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Publications
Supervising Scientist Report 175 (National River Health Program, Environmental Flows Initiative, Technical Report 4)
Erskine WD, Begg GW, Jolly P, Georges A, O'Grady A, Eamus D, Rea N, P Dostine, Townsend S & Padovan A
Environment Australia 2003
ISSN 1325-1554
ISBN 0 642 24382 4
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Flow regimes and environmental water requirements of the Daly River must be understood to set appropriate environmental flows and water licence conditions for large scale agricultural development and associated vegetation clearing. The Daly River provides a unique opportunity to address these issues before significant agricultural development impacts on streamflow regimes and to protect its long recognised wild river status.
Environment Australia and the Northern Territory Government, therefore, as part of the National River Health Environmental Flow Initiative, funded the following five projects:
The aim of these projects was to provide recommendations on environmental flows consistent with maintaining the biota and wider ecosystem values of the Daly River. Eight of the nine species of freshwater turtles found in the Northern Territory are present in the Daly River. Furthermore, at least two nationally threatened species of elasmobranchs, the Freshwater whipray (Himantura chaophraya) and the Freshwater sawfish (Pristis microdon), are also present. According to Pogonoski et al (2002), these species are critically endangered and vulnerable, respectively.
The recommendations derived from work undertaken for the five projects are given in table A. They need also to be accompanied by the following actions:
| Environmental Issue | Recommended Water Allocation and/or Restriction on water extraction | |
|---|---|---|
| 1 | Interdependence of streamflow, groundwater discharge and groundwater and surface water quality | Groundwater and streamflow quantity and quality must be managed holistically and supported by an integrated natural resource management approach. Dry season streamflows must continue to be sourced from karst aquifers with bicarbonate dominance and very low nutrient concentrations. |
| 2 | Protection of critical streamflows that cue various biotic responses | Environmental water allocations can be partly addressed by adopting a flexible and variable approach to agricultural water allocations. Flood peaks and minimum streamflows must be maintained unchanged. Agricultural extraction can be permitted from less ecologically sensitive streamflows, as outlined below. |
| 3 | Protection of flood peaks for channel maintenance, reworking of sand bars for pig-nosed turtle nesting sites, lateral connection of floodplains, natural disturbance events for riparian vegetation regeneration |
|
| 4 | Maintenance of groundwater levels and spring inflows to the Daly River | No groundwater extraction allowed within 3 km in a straight line from the Daly River. This condition is to be verified by modelling of aquifers and detailed monitoring of bore levels and revised, as needed. The assessment criterion should be based on a series of bores situated next to the Daly River and at various distances (up to about 5 km) away from the channel. Control bores next to the river must be outside the cone of depression in groundwater level caused by pumping from bores further from the river. |
| 5 | Maintenance of minimum streamflows to protect Vallisneria nana, Spirogyra and pig-nosed turtle | Agricultural water extraction allowed from the Daly River and aquifers providing spring input must be managed so that the cumulative impact on flows is < 8% when streamflows reach the following thresholds at the stated locations: Claravale Crossing - 6.2 m³s-1 Oolloo Crossing - 12 m³s-1 Mt Nancar - 12 m³s-1 At discharges greater than the above thresholds, no more than 20% of the streamflow greater than the above thresholds (ie 16 m³s-1 when streamflow is 80 m³s-1 but only 3 m³s-1 when streamflow is 15 m³s-1) can be extracted. |
| 6 | Maintenance of turtle and fish passage | Same conditions as outlined for point 5 plus: All road crossings should be built according to Erskine & Harris’s (2003) principles for unimpeded fish passage Water quality barriers (such as irrigation return flows, drain discharges, etc) to faunal passage should be prohibited. |
| 7 | Maintenance of groundwater levels for periodic/episodic use by riparian vegetation | No extraction of groundwater within 3 km of the Daly River. All of the riparian vegetation water use can be met by maintaining a streamflow of less than 2 m³s-1 during the Dry season, assuming that there is no loss of streamflow to regional aquifers. Therefore, groundwater levels next to the Daly River must not be lowered below river levels. |
| 8 | Maintenance of existing water quality | Apply ANZECC and ARMCANZ (2000) water quality guidelines so that trigger values for pH, electrical conductivity, bicarbonate, total nitrogen, total phosphorus, soluble reactive phosphorus and selected metals are derived and applied to the Daly River and groundwater. Exceedances of trigger values must induce a to-be determined response from government and agricultural industry. |
| 9 | Maintain existing structure and function of all wetlands | No dam or regulatory structure to be built on any river without an EIS. |
| 10 | Assessment of the adequacy of imposed licence conditions and discharge thresholds with appropriate revision based on monitoring results | Adopt an adaptive ecosystem management approach supported by appropriate licensing, auditing, stream gauging, groundwater level measurements, water quality monitoring, biomonitoring and benchmarking programs. There must be feedback from the monitoring/auditing results to the licence conditions. |
There are many significant potential threats to the health of the Daly River from further agricultural development and associated vegetation clearing. Such threats, should they occur, will modify the environmental water allocations recommended in table A and will necessitate future revisions, depending on the results of monitoring under an adaptive ecosystem management approach. The presently identified threats from future agricultural development and consequential land clearing are:
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The views and opinions expressed in this publication are those of the authors and do not necessarily reflect those of the Northern Territory and Commonwealth Governments. While reasonable efforts have been made to ensure that the contents of this publication are factually correct, the Northern Territory and Commonwealth Governments do not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this publication. The information contained in this work has been published by Supervising Scientist Division of Environment Australia and the Northern Territory's Department of Infrastructure, Planning and Environment to help develop community, industry and management expertise in sustainable water resources management and raise awareness of river health issues and the needs of our rivers. The Northern Territory and Commonwealth Governments recommend that readers exercise their own skill and care with respect to their use of the material published in this report and that users carefully evaluate the accuracy, currency, completeness and relevance of the material for their purposes.
