A New Flow Regime, Ethics, and Beavers: A 30-year story of Eastern Sierra Stream Restoration and An Uncertain Future
David Vance
Geosyntec Consultants
Atlanta, Georgia
Authors: David Vance, Robert Dunn, Mark Hanna, Ph.D., Dave Martin, Ph.D., Austin Orr, Judd Goodman
How will a stream and its biology respond to a change in flow regime? Will the new flow regime achieve long-term restoration objectives for over 15 miles of high and low gradient streams? Two main Eastern Sierra Nevada stream systems (Rush and Lee Vining Creeks) have been under-mandated restoration for over three decades with substantial progress in ecosystem recovery. With ecosystem recovery having reached an asymptote, a shift in flow regime was proposed by a state-appointed “stream scientist, a non-governmental organization, and supported by a closely aligned state regulator.
With limited geomorphic justifications and proofs for the new flow regime other than broad biologically centric hypotheses and assumptions. The new flow regime increased overall peak snowmelt bench and flood durations and magnitudes which led to questions of geomorphic stability (by the authors) for both systems. Therefore, we sought to quantify the geomorphic response of the stream systems to the new flow regime and resulting consequences. Our team developed a novel long-term bed degradation analysis to evaluate the average long-term bed degradation for existing and proposed flow regimes, using recent and historical geomorphic and hydrologic data to quantify the difference in bed degradation potential between the two flow regimes approximately 30 years into the future at the reach-scale with and without the effects of climate change under four scenarios.
The state regulator and state-appointed stream scientists maintained their advocation for the new flow regime even though it was not supported by this study, historical watershed conditions, or available hydrology. Given the uncertainty of the multidecade drought in the west and future watershed hydrology, the attention is now on a family of beavers who is recolonizing within the stream systems. Their presence has coincided with selective aggradation, avulsion, and selective expansion of riparian habitat following the 2017 runoff year. It’s the authors’ hope that the beaver’s habitat expansion will provide a mitigating factor against the degradation quantified in this study and be the unlikely heroes of this ecosystem recovery story.
About David Vance
David is passionate for rivers, their processes, and the ecosystems they support. He utilizes his specialization in geology and applied fluvial geomorphology to provide technical analyses along a spectrum spanning problem understanding, research, restoration design, policy development, water management, and conservation. David’s contributions have spanned numerous geographies and complex ecosystems where man-made influences typically increase that complexity and stimulate his passion to develop solutions that balance the river ecosystem needs with societal ones. David is grateful to call this profession his home for an amazing 18 years, and looks forward to all the great people, projects, and landscapes that will span the coming decades.