The Burdekin WQIP Region:
the physical, biological and socio-economic characteristics of our region

Summary

This Chapter provides a brief description of the physical, biological and socio-economic characteristics of the Burdekin WQIP region that have a bearing on water quality improvement, and the resource condition assessments and other studies that were undertaken in support of the Burdekin water quality improvement planning process. The Burdekin WQIP region covers a land area equal to approximately 8% of Queensland and drains a great diversity of tropical landscapes: semi- arid drylands, wooded grasslands, mountainous tropical rainforests, coastal plains and wetlands.

The Burdekin WQIP region is organised around 6 major basins and 48 subcatchments which represent smaller, more manageable watersheds. These basins and subcatchments provide a focus for prioritisation, and efficient and effective delivery of natural resource management (NRM) interventions for water quality improvement. Many of the studies that were commissioned to help assess the condition of the region’s natural resources and assist with development of the Burdekin WQIP are reported against these 48 subcatchments in the Burdekin WQIP Catchment Atlas.

Our regional climate is characterised by strong seasonality, with very pronounced wet and dry seasons. Rainfall is generally higher near the coastal ranges and lower in the western and southern areas adjacent to the Great Dividing Range. Climate change is predicted to bring hotter and drier conditions, while river runoff and the magnitude of wet season event flows are predicted to become still more variable and extreme than in the past.

The soils and their response to rainfall also vary widely across the region depending upon the underlying geology and local topography. This is reflected in differences between the Upper Burdekin and Belyando Basins. The former has highly erodible soils and is bordered by a thickly forested coastal range with steep terrain and high rainfall along its eastern margin, while the Belyando Basin mostly drains low relief floodplain country with wide braided channels and alluvial plains in the most arid part of the Burdekin WQIP region. Ground cover and land condition assessments through field surveys between 2004 and 2007, and satellite imagery from 1986 to 2006 were undertaken to inform the Burdekin WQIP. These studies have provided descriptive data and information to support the Burdeki WQIP resource condition assessment and prioritisation of subcatchments.

The biodiversity assets of the Burdekin WQIP region are equally diverse and of both national and international significance. Seven bioregions are identified within the Burdekin Dry Tropics NRM region and the vegetation communities in each bioregion, which are closely and consistently associated with a particular combination of geology, landform and soil, have endowed the region with a very high diversity of Regional Ecosystems.

Biodiversity loss has been widespread and affects most areas to varying degrees. The current condition of riparian vegetation and river frontage country were reviewed and assessed as part of the Burdekin WQIP development process using a combination of satellite imagery and field surveys. The results show that there has been a large decline in condition of riparian habitat in many subcatchments due to floodplain and riparian clearing.

The associated aquatic ecosystems are equally as diverse and as threatened as those of the terrestrial environment. Many wetlands are listed in the National Directory of Important Wetlands in Australia, while the Bowling Green Bay coastal wetlands are also included under the international Ramsar Convention. Nevertheless, there are many gaps in our knowledge of Burdekin wetlands and the first regional inventory of wetland condition was undertaken as part of a resource condition assessment
and development of the Burdekin WQIP. This inventory is based on the compilation of GIS information from the 2006 EPA Wetland Mapping Project, field reports and other published material, and local expertise.

Reflecting the strong seasonality in rainfall, discharge from rivers and creeks in the Burdekin region is characterised by high-magnitude pulses of water of short-duration that are associated with wet season rains. Discharge data spanning the water years (September-October) from 1921-1922 to 2004-2005 were analysed, the concept of a ‘Burdekin event flow’ defined, and water quality condition assessed to support Burdekin WQIP development. These event flows are highly variable in their magnitude seasonally as well as between years.

It is apparent that widespread soil erosion and the export of eroded material, including suspended sediment and nutrients, into the Burdekin catchment and Great Barrier Reef Lagoon has occurred historically and is continuing today. Suspended sediment and particulate nutrients in discharge from the Burdekin River and other coastal streams are typically deposited in close proximity (10- 15 km) to the river mouth, before being reworked and redeposited in low energy north facing bays. In contrast, dissolved forms of nutrients and pesticides, and very fine suspended sediment are commonly transported long distances with the freshwater plume. Discharge from the Burdekin River during wet season event flows quite frequently extends northwards for over a hundred kilometres and may, during flood conditions, cover an area of the GBR that is greater than several thousand square kilometres; such is the influence of this large river.

Grazing on native pastures (savannah woodlands and grasslands) is the dominant land use in all Burdekin WQIP region basins, while the relative proportions of other land uses varies markedly between basins. Irrigated sugar and horticulture are largely restricted to the Lower Burdekin Basin, with horticulture being a relatively minor land use compared to sugar. Grazing and sugar cane farming currently comprise around 87% of the land use and these two industries make the most significant contributions to the total contaminant load entering coastal waters.

While most horticulture lies outside the sugar growing areas and south of the Burdekin River, Lower Burdekin cane farmers commonly grow horticultural crops and cotton as part of a mixed commodity farming enterprise. The further diversification of crops on cane farms to include a range of horticultural crops and cotton is likely in the future. The expansion of irrigated agriculture in the Lower Burdekin, based around water resources that are abundant and predictable, may drive significant agricultural development in the future.