Environmental Flow - Methods, Tools, and Models

Methods, Tools, and Models

More than 200 methods are used worldwide to prescribe river flows needed to maintain healthy rivers. However, very few of these are comprehensive and holistic, accounting for seasonal and inter-annual flow variation needed to support the whole range of ecosystem services that healthy rivers provide. Such comprehensive approaches include DRIFT (Downstream Response to Imposed Flow Transformation), BBM (Building Block Methodology), and the "Savannah Process" for site-specific environmental flow assessment, and ELOHA (Ecological Limits of Hydrologic Alteration) for regional-scale water resource planning and management. The "best" method, or more likely, methods, for a given situation depends on the amount of resources and data available, the most important issues, and the level of certainty required. To facilitate environmental flow prescriptions, a number of computer models and tools have been developed by groups such as the USACE's Hydrologic Engineering Center to capture flow requirements defined in a workshop setting (e.g., HEC-RPT) or to evaluate the implications of environmental flow implementation (e.g., HEC-ResSim, HEC-RAS, and HEC-EFM).