FLOODPLAINS AND WOOD (Invited Presentation)

Wood within a river can influence floodplain dynamics by increasing hydraulic roughness and creating flow obstructions that enhance magnitude and duration of overbank flow. Enhanced overbank flow can in turn create spatially heterogeneous erosion and sedimentation on the floodplain, promote the formation of secondary channels, and enhance habitat diversity for riparian vegetation. Instream wood can also respond to floodplain dynamics, as when floodplain erosion exhumes buried wood or recruits wood from the channel banks, and overbank inundation floats wood into or out of the channel. Wood-floodplain interactions have been occurring since the Carboniferous, and have been recognized since the early years of geological research. However, there remain some important gaps in our understanding of how wood-floodplain interactions vary with spatial scale and among different climatic regions. A conceptual model of how wood-floodplain interactions vary with drainage area, wood mobility, and floodplain extent can be developed from quantitative studies of small to medium size rivers in the temperate zone, although we lack data for very large rivers. Adapting such a model to tropical or boreal regions involves even greater extrapolation as a result of a lack of quantitative, place-based studies in these environments. In considering controls on turnover times of instream wood at the reach scale, floodplain form and process influence wood recruitment, transport, storage, and decay and breakage – all of the major processes involved in wood dynamics. Because many studies of instream wood focus on laterally confined channels, however, and effectively consider the channel in isolation from the floodplain, the literature on instream wood does not reflect the critical influences that floodplains exert on wood dynamics in many environments.