I) Storage reservoir: It is the basic requirement of hydroelectric plant. Its purpose is to store water which may be utilized to run the prime mover to produce electrical power. A reservoir stores during rainy season and supplies the same during the dry season. It can be either natural or artificial.
II) Surge tank : A surge tank is the small reservoir or tank. It is open at the top. It is installed near valve house of turbine. It avoids water hammer effect when load on turbine reduces. (It stores immediately the rejected water). It avoids cavity effect when load on turbine increases as it supplies the water immediately.
III) Spillways: Acts as a safety valve for a dam. It discharges excess water when head of water increases above predetermine maximum level, at the time of heavy rainfall & during floods etc. In this way spill way avoids damage of dam due to excess pressure of water.
IV) Trash rack: The purpose of providing trash rack is to prevent entry of debris which might damage the turbine runners or choking of nozzles of impulse turbines. It is made of steel bars and is placed across the intake.