Suspended Sediment Discontinuities along Magela Creek, northern Australia — ASN Events

Suspended Sediment Discontinuities along Magela Creek, northern Australia (10635)

Wayne D Erskine 1 , Mike Saynor 1 , Kate Turner 1
  1. Hydrological, Geomorphological and Chemical Processes Group, Environmental Research Institute of the Supervising Scientist, Darwin, NT, Australia

Suspended sediment yields of tributaries of the 1600 km2 Magela Creek in World Heritage Listed Kakadu National Park have been measured by standard river gauging techniques using automatic pump samplers and continuous recording turbity probes for the last 5 years by the Environmental Research Institute of the Supervising Scientist. Yields are low by world standards (< 46 t/km2.a) but are reduced even further by the sediment trapping effect of backflow billabongs which are formed on the tributaries immediately upstream of Magela Creek. The main channel dams the tributaries trapping most of the suspended sediment.

The same techniques have been used on Magela Creek where the specific mean annual suspended sediment yield is 11.8 t/km2.a. However Magela Creek flows through extensive (220 km2) wetlands before entering the East Alligator River. These wetlands represent the remnants of a previous estuarine system that has progressively atrophied over the last 2 ka. Various methods estimate that about 50% of the inflowing suspended sediment is retained by the wetlands despite the local tributaries also producing measured specific suspended sediment yields of up to 5 t/km2.a. Bedload yields (17.5 to 60 t/km2.a) exceed suspended sediment yields in this deeply weathered, sandstone landscape but the backflow billabongs and lower wetlands trap eseentially 100 % of the bedload.

River reach mapping demonstrates that longitudinal continuity of sediment transport is rarely maintained in this landscape with major discontinuities occurring at wetlands and wide floodplains.