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.