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. The purpose of this study is to obtain an optimised surge tank configuration to reduce the cost of a hydropower plant in the future. Two methods were used for determining the optimum tank form: characteristic and finite difference methods (for the rigid and elastic method/approach). In addition, frictional losses and velocity loads inside the pipes and surge tanks were examined for different surge tank configurations in this study. In this paper, economically optimised surge tanks used for hydroelectric power plants were investigated. For this purpose, four basic surge-tank systems were numerically investigated. A 2 inclined straight V-type surge tank was found to be the most optimum configuration. Both rigid and elastic water column calculation methods were used for this study. Following this approach, an experimental model of a hydroelectric power plant with an optimised surge tank was created based on the model. This experimental model and prototype were numerically investigated. Finally, the results were compared and were found to be in agreement. (C) 2013 Elsevier Ltd. All rights reserved.