BRAIDING MECHANISMS AND BAR GEOMETRIES IN RIVERS AND SUBMARINE DENSITY CURRENT CHANNELS

Braiding is a common phenomenon in fluvial systems and occurs when the width-to-depth ratio of the channel is sufficiently large to induce the spontaneous deposition of braid bars. These bars subsequently subdivide the flow into several threads. The mechanisms by which these bars are generated in fluvial systems include: chute cutoff, multiple bar dissection, mid-channel deposition, transverse bar conversion, sweeping bar formation and an inheritance process. Recent studies indicate a similar braiding phenomenon occurs in sufficiently wide channelized submarine density currents and turbidity systems, as well as a similar relationship between dimensionless stream power and the ratio of active to inactive channel threads in both submarine and subaerial channels. We used flume experiments of braided fluvial and submarine density to assess: (1) if both braided systems exhibit similar types of braid bar mechanisms; (2) the relative frequency at which each mechanism occurs; and (3) any differences in the geometry of the bars generated. We evaluated six experiments that systematically varied sediment and water discharge. We find braiding in subaerial and submarine channelized systems occurs by similar mechanisms with broadly similar relative frequencies and generate bars with grossly similar geometries. We also evaluated braid bar mechanisms for the Platte River over a period of five years using Google Earth time lapse images. These field-scale fluvial systems display similar bar geometries to both submarine and subaerial flume experiments, despite being scales of magnitudes larger. Similar planform bar morphologies, as well as location and abundances of unvegetated bars within channels suggest that field-scale river systems are experiencing the same bar formation mechanisms as the experimental scale systems. Comparable mechanism frequency patterns are displayed within both field-scale and experimental scale fluvial systems, with bar dissection being the prominent mechanism in all cases studied.