Observation on submerged sand ripples with heights ranging from 30 to 200 cm occuring in tidal channels of S.W. Netherlands

Abstract

An investigation of submerged sand ripple fields with ripple heights from 30-200 cm in the fluvial tidal and tidal channels of the S.W. Netherlands was made. Such rippled surfaces were found in fluvial tidal channels, at the confluence of tidal channels and in pronounced ebb and flood channels. However, over large areas no ripple fields of this kind were observed. Ripple areas do not distinguish themselves from non-rippled areas by a difference in general current characteristics or composition of the bottom material, although no ripple (30-200 cm) fields were found in areas where the bottom material contains more than 15% mud. The asymmetry of ripples with heights of 30-100 cm is sometimes determined by the prevailing tidal current especially in ebb and flood channels; change of the asymmetry with the turn of the tide does occur. The asymmetry of ripples with heights from 100-200 cm showed much more constancy. It mostly did not change with the turn of the tide. The dimensions of the ripples in the fields may change rather rapidly. There is no relation between ripple height and water depth. It was observed that the orientation of the ripple crests is influenced by the spiral flow in tidal channels.