular channels, the use of the HEC2 software package will be dealt with brie¢y assuming that it is available to you, the reader, along with its manual describing the input data needed.