Study of Subaqueous and Subaerial Sand Ripples.

Abstract : Sand ripples in the marine and desert environments were studied so that comparisons of ripple structure, geometry, movement and behavior could be made with theoretical studies. Crest sediment of small wavelength oscillation ripples is slightly coarser than the material in the troughs, whereas for megaripples, trough sediment is coarser. Ripple wavelength is a function of grain size. Sediment motion on the sea floor is negligible when the average surge velocity is less than 10 cm/sec, particle motion commences at 18 to 21 cm/sec and is widespread at 27 to 30 cm/sec. Bedload exceeds 80% of the total load and 95% of all transport occurs within 15 cm of the bottom. In the aeolian environment ripple geometry is variable and wavelength is a function of crest grain size. Using tracer sand it was determined that under winds of 15-25 mph, threshold velocities range from 21 to 36 cm/sec, average grain velocity is 0.78 m/min, natural ripples travel at 0.4 cm/min and the rate of sand transport is about 0.4 metric tons/meter width/hour. (Author)