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7888762 
Journal Article 
Use Of Sednet Model To Establish Sediment Export Targets For Catchments Of The Wet Tropics Draining To The Great Barrier Reef 
Hateley, L; Armour, J; Pitt, G; Cogle, L 
2005 
Modsim 2005: International Congress on Modelling and Simulation: Advances and Applications for Management and Decision Making: Advances and Applications for Management and Decision Making 
1154-1160 
WOS:000290114101029 
Some of the inshore reefs of the Great Barrier Reef are showing impacts consistent with a decline in water quality as a result of increased sediments and nutrients. The Wet Tropics covers approximately 2.2 million hectares and includes 91 percent of the Wet Tropics World Heritage area. The climate and geomorphologic conditions of the region are unique in Australia and generally result in fast flowing streams with high discharge rates into the GBR. The exception is the drier Herbert River. SedNet is a regional scale model for estimating long-term annual sediment budgets. It identifies patterns in erosion processes and the delivery and movement of sediment in surface water. SedNet can assess management actions and priority areas to maintain or improve water quality. This paper focuses on 8 northern catchments, from the Daintree to the Herbert. Modelling of sediment generation and transport with SedNet has previously been completed in catchments from the Daintree in north Queensland to the Burnett-Mary 1300 km south. The aim of the study was to update previous SedNet modelling, improve local modelling expertise and assist the Far North Queensland Natural Resource Management board to; Establish water quality targets to meet requirements of the Reef Water Quality Protection plan Predict if management actions will reduce sediment generation and delivery to the GBR. Improved data layers such as finer scale digital elevation model, land cover and land use are being used, building on previous modelling. The modelling indicated that hillslope erosion was the dominant source of sediment in the Wet Tropics catchments. It contributed 1160 kt/yr or 59% of the sediment supply. A total of 1610 kt/yr or 82% of the suspended and bed load sediment that was generated in sub-catchments was exported to the coast. The Herbert River had the largest catchment and contributed 35% of the total sediment load to the end of catchment (490 kt/yr). The export of sediment to the coast per unit of land area was highest for Mossman and Russell-Mulgrave catchments; 120-125 t/km(2). The sub-catchments that delivered the highest loads to the coast were found in the Russell-Mulgrave and Johnstone catchments (120 and 100 t/km(2), respectively). The 10 sub-catchments that contributed the highest suspended and sediment loads to the coast occupied only 5% of the catchment area but contributed 11% of the sediment to the coast. Simulations of improved management of sugarcane and bananas resulted in a reduction of 10% (144 kt/yr) in suspended sediment export to the coast and 14% in hillslope erosion. The conversion of sugarcane to grazing and of dairy to beef cattle also resulted in a total reduction of suspended sediment to the coast of 10% (138 kt/yr) and reduced hillslope erosion by 13%. Restoration of riparian vegetation in 30% of river links (49 km) resulted in a 5% (73 kt/yr) reduction in suspended sediment to the coast. The regional scale conclusions of this study have generally been accepted by the Board. However, some concerns have been raised about the accuracy of hillslope and bank erosion at some local scales. Model validation in the near future may resolve this issue. The Board will consider these SedNet modelling results along with other data and information when meeting the requirements of the Reef Water Quality Protection. 
SedNet; sediment; Wet Tropics; water quality targets 
Argent, R. M.