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Three-Level Hierarchy of Environmental Flow Methods

The Three-Level Hierarchy for developing environmental flow methods spans relatively simple desktop estimates of flow needs to a highly sophisticated program of research and modeling to refine environmental flow targets. Each level builds information, capacity and support for subsequent levels of sophistication as deemed necessary. In this way, proactive, practical implementation can begin immediately upon completion of the level of assessment most suitable to the resources available to a particular water body or jurisdiction. 

Three key characteristics define this framework:

  1. Funds for research and modeling to support flow assessment and implementation are invested strategically to address the most important issues and reduce the most vexing uncertainties; methods are matched to the level of certainty required and the level of funding available;
  2. The framework is iterative such that higher levels are deployed to the extent they are necessary and information generated at one level can provide the foundation for, and identify the need for, higher levels and; and
  3. Processes for flow assessment and flow implementation are intertwined; many of the key characteristics of the assessment process are designed to lay the foundation for flow implementation.

All three levels of flow assessment are considered holistic because each explicitly addresses a range of flow levels and events and a range of riverine resources, processes, and values. The three levels are not mutually exclusive within an implementation process. Level 1 may be implemented widely across a large region, with Levels 2 and 3 being applied in high-priority sub-basins.

Level 1: Comprehensive hydrologic desktop methods

Level 2: Expert Panel Assessment

Level 3: Examining Tradeoffs and Predicting Results of Operational Changes