DARLING RIVERINE PLAINS BIOREGION Background Report

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16/08/02 Darling Riverine Plains Bioregion Background Report 7.1.2 Hydrological regimes The Mehi, Macintyre, Namoi and Macquarie Rivers, and Moomin, Carole, Gunningbar, and Duck Creeks are regulated rivers and parts of the Gwydir and Darling Rivers are also regulated. Regulated rivers are those that “have large dams supplying irrigation water (and some town and industrial water) for substantial distances downstream. Downstream tributary inflows are typically supplemented during the irrigation season, resulting in fairly stable and unnaturally high water levels. River flow is substantially reduced during the non- or lowirrigation seasons. At any time of year in periods which would normally have high or very high flow, flows may be substantially reduced by the trapping of water in a large dam” (EPA 2001). River Management Committees are considering and implementing environmental flows to improve this flow reduction. The Castlereagh River and all other streams within the Castlereagh catchment in the DRP, the Bogan River, Whalan Creek, Thalaba Creek, Marra Creek, and Talyawalka Creek are classified as unregulated rivers. Unregulated or uncontrolled streams are those streams where “flow patterns are largely natural. Flows can occur in these streams from local runoff. They are typically ephemeral (flowing only during floods and freshes). Frequently, they open into or flow through wetlands and billabongs” (EPA 2001). The Barwon, Culgoa, Birrie, Bokhara, Narran, and Boomi Rivers, the Gwydir Watercourse and Pian Creek, and the parts of the lower Gwydir, lower Macquarie and upper Darling Rivers are classified as controlled rivers with reduced flow. Controlled rivers with reduced flows include: 1. “River reaches downstream of the major regulated sections where the water is extracted or diverted. Flow is generally reduced throughout the year. Water is delivered from the main stream for stock, domestic, some irrigation, and town water supplies several times a year. 2. Sections of rivers immediately below town water supply dams, where water is diverted directly from the dam. Flows can be substantially reduced throughout the year, though special environmental releases may be possible” (EPA 2001). The majority of the bioregion is categorised as either over-extracted in relation to groundwater or with an extraction level of greater than 100% of the sustainable yield for groundwater systems. Two smaller areas in the east and south of the bioregion have a total extraction level of between 70 and 100%. The remainder of the bioregion has an abstraction of greater than 30% sustainable yield. This area is mostly the Darling riverine corridor of the bioregion (EPA 2000). EPA (2000) lists good-quality (or low-salinity) ground water as that found in aquifers including those in the Darling River corridor. The yields from aquifers within the Darling River corridor are generally low and more suitable for domestic and stock use or small-scale irrigation (for example, for orchards). Aquifers that have good-quality water and high yields within the DRP include the river corridors of the Namoi and Upper Gwydir. These aquifers are used mainly for irrigated agriculture and stock watering, but potable water extraction is also an important use. Ground water from the aquifers bounded by the Lachlan, Darling and Bogan rivers and the south-western corner of the State is generally of poor quality or extremely low-yielding (EPA 2000). 120
16/08/02 Darling Riverine Plains Bioregion Background Report Contamination of groundwater by pesticides has been recorded in the lower Namoi Valley but monitoring of pesticides in groundwater is limited and further sampling and monitoring is required to assess accurately levels of contamination (EPA 2000). 7.2 LISTED AND POTENTIAL THREATENING PROCESSES Key threatening processes listed under the TSC Act are those that threaten, or may have the capability of threatening, the survival or evolutionary development of species, populations or ecological communities. Eight of the key threatening processes (KTPs) listed under Schedule 3 of the TSC Act affect the ecology of the DRP bioregion. A preliminary determinations has also been made by the NSW Scientific Committee to support the listing of the ‘competition with feral honeybees Apis mellifera’ as a KTP (NPWS 2001A). The Fisheries Management Act 1994 (NSW) (FMA 1994) also lists key threatening processes. The NSW Fisheries Scientific Committee has made final recommendations to list ‘degradation of native riparian vegetation along New South Wales watercourses’, ‘removal of large woody debris’, and ‘introduction of fish to fresh waters within a river catchment outside their natural range’ as key threatening processes under the FMA 1994. The Fisheries Scientific Committee has also made a recommendation to list ‘installation and operation of instream structures that modify flow’ as a key threatening process under the FMA 1994. The EPBC Act lists nine KTPs of relevance to the DRP. Some of these identify the same process as listed on the TSC Act but may define them differently (Environment Australia 2001c). 7.2.1 Listed Threatening Processes High frequency fire ‘High frequency fire resulting in the disruption of life cycle processes in plants and animals and loss of vegetation structure and composition’ has been listed as a key threatening process under the TSC Act. The NSW Scientific Committee defines high frequency fire as ‘two or more successive fires close enough together in time to interfere with or limit the ability of plants or animals to recruit new individuals into a population, or for plants to build up a seedbank sufficient in size to maintain the population through the next fire’ (NPWS 2001A). The rate of decrease of woody vegetation across New South Wales between 1990 and 1995 due to bushfires has been estimated to be 33 520 ha / year. 66% of this area of woody vegetation is expected to regenerate quickly (Bureau of Rural Sciences 1999). Threatened species known from the DRP likely to be affected by high frequency fires include Swainsona plagiotropis, glossy black-cockatoo, malleefowl, rufous bettong, black-striped wallaby, spotted-tailed quoll and squirrel glider (NPWS 2001a). Species not yet listed but occurring in the DRP that could become threatened by high frequency fires include feathertail glider (Acrobates pygmaeus), common ringtail possum, yellow-footed antechinus (Antechinus flavipes) and sugar glider (Petaurus breviceps) (NPWS 2001a). Anthropogenic climate change Anthropogenic climate change is listed as a key threatening process under the TSC Act and the EPBC Act. Natural climate change has been a major ecological driving force throughout geological history but there is evidence to suggest that modification of the environment by 121
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DARLING RIVERINE PLAINS BIOREGION B
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For more information data contact t
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3.2 Vegetation Mapping and Descript
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10 APPENDICES 166 A CLIMATIC DATA B
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List of Maps Chapter 1 Map 1 Locati
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PROJECT SUMMARY This report forms p
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abbits are listed as key threatenin
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ainfall (mm) 900 800 700 600 500 40
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Major Rangetype Rangetype Physiogra
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Appendix C : Native Flora Other Tha
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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 Tabanidae s
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Taxa No Records Dataset Berosus sp
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