Losses of water along irrigation water courses contribute to low overall irrigation efficiencies in less developed countries. this thesis investigates discharge efficiencies of submerged gates for controlling flow in irrigation watercourses. two types of gates suitable for use as both control and measurement structures were designed in Pakistan by the Colorado State University water management research group. both were made to fit into a channel at a 45 degree inclination, so that gravity would assist in sealing against leakage. hydraulic data was collected under free flow and submerged flow conditions for test gates with both circular and rectangular openings. the method of submerged flow analysis reported by villemonte was used in developing the rating curves for the gates. these ratings were then compared with those obtained for vertical weirs in order to observe the effect of the 45 degree inclination of the test gates. the conclusions, mainly expressed mathematically, address questions of when and how free-flow weir equations should be applied. makes recommendations for further research.