ABSTRACT: Morphologic and sedimentary dynamics of a coarse-grained braided river.

CGRG Bibliography of Canadian Geomorphology
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Abstract

The morphologic evolution and sedimentary dynamics of braided rivers have been areas of interest to river scientists because of the intriguing relationship between the rapidly changing form of the river and the sedimentation patterns of the river morphology. Acquiring information that directly links river processes and sedimentology over depositional timescales has proven difficult because of constraints of field data collection and time-scales of river development. Here we demonstrate the utility of flume-based modeling of a river, combined with photogrammetric and image analysis techniques that provide information on the simulataneous development of morphology, grain size and, consequently, sedimentology in a braided river over time periods long-enough for significant morphological change. Digital photogrammetry was used to create a series of high-resolution DEMs of bed topography over a period of 22 hours in the flume. Digital image analysis techniques were used to map grain sizes of the river surface. By compiling the DEMs and grain maps, the 3D geometry of the boundary surfaces of the river deposit were mapped along continuous grain size data on those surfaces. This information provides a novel view of braided river morph- and sedimentary dynamics and, as we demonstrate, the outcome challenges the conventional view of braided river deposits. Our results show that, despite notable differences in morphology between the upper and lower boundary surfaces of the deposit, there is actually little difference in the overall sedimentology of the deposit. The basal layer (minimum elevation surface) develops in piece-meal over time and is not defined by a coarse-grained lag. Instead, we found that the basal layer has considerable relief, and has range of grain sizes rather than coarse-grained basal lag on the scour surface contrary to current gravel braided river depositional models.

Bibliography of Canadian Geomorphology