Download Yarnell et al. 2010

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