Unimpaired connectivity between active channel and floodplain
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Unimpaired connectivity between active channel and floodplain. Eliminated connectivity between active channel and floodplain. Impaired connectivity between active channel and floodplain. Unimpaired connectivity between active channel and floodplain.

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Unimpaired connectivity between active channel and floodplain

Unimpaired connectivity between active channel and floodplain

Eliminated connectivity between active channel and floodplain

Impaired connectivity between active channel and floodplain

Unimpaired connectivity between active channel and floodplain

Unimpaired connectivity between active channel and floodplain

Eliminated connectivity between active channel and floodplain

Eliminated connectivity between active channel and floodplain

Impaired connectivity between active channel and floodplain

Impaired connectivity between active channel and floodplain

Altered sediment transport dynamics

Simplified aquatic and riparian habitat

Reliable flood protection for infrastructure on the floodplain

Natural sediment transport dynamics

Complex aquatic and riparian habitat

Unreliable flood protection for infrastructure on the floodplain

MECHANISMS

OF

CHANGE

Decreasing magnitude of floodplain inundation

Increasing magnitude of peak shear stress

Decreasing frequency of floodplain inundation

Increasing frequency of “effective shear stress events”

Decreasing duration of floodplain inundation

Increasing duration of “effective shear stress events”

Altered timing of “effective shear stress events”

Altered timing of floodplain inundation

  • Restoring Active Channel – Floodplain Connections: Case Studies and Research Opportunities

  • Mark R. Tompkins, P.E.

  • Ph.D. Candidate, University of California, Berkeley - River Restoration Engineer, CH2M Hill

  • (510) 558-0192, [email protected]

  • II. Conceptual Model

    I. Background

    Floodplains 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.

    III. Case Studies

    Deer Creek, Vina, CA

    Potential 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.

    Lower Silver Creek, San Jose, CA

    Multi-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.

    IV. Restoration Design

    Uncertainty

    Lower Silver Creek:

    1) Multi-stage channel critical shear stress characteristics

    2) Multi-stage channel sediment transport characteristics

    3) Multi-stage channel evolution

    Deer Creek:

    1) Quantification of aquatic and riparian habitat degradation

    2) Levee setback shear stress characteristics

    3) Levee setback aquatic habitat change

    4) Levee setback riparian habitat change

    V. Research Opportunities

    Multi-stage channels:

    1) “Mature channel” shear stress distributions

    2) Sediment transport characteristics

    3) Riparian vegetation establishment

    4) Riparian vegetation resilience

    5) Active channel habitat development

    Levee setback:

    1) Habitat degradation metrics

    2) 3-D hydraulic modeling of shear stress distributions

    3) Field calibration of 3-D modeling

    4) Field experimentation on impacts of altered shear stress characteristics on habitat development

    VI. Acknowledgements

    U.C. Berkeley Department of Landscape Architecture and Environmental Planning Beatrix Farrand fund, CH2M Hill


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