1. 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. 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. 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, mark@markrtompkins.com II. Conceptual Model III. Case Studies 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. 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 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 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. V. Research Opportunities VI. Acknowledgements U.C. Berkeley Department of Landscape Architecture and Environmental Planning Beatrix Farrand fund, CH2M Hill