unimpaired connectivity between active channel and floodplain eliminated connectivity between active...
TRANSCRIPT
Unimpaired connectivity
between active channel and floodplain
Eliminated connectivity
between active channel and floodplain
Impaired connectivity between active channel and floodplain
Natural sediment transport dynamics
Complex aquatic and riparian habitat
Unreliable flood protection for infrastructure on the floodplain
Altered sediment transport dynamics
Simplified aquatic and riparian habitat
Reliable flood protection for
infrastructure on the floodplain
MECHANISMS
OF
CHANGE
Increasing magnitude of peak shear stress
Increasing frequency of “effective shear stress events”
Increasing duration of “effective shear stress events”
Altered timing of “effective shear stress events”
Unimpaired connectivity
between active channel and floodplain
Eliminated connectivity
between active channel and floodplain
Impaired connectivity between active channel and floodplain
Decreasing magnitude of floodplain inundation
Decreasing frequency of floodplain inundation
Decreasing duration of floodplain inundation
Altered timing of floodplain inundation
Unimpaired connectivity
between active channel and floodplain
Eliminated connectivity
between active channel and floodplain
Impaired connectivity between active channel and floodplain
I. BackgroundFloodplains provide important hydraulic, hydrologic, water quality, habitat, and aesthetic benefits, and have been recognized as critical elements of healthy river ecosystems. Therefore, the elimination of floodplains, or of the connection between active channels and their floodplains, has been a significant factor in river corridor degradation and an emerging focus of restoration efforts. However, no framework currently exists to guide ecological engineers in determining the optimal size and configuration of restored floodplains in artificially confined river corridors where incremental increases in floodplain width are limited by the high value of existing and future floodplain development. Basic research on the physical and ecological impacts of alterations to the connectivity between active channels and their floodplains is needed to improve future river restoration efforts that involve floodplains.
Restoring Active Channel – Floodplain Connections: Case Studies and Research OpportunitiesMark R. Tompkins, P.E.
Ph.D. Candidate, University of California, Berkeley - River Restoration Engineer, CH2M Hill(510) 558-0192, [email protected]
II. Conceptual Model
III. Case StudiesLower Silver Creek, San Jose, CAMulti-stage channel creation
Problem:Deeply incised channels with limited flood capacity and highly degraded aquatic and riparian habitat.
Restoration Design: Widen creek corridor and construct multi-stage channels to lower shear stress on active channel during high flow, improve sediment transport characteristics, and create conditions conducive to riparian vegetation and aquatic habitat establishment.
Multi-stage channels: 1) “Mature channel” shear stress distributions2) Sediment transport characteristics3) Riparian vegetation establishment4) Riparian vegetation resilience5) Active channel habitat development
Levee setback: 1) Habitat degradation metrics2) 3-D hydraulic modeling of shear stress distributions3) Field calibration of 3-D modeling4) Field experimentation on impacts of altered shear stress characteristics on habitat development
IV. Restoration Design UncertaintyLower Silver Creek: 1) Multi-stage channel critical shear stress characteristics 2) Multi-stage channel sediment transport characteristics3) Multi-stage channel evolution
Deer Creek: 1) Quantification of aquatic and riparian habitat degradation2) Levee setback shear stress characteristics3) Levee setback aquatic habitat change4) Levee setback riparian habitat change
Deer Creek, Vina, CAPotential levee setback
Problem: U.S. Army Corps of Engineers levee project fails catastrophically during large floods and simplifies aquatic and riparian habitat during moderate floods.
Restoration Design:Set levees back and acquire flood flow easements to improve levee reliability during extreme floods and reduce magnitude and frequency of peak shear stress events.
V. Research Opportunities
VI. Acknowledgements U.C. Berkeley Department of Landscape Architecture and Environmental Planning Beatrix Farrand fund, CH2M Hill