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Abstract

Gravel-bed river floodplains are dynamic landscapes that support a high level of ecosystem biocomplexity and biodiversity in large part because of the continual physical turnover of habitat. We evaluated the potential of a gravel-bed river to do geomorphic work on a series of floodplains below a dam by linking airborne hyperspectral imagery with corresponding groundtruth measures of flow velocity, water depth, floodplain surface topography, and vegetative cover. These data were analyzed in a geographic information system to map the spatial distribution of potential stream power over a range of discharge regimes. Nodes of flow separation at specific discharges that co-occurred with zones of high stream power were used as a metric to determine potential geomorphic threshold levels and location of channel avulsions. In order to address discharge duration as a factor affecting geomorphic change on the study floodplains, we established the relationship between discharge and total cumulative power applied to a single key floodplain and then used that relationship to examine historical discharge records and changes in flow release in terms of total cumulative power. We used the assumption that similar levels of total cumulative stream power, above a minimum geomorphic threshold, would produce similar levels of geomorphic work as a higher-magnitude, short-duration flood event. These results form the basis of an objective approach to evaluating flow releases needed from dams to maintain the dynamic structure and ecological function of gravel-bed river flood-plains. Moreover, the methodologies presented herein lend themselves to quantitative investigation of potential geomorphic changes related to complete dam removal and return of normalized flow of water and materials through the river system.

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