This book presents instructions, standards, and procedures for the selection, design, and use of structures, which measure or regulate the flow rate in open channels. It is intended to serve as a guide to good practice for engineers concerned with the design and operation of such structures. It is hoped that the book will serve this purpose in three ways: (i) by giving the hydraulic theory related to discharge measurement structures; (ii) by indicating the major demands made upon the structures; and (iii) by providing specialized and technical knowledge on the more cornrnon types of structures now being used throughout the world. The text is addressed to the designer and operator of the structure and gives the hydraulic dimensions of the structure. Construction methods are only given if they influence the hydraulic performance of the structure. Otherwise, no methods of construction nor specifications of materials are given since they vary greatly from country to country and their selection will be influenced by such factors as the availability of materials, the quality of workmanship, and by the number of structures that need to be built.