This thesis aimed at studying hydraulic behavior of flow through the outlet works of Nong Kho Reservoir. This investigation was studied using a hydraulic model at the Hydraulic and Coastal Model Laboratory, Department of Water Resources Engineering, Chulalongkorn University. The hydraulic model used in this study consisted of a reservoir model, an intake model, a 3-pipe line system, control valves and downstream weirs. The model was similitude from the physical characteristics and operating conditions of Nong Kho Reservoir. The range of reservoir water level was 6 - 68.5 cm in the model which was corresponding 58.3 to 66.8 m.MSL in the prototype, the operation of the outlet works in case of flow in 1 pipe, 2 pipes, 3 pipes and the valve opening at 100%, 75.6%, 50.2% and 26.3%. Resulting from 252 cases of experiments, the hydraulics of flow through the outlet works were concluded as followed. The losses of energy head consisted of friction loss, which was major loss, entrance loss and valve loss. The discharge equations were proposed as Q = KH[subscript T][superscript 5.0] and Q = aA[subscript r][superscript n]H[subscript T][superscript 0.5]. Also the occurrence of vortex flow was related to submergence with the Froude Number. Applying the study results to the case of Nong Kho Reservoir the following model scales were used as L[subscript r] = 13.64 for length, T[subscritp r] = 3.69 for time and Q[subscript r] = 686.66 for discharge. The discharge through the outlet works became Q = aA[subscript r][superscript n] (H - 57.05)[superscript 0.5]. The occurrence of vortex flow was analyzed from the S/d ratio and then convert tothe reservoir water level of Nong Kho Reservoir for all 3 types of vortex flow i.e. dimple, vortex strong, and air-entraining. Based on the study results, a guideline was proposed for the planning of the researvoir release and preventing the vortex flow situation for the case of Nong Kho Reservoir.