Power Generation is essentially required for improving and maintaining the infrastructure of the overall development of a nation. It is the tool to forge the economic growth of any country. Ghazi-Barotha is a runoff river hydropower project located at downstream of Tarbela and on left bank of Indus River. The project was studied to feasibility level in 1990, implementation was started in 1995 and now in operation since 2003. The project is being operated with full capacity during peak hours but be influenced by Kalabagh reservoir during August to March. The reduction in head to some extent reduces the power and energy. This research work had analyzed and evaluated the extent of reduced power and energy considering 20 year flow data. Finally conclusion and recommendations are drawn for researchers and planners. The author appreciate the efforts of Barthlemy Chaton and his team in facilitating and highly acknowledge publishing of it by VDM Publishing House Ltd., for technical knowledge sharing internationally.