Side weirs have been used extensively for water-level control in irrigation and drainage canal systems, as a means of diverting excess water into relief channels for flood protection works, and as storm overflows from urban sewage systems. In this study, flow over side weir in triangular channel is reported. Theoretical model is obtained from energy principles and is solved by a finite difference method. The results are presented in diagrammatic form for practical use. The study covers both sub- and supercritical flow regimes. Derived expressions for the water surface profiles for these regimes are compared with 'experimental results.