Resizing a River: Using Adaptive Management to Develop a Downscaled Flow Regime in a Regulated River

Setting environmental flow regimes in regulated rivers is a challenging and uncertain task for water managers.  Two fundamental, yet conflicting, realities faced by those water managers are: 1) aquatic organisms are adapted to natural flow regimes, and, 2) it is impractical to deliver natural flow regimes in most regulated rivers.  To resolve this conflict it is becoming more common to provide a downscaled environmental flow regime for regulated rivers with the hope that delivery of downscaled seasonally varied flow releases that mimic natural flows will promote physical and biological processes to needed to create a functioning, but smaller, river ecosystem.  We developed and applied an experimental approach to “resize” the Bridge River, B.C.  Based on a predetermined water budget, a seasonally varied downscaled environmental flow regime was developed to meet priority physical and ecological process requirements.  A structured decision-making framework was developed to design the flow experiment, and then later was used to guide evaluation of monitoring results and refine future flow treatments as needed to select a long term environmental flow regime.   Our experiences provide a case study of how a rigorous adaptive management framework can be used to successfully reduce biological uncertainty, thwart controversy, and manage surprise to develop an effective downscaled environmental flow regime in a regulated river.