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Functional Flows in Modified Riverscapes: Hydrographs, Habitats and Opportunities Sarah Yarnell, Geoffrey Petts, Jack Schmidt, Alison Whipple, Erin Beller, Clifford Dahm, Peter Goodwin, Joshua Viers BioScience 65(10): 963-972 Environmental Flow Methods Natural Flow Regime Paradigm Flow Regime Magnitude Frequency Duration Timing Rate of Change Water Quality Energy Sources Physical Habitat Biotic Interactions (Poff et al. 1997) Ecological Integrity • Set Percentage of Flow (Richter et al. 2012) • Downscaled Flow Regime (Hall et al. 2011) • Regional IFIM (Denslinger et al. 1998) • ELOHA (Poff et al. 2010) • Designer Flows (Acreman et al. 2014) Mimicking natural flows alone does not guarantee restoration of functional river systems Hydrogeomorphic Dynamics When temporally variable flow regimes interact with spatially variable geomorphology Complex river forms and patterns High functionality High biodiversity Functional Flows Approach Focus on hydrograph flow components that: – Support natural disturbances – Promote physical dynamics – Drive ecosystem functions – Support high biodiversity Consideration of geomorphic setting and channel-floodplain dynamics (Yarnell et al. 2010) Functional Flows Approach • “Functional Flow”* = hydrograph component that provides a distinct geomorphic, ecologic or biogeochemical function *(Escobar-Arias & Pasternack 2010) • Reflective of natural patterns that occur in space & time Wet Season Initiation Flow First Flushing Flow • prepares riverscape by: – clearing channel bed of organics, fine sediment – reconnecting channelriparian-floodplain habitats – reactivating exchanges with hyporheic zone • kick-starts ecological processes such as nutrient cycling • provides key ecological cues for native species to migrate upstream Cosumnes River, CA Delta Smelt Peak Magnitude Flow • Primary geomorphic disturbance • Resets natural processes such as succession • Redistributes large volumes of sediment • Prevents vegetation encroachment • Reduces extent of exotic species not adapted to disturbance regime • Most effective when given SPACE – levee setbacks, levee breaches to floodplain, tributary junctions Cosumnes River, CA levee breaches Spring Recession Flow High to Low Flow Transition • Redistributes and sorts sediment mobilized by high flows • Limits riparian vegetation encroachment • provides distinct annual cues for native species to reproduce and outmigrate • Extended floodplain inundation Sacramento River, CA (Jeffres et al 2008) Dry Season Low Flow • Driver of seasonal river ecosystems • Dictates extent and quality of physical instream habitat • Creates ecological niche partitioning with native species utilizing refugia • More effective when geormorphic diversity provides varied refugia • Reduces extent of exotic species not adapted to limiting conditions Santa Clara River, CA Interannual Flow Variability Magnitude, timing and duration of specific flow events vary: within their associated season depending on regional climatic conditions, and between years depending on global climate conditions Supports diversity in geomorphic habitat and subsequent diversity in native species over the long-term Interannual Flow Variability Functionality is maximized when both variability in time and space is considered • Flows alone can achieve functional benefits (e.g. migration flows) • Geomorphic restoration can achieve functional benefits (e.g. levee setbacks) • Functional flows that account for geomorphic context can restore ecological integrity and functionality Guiding Principles for Management • Maintain hydrologic connections to the riverscape • Retain flow transitions between seasons • Maintain higher baseflows in wet seasons and lower baseflows in dry seasons • Scale flow regimes to interannual climate variability • Retain a flood at full magnitude and duration while removing others • Consider seasonality of flows – greater abstraction or water delivery during wetter months Functionality in Practice • Develop a standard hydrograph for a hydrologic basin type (Lane et al. 2016, Stein et al. 2016) • Magnitude, duration set by statistical variability of unimpaired system • Timing set by aquatic species needs • Flow targets set based on water year type Example standard hydrograph for a hydrologic basin type with key functional flows required for a particular group of fish species J. Lund, S. Sandoval, B.Gray, P. Moyle, R. Frank, B. Lane, S. Yarnell, E. Stein, H. Dahlke, T. Grantham, R. Lusardi, N. Santos, A. Bell, A. Willis, SWRCB Acknowledgements • Delta Science Program, California • UC Davis Center for Aquatic Biology and Aquaculture • UC Davis Center for Watershed Sciences Staff Yarnell et al. 2015 BioScience 65(10): 963-972