IFIM and the Balancing Act for Water

The water flowing through our streams and rivers has many uses-and many demands on it. But how much water do we need for a particular use? And if we remove that water, what happens to the stream itself and the life within it?

In the early 1980's, scientists at the U.S. Geological Survey (USGS) Fort Collins Science Center (FORT) set out to answer those questions and developed the Instream Flow Incremental Methodology (IFIM). Now in use worldwide, IFIM is a decision-support methodology that provides a comprehensive technical framework for addressing the streamflow needs of fish and other living organisms within a river system. Over the years, field-testing and other refinements have led to many improvements in the original model, such as expansion to include long-term effects, and incorporation of the institutional environment as a major component of IFIM.

Instream flow requirements are the amount of water necessary to sustain instream values at acceptable levels. Instream values are the uses made of the water within the stream. These include such traditional uses as navigation, hydroelectric generation, and wastewater assimilation. Fish and wildlife needs, river-based recreation, and fresh water for estuaries are additional uses that require flowing rivers.

While an ideal management plan would provide for enough streamflow to sustain all of these instream values, the most desirable streamflow alternative will satisfy several uses at once. But determining the instream flow requirements for each of these uses is complex. Predicting their aggregate impacts for planning and management purposes is even more complicated. A tool was needed that illuminated conflicting and complementary water uses, considered and evaluated each user's needs, and was understandable, acceptable, and usable by a broad clientele.

With this general charter, IFIM was developed over time into a river network and decision analysis tool that incorporates fish habitat, recreational, and vegetation (e.g., cottonwoods and willows) responses to alternative water management schemes. Information is presented as a time series of flow and habitat at selected points within a river system for various existing and proposed water operation alternatives. With this methodology, water project developers and resource managers can evaluate many more alternatives than was previously possible.

Appropriate uses and applications of the IFIM include, for example:

1. the evaluation of future water use patterns included in area-wide planning studies,

2. the licensing of water rights under state law,

3. impact analysis of diversions of water or of channel alterations, and

4. the negotiation of flow regimes for managed rivers and streams.

Efforts to improve and expand the IFIM toolbox continue today. During the summer of 2003, the USGS and the Colorado State University Department of Fishery and Wildlife Biology sponsored a workshop in Fort Collins that brought together over 80 international scientists and IFIM users to promote discussion of the science, application, and improvement of the methodology. Scientists from the U.S. and seven other countries presented gave presentations on IFIM and other methods of instream flow determination, physical habitat simulation, fish population modeling techniques, law and policy pertaining to instream flow, space and scale considerations, and advanced modeling of instream flow issues.

Also at FORT: Instream Flow Incremental Methodology (IFIM) Short Course on the Instream Flow Incremental Methodology IFIM Stream Habitat Analysis Using the Instream Flow Incremental Methodology

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For more information, contact:

Terry Waddle