Load changes occurring in water turbines often result in pressure waves at hydroelectric power plants. Load reduction or the sudden closure of the turbines causes high pressures to build on the penstock similarly to a water hammer. This pressure can cause damage to components of the power plant. Surge tanks are used to prevent these problems. For two power plants operating at similar flow rates, diameters and lengths of the penstocks, and diameters and lengths of the tunnels, the surge tank with a smaller volume is the most economically viable.