Waterhammer is an unsteady hydraulic problem which is commonly found in the penstocks of hydropower plants, water distribution networks and pipeline systems. Due to either a malfunction of the system or inadequate operation conditions, pipeline may collapse or burst. In this paper protective measures against waterhammer problems in the penstocks of small hydropower plants are investigated. In the study, a computer program employing method of characteristics is used to solve nonlinear partial differential equations of transient flow. In a case study, waterhammer responses of a river hydropower plant under instant load rejection without a protective measure and with three different protective measures are analyzed. It is observed that, by means of protective measures waterhammer pressures in the penstock are substantially diminished, and it is shown that these measures are effective and practical.