The dynamics of a megaripple field in northern Spencer Gulf, South Australia

Abstract

The composition, form and migration of megaripples in a megaripple field in a tidal channel of northern Spencer Gulf, South Australia, were examined over a year. Migration rates of megaripples ranged from about 2 m yr −1 for sandwaves 3 m high to about 8 m yr −1 for megaripples 0.4 m high. Migration of the wave form was regular at some sites but irregular at others, where differential migration and erosion gave rise to branching or coalescence of megaripples. Winter migration rates were greater than summer rates at most sites. Estimates of sediment transport rates at two cross-sections of the field suggest only slow and minor net flood transport of sediment of 40–70 m 3 yr −1. Sediments are predominantly medium-grained sand well-sorted at the megaripple crests (and elsewhere on fast-moving megaripples) and poorly sorted in troughs between megaripples. The predominantly negative skewness values of the sediments support the conclusion that tidal currents selectively rework the sediments with little input of new material.