dune bedform (‘megaripples’) Mounds or ridges of sand which are asymmetrical, and are produced subaqueously by flowing water. The external morphology is similar to the smaller ‘ripple’ and larger ‘sand wave’, with a gently sloping, upstream side (stoss), and a steeper downstream side (lee). The crestline elongation extends transverse to the flow direction and is sinuous or lunate in plan. The height varies between 0.1 m and 2 m, while the wavelength (spacing) between dunes is 1–10 m. Size and growth are limited by water depth and, in general, dune height is less than one-sixth of the flow depth. The down-current migration of dune bedforms leads to the formation of cross-bedding in sediments.

dune bedform(‘megaripples’) Mounds or ridges of sand which are asymmetrical and are produced subaqueously by flowing water. The external morphology is similar to the smaller ‘ripple’ and larger ‘sand wave’, with a gently sloping, upstream side (stoss), and a steeper downstream side (lee). The crestline elongation extends transverse to the flow direction and is sinuous or lunate in plan. The height varies between 0.1 m and 2 m, while the wavelength (spacing) between dunes is 1–10 m. Size and growth are limited by water depth and, in general, dune height is less than one-sixth of the flow depth. The down-current migration of dune bedforms leads to the formation of cross-bedding in sediments.