DARLING RIVERINE PLAINS BIOREGION Background Report

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16/08/02 Darling Riverine Plains Bioregion Background Report Figure 2.17 Groundwater features of the Coonamble Embayment of the Great Artesian Basin (Watkins & Meakin 1996) One thousand, four hundred bores tap the deeper aquifers of the GAB in New South Wales but nearly half of these have ceased to flow as a result of artesian pressure having decreased markedly over the past 100 years. About 250 of the bores operating in New South Wales have uncontrolled flow (DLWC & AFF 2000). The Great Artesian Basin Mound Springs are wetlands found mostly within the Mulga Lands bioregion but some occur within the DRP. Mound springs in the Great Artesian Basin provide important habitat for more than 40 species of freshwater snails which are endemic to these springs and some which are endemic to an individual spring (Environment Australia 2000d). About one third of the mound springs have dried up as a result of the decreased artesian flows. Alluvial aquifers The Namoi catchment alluvial aquifer is the most extensive and most intensively developed aquifer system in New South Wales. It accounts for nearly 40% of all good quality, high yield groundwater extracted. This is mainly used for irrigation and is currently over-allocated (Table 2.4). Alluvial aquifers are also of great importance in the Gwydir and the Macquarie 50
16/08/02 Darling Riverine Plains Bioregion Background Report catchments. The alluvial aquifer near Narromine has yielded 10 litres/second and is being tapped extensively for crop irrigation between Narromine and Warren (NWCMC 1996). Table 2.4 Groundwater resources of the Lower Namoi Catchment (NWCMC 1996) Total area of alluvium (km 2 ) 5 100 Volume of storages (ML) 20 million Volume available for extraction (ML) 6.6 million Estimated recharge (ML/yr) 82 500 Entitlements (ML/yr) 208 000 About 5.4 million hectares of land in New South Wales have groundwater at or near the surface; this is mostly on the western slopes (MDBC 1999). There are estimates that up to 12.3 million hectares, about 20% of the Murray-Darling Basin in New South Wales (a more extensive area than the DRP) may be experiencing rising groundwater tables. In addition, an estimated 40% to 80% of the individual catchments east of the Bogan and Darling Rivers, which make up the majority of the DRP bioregion, have rising groundwater levels. There have been very few detailed groundwater studies in the DRP (DLWC 1999). The area of land with high water tables and which could become salt affected has not been precisely estimated, but a waterlogged area of between five and seven million hectares is considered to be realistic. Serious salination is predicted to affect between two and four million hectares (MDBC 1999). Salt loads in the Darling River also appear to be enhanced by the inflow of saline groundwater, which originates in the Cainozoic valley-fill aquifers of the Bourke Graben (Mount 1995). Sturt (1833), on his expeditions into the interior of southern Australia describes the Darling River as follows: “as a river it ceased to flow; the only supply it received was from brine springs, which, without imparting a current, rendered its waters saline and useless”. This suggests that salinities within the Darling River are affected by naturally saline ground water. 2.5 LAND CONDITION 2.5.1 Land degradation The north east portion of the bioregion, the alluvial fans of the Darling tributaries, has been extensively cleared with remnant vegetation now often only found in woodland ‘islands’ on infertile or non-arable land. Goldney and Bowie (1990) have described this region as “islands of woodlands and forests in a sea of agricultural land”. Land clearing began with the early settlement in the 1830s. The plains of the lower Namoi catchment were originally covered by grasslands and open woodlands and the black cracking clays of these plains are now mostly used for cropping. In this area there is an average tree cover of nine percent (NWCMC 1996). Important causes of land degradation in the bioregion include: soil erosion; streambank erosion; tree decline; rising groundwater and dryland salinity; 51
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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 Name Scientific Name No Reco
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Common 1983 1984 1985 1986 1987 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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DARLING RIVERINE PLAINS BIOREGION Background Report

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