Determination of Environmental Water Requirements of the Onkaparinga River Catchment Summary Report Version 1
March 2003 Determination of Environmental Water Requirements of the Onkaparinga River Catchment
Summary Report
Version 1 April 2003
Sinclair Knight Merz Pty Limited ACN 001 024 095 ABN 37 001 024 095 590 Orrong Road Armadale VIC 3143 PO Box 2500 Malvern VIC 3144 Australia Telephone: +61 3 9248 3100 Facsimile: +61 3 9248 3440
COPYRIGHT: The concepts and information contained in this document are the property of Sinclair Knight Merz Pty. Ltd. Use or copying of this document in whole or in part without the written permission of Sinclair Knight Merz constitutes an infringement of copyright. Contents
1. Introduction...... 1 1.1 Background ...... 1 1.2 Description of the Project...... 2 1.3 Document Structure...... 3 2. The Onkaparinga River Catchment ...... 4 2.1 Catchment Description ...... 4 2.2 Subcatchments...... 5 3. Environmental Water Requirements ...... 7 3.1 Overview of Approach ...... 7 3.2 Issues...... 7 3.3 Site Selection...... 8 3.4 Initial Multi-disciplinary Fieldwork...... 9 3.5 Technical Investigations...... 10 3.5.1 Fish Investigations ...... 10 3.5.2 Geomorphological investigations ...... 11 3.5.3 Macroinvertebrate investigations ...... 12 3.6 Hydrology and Hydraulics ...... 13 3.6.1 Topographic survey...... 13 3.6.2 Modelling of natural and current hydrology...... 13 3.6.3 Hydraulic modelling...... 14 3.7 Objectives...... 14 3.8 Determination of Environmental Water Requirements ...... 16 4. Environmental Flow Needs ...... 19 4.1 Approach ...... 19 4.2 Environmental Condition...... 19 4.3 Current Achievement of EWRs ...... 22 4.4 Prioritisation of Flow Components at each Site...... 24 4.5 Priority Environmental Flow Needs ...... 25 5. Options to Provide Environmental Flows...... 26 5.1 Guiding Principles and Objectives ...... 26 5.1.1 Principles...... 26 5.1.2 Objectives ...... 26 5.1.3 Evaluation criteria...... 27 5.2 Options for EWPs to meet priority needs ...... 28 5.2.1 Low flow bypass structure of Clarendon Weir ...... 28 5.2.2 Modify releases from Mt Bold Dam...... 28 5.2.3 Decommission Mt Bold Dam...... 29 5.2.4 Modify SA Water pumping schedule...... 29 5.2.5 Limit on new farm dams...... 29 5.2.6 Low flow bypass on farm dams...... 29 5.2.7 Voluntary decommissioning of farm dams...... 30 5.2.8 Indirect options to meet/support environmental needs...... 30 5.3 Summary of Options ...... 31 5.4 Non-flow Related Issues...... 32 6. Development and Implementation of Strategies...... 33 6.1 Development of Environmental Flow Strategies...... 33
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE i 6.2 Implementation of Environmental Flow Strategies ...... 34 6.3 Monitoring Program ...... 34 6.3.1 Monitoring delivery of EWPs...... 34 6.3.2 Response monitoring ...... 35 7. Conclusions ...... 38 8. References ...... 40 Appendix A Description of Flow Components ...... 43 Appendix B Environmental Objectives...... 45 Appendix C Environmental Water Requirements...... 48
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE ii Document History and Status
Rev. Date Reviewed By Approved By Revision Details Draft A 11/4/03 Peter Hill Michael Shirley Version 1 28/4/03 Peter Hill Michael Shirley
Distribution of copies: Copy No. Quantity Issued To Draft A 1 Steve Gatti via email Version 1 2 Steve Gatti as bound copies
Printed: 2 May, 2003 Last Saved: 28 April, 2003 File Name: I:\Wcms\WC01440\Reports\Summary\R02pih_Onka_Summary.Doc Author: Peter Hill Project Manager: Peter Hill Name of Organisation: Onkaparinga Catchment Water Management Board Name of Project: Determination of Environmental Water Requirements of the Onkaparinga River Catchment Name of Document: Summary Report Document Version: Version 1 Project Number: WC01440
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE iii 1. Introduction
1.1 Background The need to reform the water resource industry and provide water for the environment has been recognised by both Federal and State Governments in the Council of Australian Governments (COAG) Water Reform Agenda (ARMCANZ, 1995). Under the 1994 COAG agreement, the environment is recognised as a legitimate water user and environmental water requirements must be assessed and provided. The National Principles for the Provision of Water for Ecosystems defines environmental water requirements as: …the water regimes needed to sustain the ecological values of aquatic ecosystems at a low level of risk (ARMCANZ and ANZECC, 1996).
Given that some systems are over-allocated and unable to provide fully for environmental water requirements, negotiation between stakeholders can lead to the establishment of flows for the purpose of environmental protection. Such flows are defined in this report as environmental water provisions meaning: …that part of environmental flow requirements that can be met (ARMCANZ and ANZECC, 1996).
South Australia is a signatory to both the COAG Water Reform Agenda (ARMCANZ, 1995) and the National Principles for the Provision of Water for Ecosystems (ARMCANZ & ANZECC, 1996). These national policies are reflected in the State’s Water Resources Act 1997. The object of the Act is inter alia, to establish a system for the use and management of the water resources of the State in order to protect the ecosystems (including their biological diversity) that depend on those resources (Section 6(1)(a)(ii)). In 2000, the Government of South Australia released the State Water Plan (DWR, 2000) that includes measures to provide water to meet environmental needs. The goal for the integrated management of waterbodies and associated water-dependant ecosystems is to manage them so that the: q condition of these systems is maintained or improved; q long-term integrity of the ecological functions and dependant biodiversity is ensured; and q ecologically sustainable use of these ecosystems, which include highest value of water, is achieved (DWR, 2000).
This goal of the State Water Plan is incorporated in the Onkaparinga Catchment Water Management Plan, finalised in December 2000, by the Onkaparinga Catchment Water Management Board (OCWMB). The plan identified the issue of water for the environment as an integral component of the management of watercourses. The Board has also included in its plan the provision of water for ecosystems as one of the criteria to be considered when deciding applications for water affecting activities.
The determination of environmental water requirements is based on identifying and incorporating features of the natural flow regime that are considered essential for maintenance of riverine habitat and ecological processes. It is assumed that if the essential features of the natural flow regime can be identified and adequately incorporated into a modified regime, then the functional integrity of the ecosystem
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 1 should be maintained and the more damaging effects of flow modifications can be avoided.
The identification of environmental water requirements includes consideration of: q flow regimes in terms of the timing, duration and seasonality of flows; q components of the water cycle beyond watercourses (e.g. rainfall, surface water runoff and groundwater); q the size and shape of watercourses (e.g. pools, riffles, depth and width); q the ecosystems which depend on water (e.g. fish, macroinvertebrates and vegetation); and q determination of the relationship between water dependent ecosystems (including key processes such as migration or life-cycles) and the flow of water in the watercourse at different times (i.e. the flow regime).
1.2 Description of the Project The project examines the environmental water requirements of the surface water systems of the Onkaparinga River Catchment. The project provides a scientific basis for the OCWMB to implement provisions for water dependent ecosystems, and in doing so, meet the object of the Water Resources Act 1997 and the objectives contained in the Onkaparinga Catchment Water Management Plan. The project includes a multi-disciplinary approach, with a need to integrate information from ecology, hydrology, geomorphology, hydrogeology and water quality.
The primary aim which forms the basis for the project was: To sustain and restore ecological processes in the Onkaparinga River catchment by providing water to meet environmental needs (as far as practicable) so that the environmental, social and economic values and essential ecosystem functions of the river system are maintained and enhanced.
The project defines a clear scientific process for the determination of environmental water requirements and strategies to implement and test environmental water provisions. The project includes: q thorough investigation of existing information on catchment water resources, available habitat and dependent ecosystems; q definition of multi-disciplinary objectives and targets; q use of a sound scientific method to determine environmental water requirements; q identification of potential options for environmental water provisions; and q development of a monitoring and evaluation program to support implementation and testing of environmental water provisions.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 2 1.3 Document Structure This report is structured as follows: q Chapter 2 - The Onkaparinga River Catchment - the catchment and the relationship between the various subcatchments and reaches. q Chapter 3 - Environmental Water Requirements - the objectives and approach used to determine the EWRs and summaries of the EWRs for each site. q Chapter 4 - Environmental Flow Needs - the identification of the key environmental flow needs within the catchment based upon consideration of the environmental condition, current achievement of EWRs and prioritisation of EWR flow components. q Chapter 5 - Developing Options for Environmental Water Provisions - guiding principles and objectives and the potential options for environmental flow provisions. q Chapter 6 - Development and Implementation of Strategies - the development and implementation of detailed strategies and a monitoring program. q Chapter 7 - Conclusions
This summary report is supported by 9 technical reports which give greater detail on the different technical aspects of the project (refer to the table below). n Table 1-1 Summary of technical documents
Document Date I Integrated Issues Paper March 2001 II Preliminary Fieldwork November 2001 III Site Location and Hydrology November 2001 IV Physical Habitat Preferences of Aquatic Macroinvertebrates September 2001 V Fish Survey March 2002 VI Catchment Geomorphology March 2003 VII Environmental Water Requirements September 2002 VIII Assessment of whether Environmental Water Requirements are February 2003 being met IX Options for Environmental Water Provisions March 2003
This summary report only provides an overview of the approach and outcomes of the study. Thus, the reader is directed to the accompanying technical reports for details of the methods adopted, the results and the rationale for the recommendations contained in this summary report.
The project was undertaken over a two and a half year period finishing in March 2003 and the reports document the understanding at the time based upon the then available information. Thus, the technical reports document the "journey" of the project.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 3 2. The Onkaparinga River Catchment
2.1 Catchment Description The study area for this project includes the main channel of the Onkaparinga River from the headwaters to the estuary and all tributary streams (see Figure 2.1). The following catchment description is a summary of information contained in Technical Report I - Integrated Issues Paper.
The Onkaparinga River catchment is located in South Australia and covers an area of approximately 564 km2. The river rises near Mount Torrens in the Mount Lofty Ranges, at around 650 m elevation, approximately 30 km east of Adelaide, and flows south-westerly to the Gulf St Vincent at Port Noarlunga.
Upstream of Mount Bold Reservoir many of the tributaries of the Onkaparinga River are deeply incised. The main channel is narrow and relatively straight. The valley structure is generally asymmetric, with steep north-westerly slopes and a narrow floodplain. Terrain to the west of the river is dominated by hilly uplands while the eastern side of the catchment is characterised by undulating to hilly high plains.
Sediment deposits laid down by the river during the Quaternary (the last 2 million years) are prominent between Balhannah and Mylor where narrow terraces overlie an older alluvial base. In this reach, the river becomes more sinuous. It straightens out for a short distance near Mylor but resumes its winding pattern as it flows towards Mount Bold Reservoir.
Downstream of the Mount Bold Reservoir, the river changes course to run across the Clarendon Fault Block. It flows along a confined channel, which increases in width towards the Clarendon Weir pool. Below Clarendon Weir, the river has incised prominent gorges that steepen downstream.
The Onkaparinga River widens when it reaches the coastal plains at Old Noarlunga. River terraces and floodplain features are evident here. Shortly after flowing onto the coastal plain the river is subject to tidal influences. It passes through a short estuarine reach before flowing into Gulf St Vincent (see Bourman, 1972).
The upper portions of the Aldgate Creek and Cox Creek sub-catchments are the wettest in the catchment with a mean annual rainfall of approximately 1100 mm. In the upper catchment the mean rainfall decreases from west to east, with a mean annual rainfall of approximately 700 mm along the eastern boundary. In the lower catchment, the mean annual rainfall drops from approximately 800 mm at Mt Bold Dam to 400 mm at the coast.
Before European settlement, the upper portion of the Onkaparinga River was ephemeral. During summer, dry streambeds separated large pools.
Today, the hydrology of the Onkaparinga River catchment is influenced by the operation of the Metropolitan Adelaide Water Supply System. The Murray Bridge-Onkaparinga Pipeline is used to supplement the natural runoff from the Onkaparinga River catchment. Water from the pipeline is discharged into the
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 4 Onkaparinga River at Hahndorf and then flows into Mt Bold Reservoir. Water is then released downstream of Mt Bold Reservoir to Clarendon Weir where it is diverted to Happy Valley Reservoir (outside of the catchment) for filtration and water treatment before being supplied for metropolitan consumption.
2.2 Subcatchments For this study, the Onkaparinga River catchment has been divided into 15 subcatchments and 4 reaches of the Onkaparinga River. Although these reaches are not strictly 'subcatchments' in a hydrologic sense, they have been separately identified because they pick up specific portions of the river that have distinct hydrologic characteristics. Figure 2.1 shows the subcatchments and reaches. Subcatchments were grouped into 3 broad regions based on their similarity; Eastern, Upper Western and Lower Western (refer to Figure 2.1).
It is important to recognise that the Onkaparinga River catchment is not simply a combination of isolated subcatchments and reaches of the main river. There is connectivity between the various subcatchments, in other words, a change in one part of the catchment will impact on the hydrology and ecology of subcatchments downstream (and in some cases the ecology upstream) of the location of change.
Due to the current water supply infrastructure in the catchment, an increase in flows in one part of the catchment may not be reflected by corresponding increases downstream.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 5 n Figure 2.1 Subcatchments and reaches of the Onkaparinga River catchment.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 6 3. Environmental Water Requirements
3.1 Overview of Approach The approach adopted for determining environmental water requirements builds on the the recently documented FLOWS method prepared by Sinclair Knight Merz for NRE (NRE, 2002). The key tasks are summarised in the following figure:
Issues Paper
Identify sites Investigations Initial Fieldwork
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g Topographic Model natural and
o l Surveying current hydrology
o
h
h
p
s
r
i
o
F
m
o
e
G Identify flow bands
Macroinvertebrates & model scenarios
Multi-disciplinary fieldwork
Develop & report EWRs n Figure 3-1 Overview of approach adopted for determining EWRs for the Onkaparinga River Catchment
3.2 Issues An issues paper was prepared that identifies and reviews the available background information on the values and issues in the catchment and river system, assesses critical knowledge gaps and considers key issues for consideration in developing an approach to determining the environmental water requirements of the catchment. Each issue is discussed in relation to its impact and the proposed response.
The EWR related issues identified and discussed were: q unmanaged abstractions;
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 7 q unmanaged groundwater abstractions; q impact of farm dams; q occurrence of unseasonal flows; q reduced medium and high flows below Mt Bold Reservoir; q presence of instream barriers; q deterioration of water quality; and q lack of integrated system management.
In addition to the above issues related to EWR, the following non-flow related issues were also identified and discussed: q erosion; q land management practices; q loss of riparian vegetation; and q presence of exotic vegetation.
Information on each of the above issues is provided in Technical Report I - Integrated Issues Paper.
3.3 Site Selection Representative field sites were chosen as the focus of the fieldwork and for determining the environmental water requirements. The sites were chosen by a multi- disciplinary team and considered: q stream gauge location; q length and completeness of stream gauge record; q proximity to regulating structures; q biological data (date collected, content and availability); q ecological significance (river and floodplain values); q cross-section data (location and availability); and q the ability to make, and the relevance of, calculated EWRs at that site.
At each site stream channel measurements were taken along with notes regarding the key ecological, hydrological and geomorphological features.
A total of 11 sites were selected and these are summarised in Table 3-1 and Figure 2.1.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 8 n Table 3-1 Study sites in the Onkaparinga River Catchment Site number Site name 1 Lenswood Creek at Peacock Rd 2 Inverbrackie Creek at landing strip 3 Onkaparinga River at Oakbank 4 Onkaparinga River at Allens 5 Onkaparinga River at Rowlands 6 Onkaparinga River at Houlgraves 7 Onkaparinga River downstream of Mt Bold 8 Scott Creek at Dorset Vale 9 Onkaparinga River at Brooks 10 Onkaparinga River at Gorge 11 Onkaparinga River at Noarlunga
The sites are described (with accompanying photos) in: q Technical Report III - Site Location and Hydrology; q Technical Report VI - Catchment Geomorphology; and q Technical Report VII - Environmental Water Requirements.
3.4 Initial Multi-disciplinary Fieldwork The initial multi-disciplinary fieldwork was conducted to finalise the location of sites, describe and assess each site, as well as locate and describe cross sections within a site. The field assessment was conducted during a low flow period to ensure the sites were observed with limited water in the river channel and the greatest representation of habitats and features was visible.
Basic site information was collected at each site using a standard set of descriptors and field sheets (NRE, 2002). This information included a description of the flow type that would be expected at that site e.g. perennial, ephemeral. The information collected also included a broad description of site features, substrate, availability of instream habitat and a description of the flow components that would be expected to occur at this site.
On completing the site description, between 4 and 6 cross-sections were identified at each site to allow subsequent development of a hydraulic model for that site. Cross sections were located to: q describe key habitat features; q include key flow restrictions; q indicate changes in flow direction or major changes in wetted area; q characterise areas of minimum depth (e.g. bars isolating pools longitudinally); and q key flow features (riffles, runs, pools etc.).
Figure 3-2 shows an aerial photo of a sample field site (Site 4 - Onkaparinga at Allens). The 5 cross-sections are shown on the photo along with sample photos.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 9 Similar figures are included in Technical Report III - Site Location and Hydrology for the other 10 field sites.
n Figure 3-2 Field site 4 - Onkaparinga River at Allens (upstream of Dissipator)
Each cross section was then sketched to summarise key features of ecological or structural relevance within the section. These drawings were later used to assist in identifying flow components that are necessary to maintain environmental values for each site. In addition, photos of general site features and features of each cross section (looking across as well as both upstream) were collected for later reference.
Further details of the approach and results of the preliminary fieldwork are provided in Technical Report II - Preliminary Fieldwork.
3.5 Technical Investigations
3.5.1 Fish Investigations The distribution of the fish community within the Onkaparinga River Catchment was identified as a key knowledge gap (refer to Technical Report I - Issues Paper). Historical data is non-specific regarding the location and extent of the different species within the catchment. There are numerous species that are important for either
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 10 conservation or recreation values within the catchment. The exact distribution of these species, specifically in regard to flow management points and potential barriers has a direct impact on EWRs and the efficacy of their implementation.
The objectives of the investigation were therefore to: q determine the abundance and distribution of fish species; q determine the distribution and extent of the key fish populations; and q examine any key fish barriers that may affect connectivity within the river system.
Sampling was undertaken at 19 sites throughout the Onkaparinga River catchment, between 12 November and 16 February 2002. Fish sampling was spread over two distinct trips (November and February) to investigate the variation in fish distribution over time and to identify fish species that occur at additional sites not sampled during November. The fish sampling covered all of the 11 study sites and an number of additional sites.
A range of fish sampling techniques were utilised depending on the site conditions and comprised backpack electrofishing, bait trapping, gill and fyke nets. A total of 18 fish species were recorded from throughout the catchment. Three of the species recorded have not previously been recorded from within the catchment (Dwarf Flathead Gudgeon, Callop and Australian Smelt). The abundance and distribution of fish species varied greatly throughout the study area, possibly attributable to a variation in availability of suitable aquatic habitat at each survey site.
The most widely distributed fish throughout the catchment were a native group, gudgeons (comprising both Flathead Gudgeon and Dwarf Flathead Gudgeon). Redfin Perch, an introduced species that predate on small fish species, was also widely distributed. The wide spread distribution of this exotic species may impact on the distribution of native species.
Details of the fish investigations and results are provided in Technical Report V - Fish Survey.
3.5.2 Geomorphological investigations Little has been published on the geomorphology of the Onkaparinga River catchment and this lack of knowledge presented an impediment to assessing the effects of changed flow regimes on the catchment’s channel network.
Investigating geomorphological form and process at particular sites has many advantages, not least of which is capitalising on the interdisciplinary links and common study questions (e.g. effects of large wood debris on channel form and biota) that exist at each site.
Technical Report VI - Catchment Geomorphology describes and assesses the geomorphological issues of the Onkaparinga River catchment. It relies on the published literature, unpublished reports, topographic and geological maps, aerial photography and field observations of the catchment.
The geomorphological analyses included a qualitative assessment of the likely influences (on channel form) of geomorphological processes including evidence for
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 11 channel change, preliminary knowledge of hydrology and hydrological changes and general geomorphological principles.
During the study, erosion pins were installed at all upper catchment field sites to quantify the rate of bank erosion at various points through the upper catchment. However, the predominance of low flows during the period of instrumentation means that the results are unemphatic. Monitoring will need to continue over a number of higher flows (around bankfull) before the erosivity of the banks can be assessed.
The process of channel adjustment changes dramatically downstream of the dissipator. Murray River water entering the upland section of the Onkaparinga River at this point augments riverflow considerably. During the study, a number of gravel bars were painted (on the bed of the river) above and below the dissipator to assess the competence of flows to transport sands and gravels along the riverbed.
Details of the geomorphological investigations and results are provided in Technical Report VI - Catchment Geomorphology.
3.5.3 Macroinvertebrate investigations Macroinvertebrate data have been collected to report on river health in the Onkaparinga River catchment. The information collected from AUSRIVAS models, that utilise collected biological data to assess river health, was utilised as background information for the multi-disciplinary fieldwork.
River health is primarily described by taxonomic richness. If species requirements for flow were well documented, it might be possible to infer from their presence or absence the flow conditions at particular locations using the existing river health data. However such requirements have not been well documented and the specific flow requirements of most species are unknown.
Empirical determination of the flow preference of macroinvertebrates in the Onkaparinga River catchment was made using existing macroinvertebrate distribution and flow data. This analysis utilised a subset of species, focusing on taxa which are icons, occur across the entire area of the OCWMB and that can be found in sufficient numbers. The data comprised existing data sets of macroinvertebrate species and environmental variables from the Monitoring River Health Initiative (1994-2000) and OCWMB monitoring (1999-2001).
The output for this investigation were: q a description of the substrate and flow requirements for each species examined; q a summary of the data utilised, in tabular and graphic format; and q scenarios of where in the catchment, and at what times, species will be found and this information linked back to the flow requirements of that species.
Although much of the data used in the analysis was collected at sites within the same reach as the study field sites, the collections were at different times and from different bed and flow conditions. Further, the multi-disciplinary fieldwork did not describe stream channels at the same scale as that used for macroinvertebrate monitoring. Thus the linkages that are presented are based on a subset of the outcomes of the analysis (channel depth, channel profile, current velocity) and there has not been any ground
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 12 truthing of them. Conducting macroinvertebrate sampling at the precise location of each field site would permit the linking of invertebrate-habitat relationships for each of the 14 factors analysed and provide field validation of the results of the desktop analysis.
Details of the macroinvertebrates investigations and results are provided in Technical Report IV Physical Habitat Preferences of Aquatic Macroinvertebrates.
3.6 Hydrology and Hydraulics
3.6.1 Topographic survey The cross sections at each site were surveyed using a total station for channel shape. The survey was conducted at a detailed scale to indicate any significant changes in channel shape and wetted habitat.
The surveying was undertaken by both an ecologist and geomorphologist, to ensure that key habitat features were surveyed in appropriate detail and identified by the survey. The following information was recorded: q locations of hydraulic control sections, and other representative sections for use in the modelling; and q flow depths at major hydraulic control sections.
All cross sections within a site were linked to each other to indicate the slope and meanders of the river at that site. The intervals between point measurements were such that they showed changes in slope, structure and substrate type, rather than at regularly spaced intervals.
An additional cross section was surveyed downstream of the specified site, to assist in setting the downstream boundary conditions for the hydraulic model. The distance of this cross section from the downstream limits of the site was, at a minimum, the distance of the greatest separation between cross sections within the site.
3.6.2 Modelling of natural and current hydrology A hydrologic model of the catchment was developed by the Department for Water Resources (DWR, now Department of Water, Land and Biodiversity Conservation (DWLBC)) to determine the impact of farm dams in the Onkaparinga River catchment using the modelling platform WaterCress. Information on farm dam development and water extractions was collated and the model calibrated to flows recorded at streamflow gauging stations. Full details of the model can be found in Teoh (2001).
For this study the DWR model was run for 100 years of recorded rainfall. Some minor modifications were required to the model configuration to allow model outputs to be obtained for all study sites. The model was then used to simulate the existing streamflow in the catchment at the 11 study sites. As the data were not available to model the SA Water infrastructure over the 100 year period, the streamflow at the 6 study sites downstream of the dissipator were obtained directly from the available gauged data (between 15 and 33 years).
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 13 The natural1 condition of the catchment was modelled as a separate scenario, in which the impact of farm dams and water supply infrastructure, such as Mt Bold Reservoir and Clarendon Weir and their associated flow inputs from the Murray River, were removed. The natural scenario was then run for the 100 years of recorded rainfall data at the 11 study sites.
3.6.3 Hydraulic modelling A hydraulic model was used to develop the relationships between flow and water level for each site. The hydraulic modelling was undertaken using the HEC-RAS software. The model utilises the cross sections surveyed from each site to indicate channel morphology. In addition, the water surface levels recorded during the surveying process are incorporated to assist in calibration of the model. Sensitivity analyses were utilised to assess impacts on results of a range of possible model parameters, particularly boundary conditions and hydraulic roughness.
At a minimum, model cross sections have been located at significant hydraulic controls; where flow passes through critical depth; and at the extremities of major flow expansions and constrictions. Where required, additional cross sections have been placed between such controls, at representative locations. Model results at locations other than cross sections will generally become more reliable as flow and depth increase.
Once developed, the hydraulic model was run for a variety of flows to establish the relationships between streamflow and water level for a range of flows up to bankfull.
3.7 Objectives The specific objectives for developing Environmental Water Requirements relate to flow, structure and more specifically species as well as environmental processes. In addition to the objectives setting, attention is also given to regional strategy plans, local catchment plans and any existing metropolitan planning strategies.
A series of broad scale catchment objectives have been developed for the Onkaparinga River catchment based on maintaining and, where necessary restoring, the key processes and communities identified within the catchment. Catchment objectives lead into the more quantifiable environmental objectives. These catchment scale objectives have been presented in tables with reference made to the specific region to which they relate (refer to Technical Report VII - Environmental Water Requirements.)
The process of setting environmental objectives involves identifying the environmental assets, setting environmental objectives against these, and then identifying the flow objectives required to meet the environmental objectives. Environmental objectives were developed only for those assets that have a clear dependence on some aspect of the flow regime.
1 The natural flow regime is defined as the flows that would exist if no diversions or storage of water occurred, accepting that there have been changes in flow associated with landuse alterations.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 14 The objectives were developed such that, if met, the flow could sustain an ecologically healthy river. Therefore the objectives were developed not only to protect current conditions or environmental assets of special concern, such as threatened species, but also to sustain the natural communities and processes that are essential for river health.
The environmental objectives are detailed in Appendix B and further descriptions are provided in Technical Report VII - Environmental Water Requirements. Specific environmental objectives were developed for:
Fish Twenty environmental objectives specific to fish species have been developed. These objectives are aimed at maintaining and in some cases restoring the populations of native fish recorded from within the catchment. This objective is achieved through providing low flows that will assist in the maintenance of a wetted stream during the low flow period while freshes will assist in triggering spawning in many native freshwater fish.
Macroinvertebrates Three environmental objectives has been identified to maintain and restore the macroinvertebrate community diversity. This objective is achieved through providing low and high flows. The maintenance of low flows ensure some aquatic habitat is maintained during the flow stressed period. High flows are aimed at causing a disturbance that would lead to the die back of some species and ultimately lead to increased species diversity on re-establishment.
Physical feature A single environmental objective has been identified to maintain the existing physical features of sites. This is achieved through providing both low and high flows. Low flows lead to disturbance particularly of the exposed banks that facilitates decomposition and processing of organic matter that contributes nutrients and carbon on re-wetting. Wetting of physical features prevents the cracking of banks that can often lead to erosion of the particulate material. In addition, high flows can also lead to disturbance that transports sediment downstream to prevent the smothering of key habitats.
Vegetation Nine objectives have been identified to maintain or restore the vegetation communities of the catchment. The species selected are a small representative group of natives that occur within the catchment. The maintenance or restoration of these species endeavours to maintain or restore a much larger group of native vegetation within the catchment.
Water quality A single environmental objective has been established to maintain water quality within the catchment. This objective may be achieved through providing both low and high flows. Low flows assist in maintaining suitable aquatic conditions by minimising the increase in temperature and decrease in dissolved oxygen. Subsequently freshes lead to improvements in water quality due to the presence of mixing that leads to destratification.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 15 3.8 Determination of Environmental Water Requirements A multi-disciplinary project team covering the disciplines of macroinvertebrate and fish ecology, water quality, fluvial geomorphology and hydrology undertook the determination of the environmental water requirements (EWRs).
The concept of flow components is critical to the development of EWRs (refer to Appendix A). The project team met to identify critical parts of the flow regime as well as discuss the ecological and geomorphological roles of these flow components. An additional output of this meeting was the confirmation of the critical flow components using the material in Technical Report I - Integrated Issues Paper. The information collected from the initial fieldtrip by the team and subsequent field trips, and the modelled natural and current flow regime for each site were utilised to specify the flow components.
The assessment of EWRs for each site was undertaken on site by the project team to integrate all of the outputs generated in the prior tasks to determine the environmental water requirements of the Onkaparinga River catchment. The initial analysis utilised all information collected to date, including: q daily flow series; q objectives; q flow components; q photos; q field summary sheets; q hydraulic model; and q issues summary.
The analysis was an interactive process with the project team utilising the data and models (hydraulic and hydrology) to determine the EWRs for each site. The EWR process for each site was documented. The documentation is the initial basis for the justification of the EWRs in the final report. The documentation included: q the scientific basis behind decisions or any assumptions made; q the rationale for the decision and the data summary used; q the risk of the determined EWRs not having the desired effect or other constraints impacting on its efficacy; and q the relative priority of different EWRs.
These EWRs were determined to describe the entire flow regime, not solely a minimum flow over a defined period.
The identified environmental water requirements were framed for each site and tabulated with a description of each identified flow objective using a summary table. This table provides a link between the identified EWRs and flow components to the objectives. The rationale for each component is then discussed below this table. The discussion of each EWR explains the basis for the EWR and the benefits that that EWR will provide to the environment.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 16 The EWRs for each site are contained in Appendix C. Each flow component is specified in terms of a magnitude (ML), frequency (occurrences per year) and duration (days). The rationale for each EWR is presented with respect to the detailed environmental objectives relating to fish, macroinvertebrates, physical, vegetation and water quality (refer to Section 3.7).
Detailed discussion on the selection and rationale are provided for each flow component for each of the 11 sites (refer to Technical Report VII - Environmental Water Requirements).
The EWRs for each site have been plotted to indicate the variation in the magnitude of the flows with distance downstream within the Onkaparinga River catchment. Sites have been plotted in order from most upstream (Onkaparinga River at Oakbank) to most downstream (Onkaparinga River at Old Noarlunga) for those sites on the Onkaparinga River itself. Sites on tributaries have been separated on the left-hand side of the plots as these have much lower magnitudes than the Onkaparinga River due to smaller catchment areas and hence flow.
The identified EWRs are shown for the low flow period in Figure 3-3 and the high flow period in Figure 3-4.
25 Low Flow Low Flow Fresh
0 2 20 19.5 19.5
17
15 14
11 11 10 10 Flow (ML/day) 8 5 5 7. 7. 7 Tributaries 6 5 5 5
2.5 2 1 1 1 1 1 0 s e d s ge trip ok r Rd s bank lands rave lunga ck k w g r Mt Bol Bro set Val o oa R s @ N Peaco iver @ Allens @ er iver @ Go @ R r @ iver @ Oa R ver @ Houl ve Ck Ck @ landing i ver @ d/ Ri t Ck @ Dor inga e ga River Ri r ki ot inga aringa R n ga c r p paringa Riv in Sc inga aringa R a Onka p par nk Onkapa apar Lenswood O Onkapa nk Inverbra Onkapari O Onka Onka Site n Figure 3-3 Magnitude of EWRs during the low flow period within the Onkaparinga River catchment
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 17 1200 High Flow 0 0 1 High Flow Fresh 1 1
High Flow Fresh 2 0 0 5 5 1000 9 9 0 0 9 900
800
0 5 650 6
600 550 Tributaries Flow (ML/day) 400
260
200 0 0 4 100 1 100 7 7 87 8 5 57 2 8 5 3 33 3 3 3 40 35 3 15 .5 4 23 2 7 1 4 1 3 7 9 0
p s s d e i le n ve rg str a e a o V ll r Bol lunga g t A t G r in e akbank M a d s O @ @ n r r /s @ Brooks r No a o @ d e l D r ive iv @ e @ Houlg @ r @ @ R r R e k a e River a v k g ver a g i C C n i n R d Ck @ Peacock Rd tt Riv R ri a o o a g c a aringa Riv inga g rin rackie S p r in a rb a nkapari a nkap p e k O p par O Lenswo v a a Onkaparing n On k k I Onkaparinga Rivern @ Rowlandsn Onka O O Site n Figure 3-4 Magnitude of EWRs during the high flow period within the Onkaparinga River catchment
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 18 4. Environmental Flow Needs
4.1 Approach Before options for providing water for the environment were developed, the environmental flow needs in the catchment were prioritised. This prioritisation was based upon the following information:
Environmental condition – The relative merit of preserving the subcatchments and reaches of the Onkaparinga are assessed based on the current aquatic ecosystem condition and values, the risk and consequence of further degradation under the current flow regime, the potential for improvement and the timeframe for improvement in condition (section 4.2).
Current achievement of EWRs – The current condition is assessed based on the level of achievement of the EWRs. Each subcatchment is ranked (from low to high) on its achievement of EWRs during the low flow and high flow periods (section 4.3).
Prioritisation of EWR flow components – The relative importance of the various flow components is identified for each subcatchment based on the likely ecological benefit of providing that flow component (section 4.4).
4.2 Environmental Condition The relative merit of preserving the subcatchments and reaches of the Onkaparinga are assessed based on the current aquatic ecosystem condition and values, the risk and consequence of further degradation under the current flow regime, the potential for improvement and the timeframe for improvement in condition. Technical Report IX - Options for Environmental Water Provisions provides a discussion of the aquatic ecosystem condition and assigns a category for each subcatchment using the criteria shown in Table 4.1. The results are shown in the following 4 figures. n Table 4.1 Categories used to assess current environmental condition
Issues Categories
Poor - heavily impacted by historic development, far from natural condition Current environmental condition Average - moderate impact due to development to date
High - high risk of rapid further degradation Potential for further degradation Medium - risk of further degradation, this will occur slowly as a lot of damage (under current level of development) has occurred to date Low - communities have ‘stabilised’ under current flow regime, thus further degradation unlikely Low - significant change is required to improve environmental condition Potential for improvement in Medium - relatively small change is required to improve condition from the environmental condition through current EWPs alone High - small change is required to show large improvement in environmental condition Long term - significant change required as well as stakeholder cooperation, thus long time frame for change Timeframe for improvement in Medium term - once flows are returned, the environment will respond in the environmental condition medium term due to the average current condition Short term - Little change is required for benefits to become apparent
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 19 n Figure 4-1 Current environmental condition
n Figure 4-2 Potential for further degradation
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 20 n Figure 4-3 Potential for improvement in environmental condition through EWPs alone
n Figure 4-4 Timeframe for improvement in environmental condition
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 21 4.3 Current Achievement of EWRs The WaterCress model of the Onkaparinga River catchment developed by DWLBC has been used to model the hydrology of the catchment for the current situation, the natural state and for two scenarios of continued farm dam development.
Initially, an assessment was made at each site of whether the minimum volume of water required to achieve all of the EWRs is currently available. While this is a very coarse measurement, it gives an idea of how much water is available in the catchment and more specifically, how much additional water might be needed (at the right time and place) to meet EWRs.
Currently the annual volume of water in the catchment could (when supplied at the right time and place) satisfy EWRs with over 80% reliability at all sites apart for the three sites in the lower catchment (downstream of Clarendon Weir). Downstream of Clarendon Weir there is significantly less water than occurred naturally, especially during the low flow period. The upper catchment also has significantly lower volumes of water during the low flow period than naturally occurred. The opposite is true in the reach of the Onkaparinga River between the dissipator and Clarendon Weir, where there is significantly more water than naturally occurred.
A rating from ‘Poor’ to ‘Good’ indicating the achievement of EWRs was assigned to each site during both the high and low flow periods. This was a qualitative assessment integrating three parts of the recommended flow regime, namely the timing, duration and frequency of flows. The magnitude of the departure from the natural condition for each of these was the basis for the rating of achievement given.
The results from the 11 representative sites were used to infer the current degree to which the EWRs are being satisfied for each of the subcatchments and reaches in the catchment. The conclusions are: q In the upper catchment (both eastern and upper western subcatchments upstream of the dissipator), there is currently poor achievement of EWRs during the low flow period and good to moderate achievement of EWRs during the high flow period. q In the region downstream of the dissipator and upstream of Clarendon Weir there is currently moderate to poor achievement of both high and low flow EWRs. q In the lower catchment (the gorge and estuary), the current achievement of both high and low flow EWRs is poor.
The above assessment is summarised in Figures 6.1 and 6.2 for both the high and low flow periods.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 22 n Figure 4.5 Current achievement of EWRs during the low flow period
n Figure 4.6 Current achievement of EWRs during the high flow period
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 23 Continued farm dam development in the catchment is expected to lead to further modification of the streamflow from the natural condition. Two scenarios of future farm dam development have been modelled in the catchment, the year 2010 and the 5% rainfall (full development of the 50% rule) scenarios. The modelling results show that both scenarios will lead to further decrease in the achievement of EWRs across the catchment. The impact of continued farm dam development will be greater during the low flow period at all sites and will be felt more at locations that are not influenced by the public water supply infrastructure in the catchment.
4.4 Prioritisation of Flow Components at each Site The EWRs have been based on the flow component philosophy (refer to Appendix A) to identify important parts of the flow regime. While all flow components are recommended to help maintain and rehabilitate the ecological health of the catchment, some flows are more vital to ecological health in the short term than others.
In determining the relative priorities of flow components within each subcatchment, emphasis has been placed on the components of the natural flow regime that are considered to have the most influence over the ecological processes in that region. Therefore it is likely that the restoration or maintenance of these flow components would result in the most ecological benefit for the catchment in the future. The rationale for the key priorities in each subcatchment is further discussed in Technical Report IX - Options for Environmental Water Provisions.
The relative importance of the six flow components for each subcatchment or reach in the catchment is shown in Table 4.2. The prioritisation is a relative measure within each subcatchment. n Table 4.2 Priority of EWR flow components in terms of influence on the ecological processes in each sub catchment
Subcatchment Low Flow Period (Jan-May) High Flow Period (Jul-Nov) Region or Onkaparinga Reach Cease to flow Low Fresh Low Minor Fresh Major Fresh
Eastern 642135
Upper Western 624135
Lower Western 624135
Downstream of 613245 dissipator Downstream of 613245 Mt Bold Gorge 614253
Estuary 615143 Note: 1. The numbers refer to the prioritisation of flow components where 1 is most important 2. Cease to flow recommendations were only made for two study sites located in the eastern and upper western subcatchments
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 24 4.5 Priority Environmental Flow Needs The information from the preceding sections was combined to identify the priority environmental flow needs in the catchment. This is a multifaceted issue and requires the integration of different sources of information and consideration of the different temporal (ie variations throughout the year) and spatial (variation between subcatchments and different reaches) nature of the existing and required flow.
The information from the preceding sections was combined to identify the priority environmental flow needs as shown in Table 4.3 and Figure 4.7. n Table 4.3 Priority environmental flow needs for the Onkaparinga catchment
Relevant Rank Environmental Flow Need Flow Subcatchments or reaches impacted Period/s
1 Low flows in the gorge High & low Gorge & estuary
2 Major fresh in the gorge High Gorge & estuary
3 Low flow in lower western subcatchments low Lower western subcatchments & downstream of Mt Bold
4 Low flows downstream of the dissipator High & low D/s dissipator
5 Low flow fresh downstream of the dissipator low D/s dissipator
6 Low flow in upper western subcatchments low Upper western subcatchments & d/s dissipator
7 Low flow fresh in eastern subcatchments Low Eastern subcatchments & either d/s dissipator or gorge
8 Low flows in eastern subcatchments low Eastern subcatchments & either d/s dissipator or gorge
n Figure 4.7 The location of the identified priority environmental flow needs
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 25 5. Options to Provide Environmental Flows
5.1 Guiding Principles and Objectives Recognising the complexity inherent in defining Environmental Water Provisions (EWPs), we have provided a structure to both the basis for decision making (principles and objectives) and the process. The principles specify the ‘rules’ for EWPs that are generally recognised and accepted and provided the logical foundation for discussing the options for EWPs.
5.1.1 Principles The principles that provide the basis for determining EWPs are listed below (ARMCANZ and ANZECC, 1996; DWR, 2000; WRC, 2000).
(i) All relevant stakeholders (having environmental, social and/or economic interests) should be involved in defining EWPs. (ii) EWPs should be linked to ecological objectives. (iii) EWPs should be legally recognised. (iv) Water should be allocated to meet environmental needs before being allocated to consumptive uses. (v) In catchments where there are existing consumptive water uses, EWPs should be as close as possible to the EWRs while recognising existing water uses and the rights of the existing users. (vi) Planning and implementation processes should allow for EWPs to be adapted as knowledge improves.
5.1.2 Objectives The objectives listed below define the multiple outcomes that are sought simultaneously. It is likely that not all of these objectives will be able to be met fully, and so defining EWPs involves the search for the optimum balance consistent with government policy and community expectations.
1. Environmental: q To provide an adequate streamflow regime throughout the year to restore the key flow components (as defined by the EWRs) consistent with catchment environmental values and focussing on areas where EWRs are not currently being achieved. q To identify complementary non-flow related options to support the changes to the flow regime in providing ecological benefit to the communities of the catchment.
2. Social: q To ensure that a reasonable security of water supply is maintained in terms of quality and availability.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 26 q To ensure that key social and cultural assets dependent on water within the catchment are maintained.
3. Economic: q To ensure that the viability of existing catchment enterprises is not undermined. q To ensure that EWPs can be introduced and maintained at a monetary cost acceptable to the community and relevant stakeholders.
5.1.3 Evaluation criteria In order to select the most appropriate option(s) for EWPs, it would be necessary to evaluate the extent to which each option fulfils the objectives defined above. Full economic and social impact assessments are outside of the scope of this study, hence the following evaluation criteria were considered in the preliminary discussion of each option for EWPs in Section 5.2. A more rigorous assessment of options against these criteria would be necessary before the adoption of any options for EWPs.
The criteria listed below define the principal factors that have been considered in the discussion and preliminary assessment of the options.
(i) Environmental outcomes - What is the likelihood of the catchment responding? - What is the potential speed of response? - What is the expected ecological benefit of implementing the option compared to a “no intervention” scenario?
(ii) Technical and operational feasibility - What is the likelihood of the option delivering the desired flow regime? - Does the current infrastructure have the capacity to accommodate the required change? If not, are the necessary changes technically feasible?
(iii) Social acceptability - What is the anticipated impact on security of water supply to public and private consumers? - What is the likely impact on the current practice of existing water users?
(iv) Economic feasibility - What is the commercial cost of implementation? (including capital and operation & maintenance costs) - Are the associated costs likely to be acceptable to the community?
There are a suite of other factors that options should be tested against prior to the adoption of any EWP options, such as: recreational users, indigenous values, aesthetic values, and the equitable distribution of costs and benefits among stakeholders. These issues should be examined in consultation with the relevant stakeholders.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 27 5.2 Options for EWPs to meet priority needs The options considered to provide the priority flow needs are discussed below:
5.2.1 Low flow bypass structure of Clarendon Weir Currently, virtually no flow passes Clarendon Weir to the gorge and estuary reaches of the Onkaparinga River. A bypass structure constructed at Clarendon Weir would enable low flows to be provided downstream. It is unlikely that a bypass structure on Clarendon Weir alone could provide the required environmental flows downstream and additional releases from Mt Bold Dam would be required to ensure the desired operation of the bypass structure.
The construction of a low flow bypass of Clarendon Weir is likely to lead to large environmental benefits downstream (particularly in the gorge) at relatively low cost and with minimal impact on landholders. It is likely that this option will be able to meet the minimum flow EWRs during both the low flow and high flow periods and contribute to meeting the major fresh during the high flow period. The volume of water required to provide low flows downstream of Clarendon Weir throughout the year is 9,100 ML/a.
Clarendon Weir is on the Register of the National Estate (Australian Heritage Commission register) and hence heritage preservation requirements will need to be factored into any works to modify the structure. As an alternative, it may be possible (or necessary) to construct an offtake from the existing tunnel that runs from the weir to the Happy Valley Reservoir to reduce any impact on the weir itself.
5.2.2 Modify releases from Mt Bold Dam As Mt Bold Dam regulates all flows downstream, the flow regime downstream of Clarendon Weir is highly dependant on the releases from Mt Bold. While the modification of releases from Mt Bold can be done without the construction of a bypass structure at Clarendon Weir, the flexibility of the flows provided downstream of the Weir will be greatly increased with the two options working in combination. This will involve a change in both the timing and volume of releases to enable more water to be provided downstream of Clarendon Weir at the required times.
Additionally it is possible that more water would be required to be sourced in order to provide both the low flows and the large freshes downstream of Clarendon Weir at the required times than is currently available from Mt Bold. There may be a significant cost associated with the purchase and/or pumping of additional water. To meet the major fresh during the high flow period, an additional 6,500 ML/a is required to be released from Mt Bold, assuming that there is no additional flow from downstream tributaries. The additional volume required could be minimised if releases are done in times when Scott Creek, Angels Gully and Kangarilla Creek are contributing high flows downstream of Mt Bold.
The mini hydro plant that is proposed for Mt Bold Dam could potentially impact on the ability to release from Mt Bold to provide flows downstream of Clarendon Weir.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 28 5.2.3 Decommission Mt Bold Dam Decommissioning Mt Bold Dam is mentioned as it is likely to deliver the majority of the priority environmental needs downstream of the dam, however due to the high degree of technical, social and economic difficulties with decommissioning such a large dam, it is not considered further.
5.2.4 Modify SA Water pumping schedule During periods of operation of the dissipator, the water introduced from the River Murray dominates the flow in the Onkaparinga River between the dissipator and Mt Bold Dam. In order to restore key flow components to the reach of the Onkaparinga River between the dissipator and Mt Bold, it is proposed that the pumping schedule from the River Murray be modified to closer reflect the natural flow behaviour.
The current pumping schedule is optimised such that the cost of pumping is minimised. Therefore, pumping is carried out overnight during the off-peak electricity hours into a holding tank and then released via the dissipator over a 24 hour period.
To provide low flows downstream of the dissipator, the current pumping regime will need to be reduced over the dry summer months. Further modelling of the water supply system is required to determine the technical constraints and any additional cost of such a change to the pumping regime.
5.2.5 Limit on new farm dams This option involves the introduction of a limit on new farm dams in the catchment, ie. a revised cap at the current (2003) level of farm dams. Modelling has shown that if the volume of farm dams continues to increase up to the current management cap (the 50% rule) there will be a significant reduction in the low flows (Teoh, 2001).
This will allow time to undertake a study of the sustainability of diversions across the catchment, leading to an assessment of the sustainable limit of farm dams in each subcatchment. The results of this investigation will identify any areas in the catchment that can be developed further without major environmental damage and other areas that may already be above a sustainable level of farm dam development.
Similar caps have been introduced in other catchments across Australia, eg. a sustainable diversion limit (SDL) has been introduced for each of over 1,600 catchments across Victoria. In the Onkaparinga River catchment, the prescription of the water resource is likely to be required in order to implement any change to the current management of farm dams.
5.2.6 Low flow bypass on farm dams The main impact that farm dams currently have on the flow regime is the significant reduction of low flows across the subcatchments. The installation of mechanisms to bypass low flows from some or all farm dams in the catchment will reduce the impact of farm dams without requiring their removal. This way farm dams can continue to supply virtually the same amount of water for agricultural purposes across the catchment, while having a significantly reduced impact on low flows.
Further modelling of farm dams scenarios is required, as the model used to date may not be able to incorporate the range of considerations desired, such as low flow bypass
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 29 mechanisms, treating off-stream dams differently (ie. effectively bypassing low flows by restricting times of pumping) and decommissioning farm dams. A useful tool that would enable this to be done relatively easily, is the Tool for Estimating Dam Impacts (TEDI). TEDI uses information on the dam sizes, aggregated volume, demands, climate data, low flow bypass criteria and potential future levels of dam development to determine the impact of farm dams on the seasonal streamflow.
5.2.7 Voluntary decommissioning of farm dams The voluntary decommissioning of farm dams is an option for subcatchments that currently have a high density of farm dams or in areas where farm dams are not utilised. It is expected that the decommissioning of farm dams will only be proposed after investigations are carried out into the sustainable limit of farm dams in each subcatchment as well as the usage of farm dams across the catchment. It is likely that decommissioning will be an option considered in combination with other farm dam options, as this alone will not deliver the desired environmental flow needs.
Community education as well as a program of financial incentives is likely to be required in order to achieve voluntary support from dam owners to decommission their dams. Incentives are likely to be targeted at dam owners in high impact subcatchments. Based on consultation carried out as part of this study to date, there is expected to be (at least some) community support for voluntary decommissioning of farm dams.
5.2.8 Indirect options to meet/support environmental needs This report concentrates on the direct options to provide environmental flows in the Onkaparinga River catchment. It is recognised however, that there are additional broadscale options that could meet (or support direct options in meeting) environmental flow needs within the catchment. While the investigation of these indirect options is not within the scope of this study, a few examples are listed below for completeness. q Landuse change – The change in crops grown across the catchment and/or removal of some agricultural land to be revegetated with native species could lead to a decrease in water requirements from local water sources within the catchment and hence increase streamflow in waterways. In some cases where new water intensive landuses are introduced, a reduction in streamflow may result. q Water use efficiency - Any increase in the efficiency of water use across the catchment so that less irrigation water is required would results in less extraction and hence more low flows. q Reduction in water demand - By reducing Adelaide’s water demand, there will be a decrease in the dependence on River Murray water. This will require less water to be pumped into the Onkaparinga catchment at the dissipator and thus less water to be released from Mt Bold Dam. Therefore, there would be a reduction in the impact felt in the catchment due to unseasonably high flows in the reaches of the Onkaparinga River between the dissipator and Clarendon Weir. Alternatively, this additional water could be released downstream of Clarendon Weir as part of an environmental release.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 30 5.3 Summary of Options The potential options to meet the priority environmental flow needs are summarised in Table 5.1. The circles indicate which environmental flow needs are satisfied by each option. The solid circles indicate the primary option to satisfy the flow need and the hollow circles indicate an option is of secondary importance. For example, the primary option for addressing needs 4 and 5 downstream of the dissipator is to modify SA Water’s pumping schedule. However, there would also be some benefit from those options relating to improved management of farm dams and hence they are indicated as a secondary option. In most cases, the secondary option would not be able to meet the environmental flow need in isolation and it is likely that they would support another option. n Table 5.1 Options to provide priority environmental flow needs, where solid circles represent primary options and hollow circles secondary options
Potential Provision Options
Rank Environmental Flow Need Weir Dams Releases Voluntary Farm Dams Farm of Farm Dams Farm of Modify Mt Bold Modify SA Water Decommissioning Limit on new Farm Pumping Schedule Low flow Bypass on Bypass of Clarendon of Bypass
1 Low flows in the gorge l l ¢¢¢¢
2 Major fresh in the gorge ¢ l ¢¢¢¢ l Primary Low flow in lower western - 3 lll subcatchments ¢ Secondary Low flows downstream of - 4 l ¢¢¢ the dissipator Low flow fresh downstream 5 l ¢¢¢ of the dissipator Low flow in upper western 6 lll subcatchments Low flow fresh in eastern 7 lll subcatchments Low flows in eastern 8 lll subcatchments NB. Where there is more than one primary option to meet one need, a combination of these options would deliver the best outcome.
Although the decommissioning of Mt Bold Dam was initially considered, it is not shown in the table above as it has been omitted from further consideration due to the prohibitive cost.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 31 5.4 Non-flow Related Issues It is recognised that a number of sections of the Onkaparinga River Catchment are strongly influenced (or dominated) by environmental factors other than reduced streamflows (Technical Report I - Integrated Issues Paper). Therefore, the provision of water to meet EWRs may have minimal or limited benefits to the ecosystem without complementary actions to address the associated issues. By addressing these additional issues, the provision of the same amount of water will be much more effective in improving catchment health and may also speed up any improvements that would occur if the streamflow regime alone were changed.
The following non-flow related issues are discussed in Technical Report IX - Options for Environmental Water Provisions: q barriers to movement of fauna; q thermal pollution; q riparian issues; q inchannel issues; and q channel adjustment.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 32 6. Development and Implementation of Strategies
6.1 Development of Environmental Flow Strategies This preliminary assessment of options in the preceding chapter has identified a range of technical issues that will require further investigation in order to develop the options into detailed strategies. The following table identifies the required further investigations and the potential key agencies to work with the OCWMB to complete the studies. n Table 6.1 Summary of work required to develop EWP strategies
Potential Environmental water Subcatchment or reach Further investigation required key partner provision option benefited agencies
Investigation into engineering aspects SA Water Low flow bypass structure Gorge and estuary of Clarendon Weir of constructing a low flow bypass DWLBC
Investigation of operational SA Water Modify releases from Mt Gorge and estuary Bold implications of modifying releases DWLBC
Investigation of operational SA Water Modify SA Water pumping Downstream of dissipator implications of different pumping regime DWLBC regimes Subcatchments where Investigation into sustainable limit of DWLBC Limit on new farm dams implemented, and in some cases farm dams in each subcatchment PIRSA the downstream reaches Subcatchments where Further modelling of farm dam DWLBC Low flow bypass of farm implemented, and in some cases scenarios, with various levels of dams PIRSA the downstream reaches bypass flows Subcatchments where Further investigation into dam usage Voluntary DWLBC decommissioning of farm implemented, and in some cases and identification of priority PIRSA dams the downstream reaches subcatchments
The option of constructing a low flow bypass of Clarendon Weir and modifying the releases from Mt Bold to provide flows in the Gorge and Estuary will involve the sourcing of additional water. The discussion of these options has identified the potential volume but not the source of this water.
The additional water could be obtained from a number of sources including reduction in extraction from farm dams or freeing up of water through reducing Adelaide's dependence on the River Murray. However, in the short term it is likely that any such additional water for environmental flows would be sourced by pumping additional water from the River Murray, within the constraints of SA Water’s current license/allocation. Further modelling would be required to determine if this is possible.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 33 Additionally, it would be necessary to carefully consider any disbenefits associated with extracting more water from the River Murray to ensure that these would be outweighed by the benefit of providing this water as environmental flows in the Onkaparinga River. These disbenefits could include the various issues relating to the poor water quality of the River Murray compared to the Onkaparinga River and the impacts of increased extraction from the River Murray itself.
6.2 Implementation of Environmental Flow Strategies The eventual implementation of EWPs is complicated because it requires decisions involving trade-offs relating to the social, economic, environmental and political influences.
The next phase of the EWP process is for key stakeholders to work together to develop the proposed options into full strategies and then undertake wide ranging consultation. The OCWMB should take a key role in identifying and promoting partnerships between these key stakeholders to further this process towards implementing EWPs.
While prescription of the water resource is not essential in order to implement any of the options, prescribing the resource will give DWLBC more influence over management and use of the water resources in the Mt Lofty Ranges and surrounds and potentially enable the acceleration of option implementation.
6.3 Monitoring Program If these EWRs are to be reviewed in a meaningful manner, and management of rivers in the catchment improved, it is essential that monitoring of the effectiveness of any environmental flow releases be undertaken.
There are two components to an effective environmental flow monitoring program. Firstly the hydrologic monitoring to assess whether water is being delivered as intended for EWPs. Secondly, the response monitoring to assess if the flow delivered is having the expected ecological response.
6.3.1 Monitoring delivery of EWPs Recommendations have been made for streamflow gauges in order to measure the delivery of EWP to meet the eight priority environmental flow needs identified in Section 4.5. The recommendations build upon a recent review by DWLBC of monitoring across the Onkaparinga River Catchment (Greenwood, 2001).
The hydrological monitoring recommendations for this study are summarised in Table 6.2. The recommendations are contained in Chapter 7 of Technical Report IX - Options for Environmental Water Provisions.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 34 n Table 6.2 Key gauging stations required to monitor the delivery of EWPs
Priority Subcatchment or Existing Location Owner Recommendation Need(s) Reach monitored Gauge? Delivered
Introduce new gauge Clarendon Weir Gorge & Estuary New N/a downstream to monitor 1 & 2 (downstream) overflows & bypass Replace AW503509 (high up Aldgate Creek upstream Aldgate Creek New N/a in catchment) to monitor the 6 of Onkaparinga majority of subcatchment Lenswood (Cock) Creek Additional gauge to monitor upstream of Lenswood Creek New N/a 6 entire subcatchment Onkaparinga Onkaparinga upstream Upper western & Maintain and upgrade as AW503904 BOM 6, 7 & 8 of dissipator eastern subcatchments required Onkaparinga at Maintain and upgrade if Charleston AW503903 BOM 7 & 8 Woodside required Onkaparinga River at Gorge & Estuary AW503522 DWLBC Upgrade instrumentation 1 & 2 Noarlunga Bakers Gully Kangarilla AW503503 DWLBC Maintain gauge 7 & 8 Scott Creek at Scott Scott Creek AW503502 DWLBC Maintain gauge 3 Bottom Echunga Creek Echunga Creek AW503506 DWLBC Maintain gauge 7 & 8 upstream of Mt Bold Onkaparinga River at Downstream of Maintain gauge and modify if AW503504 DWLBC 4 & 5 Houlgraves Weir dissipator required Notes: 1. BOM = Bureau of Meteorology; DWLBC = Department of Water Land and Biodiversity Conservation 2. Refer to priority needs discussed in section 4.5.
Any new or upgraded gauging stations should be designed to minimise their impact on the movement of fish and other aquatic fauna. For gauging stations required solely for monitoring the delivery of EWPs, the use of water level data loggers is preferable. For many ecological purposes the information required is water level, and timing (start to flow, rate of rise/fall, duration of flow, etc) and the accuracy of water level data logger is sufficient. These data logger devices are cheaper than a traditional gauging station and importantly, avoid all the related problems of large barriers to migration. The data logger would take advantage of natural flow controls and as a consequence not increase the level of stream discontinuity.
6.3.2 Response monitoring The objectives of response monitoring in the Onkaparinga River Catchment are to: q investigate the relationships between water regimes, biodiversity and ecosystem processes; and q assess the responses in hydrology, habitats, biota and ecological processes associated with specific flow events targeted by the EWR.
A number of key tasks need to be completed to achieve the best possible ecological response monitoring program. These include the selection of indicators, program design, sampling method and sites. In addition the outcomes of the monitoring program will be used to develop our understanding of the responses of the ecosystem to different flow components. Specific components of the monitoring program have been included to allow interpretation of the responses beyond just a community response to flow improvement.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 35 Indicators To effectively assess the benefits of an altered flow regime on the ecology of the Onkaparinga River catchment, it is important to monitor ecological indicators. Ecological indicators are selected to effectively monitor the important environmental values or objectives developed for particular species and communities, habitats and ecological processes (Technical Report VII - Environmental Water Requirements).
It is proposed that at a minimum, both the abundance and distribution of fish and macroinvertebrates and a range of water quality parameters be monitored for determining the benefits of EWR. These values relate specifically to cease to flow, low flow, freshes, high flow and bankfull flow components.
The recommended monitoring program should assess all fish and macroinvertebrate species, rather than target particular species or objectives. This broad assessment permits the determination of benefits or threats to the populations that may be identified as the monitoring progresses and may also reduce the sampling effort.
Water quality sampling is a component of the macroinvertebrate sampling regime suggested (eg. AusRivAS) and will complement the longer-term biotic indicators with a highly temporal physico-chemical assessment.
Program design The capacity of a monitoring program to achieve its objectives is dependent not only on the selection of appropriate indicators, but also upon a sound study design. Three statistical designs are commonly used in the design of monitoring programs and range from simple and economic to statistically defensible and costly.
The most basic monitoring design measures and detects changes at selected sites before and after the onset of the EWR. This enables the minimisation of confounding effects that are totally unrelated to the change in management (ie. seasonal change, community succession, longer term cyclic change).
The second approach to the monitoring design is to compare sites affected by the EWR (impact sites) with sites that are unaffected by the change (reference or control sites). Sites unaffected by the change may include tributaries in the catchment that possess similar conditions (eg. substrate type) to the impact sites. Even where the selection of control sites is relatively straightforward, pre-existing differences between impact and control sites may confound the results of monitoring, making it difficult to specifically assign changes in the selected indicators to changes caused by the new water management strategy.
The last approach to the design of monitoring programs combines the first two approaches to form what is generally termed the ‘BACI’ (Before After Control Impact) design. The ‘BACI’ approach is to monitor impact and control sites before and after the implementation of changes to the EWR.
When selecting a statistical design for any environmental change the following issues need to be considered: q The availability of control/reference sites to be used in comparison for the effects observed at the study site; q The amount of existing data available at these sites; and
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 36 q The timing of the response of the selected indicators to the EWR, so that data can be collected before the changes occur.
The length of the sampling program will take these factors into consideration.
Selection of sites for ecological monitoring To effectively monitor any environmental change that occurs under the revised flow regime, sites should be selected in recognition of the spatial relationships within the river system, availability of scientifically sound pre-existing data and study design. Ideally, sites for monitoring would be selected from those previously visited by the project team, and a representative from within each subcatchment and reach (as defined in chapter 2). The proposed sampling regime is summarised below. n Table 6-3 Summary of proposed monitoring regime Site Comment Parameter Sampled Frequency Lenswood Creek Existing EWR site Fish Annual Macroinvertebrates 2 seasons annually Water Quality Monthly Physical features Triennial Inverbrackie Creek Existing EWR site Fish Annual Macroinvertebrates 2 seasons annually Water Quality Monthly Physical features Triennial Scott Creek Site where restoration Fish Annual activity has occurred Macroinvertebrates 2 seasons annually upstream of EWR site Water Quality Monthly Physical features Triennial Onkaparinga River at Oakbank Existing EWR site Fish Annual Macroinvertebrates 2 seasons annually Water Quality Monthly Physical features Triennial Onkaparinga River at Handorf Existing EWR site Fish Annual Macroinvertebrates 2 seasons annually Water Quality Monthly Physical features Triennial Onkaparinga River ds dissipator Existing EWR site Physical features Triennial Onkaparinga River Houlgraves Existing EWR site Fish Annual Macroinvertebrates 2 seasons annually Water Quality Monthly Physical features Triennial Onkaparinga River ds Mt Bold Existing EWR site Fish Annual Macroinvertebrates 2 seasons annually Water Quality Monthly Physical features Triennial Onkaparinga River at Gorge Existing EWR site Fish Annual Macroinvertebrates 2 seasons annually Water Quality Monthly Physical features Triennial Onkaparinga River at Estuary Site at mouth of Fish Annual estuary used for fish Water Quality Monthly surveys Physical features Triennial
Further details of the recommended sampling techniques are provided in Chapter 7 of Technical Report IX - Options for Environmental Water Provisions.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 37 7. Conclusions
This project examines the environmental water requirements (EWRs) of the surface water systems of the Onkaparinga River catchment. The aim of this project is to provide a scientific basis for the OCWMB to implement provisions for water dependent ecosystems, and in doing so, meet the object of the Water Resources Act 1997 and the objectives contained in the Onkaparinga Catchment Water Management Plan.
This report details the determination of EWRs, identification of priority flow needs for the Onkaparinga River catchment and the recommendation of a range of options for the provision of water to address these needs.
The approach adopted for determining environmental water requirements builds on the the recently documented FLOWS method prepared by Sinclair Knight Merz for NRE (NRE, 2002). A key feature of the adopted approach is the recognition of flow components.
These EWRs were determined to provide a range of flows which serve to restore the components of the natural flow regime, not solely a minimum flow over a defined period. Each flow component is specified in terms of a magnitude (ML), frequency (occurrences per year) and duration (days). The rationale for each EWR is presented with respect to the detailed environmental objectives relating to fish, macroinvertebrates, physical, vegetation and water quality
A multi-disciplinary project team covering the disciplines of macroinvertebrate and fish ecology, water quality, fluvial geomorphology and hydrology developed the environmental water requirements. The approach utilises inputs from a range of different disciplines in a transparent and repeatable process.
The prioritisation of environmental flow needs is a multifaceted issue and requires the integration of different sources of information and consideration of the different temporal (ie variations throughout the year) and spatial (variation between subcatchments and different reaches) nature of the existing and required flow. The factors considered in this prioritisation were the ecological value of a subcatchment, the risk of further degradation and likelihood of improvement, the degree to which the EWRs are currently being achieved and the priority of flow components in terms of their ecological benefit.
The process of defining options for providing Environmental Water Provisions (EWPs) is complicated because it requires consideration of the social, economic, environmental and political influences associated with alternative means of providing water to meet environmental needs. Thus, a preliminary assessment was made of the potential options in terms of environmental outcomes, technical and operational feasibility, social acceptability and economic feasibility. The identification of these options represents the end point of this current technical study.
The next phase of the EWP process is for key stakeholders to work together to develop the proposed options into full strategies and then undertake wide ranging consultation. The final EWPs will involve tradeoffs through a negotiation process. The OCWMB should take a key role in identifying and promoting partnerships between
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 38 these key stakeholders to further this process towards developing and implementing EWPs.
It is recognised that a number of sections of the Onkaparinga River catchment are strongly influenced (or dominated) by environmental factors other than reduced streamflows. Therefore, the provision of water to meet EWRs may have minimal or limited benefits to the ecosystem without complementary actions to address the associated issues. By addressing these additional issues, the provision of the same amount of water will be much more effective in improving catchment health and may also speed up any improvements that would occur if the streamflow regime alone were changed.
The strategies for EWPs should be developed in the context of adaptive environmental management; ie the suitability of any EWP strategies will need to be reviewed and updated as necessary, based on improved information (eg. monitoring and new research). It is therefore important that there is an appropriate monitoring program in place to measure the effectiveness of the EWPs. Recommendations have been made for hydrologic monitoring to assess whether water is being delivered as intended for EWPs and for the response monitoring to assess if the flow delivered is having the expected ecological response.
This summary report is supported by 9 technical reports which give much greater detail on different technical aspects of the project (refer to the table below). These technical reports provide valuable detail which underpinned the determination of environmental water requirements and the identification of options for providing water for the environment.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 39 8. References
ARMCANZ (1995), Water Allocations and Entitlements – A national Framework for the implementation of property rights in water, Task Force of COAG water reform, Occasional paper no. 1, Commonwealth of Australia, Canberra. ARMCANZ and ANZECC (1996), National Principles for the Provision of Water for Ecosystems, Agriculture and Resource Management Council of Australia and New Zealand / Australian and New Zealand Environment and Conservation Council, Occasional Paper SWR No 3, Canberra, July 1996. Baldwin, D.S. and Mitchell, A.M. (2000), The effects of drying and re-flooding on the sediment or soil nutrient dynamics of lowland river floodplain systems: a synthesis, Regulated Rivers: Research & Management, 16(5): 457-67. Benn, P.C. and Erskine, W.D. (1994), Complex channel response to flow regulation: Cudgegong River below Windamere Dam, Australia. Applied Geography, 14: 153-68. Boulton, A.J. and Lloyd, L.N. (1991) Macroinvertebrate assemblages in floodplain habitats of the lower River Murray, South Australia. Regulated Rivers: Research and Management, 6: 183-201. Boulton, A.J., Sheldon, F., Thoms M.C. and Stanley, E.H. (2000) Problems and constraints in managing rivers with variable flow regimes, In P.J. Boon, B.R. Davies and G.E. Petts (eds.), Global perspectives on river conservation, policy and practice. Wiley, Chichester. Bourman, R.P. (1972), Some geomorphic aspects of the Onkaparinga drainage system, Taminga, 9: 117-43. Brooks, A.P. and Brierley, G.J. (1997), Geomorphic responses of the lower Bega River to catchment disturbance 1851-1926, Geomorphology, 18: 291-304. Burns, A. and Walker, K. F. (2000), Effects of water level regulation on algal biofilms in the River Murray, South Australia, Regulated Rivers: Research & Management, Special Issue: Australian Lowland Rivers, M. C. Thoms and F. Sheldon. Volume 16, Issue 5: 433-444. Burston, J. and Good, M. (1996), The impact of European settlement on erosion and sedimentation in the Inman River catchment South Australia, In I.D. Rutherfurd and M. Walker (eds.), Stream Management ’96, Proceedings of the First National Conference on Stream Management in Australia, Merrijig, Cooperative Research Centre for Catchment Hydrology, Melbourne: 259-64. Chorley, R.J. (1962), Geomorphology and general systems theory, United States Geological Survey Professional Paper, 500-B. Closs, G.P. and Lake, P.S. (1996) Drought, differential mortality and the coexistence of a native and an introduced fish species in a south east Australian intermittent stream, Environmental Biology of Fishes, 47: 17-26. DWR (2000), South Australia's Water resources. State Water Plan 2002, Volumes 1 and 2, Department for Water Resources, South Australia. Geddes, M. C. and Puckridge, J. T. (1989), Survival and growth of larval and juvenile native fish: the importance of the floodplain, Proceedings of the workshop on Native Fish Management, Murray-Darling Basin Commission.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 40 Gehrke, P. C. (1991), Avoidance of inundated floodplain habitat by larvae if golden perch (Macquaria ambigua Richardson): influence of water quality or food distribution?, Aust J Mar Freshw Res, 42: 707©19. Gehrke, P.C., Brown, P., Schiller, C.B., Moffatt, D.B. and Bruce, A.M. (1995), River regulation and fish communities in the Murray-Darling River System, Australia, Regulated Rivers: Research & Management, 11: 363-75. Greenwood et al (2001), South Australian Surface Water Monitoring Review 2001, Volume 1: The Mount Lofty Ranges, Draft Report, Department for Water Resources. Harris, J.H. and Gehrke, P.C. (1997), Fish and Rivers, The NSW Rivers Survey, NSW Fisheries Research Institute. Hughes, J.M.R. and James, B. (1989), A hyhdrological regionalization of streams in Victoria, Australia, with implications for stream ecology, Australian Journal of Marine and Freshwater Research, 40: 303-26. Humphries, P. and Lake, P.S. (2000), Fish larvae and the management of regulated rivers, Regulated Rivers: Research & Management, 16(5): 421-32. Humphries, P. (1995), Life history, food and habitat of Southern Pygmy Perch, Nannoperca australis, in the Macquarie River, Tasmania, Marine and Freshwater Research, 46: 1159-69. Humphries, P., King, A.J. and Koehn, J.D. (1999), Fishes, flows and floodplains: links between Murray-Darling freshwater fish and their environment, Environmental Biology of Fishes, 56: 129-51. Jowett, I.G. and Duncan, M.J. (1990), Flow variability in New Zealand rivers and its relationship to in-stream habitat and biota, New Zealand Journal of Marine and Freshwater Research, 24: 305-17. Kingsford, R.T., Curtin, A. L. et al. (1999), Water flows on Cooper Creek in arid Australia determine 'boom' and 'bust' periods for waterbirds, Biological Conservation, 88(2): 231-248. Koehn, J. D. and O'Connor, W. G. (1990), Biological information for Management of Native Freshwater Fish in Victoria, Arthur Rylah Institute for Environmental Research, Melbourne, Victorian Government Printing Office. Leopold, L.B. and Maddock, T. (1953), The hydraulic geometry of stream channels and some physiographic implications, United States Geological Survey Professional Paper 252. Nielsen, D.L. and Chick, A.J. (1997), Flood-mediated changes in aquatic macrophyte community structure, Marine and Freshwater Research, 48(2): 153-7. Nielsen, D., Hillman, T. J. and Smith, F. J. (1999), Effects of hydrological variation and planktivorous competition on macroinvertebrate community structure in experimental billabongs, Freshwater Biology, 42: 427-444. NRE (2002), FLOWS - a method for determining environmental water requirements in Victoria, Report to the Department of Natural Resources and Environment, prepared by Sinclair Knight Merz, Melbourne. O'Connor, W.G. and Koehn, J.D. (1998), Spawning of the broad-finned Galaxias, Galaxias brevipinnis Gunther (Pisces: Galaxiidae) in coastal streams of southeastern Australia, Ecology of Freshwater Fish, 7: 95-100.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 41 OCWMB (2000), Onkaparinga Catchment Water Management Plan, Onkaparinga Catchment Water Management Board, 1/12/2000. Poff, L.N. and Allan, J.D. (1995), Functional organization of stream fish assemblages in relation to hydrological variability, Ecology, 76(2): 606-27. Poff, N.L. and Ward, J.V. (1989), Implications of streamflow variability and predictability for lotic community structure: a regional analysis of streamflow patterns, Can J Fish Aquat Sci, 46: 1805©18. Prosser, I.P., Rutherfurd, I.D., Olley, J.M., Young, W.J. and Wallbrink, P.J. (in press), Patterns and processes of erosion and sediment transport in Australian rivers, Marine and Freshwater Research. Puckridge, J.T., Sheldon, F., Walker, K.F. and Boulton, A.J. (1998), Flow variability and the ecology of large rivers, Marine and Freshwater Research, 49: 55-72. Puckridge, J.T., Walker, K.F. and Costelloe, J.F. (2000), Hydrological persistence and the ecology of dryland rivers, Regulated Rivers: Research & Management, 16(5): 385- 402. Quinn, G. P., Hillman, T. J. et al. (2000), The response of macroinvertebrates to inundation in floodplain wetlands: a possible effect of river regulation?, Regulated Rivers: Research & Management, Special Issue: Australian Lowland Rivers, M.C. Thoms and F. Sheldon. Volume 16, Issue 5: 469-477. Richter, B. D., Baumgartner, J. V. et al. (1996), A method for assessing hydrologic alteration within ecosystems, Conservation Biology, 10(4): 1163-1174. Robertson, A. I., Bacon, P. et al. (2001), The responses of floodplain primary production to flood frequency and timing, Journal of Applied Ecology, 38: 126-136. Teoh, K. (2001), Estimating the Impact of Current Farm Dams Development on the Onkaparinga River Catchment Streamflow, Surface Water Branch, Resource Assessment Division of the South Australian Department of Water, Land and Biodiversity Conservation, September 2001. WRC (2000), Environmental Water Provisions Policy for Western Australia, Water and Rivers Commission, Statewide Policy No. 5, November 2000.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 42 Appendix A Description of Flow Components
The magnitude, duration, frequency and timing of flows are key aspects of a natural flow regime to maintain channel form and viable populations of freshwater biota. Alteration of the natural flow regime of Australian rivers has been shown to interfere vwith the biology and assemblage structures of aquatic flora and fauna (Gehrke et al., 1995) and alter natural geomorphic processes such as erosion and sedimentation (Benn and Erskine, 1994; Brooks and Brierley, 1997; Burston and Good, 1996; Prosser et al., in press).
A key feature of the adopted approach is the recognition of flow components. Richter et al. (1996) emphasise the importance of the components of the natural flow regime, including the range and variability of flows. Flow components are the conceptual link between hydrology and the ecological processes, and a description of different parts of a flow regime relevant to the ecosystem. The following section describes the six key flow components, and their importance for the ecosystem.
Cease to flow is a period of no discernible flow in a river. The cessation of flow is a common natural occurrence in lowland rivers and there are a range of ecological functions provided by this flow component (Boulton et al., 2000; Burns and Walker, 2000; Poff and Ward, 1989). Periods of cease to flow often result in short term localised extinction of certain species (Puckridge et al., 2000) with long term increases in diversity and biomass (Humphries and Lake, 2000; Puckridge et al., 2000).
Low flows are the minimum flow that provides a continuous flow through the channel. During summer periods the low flow may be a critical flow sustaining habitats in flow stress. Low flows have also been suggested to be a critical flow component in the recruitment of native fish in lowland rivers (Humphries et al., 1999).
A fresh is a small, short duration peak flow event. Freshes are a key component of the variability of flow regimes, providing short pulses in flow and the short temporal scale variability that are identified as a key components of natural flow regimes for a range of ecosystem factors (e.g. Hughes and James, 1989; Jowett and Duncan, 1990; Poff and Allan, 1995; Poff and Ward, 1989; Puckridge et al., 1998).
In channel high flows are distinct from freshes due to the persistent increases in the seasonal baseflow that remain within the channel. High flows are unlikely to provide substantial channel forming forces but may be linked to the breeding of some fish species (Koehn and O'Conner, 1990; O'Connor and Koehn, 1998). These factors can also act as triggers for breeding for other species (Harris and Gehrke, 1997; Humphries, 1995; Koehn and O'Conner, 1990) and are important to provide connectivity for fish migration through a system.
Bankfull flows are the highest flows confined within the channel, with little flow spilling onto the floodplain. Such flow inundates all in-channel features, creating further habitat for macroinvertebrates, plants and fish. Bankfull flows are also important geomorphologically in shaping and maintaining river and distributary channels and in preserving the condition and availability of instream habitats (Leopold and Maddock, 1953; Chorley, 1962).
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 43 Overbank flows are greater than bankfull and result in inundation of the adjacent floodplain habitats. Maintaining occasional inundation of the flood plain is ecologically important and is known to provide significant carbon returns to the river after a period of significant production (Baldwin and Mitchell, 2000; Gehrke, 1991; Robertson et al., 2001). Overbank flows are critical for a range of ecological factors including floodplain productivity (Boulton and Lloyd, 1991), invertebrate colonisation (Boulton and Lloyd, 1991; Nielsen et al., 1999; Quinn et al., 2000), fish community diversity (Geddes and Puckridge, 1989) vegetation community maintenance (Nielsen and Chick, 1997), waterbirds (Kingsford et al., 1999) and linkages with the stream channel.
The use of the main channel to carry inflows from the Murray pipeline, from the dissipator downstream to Mt Bold Reservoir and then beyond the reservoir to Clarendon Weir has reduced the natural variability in flows. In addition, the annual flow pattern has been altered to peak when demand for water is greatest, rather than when natural peaks would occur.
Maintaining natural variability in stream discharge throughout the year is important for both ecological and geomorphological processes. Under natural conditions variations in water surface level and associated wetting and drying regimes of stream banks are important for the creation of channel forms (e.g. pools, riffles, bars, benches) and habitat attributes (e.g. large woody debris transport and placement). However, constant flows and water surface levels tend to accelerate the rate of scour at the bank toe which, in turn, may lead to bank slumping. Furthermore, constant discharge may have some deleterious effects on life history strategies and subsequent recruitment of native fish, macrophyte and macroinvertebrate species.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 44 Appendix B Environmental Objectives
n Table B-1 Fish objectives for the Onkaparinga River Catchment.
Objective
Code Region Upper Aqueduct Clarendoon Gorge Estuary Sites 1,2,3 4,5,6 7,8 9,10,11 - Self sustaining populations of F1 - - - Maintain - Australian Smelt Self sustaining populations of F2 Restore Maintain Maintain Maintain - Climbing Galaxias F3 Self sustaining populations of Congolli - - - Maintain Maintain Self sustaining populations of F4 Maintain Maintain Restore Maintain - gudgeon species Self sustaining populations of F5 Maintain - - - - Mountain Galaxias Self sustaining populations of F6 Restore - - - - Southern-purple Spotted Gudgeon Self sustaining populations of Black F7 - - - - Maintain Bream Self sustaining populations of Bridled F8 - - - - Maintain Goby Self sustaining populations of F9 Restore Maintain - Maintain - Common galaxias Self sustaining populations of Dusky F10 - - - - Maintain Flathead Self sustaining populations of F11 - - - - Maintain Greenback Flounder Self sustaining populations of F12 - - - - Maintain gudgeon species Self sustaining populations of mullet F13 - - - - Maintain species Self sustaining populations of Old F14 - - - - Maintain Wife Self sustaining populations of Six F15 - - - - Maintain Spined Leatherjacket Self sustaining populations of F16 - - - - Maintain Smallmouthed hardyhead Self sustaining populations of Smooth F17 - - - - Maintain Toadfish Self sustaining populations of South F18 - - - - Maintain Australian Cobbler Self sustaining populations of South F19 - - - - Maintain Australian Garfish F20 Self sustaining populations of whiting - - - - Maintain n Table B-2 Process objectives and flow components for fish. Sub code Process objective Relevant flow component Timing of flow component
a Habitat Low All year b Recruitment Freshes High/Spring
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 45 n Table B-3 Macroinvertebrates objectives for the Onkaparinga River Catchment.
Objective
Code Region Upper Aqueduct Clarendoon Gorge Estuary Sites 1,2,3 4,5,6 7,8 9,10,11 - Diversity in edge and backwater M1 Restore Restore Restore Restore - habitats M2 Provision of riffle habitat Restore Restore Restore Restore Enhancing diversity and M3 Maintain Maintain Maintain Maintain productivity of riffle habitat n Table B-4 Process objectives and flow components for macroinvertebrates. Sub code Process objective Relevant flow component Timing of flow component
a Habitat Low Low b Disturbance High High
n Table B-5 Physical objectives for the Onkaparinga River Catchment.
Objective
Code Region Upper Aqueduct Clarendoon Gorge Estuary Sites 1,2,3 4,5,6 7,8 9,10,11 - P1 Instream habitat diversity Maintain Maintain Maintain Maintain Restore n Table B-6 Process objectives and flow components to maintain physical features. Sub code Process objective Relevant flow component Timing of flow component
a Disturbance Low Low b Wetting Low Low c Disturbance High High
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 46 n Table B-7 Vegetation objectives for the Onkaparinga River Catchment.
Objective
Code Region Upper Aqueduct Clarendoon Gorge Estuary Sites 1,2,3 4,5,6 7,8 9,10,11 - Self sustaining populations of Broad V1 Maintain Maintain Maintain Maintain - Milfoil Self sustaining populations of V2 Maintain Maintain Maintain Maintain - Cumbungi Self sustaining populations of V3 Maintain Maintain Maintain Maintain - Fishbone Water Fern Self sustaining populations of Plain V4 Maintain Maintain Maintain Maintain - Quillwort Self sustaining populations of Prickly V5 Maintain Maintain Maintain Maintain - Bottlebrush Self sustaining populations of Small V6 Maintain Maintain Maintain Maintain - River Buttercup Self sustaining populations of Water V7 Maintain Maintain Maintain Maintain - Ribbons Self sustaining populations of Wetland V8 Maintain Maintain Maintain Maintain - Wallaby Grass Self sustaining populations of River V9 Restore Restore Restore - - Red Gum
n Table B-8 Water quality objectives for the Onkaparinga River Catchment.
Objective
Code Region Upper Aqueduct Clarendoon Gorge Estuary Sites 1,2,3 4,5,6 7,8 9,10,11 - WQ1 Water quality in pools Maintain Maintain Maintain Maintain -
n Table B-9 Process objectives and flow components for water quality. Sub code Process objective Relevant flow component Timing of flow component
a Habitat Low Low b Mixing/destratification Freshes Low/High
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 47 Appendix C Environmental Water Requirements
n Table C-1 EWRs for Site 1 – Lenswood Creek at Peacock Road.
EWR Season Magnitude Frequency Duration
Low flow Cease to flow Maximum 1.1 Annually (Dec – May) (<1 ML/day) 120 days 1.2 1 ML/day Annually * 1.3 >1 ML/day 3 annually 10 days High flow 7 ML/day 1.4 High flow period * (Jul – Oct) (minimum) 1.5 >15 ML/day 3 annually 5 days 1.6 >15 ML/day Annually 13 days 1.7 >38 ML/day 2 annually 3 days * - duration of streamflow is for the remainder of that period. n Table C-2 EWRs for Site 2 – Inverbrackie Creek at landing strip
EWR Season Magnitude Frequency Duration
Low flow Cease to flow Maximum 2.1 Annually (Feb – May) (<1 ML/day) 115 days 2.2 1 ML/day Annually * 2.3 >1 ML/day 3 annually 6 days High flow 1.5 ML/day 2.4 High flow period * (Jul – Dec) (minimum) 2.5 >4 ML/day 3 annually 4 days 2.6 >14 ML/day 6 annually 2 days * - duration of streamflow is for the remainder of that period. n Table C-3 EWRs for Site 3 – Onkaparinga River at Oakbank
EWR Season Magnitude Frequency Duration
Low flow 2.5 ML/day 3.1 Annually * (Jan – May) (minimum) 3.2 >6 ML/day 3 annually 8 days High flow 9 ML/day 3.3 High flow period * (Jul – Nov) (minimum) 3.4 >40 ML/day 4 annually 4 days 3.5 >650 ML/day 4 annually 1 days * - duration of streamflow is for the remainder of that period.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 48 n Table C-4 EWRs for Site 4 – Onkaparinga River at Allens
EWR Season Magnitude Frequency Duration
Low flow 5 ML/day 4.1 Annually * (Jan – May) (minimum) 4.2 >11 ML/day 2-3 annually 10 days High flow 23 ML/day 4.3 High flow period * (Jul – Nov) (minimum) 4.4 >57 ML/day 3 annually 3 days 4.5 >950 ML/day 4 annually 2 days * - duration of streamflow is for the remainder of that period. n Table C-5 EWRs for Site 5 – Onkaparinga River at Rowlands
EWR Season Magnitude Frequency Duration
Low flow 5 ML/day 5.1 Annually * (Jan – May) (minimum) 5.2 >11 ML/day 2-3 annually 10 days High flow 23 ML/day 5.3 High flow period * (Jul – Nov) (minimum) 5.4 >57 ML/day 3 annually 3 days 5.5 >950 ML/day 4 annually 2 days * - duration of streamflow is for the remainder of that period. n Table C-6 EWRs for Site 6 – Onkaparinga River at Houlgraves.
EWR Season Magnitude Frequency Duration
Low flow 7 ML/day 6.1 Annually * (Jan – May) (minimum) 6.2 >14 ML/day 2 annually 15 days High flow 32 ML/day 6.3 High flow period * (Jul – Nov) (minimum) 6.4 >74 ML/day 3 annually 6 days 6.5 >1100 ML/day 4 annually 2 days * - duration of streamflow is for the remainder of that period.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 49 n Table C-7 EWRs for Site 7 – Onkaparinga River downstream Mt Bold
EWR Season Magnitude Frequency Duration
Low flow 8 ML/day 7.1 Annually * (Jan – May) (minimum) 7.2 >17 ML/day 2 annually 14 days High flow 38 ML/day 7.3 High flow period * (Jul – Nov) (minimum) 7.4 >87 ML/day 4 annually 5 days 7.5 >550 ML/day 5 annually 2 days * - duration of streamflow is for the remainder of that period. n Table C-8 Flow EWRs Site 8 – Scott Creek at Dorset Vale Road
EWR Season Magnitude Frequency Duration
Low flow 1 ML/day 8.1 Annually * (Dec – May) (minimum) 8.2 >2 ML/day 2 annually 10 days High flow 3 ML/day 8.3 High flow period * (Jul – Oct) (minimum) 8.4 >7 ML/day 3 annually 9 days 8.5 >260 ML/day 1-2 annually 1 days * - duration of streamflow is for the remainder of that period. n Table C-9 EWRs for Site 9 – Onkaparinga River at Brooks Road
EWR Season Magnitude Frequency Duration
Low flow 10 ML/day 9.1 Annually * (Jan – May) (minimum) 9.2 >20 ML/day 2 annually 10 days High flow 40 ML/day 9.3 High flow period * (Jul – Nov) (minimum) 9.4 >100 ML/day 4 annually 5 days 9.5 >650 ML/day 5 annually 2 days * - duration of streamflow is for the remainder of that period.
WC01440:R02PIH_ONKA_SUMMARY.DOC Version 1 PAGE 50 n Table C-10 Flow EWRs Site 10 – Onkaparinga River at gorge
EWR Season Magnitude Frequency Duration
Low flow 7.5 ML/day 10.1 Annually * (Feb – May) (minimum) 10.2 19.5 ML/day 2 annually 15 days High flow 35 ML/day 10.3 High flow period * (Jul – Dec) (minimum) 10.4 100 ML/day 5 annually 5 days 10.5 >900 ML/day 5 annually 2 days * - duration of streamflow is for the remainder of that period. n Table C-11 EWRs for Site 11 – Onkaparinga River at Old Noarlunga
EWR Season Magnitude Frequency Duration
Low flow 7.5 ML/day 11.1 Annually * (Feb – May) (minimum) 11.2 19.5 ML/day 2 annually 15 days High flow 35 ML/day 11.3 High flow period * (Jul – Dec) (minimum) 11.4 100 ML/day 5 annually 5 days 11.5 >900 ML/day 5 annually 2 days * - duration of streamflow is for the remainder of that period.
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