Process sedimentology of the Waikato River mouth, Port Waikato, New Zealand: The depositional record of a mixed-energy river mouth

Abstract

Interacting fluvial and marine processes at the Waikato River mouth control sedimentation patterns at the sand spit. These interacting processes cause tidal asymmetry between the ebb and flood tide, and produce multidirectional currents, orientated east, west, north, north-west, and south. Depositional processes at the Waikato River mouth are recorded using oceanographic instrumentation, and are linked to their corresponding sedimentary deposits. Sedimentary bedforms on the sand spit include wave- and combined-flow ripples and dunes, and planar bedding, produced from interacting fluvial and wave currents. Despite tides directly controlling sediment deposition, tides manifest as rising and falling water levels, affecting current magnitude and velocity, but are not directly indicated in terms of “tidal” sedimentary structures. Preservation potential of bedforms are low, with the sedimentary recorded dominated by structureless sand, from rarely occurring low flow velocity periods in the early- to mid-ebb tide. The Waikato River mouth is classified as wave-dominated, fluvially influenced and tide affected (Wft).