Sudden flow changes in confined pipe systems generate transient flow (waterhammer) conditions accompanied with very high or sometimes very low pressures traveling back and forth in the system. Depending on the magnitude of those pressures, pipe collapse or pipe bursting may take place at the weakest points of the system, resulting in costly damages as well as loss of human lives in some cases. In general, it may be encountered in the penstocks of hydropower plants, water transmission lines and water networks, etc. It is essential that the safe operation guidelines of the hydropower plants be defined accurately, in advance. To achieve that, detailed numerical simulations should be done with reliable software. In some cases, even physical modeling may also be necessary. In the present study, waterhammer problems in the penstocks of Yahyali Wind-Hydro Hybrid Plant are investigated (the construction of the plant has not started yet). Time-dependent flow conditions in the penstocks are simulated by the help of computer software. It solves nonlinear differential equations by using the method of characteristics that uses the principles of finite difference method. Firstly, hydraulic transients for various operational cases are investigated using some scenarios. Then, a surge tank, protective device, for waterhammer, is added to the system, and for the same operational cases, hydraulic transients are studied again.