Assessment Process for Evaluating Functional Environmental Performance of Rivers Regulated for Hydropower Operation

Assessment Process for Evaluating Functional Environmental Performance of Rivers Regulated for Hydropower Operation

Environmental concerns associated with rivers regulated for hydropower operations are generally addressed by providing flows to benefit a few static within-channel features of a river, such as providing minimum flows, rather than simultaneously considering multiple competing objectives, which can range from provision of suitable instream habitat conditions to the periodic connection of rivers with floodplains.  As part of a U.S. Department of Energy program to develop tools that can be used to assist with operational planning  for hydropower facilities, we developed a framework for assessing the degree to which desired environmental objectives for downstream ecosystems can be achieved by water releases.  The framework will be one component of an integrated optimization system for reservoir operational planning that simultaneously considers both environmental and power needs based on projected inflow and storage.  Under this framework, users (e.g., environmental managers) apply available scientific information to identify specific environmental objectives to be met by discharges from a hydropower facility (including period of the year and time of the day, duration, and frequency with which environmental objectives should be met) and then define functional relationships among the resulting downstream conditions (e.g., discharge, water temperature) in designated reaches of the river and the desired environmental objectives.  Operational constraints, such as minimum and maximum discharges, can also be incorporated into the assessment process.  The degree to which a flow regime would meet environmental objectives is quantified by an overall environmental performance score (index of river functionality), which is based upon the functional relationships defined, the required frequency for each objective, the history of meeting each objective during previous time periods, and the suitability of current hydrologic conditions for accomplishing each objective.  Natural resource managers can prioritize management objectives by adjusting the required frequencies of occurrence for each environmental objective, which in turn can help resolve potential conflicts among the various environmental needs.  The framework is intended to assist in objectively evaluating environmental performance of existing, planned, or alternative hydropower operations and is designed to allow it to be applied to different regulated systems.  Comprehensive methods for meeting and prioritizing environmental functionalities in the optimization tool will aid in policy development and sustainable water management.  

 Argonne National Laboratory’s work was supported by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Wind and Water Technology Program, under contract DE-AC02-06CH11357.