Efficient management of water in unregulated river systems is essential in meeting current and future needs of water users and the environment. As an integral part of the new water management process, volumetric conversions convert current area based licences into volume based licences. Hydrology modelling determines the Daily Extraction Limits for different flow conditions in each management rule proposed for meeting environmental objectives in the catchment. The case study is the Adelong Creek Catchment, an unregulated river catchment in southeastern New South Wales. Economic and hydrological modelling assesses the impacts of proposed extraction rules, designed to meet environmental flow objectives, on water availability in the catchment. A spreadsheet based optimisation model was developed to assess the impacts of different flow management rules on the regional agricultural economy. The suitability of this approach will be assessed for application to other unregulated stream catchments.