This white paper examines and synthesizes the literature pertaining to the current state of knowledge on the physical and biological effects of alluvial river channelization, channel confinement, and various channel and floodplain modifications. It also examines and summarizes literature on the mitigation, rehabilitation and restoration of rivers affected by these human modifications. Data gaps in our current understanding of physical and biological process, the effects of human modifications, and appropriate rehabilitation or restoration techniques are also reviewed.
The paper overviews ecological and habitat issues associated with streams and riparian zones in Washington State and the Pacific Northwest. The results of the literature review are documented in a synthesis of the ecological and habitat effects of channelization, channel confinement and construction. The physical and morphologic effects of channelization are first reviewed to highlight how habitat templates have been or potentially could be modified. Then, the responses of different groups of organisms (invertebrates, fish, plants, birds, mammals) that are dependent on functional riparian corridors are reviewed. Data gaps in our current knowledge in connecting cause and effects relationships in complex ecological systems are reviewed. The functional importance of hyporheic and perirheic zones in alluvial streams is also reviewed.
The paper includes a section on habitat protection and mitigation techniques. Alternative management strategies such as passive (vs. active) restoration, streamside vegetation retention or promotion, and modified in-channel vegetation removal are reviewed. Recommendations by various authors on minimizing impacts during design and construction are also summarized. Preservation of channel morphology, incorporation of vegetation into embankments, and alternative bank protection techniques are also explored.
In recent years there has been a societal push to rehabilitate and/or restore streams and rivers degraded by channel modifications. The paper ends with a review of large-scale rehabilitation and restoration projects and techniques in the literature.