Cascade stilling basins system, consisting of a series of falls and stilling basins, may be a good alternative energy dissipation system for high head dams. Traditional design of such a system is based on a trial and error procedure by which the number and the size of falls and stilling basins are determined. Optimization tools can help find the best economic design while keeping hydraulic and topographic considerations satisfied. This paper uses genetic algorithms (GAs) for optimum design of cascade stilling basins in which decision variables are the height of falls and length of stilling basins. The objective is to minimize the construction costs. The presented model is used to design the energy dissipation system of Tehri dam in India as a case study. Comparison of the proposed method with a model not utilizing an optimization tool reveals that GAs lead to significant saving in construction cost.