Flow separation and complex streaming of flow occurred over the steepest 3-D dunes. Cross-beds are thin and few approach the angle of repose; consequently most dunes did not migrate primarily by avalanching but by stoss-entrained gravel transported over the crests rolling-down and depositing on...
Ripples formed by currents just capable of moving sand grains have relatively continuous but sinuous crests, uniform height and spacing, and asymmetric, angular profiles with downstream faces that slope at the angle of static repose. As current energy increases, crests become shorter and more curved...