84-3 Episodic and Incremental River Channel Dynamism Associated With In-Channel Wood

Abstract:

Natural rivers are dynamic over space and time due to variations in water, sediment, and wood fluxes. In addition to the influences of water and sediment on river corridor dynamism, wood can be a first-order control on river form and process in forested regions. Wood can play a role in many elements of channel dynamism including island formation, meander migration and cutoff, secondary channel creation, and avulsion. However, the relationship between in-channel wood and magnitudes of channel dynamism is poorly understood. As airborne and satellite imagery has become more frequently collected, of higher quality, and more widely available, analysis of river dynamism across large areas has become possible at the decadal timescale. We use up to 20 years of aerial imagery from 7 sites across North America with relatively unaltered wood regimes to investigate the effects of in-channel large wood on channel dynamism. Channel dynamism was quantified as the change over time of i) sinuosity, ii) shoreline complexity, and iii) floodplain creation and destruction. Preliminary results suggest that there is an association between the area of wood accumulations present and the magnitude of change to river form; large wood accumulations were associated with dynamic channel and floodplain change. Additionally, we characterized two types of channel dynamism: episodic channel adjustment was associated with large wood accumulations whereas reaches with incremental adjustment primarily stored individual pieces of wood. These findings imply that wood accumulations can trigger high-magnitude changes in otherwise homogenous river systems.

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