Export of nutrients and suspended sediment from the Herbert River catchment, northern Queensland, during a flood event associated with Cyclone Sadie (1994)

Water samples were collected by both AIMS and CSIRO in the Herbert River catchment 10-15 days before the Cyclone Sadie flood. During the flood event, the John Row Bridge was the only site continuously accessible through the peak flow. Independent concurrent sampling was carried out by AIMS and CSIRO at the John Row Bridge, allowing for comparison of the different sampling and analytical methods used by each agency. Time-series sampling commenced 10 h before the flood peak (approximately 13 h after the initial rise began) and continued for two and a half days, covering most of the flow event. Following the Cyclone Sadie flood, sampling was continued at this and other sites at lower frequency for a further three weeks, which included a second, smaller flood event. Surface water samples were collected at bridges, in clean plastic containers, from the mid- or deepest point of the river. At sites where bridge access was restricted, the sampling container was thrown out into the main flow of water and retrieved by rope.Water samples were analysed to determine: dissolved inorganic nitrogen (DIN)= (NH4+NO2+NO3), dissolved inorganic phosphorus (DIP)=PO4=orthophosphate; silicate; total dissolved nitrogen (TDN); total dissolved phosphorus (TDP); particulate nitrogen (PN); particulate phosphorus (PP); suspended sediment; potassium; and salinity. pH was also measured.Concentrations of dissolved organic nitrogen (DON) and phosphorus (DOP) were calculated as the difference between the total dissolved and dissolved inorganic nutrients. Water discharge in the Herbert River was monitored at two flow gauging stations, one located immediately upstream of the John Row Bridge (116001E) and the other at Gleneagle on the upper Herbert (116004C).
 This study was targeted at estimating nutrient and sediment export from the Herbert River catchment during a major flood event.
 Tropical cyclone Sadie degenerated into an intense rain depression over the North Queensland coast on 31 January 1994. A flood plume from the Herbert River and adjacent streams extended approximately 20 km offshore on 2 February 1994. Further heavy rain occurred some two weeks following the cyclone, particularly in the Ingham area causing a second flood of smaller magnitude than that associated with cyclone Sadie.At the time of this study, water-borne nutrients and sediments within the lower catchment of the Herbert River were being sampled by three research agencies, AIMS, CSIRO (Townsville) and the Bureau of Sugar Experimental Stations (BSES, Ingham). The collaborative sampling program of AIMS/BSES, carried out at John Row Bridge, Abergowrie Bridge and Nash's Bridge, was primarily concerned with assessing riverine export of nutrients and suspended sediment to the Great Barrier Reef lagoon. The broader CSIRO program sought to resolve the major source areas for sediments leaving the lower catchment.Stream gauging data was supplied by the Queensland Department of Natural Resources Hydrography Section, Mareeba. Rainfall data was supplied by the Hinchinbrook Shire Council.

Organization: Australian Ocean Data Network