A multitude of environmental flow assessment approaches have been used in different management contexts, at various spatial scales, and within diverse socio-ecological settings. The tools and methods used in EFAs have expanded rapidly in the past 30 years and are described in several published review papers (Tharme 2003, Hatfield et al. 2003, Annear et al. 2004, Acremen and Dunbar 2004). Here we cite some of the most common approaches, or frameworks, for conducting environmental flow assessments.

Instream Flow Incremental Methodology (IFIM)

Developed by FORT researchers, IFIM is a decision-support system designed to help managers examine the benefits or consequences of water management alternatives. The Physical Habitat Simulation System, PHABSIM, is a hydraulic habitat simulation model utilized in the IFIM framework to quantify available physical habitat of aquatic species as a function stream discharge. 

Ecological Limits of Hydrologic Alteration (ELOHA)

The ELOHA framework was developed by an interdisciplinary group of river scientists and combines hydrologic, biological, social and geomorphic information to help managers integrate ecological flows into water management activities. It is designed for developing environmental flow standards at the regional scale.

Range of Variability Approach (RVA)

The RVA is a method for setting initial streamflow thresholds this is based on the natural hydrologic variability of a system. The approach was developed by Brian Richter and colleagues with the Nature Conservancy and relies upon the calculation of Indicators of Hydrologic Alteration (IHA), flow statistics that describe the magnitude, duration, timing, and rate of change of flow from daily time series, which used to assess the hydrologic effects of an existing or proposed management regime.

Downstream Response to Imposed Flow Transformations (DRIFT)

DRIFT is a holistic EFA framework developed by scientists in South Africa and Australia. It is a structured process for combining data and knowledge from multiple disciplines, including hydrology, ecology, and economics, to produce flow‐related scenarios for water managers to consider.

Redwater River. USGS photo.
Redwater River. USGS photo.