It is essential to make the best use of water resources management to create a good plan and development strategy. As such, water is a important source for a diversity of users such as irrigation, industrial manufacturers, and residential clients. Therefore, this study was conducted to determine the appropriate value of the discharge coefficient (C_d) for the selected outlet calibration. In this connection, six watercourses in which 3 Adjustable Proportionate Module (APM) and 3 Open Flume (OF) of Rahuki distributary were selected. The actual discharge was determined by using Cutthroat Flume and Current meter, and the empirical formula was used to determine the theoretical discharge, then the C_d values (minimum, maximum and average) for both types of the selected outlets were computed the calibration purpose. The rating/calibrated curves were developed for all chosen watercourses on the basis of computed C_d values. These calibrated, stage vs discharge curves can be used to govern the discharge of nominated watercourses. Using established empirical formulas, the flow rate of the selected water cources can be determined with confidence. The results suggested that the APM module generates higher C_d value than the OF module. Therefore, it is recommended to use the APM module in the field to increase accuracy.