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The Morphology and Stability of Bifurcations in the Mossy River Delta, Saskatchewan Canada

Douglas A. Edmonds

Department of Geosciences, The Pennsylvania State University

State College, PA USA

[email protected]

Channel bifurcation is a fundamental process in the initiation and evolution of braided rivers, anastomosed rivers, alluvial fans, and deltas. To better understand deltaic distributary bifurcations, we have initiated a study of five bifurcations in the Mossy River Delta, Saskatchewan, Canada. Preliminary data were collected using an Eagle single-beam echo sounder, a Sontek 1500 KHz acoustic Doppler profiler, and Sokkia total station. At the flow discharge investigated, the flow diverges from the trunk channel orientation into each bifurcate channel close to the bifurcation point. Moreover, for four of the five bifurcations, the wider bifurcate channel generally has discharge (Q) that is 13 to 28% less than the narrower bifurcate channel, cross-sectional mean velocity that is slower by a few percent, depth (d) that is shallower by half, water surface slope (S) that is steeper by a few percent, and higher dune height relative to water depth. Furthermore, a morphological ramp with slope from 0.1 to 1 degree leads from the deeper, undivided channel at the bifurcation point to the shallower channel. The origin of these geomorphic and hydraulic relationships remains an open question, and must await further investigation. However, relative values of S, Q, and d for the bifurcate channels in the Mossy River Delta are opposite of published theory in which bifurcations are stable if the bifurcate channel with the lower S has a smaller Q and d.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid