Sedimentation in an ebb-tidal delta, Rangaunu Harbour, Northland, New Zealand

Abstract

Abstract Rangaunu Harbour is a shallow estuary drained northward by a dendritic channel system onto an extensive ebb-tidal delta. The inlet trough is lined with lag sediments, over which sand is occasionally transported in ribbons. Most sediment transport is confined to channel-margin megaripple fields moving sand seaward onto the terminal lobe of the delta. Interacting wave and tidal forces direct sediment landward from the lobe in anticlockwise gyres, generating recurved bars and furrows on the delta platform and feeding sediment to Te Puke te Huri Spit around the outer face of the delta. Flood tides and shoaling waves return this sediment to the shoreface and back to the harbour mouth. Flood flow is concentrated in a marginal channel on the eastern side ofthe delta; wavereinforced flood flowstransport sediment landward in sand ribbons from the floor of Rangaunu Bay into the harbour. The bay floor probably supplies 80%of the sediment for delta growth. Between 1958 and 1979, 7.8 x 106 m3 of sediment was ...