Geothermal power plants are designed for optimal utilization of geothermal resource. However, geothermal fields typically undergo significant changes in resource characteristics such as pressure, temperature and steam quality over their life span. With appropriate reservoir modelling it is possible to predict the future resource characteristics of a geothermal field to a reasonable degree of accuracy. We propose a new adaptive design approach that would allow geothermal power plants to take into account the change of resource characteristics that occur over a 30-40 years time horizon based on the results of reservoir modelling. Currently, it is difficult and expensive to modify or renovate an existing plant due to space constraints, piping arrangements, transportation of machinery etc. The adaptive design approach would allow cost effective modifications in operation and equipment to adjust to changes in resource characteristics in the future. A simple model for a typical combined cycle geothermal power plant is considered as a test case for the adaptive design approach. Simulation is carried out using changes in both wellhead specific enthalpy and mass flow rate. There are four case studies presented in this paper that analysed various possible options of the hypothetical power plant depending on the changes in resource characteristics. Taking into account the results of the simulation, alternative plant designs are presented and improvements in performance are discussed. Although, the initial investment cost might go up as a consequence of adaptive design, over the life span of the plant the total benefit may be greater.