BED-FORM DYNAMICS - DOES THE TAIL WAG THE DOG

Bed-form patterns reflect the dynamics of the defects in the pattern. From this new hypothesis, the differential migration of defects within a field of bed forms determines how crest-line orientation responds t o changing transport conditions. Predictions from a model for defect d ynamics compare well to field measurements and computer simulations of bed-form orientation. This model permits quantification of the time f or bed-form reorientation across a broad range of scales, from hours i n the rapidly changing nearshore environment to thousands of years for linear dune fields.