CRC River Plume Final Report
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Modelling the impact of the Burdekin, Herbert, Tully and Johnstone River plumes on the Central Great Barrier Reef Brian King1, Felicity McAllister2, Terry Done2 1Asia-Pacific Applied Science Associates 2 Australian Institute of Marine Science Established and supported under the Australian Government’s Cooperative Research Centres Program www.reef.crc.org.au CRC REEF RESEARCH CENTRE TECHNICAL REPORT NO 44 CRC Reef Research Centre Ltd is a joint venture between: Association of Marine Park Tourism Operators, Australian Institute of Marine Science, Great Barrier Reef Marine Park Authority, Great Barrier Reef Research Foundation, James Cook University, Queensland Department of Primary industries, Queensland Seafood Industry Association and Sunfish Queensland Inc. CRC REEF RESEARCH CENTRE TECHNICAL REPORT NO 44 Modelling the impact of the Burdekin, Herbert, Tully and Johnstone River plumes on the Central Great Barrier Reef Brian King1, Felicity McAllister2, Terry Done2 1Asia-Pacific Applied Science Associates PO Box 1679, Surfers Paradise Qld 4217 Australia. Phone 61-7-5574 1112 2Australian Institute of Marine Science PMB #3 Townsville MC, Townsville Qld 4810, Australia. Phone: +61-7-4753 4444 A report funded by the CRC Reef Research Centre Ltd. The CRC Reef Research Centre was established and is supported under the Australian Government's Cooperative Research Centres Program. It is a knowledge-based partnership of coral reef managers, researchers and industry. Its mission is to plan, fund and manage world- leading science for the sustainable use of the Great Barrier Reef World He ritage Area. Members are: · Association of Marine Park Tourism Operators · Australian Institute of Marine Science · Great Barrier Reef Marine Park Authority · Great Barrier Reef Research Foundation · James Cook University · Queensland Department of Primary Industries · Queensland Seafood Industry Association · Sunfish Queensland Inc. CRC Reef Research Centre Ltd PO Box 772 Townsville Queensland 4810 Australia Website: www.reef.crc.org.au Ph: +61 7 4729 8400 Fax: +61 7 4729 8499 CRC Reef Research Centre Technical Report No 44 2 ã CRC Reef Research Centre Ltd. National Library of Australia Cataloguing-in-Publication entry King, Brian, 1964- . Modelling the impact of the Burdekin, Herbert, Tully and Johnstone River plumes on the central Great Barrier Reef. Bibliography. Includes index. ISBN 1 876054 53 0. 1. Plumes (Fluid dynamics). 2. Rivers - Queensland – Great Barrier Reef Region. 3. Runoff - Queensland – Great Barrier Reef Region. I. Done, T. J. (Terrance John), 1947- .II. McAllister, Felicity. III. Cooperative Research Centre for the Great Barrier Reef World Heritage Area. IV. Title. (Series : CRC Reef Research Centre technical report ; no. 44). 551.48809943 This publication should be cited as: King B, McAllister F, Done T. 2002.Modelling the impact of the Burdekin, Herbert, Tully and Johnstone River plumes on the Central Great Barrier Reef. CRC Reef Research Centre Technical Report No 44, CRC Reef Research Centre, Townsville. This work is copyright. The Copyright Act 1968 permits the making of a fair dealing for study, research, news reporting, criticism or review. Although the use of the pdf format causes the whole work to be downloaded, any subsequent use is restricted to the reproduction of selected passages constituting less than 10% of the whole work, or individual tables or diagrams for the fair dealing purposes. In each use the source must be properly acknowledged. Major extracts, or the entire document may not be reproduced by any process whatsoever without written permission of the Chief Executive Officer, CRC Reef Research Centre. While every effort has been made to ensure the accuracy and completeness of information in this report, CRC Reef Research Centre Ltd accepts no responsibility for losses, damage, costs and other consequences resulting directly or indirectly from its use. In some cases, the material may incorporate or summarise views, standards or recommendations of a third party. Such material is assembled in good faith but does not necessarily reflect the considered views of CRC Reef Research Centre Ltd or indicate a commitment to a particular course of action. Published by CRC Reef Research Centre Ltd., PO Box 772, Townsville, QLD 4810 Australia. CRC Reef Research Centre Technical Report No 44 3 TABLE OF CONTENTS INTRODUCTION..............................................................................................................................................................................5 GEOGRAPHIC SETTING................................................................................................................................................................6 RIVER DISCHARGE CHARACTERISTICS ...............................................................................................................................7 MODELLING RIVER PLUMES IN THE CENTRAL GBR...................................................................................................... 15 EXAMPLES FROM THE FLOOD SIMULATIONS................................................................................................................. 17 MINIMUM SALINITY ANALYSIS..............................................................................................................................................23 MINIMUM SALINITY PLOTS....................................................................................................................................................24 EXPOSURE TIMES.......................................................................................................................................................................29 SIMULATING THE 1974 FLOOD EVENT. .................................................................................................................................30 SIMULATING THE 1991 FLOOD EVENT. .................................................................................................................................32 SIMULATING THE 1979 FLOOD EVENT. .................................................................................................................................34 SIMULATING THE 1983 FLOOD EVENT. .................................................................................................................................36 SIMULATING THE 1977 FLOOD EVENT. .................................................................................................................................38 SIMULATING THE 1986 FLOOD EVENT. .................................................................................................................................40 RETURN PERIOD ESTIMATIONS OF PLUME IMPACTS..........................................................................................................42 CONCLUSION............................................................................................................................................................................... 48 DISCUSSION ................................................................................................................................................................................. 50 REFERENCES ................................................................................................................................................................................. 51 CRC Reef Research Centre Technical Report No 44 4 INTRODUCTION As part of the water cycle, rivers drain freshwater runoff from rainfall events over land. The runoff collects a variety of substances as it moves through the river’s catchment-lands and waterways including nutrients, sediments and contaminants depending on the catchment characteristics and land-use practices. Upon reaching the sea at the river’s mouth, the runoff drives a buoyant plume into coastal and shelf waters. The plume eventually spreads and mixes and moves around with the winds and currents. This mixing with ambient coastal waters will ultimately dilute the runoff plume as well as any concentrations of sediments, nutrients and contaminants carried within the plume. In the wet and dry tropical catchments adjoining the Great Barrier Reef (GBR), river discharges are highly seasonal and usually event-driven in nature and result from rainfall events associated with evolving monsoon troughs or passing tropical cyclones (Furnas and Mitchell 2000; Wolanski, 1994). Also, the unpredictable nature of rainfall and runoff events, and the unsteadiness and patchiness of the resulting plume intrusions in a complex region such as the GBR, has traditionally made data logistically difficult to collect. Further, direct rainfall inputs onto the shelf-waters can also lower surface salinity significantly (Wolanski, 1994) and at a time when river discharges are also significant. Thus large spatial mapping of salinities was needed to determine the origins of lower salinity events (< 34 ppt) within the reef matrix of the GBR. Historically, significant plume intrusions into the GBR have been observed. Data presented in the literature (Wolanski et al., 1997; Ayukai et al., 1997; Wolanski, 1994; O’Neill et al., 1992; Wolanski and Ruddick, 1981) report measurements of reduced salinities associated with particular events. Wolanski and Van Senden (1983) reported the most detailed survey todate, which covered the 1981 flood events from the Burdekin, Herbert, Tully, Johnstone and Barron Rivers. These studies have also provided some insight into the dynamics influencing