Landscapes and Soils
Physical environments within the region are diverse ranging from mountain ranges, basement rock hills, coastal plains, floodplains, deltas, beach ridges, embayments, continental islands and coral reefs in coastal areas to undulating plains with escarpments, dissected plateaus and mesas inland to the Great Dividing Range. Soil types in the region reflect the diversity of parent rock materials,landscapes and rainfall patterns. Drainage is actively incising with substantial areas of contemporary erosion. Sediments from erosion are generally redistributed within the undulating landscape with suspended material entering the Great Barrier Reef lagoon in major rain events.
The Upper Burdekin sub-catchment is bound by mountain ranges and drains the western side of the coastal ranges, and the eastern side of the Great Dividing Range. The coastal ranges consist of rugged mountains, hills and dissected plateaus of granite, and granodirorite, with the eastern side of the Great Dividing Range comprised of young basalt plateaus, high plains and rugged hills of volcanic and sedimentary origins. The basin itself contains remnants of old sedimentary basins and is strongly undulating but also contains gently undulating to flat plateaus and riverbeds.
A range of soil types exist in the region including extensive areas of moderately productive and fairly erodible red duplex soils, widespread high productivity black and red soils on basalt, and large areas of poor to moderate fertility sands, sodic duplex soils, red and yellow earths. With the exception of the basalt soils, most have relatively low levels of nitrogen and organic matter as a result of the high temperature, low humidity and intense weathering and leaching.
Most of the Belyando-Suttor sub-catchment consists of a series of remnant sedimentary basins. Almost half is comprised of extensive plains and lowlands that form the central southern portion of the broader Burdekin Dry Tropics region. Much of this area has formed from Quaternary alluvial deposits composed of sand, gravel, soil and cemented volcanic products. The Suttor originates in the Central Hills in the east of the sub-catchment. The south west of the Belyando-Suttor subcatchment drains isolated low ranges and gently undulating plains formed of low tablelands covered by Tertiary detrital rocks and laterite.
The south and south east drains gently undulating lands derived from Tertiary sandstone and includes shallow scarps and long ridges formed over dipping sedimentary rocks of the Drummond Range. Alluvial plains and braided channels are found along most stream tracts and extensive low gradient fans several kilometres across are characteristic of the Belyando River. The Cape River in the northwest drains the high western plateau and plains.
Cracking clays predominate through much of the Belyando-Suttor sub-catchment due to the presence of basic igneous parent rock, clay containing sedimentary rocks, and fine textured hillslope and river bank deposits. Widespread soils include grey/brown clays and red/yellow earths. Large areas in the eastern plains and adjacent slopes have dispersive properties due to past salinisation and leaching. The low rainfall and high evaporation rates generally limit leaching on all but the coarse textured soils. Soil organic matter is also generally low due to low humidity, high temperature and seasonal aridity. The south east of the sub catchment is considered to have a high salinity hazard.
The Bowen-Broken sub-catchment is largely comprised of sedimentary and volcanic parent rock. Sandstones and siltstones form the main rock types in the sedimentary basins while conglomerates, quartz rich sandstones and limestone form ridges, escarpments and rugged gorges. The Bowen River originates in the Central Hills and Tablelands and runs through low undulating hills with some steeper ridges and dissected tablelands. The Broken River originates in the North Eastern Highlands and flows through an incised valley to Eungella Dam, and then through a tortuous valley system through rugged volcanic hills before opening out to join the Bowen River. The lower Bowen valley contains alluvial levees, rolling plains and gentle rises.
Predominant soils within the Bowen - Broken include red/brown earths and yellow podsolic/soloths. On the drier western slopes of the coastal ranges the strongly undulating landscape is covered by yellow soils derived from weathered intermediate rocks. Much of the eastern slopes of the Leichhardt Range to the west are covered by shallow, gravelly, sandy soils of granite and sandstone origins. Areas of black earths lie between Collinsville and the Burdekin and Bowen Rivers with smaller isolated occurrences at Exe Creek near Redcliffe and Broken River near Emu Plains.
Coastal Catchments, Bowen to Townsville
The coastal catchment landscapes stretch from the Don River in the south to Crystal Creek in the north and include the Burdekin, Haughton, Ross and Black Rivers. These systems host acid volcanic, acid igneous and sedimentary rocks. A contiguous Quaternary coastal plain formed from superficial sand, gravels and silt deposits backed by coastal hills and mountain ranges, extends to the northern and southern margins of the region having its broadest expression at the lower Burdekin floodplain, which extends inland almost to the base of the Leichhardt Range. The lowlands of the Lower Burdekin are comprised of alluvial levees, floodplains and the Burdekin delta, which is the largest on the Australian east coast. Prior channels of the Burdekin River including the current lower Haughton River channel form distributary systems for the greater floodplain. The Don River to the south and the Ross and Black Rivers to the North of the Burdekin form similar albeit much smaller coastal land systems to the lower Burdekin.
Granite basement rock outcrops form isolated coastal hills, rocky capes and off shore continental islands and have their greatest expression in the isolated massif of Mt Elliot which lies between the Ross and Haughton River catchments and at 1234m represents the fifth highest peak in Queensland. Other coastal land forms of significance include extensive marine plains with salt pans, tidal creek channels and estuary complexes, elevated beach ridge and dune systems, beaches, sand spits, and shallow embayments with off shore continental islands including Magnetic and the Palm group having fringing reefs. The edge of the continental shelf 80-100km offshore forms the foundation for the Great Barrier Reef enclosing the Great Barrier Reef lagoon which receives the discharge from the Burdekin River and smaller coastal catchments.
Higher rainfall results in the formation of deeper fine textured, strongly weathered soils particularly on footslope areas. Severe leaching and weathering affects the nutrient status of soils, which with the exception of younger alluvials, is generally low. Soils of the Lower Burdekin and coastal catchment lowlands are variable reflecting the nature of the river deposits and their variable age. Soils include black cracking clays, silts, sands and a range of duplex and sodic soils some of which are highly dispersive. Generally young alluvial soils of the levees and deltas of rivers and active smaller coastal catchments are coarser textured and more fertile while older, broader less active floodplains are finer grained and less fertile. Near coastal areas have humic gleys and acid sulphate soils that have formed in anaerobic marine swamp environments during previous elevated sea levels.
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