POINT-BAR DEPOSITS IN NARROW SHARP BENDS

Meandering channels typically deposit sediments near their inner bank to form point bars. Laboratory experiments with narrow sharp bends sho w that under identical flow conditions the configuration of point bars depends on particle size. Explanation to this grain-size effect is fo und in a three-dimensional particle stability. Despite favorable secon dary currents, coarse grains tend to move toward the thalweg and coars e-grained point bar deposits are eroded as the side-slope angle approa ches the angle of repose of the bed material. Calculated results coinc ide with experimental observations. Point bars are considerably smalle r for coarse-sand deposits than fine sands.