Ord River and Cambridge Gulf hydrodynamics and sediment movement study, Western Australia

In August 1999, a preliminary field trip was undertaken to study the sediment dynamics of the East and West Arms of Cambridge Gulf. A self-logging Analite nephelometer was deployed for 6 days during spring tides, attached near low tide level at a pile of the Wyndham Harbour jetty in the West Arm. Tide gauges were bottom deployed for 2 days at 3 stations in the East Arm during spring tides and Analite nephelometers were also deployed at two of these stations for the same period. In the thalweg of both the West and East Arms, vertical profiles of currents, temperature, salinity and suspended sediment concentration were obtained hourly from a small boat at anchor for 13 h in the West arm and 10 h in the East Arm. In the West Arm, a Seabird CTD with Analite nephelometer attached was bottom deployed along the sloping banks during the passage of a tidal bore. Photographs of flocs of suspended matter in near surface waters were obtained during CTD stations in both the West and East Arms. Two additional samples were collected in King River estuary south of Wyndham. Floc size data for near bottom waters were also obtained during the 13 h tidal station in the West Arm. The bathymetry of cross-sections of the East Arm was measured using an echo sounder. Two aerial surveys were completed, once during low tide and once over the tidal bore.In December 1999, tide gauges were deployed in the East Arm for two days at 2 sites, which were last surveyed in 1969. The bathymetry of a cross-section of the estuary, which was also last surveyed in 1969 was resurveyed using an echo sounder.In June 2000, work continued in the East Arm, with several cross-sections across the estuary completed in upstream locations. Two Aanderaa tide gauges were also deployed to study the tidal bore observed on a previous trip.In September/October 2000 (dry season), four moorings were deployed in the East Arm and in Cambridge Gulf. Various instruments were attached to these, which included nephelometers, InterOcean S4 current meters, Dataflow temperature and salinity loggers and tide gauges. CTD casts were made at moorings and other locations within the estuaries. From the 24th October to 6th November 2000, a second field trip was undertaken to retrieve instruments and additional CTD casts were made. During this trip two frames, with a similar range of instruments were deployed for 5 days.In December 2000, a CTD survey of the King River and the West Arm was carried out.In January 2002 (wet season), in a similar program to September/October 2000, a further 5 moorings were deployed in the West Arm and in Cambridge Gulf. The instruments were recovered approximately 1 month later. CTD casts were also done.
 This field and model study of the water and fine sediment dynamics of both the West and East Arms of the Cambridge Gulf was undertaken to determine the impacts of increased sediment runoff due to land clearing and the suppression of river floods by damming of the Ord River on the physical features of the Ord River estuary. At the time that this research was undertaken, the Marine Parks and Reserves Authority of Western Australia had identified Cambridge Gulf and its adjoining estuarine systems as worthy of investigation for suitability as a marine reserve.
 Cambridge Gulf has two estuaries, the West and East Arms. The West Arm, is the estuary of the mostly undisturbed Durack, Pentecost and King Rivers. The East Arm is the estuary of the Ord River and flows are affected by land clearing and two dams constructed between 1969 and 1972. The only natural river flow in the East Arm is from the Dunham River, a small tributary of the Ord River, downstream of the dams. The bathymetry of the West Arm during the last 111 years was obtained from bathymetric charts of the Royal Navy before 1900, of the Royal Australian Navy before 1960 and after that from annual surveys by the Western Australia Department of Transport.

Organization: Australian Ocean Data Network