5 Pardee Keynote Symposia: River Restoration: Environmental Success or Strategic Failure?

Tuesday, 7 October 2008
8:00 AM - 12:00 PM

Stream Restoration Efforts Must Consider Ecological Connectivity, Watershed-Scale Processes, and Historic Land Use Changes

Paper number: 5-5
Program: Overarching Sessions
Time: 9:40 AM – 10:05 AM

Authors

Abstract

Stream restoration projects often fail because channel modifications or restoration structures are designed and installed without adequate consideration of: (1) ecological connectivity, (2) watershed-scale processes, and (3) how the channel is responding to historic land use changes. Reach-scale restoration templates rarely account for upstream and downstream processes and how land use changes have altered sediment delivery and storage in the watershed. Most stream channels remain in a prolonged state of channel adjustment to extensive logging, dam construction, and urbanization over the past century. Idealized “reference” conditions no longer exist in these watersheds and efforts to “restore” isolated reaches of a stream are often unsustainable because conditions elsewhere in the watershed continue to change.

Greater success occurs when stream restoration efforts accommodate the complex processes ongoing in the watershed. Restoration plans must consider sediment delivery and storage, channel evolution, recruitment of wood and organics to the channel, and ways to reconnect artificially straightened channels to abandoned side channels and the floodplain. Where human activities exert a continuing negative influence on the ecological potential or hazard risk at a potential restoration site, the project design must incorporate ways to alleviate the pressures acting on the site even if they are occurring elsewhere in the watershed. If such watershed scale restoration is not possible, then project designers must plan for long-term maintenance at the project site and mitigation to adjacent reaches that are invariably influenced by the implementation of restoration options that do not address the underlying instabilities within the watershed.