A theoretical analysis based on the energy principle for discharge over side weirs was presented, and its application was demonstrated using a numerical approach. The decrease in water surface elevation in lateral direction was considered. The inclination of the deflected flow over the weir was also taken into account. The side weir was divided into elementary strips to develop generalized equations for discharge and surface profile. Dimensionless parameters were used, and equations were solved using numerical methods and computer techniques. Discharges and water surface elevations that were computed were compared with the experimental results. Equations that were developed were also used to obtain hydraulic characteristics of storm water overflows as a practical application.