DARLING RIVERINE PLAINS BIOREGION Background Report

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16/08/02 Darling Riverine Plains Bioregion Background Report Table 2.5 Actual and predicted average salinity levels for major rivers in the DRP (MDBC, 1999) River valley 1998 2020 2050 2100 Bogan River 730 1 500 1 950 2 320 Macquarie River 620 1 290 1 730 2 110 Castlereagh River 640 760 1 100 1 230 Namoi River 680 1 050 1 280 1 550 Gwydir River 560 600 700 740 Trends in the levels of salt concentrations in the rivers have indicated that within the DRP they are increasing by 2-4 tonnes per km per annum in the Castlereagh / Macquarie systems, and more than 1 tonne per km per annum in the Namoi River. The amount of salt mobilised to the land surface in the Murray Darling Basin is predicted to double from five million tonnes annually in 1998 to 10 million tonnes annually in 2100. The predictions are significant for the river catchments within the DRP (Table 2.6) (MDBC 1999). Table 2.6 Predictions of the tonnes of salt mobilised to the land surface per year for river catchments of the DRP (MDBC 1999) Catchment 1998 2020 2050 2100 Macquarie River 240 000 490 000 660 000 790 000 Castlereagh River 161 000 180 000 320 000 330 000 Namoi River 60 000 100 000 120 000 150 000 Gwydir River 7 000 20 000 50 000 60 000 Macintyre River 80 000 80 000 80 000 80 000 The economic impact of rising watertables and salinity has been estimated for the Little and Talbragar Rivers in the Upper Macquarie catchment. The estimated annual cost of rising water tables and salinity for the Talbragar River catchment was $1 612 421, with the major costs for repairs, maintenance and preventative works being borne by farmers (MDBC 1999). In the lower Macquarie area water tables are rising at 0.3m/year in some areas and between 15 and 20 thousand hectares have water less than three metres below the surface. Water will be unsuitable for irrigation in this area as a result of high salinity loads by 2100 (Macquarie 2100 Plan 1999). 54
16/08/02 Darling Riverine Plains Bioregion Background Report 2.6 BOUNDARIES WITHIN THE DRP The land within the DRP has been described and subdivided using a variety of criteria and scales. Some descriptions most widely used by land managers are the province and regional descriptions by Morgan and Terrey (1992) and land system descriptions of the Western Division by Walker (1991). 2.6.1 Provinces In NSW nine provinces have been described for the DRP (Morgan & Terrey 1992). Five of these cover each of the northern alluvial fans, one is an interfluve of the weathered sandstones near Collarenebri and three are different types of alluvial deposits along the Darling River, south from Bourke (Map 21). Within Queensland the northern extent of the DRP is described as two distinct provinces of the Brigalow Belt South Bioregion (Sattler & Williams 1999). Northern Alluvial Fans The catchment characteristics of each of the northern alluvial fans have resulted in variation in the flood patterns and alluvial deposits between each province. Bogan-Macquarie Province This alluvial complex formed by the Bogan and Macquarie Rivers lies in the south east of the bioregion. The province has a large catchment extending beyond the DRP bioregion south east of Bathurst and east to the Liverpool Range. Quaternary alluvials are underlain mostly by Paleozoic sediments and small areas of basalt and sandstone. The coarser-textured high red ridges and Eucalyptus populnea subsp. bimbil (poplar box) woodlands dominate the eastern portion of this province. Grey and brown clays dominate on the plains and depressions, alluvial soils on levees and river channels with texture contrast soils occurring on the low and gently undulating rises. The wetlands and low-level floodplains of the Macquarie River dominate the central areas of the province. Much of this area has been cleared, although the wettest areas within the Macquarie Marshes Nature Reserve retain significant areas of native vegetation. The western parts of this province are associated with the Bogan River and receive high level overflows from the Macquarie River. Flooding is infrequent and the finer soils of low scalded rises and clay plains are dominant. Castlereagh-Barwon Province Extensive plains of quaternary alluvials with a strong basaltic influence form the Castlereagh- Barwon province. This is the most intensively developed province of the bioregion, including both dryland and irrigated cropping. It includes the alluvial fans of the Castlereagh, Namoi, Gwydir and Macintyre Rivers and the broad plains of the Barwon and upper Darling Rivers. Seasonal and semi-permanent wetlands are present on the major tributaries including the significant wetlands of the Gwydir. The landform contains three co-dominant formations: river channels, levees and lower floodplains with riparian woodland vegetation; upper floodplains predominantly covered by Astrebla lappacea (curly Mitchell grass); and wooded low rises with some higher gently undulating areas. Soils range from grey clays of the floodplains to texture contrast soils, 55
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DARLING RIVERINE PLAINS BIOREGION B
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Page 5 and 6: 3.2 Vegetation Mapping and Descript
Page 7 and 8: 10 APPENDICES 166 A CLIMATIC DATA B
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Initial Phase Assessment Phase 16/0
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Appendix A: Mean Monthly Rainfall a
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Major Rangetype Rangetype Physiogra
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Appendix C : Native Flora Other Tha
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Family Scientific Name Common Name
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Family Scientific Name cretica Comm
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APPENDIX E: Fauna Other than Those
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Common 1983 1984 1985 1986 1987 198
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Common Name 1983 1984 1985 1986 198
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Taxa No Records Dataset Class Arach
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Taxa No Records Dataset Family Hebr
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Taxa No Records Dataset Tabanidae s
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Taxa No Records Dataset Berosus sp
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