Abstract

In the sandy, braided South Saskatchewan River, ripples, sand waves, and dunes are recognized as lower flow regime bedforms on the basis of a morphological classification. Sand waves are straight-crested to rhomboidal and are very regular in the direction transverse to flow, lacking scour troughs or spurs. The amplitudes of sand waves may gradually increase or decrease along their crestlines, but abrupt changes are rare. Dunes are sinuous to strongly three-dimensional bedforms, showing marked irregularities in crestline height and well developed spurs and scour troughs. Sand waves occur with ripples superimposed on their stoss sides at flow velocities less than 0.5-0.7 m/sec depending on depth. Dunes occur in most cases with no superimposed ripples at velocities greater than sand waves for each depth. Slipface-bounded bars up to 3 m in height form where the flow is non-uniform and expands laterally or vertically. This happens where channels widen or bend or where the flow passes over an abrupt downward step such as the junction of channels of different depths. Bars may have ripples, sand waves, or dunes superimposed on their upper surfaces and are less sensitive to changing flow conditions than are these others. Sand flats are large-scale sandy braid bars which are complexes of all the smaller forms. They are comparable in scale to the point bars of meandering streams.

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