Evolution of a value-based process for protecting instream flow

The value-based process (Jackson et al., 1989) for protecting instream flow s has been used successfully by the U.S. Bureau of Land Management for more than 10 years. Over the last decade, the methodology has evolved significa ntly as it has been applied to increasingly complete river systems. In the original process, which was somewhat linear, hydrologic characterization wa s an early step and development of a flow-protection strategy was a late st ep, and the focus was primarily on resource values and their flow dependenc y. The procedure has evolved into a trichotomous process in which legal/ins titutional analyses and hydrologic characterization occur concurrently with and frequently overshadow the assessment of flow-dependent resources. For complex river systems, the legal/institutional analysis usually includes hi storical analysis of water management in the basin, a geographical descript ion of projects and facilities controlling streamflows, a review of operati ng principles and other institutional constraints, development of potential flow scenarios, and identification of other management opportunities, Simi larly, hydrologic characterization may include detailed ground-water and ge omorphological investigations to support assessment of flow-dependent resou rces, and extensive historical analysis to support the legal/institutional framework. Thus, whereas the resource assessment identifies flows needed to support resource values, the legal/institutional analysis and hydrologic c haracterization identify both the physical and institutional limits that wi ll influence management decisions.