ABSTRACT Principles of sustainable development are inviting a change in the approach used for reservoir management. Instead of designing and planning new reservoirs, more emphasis will be placed on management of existing reservoirs. Reservoir storage reallocation and reassessment of reservoir operational rules are considered to be the two main problems to be addressed by reservoir research in the near future. Appropriate techniques for solving these two problems are necessary An attempt at developing a sound methodology for a reservoir reassessment has been presented here. A simulation approach, based on the four probability criteria, has been used in this context for storage analysis. Reservoir management strategies have been reassessed using an implicit stochastic optimization model. The methodology has been applied to Wonogiri Reservoir located in Central Java, Indonesia. Analysis of the storage capacity indicated that the current capacity is larger than that required for the irrigation of an area of 2...