Harrow marks, patterns of current-aligned, fine-grained ridges, and intervening trough-like strips of coarser sediment are found along the riverbeds of the ephemeral streams of southern Israel. These structures are believed to be caused by patterns of tubular vortices with an alternating sense of rotation and with axes parallel to the direction of main flow. This type of flow structure, in which the individual flow filaments advance helically, results from secondary, transverse instability of flow.
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Iaakov Karcz (1967) studied this question.