This document specifies the radiation transmission method for measurement of density of the water-sediment mixture, suspended or deposited, in water bodies such as streams, canals, harbour basins, dams and reservoirs. The method is based on principles of transmission of X or Gamma rays. This document covers brief description of the operating principle of the method and details of some of the instruments used. This document applies to the measurement of water-sediment mixture density in water bodies using radiation transmission method, particularly gamma and X-ray transmission method. The working principles, applications, advantages and associated instruments are elaborated in this document.