A Tale of Two Rivers: Evaluating Environmental Performance of the Regulated Green and Gunnison Rivers using the Index of River Functionality IRF Tool
Evaluating environmental performance of a regulated river is a critical prerequisite for managing downstream effects of reservoir operations. However, it is not an easy task considering units of measure vary among environmental objectives and that objectives are occasionally in conflict with each other. Currently the issue is avoided by prescribing minimum or maximum flows (and in some cases restrictions on ramping rates and water temperatures) for managing downstream environmental effects. However, recent studies have stressed that these criteria alone are inadequate for maintaining long term sustainability of downstream ecological resources. Moreover from a management perspective, information confirming that thresholds have been met (or violated) is ineffective in gauging the ultimate effect on specific ecological resources.
To this end, the Environmental Science Division at Argonne National Laboratory has been developing an environmental performance evaluation and decision making tool (Index of River Functionality or IRF tool) that can be used to explicitly consider and optimize environmental performance during hydropower operations planning. Integration of the IRF tool with other reservoir operation planning tools will assist in developing dynamic flow-regimes that are co-optimized for environmental and economic objectives based on operational constraints and in light of predicted water availability. The IRF tool provides the ability to define environmental objectives for instream and riparian areas based on the requirements of site-specific resources. The IRF tool then calculates an index (IRF score) as an overall indicator of the relative degree to which environmental objectives are accomplished.
Distinct objectives can be defined for multiple locations within a basin, thereby providing a means to accomplish evaluations of overall environmental performance for basins that have multiple regulated facilities. This presentation will highlight some of the complications in development of an environmental performance evaluation tool and explain features of the IRF tool and its application in management of regulated rivers. Examples of results from the IRF tool will be presented depicting environmental performance from hydropower operation over time for two major tributaries of the Upper Colorado River (the Green and Gunnison Rivers) using long term (>25y) stream-flow data from USGS gaging stations.