Origin and development of ridge-furrow systems in beachrock in Barbados, West Indies

Abstract

Ridge-furrow systems developed perpendicular to the shore are characteristic of beachrock which straddles the strandline in tropical areas. In Barbados, mean spacing is 60 cm, mean furrow length 5 m, mean furrow width 28 cm, and mean furrow depth 18 cm. The near parallel pattern of equi-spaced furrows may be initiated in incipient beachrock by the transport of sand by fresh-water rilling or backwash channelling. On exposure, elongation deepening and widening of furrows is accomplished mainly by corrasion. Measurements of furrow current velocities indicate a decrease in abrasion potential with increasing water depth. Furrow abrasion is greater during backwash than upwash, while maximum erosion takes place at wave breakpoint. Morphological variations in ridge-furrow systems result in part from differences in stage of development. Initially, furrow deepening is in excess of widening, but with time basal widening may cause adjacent furrows to join laterally, destroying the separating ridge.