Environmental Water Requirements for the Swan River
Rebecca Pinto and Bryce Graham Aquatic Ecologist and Hydrologist Water Assessment Section Resource Management and Conservation Division DPIWE.
Report Series WRA 01/02 March, 2001 Acknowledgments
This study has been conducted under the Natural Heritage Trust as part of the project "Tasmanian Environmental Flows" (NRC13182) and has received funding from the Commonwealth Government and the Department of Primary Industries, Water and Environment.
The authors would like to thank the following individuals from DPIWE for their assistance in field data collection, laboratory sample processing and taxonomic identification and for assistance in preparation of this report: Henry Maxwell, Claire McKenny, Colin Shepherd, Tom Krasnicki, David Horner, Justine Latton.
The authors would also like to acknowledge the support received from landowners and stakeholders within the Swan River catchment.
Copyright Notice: Material contained in the report provided is subject to Australian copyright law. Other than in accordance with the Copyright Act 1968 of the Commonwealth Parliament, no part of this report may, in any form or by any means, be reproduced, transmitted or used. This report cannot be redistributed for any commercial purpose whatsoever, or distributed to a third party for such purpose, without prior written permission being sought from the Department of Primary Industries, Water and Environment, on behalf of the Crown in Right of the State of Tasmania. Disclaimer: Whilst DPIWE has made every attempt to ensure the accuracy and reliability of the information and data provided, it is the responsibility of the data user to make their own decisions about the accuracy, currency, reliability and correctness of information provided. This report was written in 2001; it relies on information current at that time. The Department of Primary Industries, Water and Environment, its employees and agents, and the Crown in the Right of the State of Tasmania do not accept any liability for any damage caused by, or economic loss arising from, reliance on this information. Preferred Citation: Pinto, R. and Graham, B. (2001). Environmental Water Requirements for the Swan River. Department of Primary Industries, Water and Environment, Hobart. Technical Report No. WRA 01/02 ISSN: 1448-1626
The Department of Primary Industries, Water and Environment The Department of Primary Industries, Water and Environment provides leadership in the sustainable management and development of Tasmania’s resources. The Mission of the Department is to advance Tasmania’s prosperity through the sustainable development of our natural resources and the conservation of our natural and cultural heritage for the future. The Water Resources Division provides a focus for water management and water development in Tasmania through a diverse range of functions including the design of policy and regulatory frameworks to ensure sustainable use of the surface water and groundwater resources; monitoring, assessment and reporting on the condition of the State’s freshwater resources; facilitation of infrastructure development projects to ensure the efficient and sustainable supply of water; and implementation of the Water Management Act 1999, related legislation and the State Water Development Plan. Table of Contents
A. GLOSSARY OF TERMS 1
B. EXECUTIVE SUMMARY 2
1. INTRODUCTION 4
2. SWAN RIVER 4
2.1 General Description 4 2.1.1 Catchment and Drainage System 4 2.1.2 Geomorphology and Geology 5 2.1.3 Climate and Rainfall 7 2.1.4 Vegetation 7 2.1.5 Land Use and Degradation 8 2.1.6 Hydrology 8
2.2. Site Selection 10 2.2.1 The Swan River at Waters Meeting 10
3. VALUES 11
3.1 Community Values 11
3.2 State Technical Values 12
3.3 Endangered species 13
3.4 Moulting Lagoon Estuary 14
3.5 Values Assessed 15
4. METHODOLOGY 16
4.1 Physical Habitat Data 16
4.2 Biological Data 17 4.2.1 Invertebrates 17 4.2.2 Fish 17
4.3 Hydraulic Simulation 17
4.4 Risk Analysis 18
5. RESULTS 19
5.1 Physical Habitat Data 19
5.2 Biological Data 20
5.3 Risk Analysis 21 6. DISCUSSION 24
6.1 Fish 24 6.1.1 Galaxias fontanus 24 6.1.2 Galaxias truttaceus and Galaxias maculatus 25 6.1.3 Pseudaphritis urvillii 25 6.1.4 Prototroctes maraena 25 6.1.5 Salmo trutta 26
6.2 Crayfish 26 6.2.1 Astacopsis franklinii 26
6.3 Flow Recommendations 26 6.3.1 Waters Meeting 27
7. REFERENCES 28
APPENDIX 1. WUA GRAPHS FOR THE SWAN RIVER AT WATERS MEETING 31
Front cover: Swan River at Tasman Highway Photo: Rebecca Pinto A. Glossary of Terms ARMCANZ Agriculture and Resource Management Council of Australia and New Zealand ANZECC Australian and New Zealand Environment and Conservation Council CAMBA China/Australia Migratory Bird Agreement cumec a measure of flow discharge. 1 cubic metre per second; equivalent to 86.4 ML/day Commissional Water Under the Water Act 1957, the right to take water from a water resource Right (C.W.R.) (watercourse, lake, river, stream or any surface water or groundwater) for commercial (irrigation) use. Under the current Water Management Act 1999 these Rights no longer exist; instead water licences are issued for taking water. discharge a volume of water passing a given point in unit time Environmental Water Descriptions of the water regimes needed to sustain ecological values of aquatic Requirements ecosystems at a low level of risk. These descriptions are developed through the (EWRs) application of scientific methods and techniques or through the application of local knowledge based on many years of observations. IFIM Instream Flow Incremental Methodology JAMBA Japan/Australia Migratory Bird Agreement macrophytes vascular aquatic plants (e.g. reeds, water ferns, strap weed) macroinvertebrates invertebrate (without a backbone) animals which can be seen with the naked eye. Megalitre (ML) a measure of water equivalent to 1 000 000 litres (or about the size of an Olympic swimming pool) NPWA National Parks and Wildlife Act 1970 pool area of still, often deep water , usually within the main river channel Ramsar Convention The Ramsar Convention is the intergovernmental treaty, which provides the framework for international cooperation for the conservation and wise use of wetlands. riffle area of fast moving, broken water Riparian Right Under the Water Management Act 1999 a person who owns land or occupies a property may take water from a watercourse or lake on, or adjoining, that land for the purposes of domestic use, or irrigation of a household garden, or stock watering, or firefighting, or drilling. riparian vegetation vegetation on the banks of streams and rivers that is directly affected by the flow regime run unbroken, moving water sinuosity degree of “bendiness” of a river (ratio of valley length: river length) substrate the structural elements of the river bed; boulder, cobble etc. taxon (plural: taxa) a particular taxonomic group of living organisms, eg. a particular species, family etc. transect in this study, a line across the river bed perpendicular to flow, used for a standardised collection of depth, velocity and substrate information WL Water licence – Under the Water Management Act 1999 water licences are issued for the purpose of taking water from a water resource (watercourse, lake, river, stream or any surface water or groundwater). The amount of water taken depends upon the water allocation under the issued licence. The Department of Primary Industries, Water and Environment allocates water for irrigation, commercial and industrial purposes. Environmental Water That part of the Environmental Water Requirements that can be met. That is, the Provisions (EWPs) amount of water that is allocated to the environment after consultation and negotiation with stakeholders (of which the environment is one). woody debris instream pieces of wood such as snags, logs and large branches WUA Weighted Useable Area, or the amount of useable habitat available in the river for a species
1 B. Executive Summary
This report details the ecological assessment of flow requirements for the Swan River. Both community and State technical values were identified as part of the assessment process and the ecological values identified from this process were used to focus the assessment of Environmental Water Requirements (EWRs).
Ecological values specifically targeted included:
• Maintain habitat for common jollytail (Galaxias maculatus), brown trout (Salmo trutta), and shortfinned eel (Anguilla australis) populations; and • Maintain habitat for macroinvertebrate populations found in the Swan River.
A risk analysis was performed to provide (1) a series of options for negotiation of Environmental Water Provisions (EWPs), and (2) the ecological risk of failure in not achieving these flows for each of these values. This was achieved by determining the flow at which the useable habitat available to a species changes by a certain percentage, relative to a reference flow. The percentage changes in habitat that determined risk categories were taken from Davies and Humphries (1996). This analysis was done for each of the key biota (including both fish and invertebrate species).
Other values identified and discussed elsewhere in the report include:
• Maintain suitable flow for the protection of Australian grayling (Prototroctes maraena). • Maintain fish stocks, including Australian grayling, brown trout, shortfinned eel, freshwater flathead (Pseudaphritis urvillii), spotted galaxias (Galaxias truttaceus), and common jollytail. • Maintain rearing and/or spawning habitat for brown trout, freshwater flathead, spotted galaxias, and common jollytail, and • Maintain instream woody debris as habitat for native fish populations.
One site was selected to represent the river, identified by preliminary analysis of river reach characteristics along the length of the river. The Environmental Water Requirements and associated risk of failure to provide these flows are as follows.
Swan River – Waters Meeting
The EWRs relate to the Swan River reach, which extends from the point two kilometres downstream of Waters Meeting (the convergence of the West Swan and Swan Rivers), to where the Tasman Highway crosses the river.
The flows for each risk category at the Waters Meeting reach. The Environmental Water Requirements are the "Low risk" flows.
Risk Category I II III Low risk (EWR) Moderate risk High risk Month cumecs ML/day cumecs ML/day cumecs ML/day Dec > 0.4 > 34.6 0.4 – 0.3 34.6 – 25.9 < 0.3 < 25.9 Jan > 0.2 > 17.3 0.2 – 0.1 17.3 – 8.6 < 0.1 < 8.6 Feb > 0.2 > 17.3 0.2 – 0.1 17.3 – 8.6 < 0.1 < 8.6 Mar > 0.2 > 17.3 0.2 – 0.1 17.3 – 8.6 < 0.1 < 8.6 Apr > 0.4 > 34.6 0.4 – 0.3 34.6 – 25.9 < 0.3 < 25.9
2 The flow recommendations resulting from the risk analysis are considerably influenced by the water requirements for macroinvertebrate species found in the Swan River. However, we consider these flows are necessary also to adequately protect other significant aquatic fauna such as Swan galaxias (Galaxias fontanus) and the eastern freshwater lobster (Astacopsis franklinii) and strongly recommend that flows remain in the ‘Low Risk’ category to ensure these values are maintained.
An important caveat to this report is that the flows recommended for each month are the minimum flows for a low risk of failure to meet ecological values. Since there is little regulation of this river during the months of high flow, rates for this period have not been considered. If high flow rates are impacted or threatened in any month, including the irrigation season, additional work will be required. Minimum flow rates for months outside the irrigation season have not been identified in this report and will also require additional work if significant water developments (e.g. dams) are proposed in this catchment.
3 1. Introduction
In accordance with the water reform agenda set out by the Council of Australian Governments, or COAG (ARMCANZ and ANZECC, 1996), Tasmania is currently estimating Environmental Water Requirements (EWRs) for many of its rivers. Intrinsic to this process is the requirement that a supply of water will be provided to the environment as well as to human users to maintain or improve ecosystem quality and health of river systems. For full details about the process refer to Fuller and Read (1997). Briefly, the process involves:
• the identification of water values by the community and the State Technical Committee for Environmental Flows (a panel representing the State government’s technical and scientific expertise); • the assessment of the flow necessary to maintain these values, which includes an environmental flow assessment; • negotiation and tradeoff of these values if required when determining a new flow management regime; and • monitoring of both compliance and environmental benefit of the new flow regime once this is in place.
This report details the assessment of the environmental water requirements of key aquatic fauna that show distinct preferences to changes in discharge. The values identified by the community and the State Technical Panel play a key role in focussing this assessment. Therefore both sets of values for the Swan River have been provided in the report, and addressed where appropriate.
The Swan River has been subject to water abstraction for many years in order to provide irrigation for agricultural purposes and water for town use and consumption. The water is diverted throughout the year, but this assessment will concentrate on the low flow period between December to April, as this is when the river is suspected to be most under stress. The issue of non-summer flows will need attention in future if abstraction increases or there is further development of the water resource.
2. Swan River
2.1 General Description
2.1.1 Catchment and Drainage System
The Swan River originates from the slopes of Mt St John and Little John Peak at an average elevation of around 700m above sea level (ASL). The river’s headwaters flow in a southerly direction winding through low hills and crests for approximately 10km down to an altitude of 300mASL at Hardings Falls. From this point the river flows through a short gorge section where it drops a further 140m in altitude over approximately 3km. The river then meanders in a southerly direction through a gentle gradient, for several kilometres to the confluence with the West Swan River at Waters Meeting at around 75mASL. The river continues to wind down through undulating plains to the point where the Cygnet and Wye River tributaries join the main channel. Throughout the lower reach the river flows through river flats to its point of discharge between Reedy Duckhole and Bayles Backwater marshes into King Bay of Moulting Lagoon. The lagoon opens to the sea via the Great Swanport estuary past Point Bagot.
4 The general topography of the catchment is typified by hills extending north westerly at the source grading down to undulating plains and river terraces. The Swan catchment is bounded by the Apsley River catchment to the east, the St. Pauls River catchment to the north, the Macquarie River catchment to the west and by the Meredith River catchment to the south. Major tributaries of the river all drain land to the west of the main channel of the river, with a dominance of smaller tributaries draining land to the east of the main channel. The large tributaries include the West Swan River, Cygnet River and the Wye River. These tributaries enter the river through the middle and lower reaches, with other smaller tributaries entering throughout the catchment.
The Swan River has a catchment area of approximately 660km2 and a total length of approximately 45km. Due to the topographical nature of the catchment, the majority of irrigation occurs in the middle and lower reaches of the river (Figure 1). In addition to small- scale offstream dams there is a concrete weir of approximately 0.6m in height running across the river approximately 100m downstream of the stream-gauging site at the Grange. This has created a large pool, extending several hundred metres from the weir and it is from this pool that water is pumped to supply the Swansea township with drinking water via a water treatment plant.
2.1.2 Geomorphology and Geology
The Swan River originates from the Mt. Allen land system, where low mountains and hills and associated marshes and swamps, have developed on Jurassic dolerite and basalts. This extends from the point of origin of the river, to the Hardings Falls area. The instream habitat is composed of short cobble/boulder riffles punctuated by short medium to fast flowing runs of cobble and boulder, interspersed with some areas of exposed bedrock. The swampy areas contain a build-up of finer material with small pebbles, gravels and silt dominating the substrate.
Downstream of Hardings Falls to the confluence with the West Swan River, the land system includes hilly lowland dolerite country. This Jurassic dolerite base also extends down through to areas near the Swan River and Moulting Lagoon. Below Waters Meeting the undulating plains and river flats were formed from alluvium composed of Quaternary clays, sands and gravels and low crests of dolerite (Davies, 1988). The instream habitat throughout the Waters Meeting reach is composed of cobble-dominated riffles interspersed with variable flowing runs of similar substrate. Further downstream the substrate becomes more pebbly, and flow decreases making pools and runs the dominant habitat, with only a few short riffles present.
5 6 2.1.3 Climate and Rainfall
The Swan River catchment falls within the coastal district in the eastern region of the State. The area generally experiences a temperate marine climate, with moderate to low rainfall (Davies, 1988). The catchment area comprises undulating plains and river flats through the middle and lower reaches of the river, flanked by hilly country with a short mountainous belt in the upper extent of the catchment. Rainfall is slightly higher in the upper reaches where the influence of topography generates around 750 – 1000mm of rain per year. Throughout the lower reaches of the river and surrounding country, the rainfall totals around 500 – 625mm per annum. The highest monthly rainfall occurs in winter, with July and August generally being the wettest months and February and March the driest through the summer period.
2.1.4 Vegetation
Throughout the catchment, vegetation varies according to topography, rainfall and soil type. Around the top of the catchment the Swan River flows south down a relatively steep gradient, through State Forest. Here, the soils are generally shallow, stony, dark brown loam, supporting low open woodland dominated by black peppermint (Eucalyptus amygdalina) with an understory of sunshine wattle (Acacia botrycephala), round-head riceflower (Pimelea nivea), native olive (Notelaea ligustrina), Tasmanian speedwell (Veronica formosa) and native fuchsia (Correa lawrenciana). Similarly exposed upper slopes and rocky flats support woodland composed of white gum (Eucalyptus viminalis) and black peppermint with an understory of bull oak (Casuarina littoralis), black boy (Xanthorrhoea australis), guitar plant (Lomatia tinctoria), banksia (Banksia marginata) and peach berry (Lissanthe strigosa). Marshes and swamps occurring in the upper reaches of the Swan upstream of Hardings Falls, support scrub and heath vegetation such as black gum (Eucalyptus ovata) and Eucalyptus rodwayi with understory species including woolly tea-tree (Leptospermum lanigerum), sedge (Carex iynx) and cutting grass (Gahnia grandis) (Davies, 1988).
The mid-catchment topography comprises exposed and protected crests and slopes divided by well-drained rocky flats, with drainage flats in the lower sections. The crest and slopes contain extremely shallow soils that support vegetation dominated by low and low-open woodland of black peppermint, white gum and white peppermint (Eucalyptus pulchella), with an understory including species such as she-oak (Casuarina stricta), southern giant tea-tree (Cyathodes divaricata) and black boy. Along the drainage flats the soil is generally deeper, supporting woodland and open forest vegetation dominated by black gum, over an understory of woolly tea tree, scented paperbark (Melaleuca squarrosa), and cutting grass.
Vegetation through the lower reaches has been largely altered through clearing for the development of agricultural land. Those areas with remnant native vegetation are generally characterised by open woodland on dolerite crests and stony flats, and woodland areas over the sandy flats, river terraces and drainage flats. Low dolerite crests with shallow, stony clay loam support black peppermint and white gum over understory plants including she-oak, black wattle (Acacia mearnsii), kangaroo grass (Themeda australis), spear-grass (Stipa sp.), broad sword-edge (Lepidosperma laterale), blackthorn (Bursaria spinosa), sagg (Lomandra longifolia), and peach berry. The deeper loamy sands support woodland comprising the same eucalypt species along with understory species of sagg, black wattle, native cranberry (Astroloma humifusum), and peach berry. The deep clay soils of the river terraces support vegetation of white gum, silver wattle (Acacia dealbata) and black wattle whereas the heavier clays of the drainage flats support black gum and white gum, with the same understory species. In those areas that have been cleared throughout the lower reaches of the river for agricultural use, there are some tracts where crack willows (Salix fragilis), blackberries (Rubus fruticosus) and vast areas of gorse (Ulex europaeus) dominate the riparian zone.
7 It should be noted that several rare and threatened species of Tasmanian native plants can be found inhabiting areas of the Swan River catchment and these are listed under the Threatened Species Protection Act 1995. They include Midlands mimosa (Acacia axillaris), hairy cutleaf daisy (Brachyscome rigidula), bitter cryptandra (Cryptandra amara), clasping-leaf heath (Epacris acuminata), Douglas heath (E. grandis), Duncan's heath (E. limbata), Tasmanian velvet bush (Lasiopetalum micranthum), bush pea (Pultenaea prostrata, P. selaginoides) small-leaf spyridium (Spyridium microphyllum), and stenanthemum (Stenanthemum pimeleoides). Many of the species listed are found within riparian zones and are facultative riparian species that are dependent on this habitat and rely on natural seasonal disturbance events (eg. flooding) for continued growth and propagation.
2.1.5 Land Use and Degradation
The soils found in the Swan River catchment have been formed largely over Jurassic dolerite, with Quaternary sediments forming the more productive areas throughout the lower reaches of the river. In the upper sections of the catchment the dolerite and basalt loams and clay loams support large areas of native vegetation. Here forestry is the primary land use as the tall forests are widely exploited as a timber resource, although these areas also serve as zones of nature conservation (Davies, 1988). Erosion through the gullies is evident in some areas on the lower slopes associated with drainage lines, however waterlogging and flooding pose more hazards throughout the marsh and swamp areas.
Through the mid and lower reaches of the river, the terraces and floodplains contain complex alluvial soils that are composed of a mixture of sand and clay with peat present through the deeper drainage lines. Many areas throughout these sections of the catchment have been cleared and are used for grazing (sheep and cattle) and various types of cropping ranging from specialised horticultural crops (eg. olive groves, walnuts and vineyards) to vegetable and cereal crops. Timbered land also remains in areas where forestry and nature conservation is still present. Cropping is present in some parts of the lower section of the river system where land has been largely cleared and drained and these tracts of land support an extensive walnut industry as well as viticulture. Anglers are key recreational users of the river and trout is the major fish species caught. Within the Great Swanport Estuary, four commercial aquaculture operations grow native oysters (Ostrea angasi) and Pacific oysters (Crassostrea gigas) in or near Pelican Bay and Point Meredith (Colin Shepherd, Marine Environment, DPIWE, pers. comm.).
Present factors contributing to land and soil degradation in the catchment include: sheet, rill and gully erosion; nutrient and structural decline of soils; waterlogging, streambank erosion, flooding; and possibly salinity. The sandier soils are generally highly erodible due to their light texture and low organic matter content. Waterlogging from poor surface drainage resulting in high water tables means that salinity may become a potential problem (Davies, 1988). There are also significant problems with stream bank erosion through flooding and waterlogging as well as large areas of gorse and to a lesser extent willow infestations along some stretches of the river and its tributaries.
2.1.6 Hydrology
Stream gauging data has been collected from the Swan River catchment from 1964 to the present. There are two gauging sites located on the Swan River; one in the upper catchment upstream of Hardings Falls, and one in the lower end of the catchment at the Grange property approximately 13km downstream from the assessment site used in this study. The stream gauging station at the Grange has a catchment area of 448 km2. The seasonality and variability of monthly flows in the Swan catchment is shown in Figure 2 by a box and whisker plot of the data from the stream gauging site Swan River at The Grange. The major
8 note from Figure 2 is the highly variable flows experienced in summer and winter at the site, which is typical of Tasmanian East Coast rivers. While the scale of the plot is extended to 2,500 ML/day to display the variability of monthly flows, the seasonal pattern is still evident, with higher flows experienced from June to September and the lowest flows recorded in February and March.
Swan River @ The Grange Recorded Flows
2500
2250
2000
1750
1500
1250
1000
750
500
250 Recorded Average Monthly Flow (ML/Day) Flow Monthly Average Recorded 0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month
Figure 2. Box and whisker plots of monthly flows from the Swan River at the Grange gauging station (1 cumec = 86.4ML/day). The plot displays the median (or middle of the data) as a line across the inside of the box. The bottom and top edges of the box mark the first and third quartiles respectively, indicating the middle 50% of the data. The ends of the whiskers show the spread of the data and together enclose 95% of the data. The dots beyond the whiskers indicate the high and low extremes.
To estimate the natural monthly volumes, the water licence allocations were added to the stream gauging data. As the water licence dataset is for the current irrigation period, water licences were adjusted downward by 6% each year to reflect the water licence allocations for any particular year (Sustainable Development Advisory Council, 1996).
To estimate the natural flows at the Waters Meeting study site the natural flow estimates from the gauging station at the Grange were scaled back to the site using the ratio of catchment areas (290.5:448km2). Areal scaling back to the study site was based on the strong correlations of flow records within and between catchments in the region and is also a commonly employed hydrological technique.
The strong seasonal flow pattern (Figure 2) indicates flows peaking in the period April through to September. Lowest flows are experienced between January and March and this also corresponds to the peak irrigation demand in the river. This seasonality ensures that many ecological processes essential in riverine and wetland ecosystems are maintained including fish spawning (Beumer, 1980), channel maintenance and flushing flows (Arthington
9 et al., 1992), estuary productivity (Jones et al., 1993; Whitfield, 1996, Davies, 1997; Loneragan & Bunn, 1999) and wetland ecosystems (Thomas et al., 2000).
Water abstraction demands on the river come from Commissional Water Rights (CWRs) issued under the Water Act 1957. These CWRs will soon be converted to Water Licences under the Water Management Act 1999. There are 26 water rights situated along the upper and lower reaches of the river and its tributaries (see Figure 1). Primary water use is for irrigation for agricultural purposes. Annual water takes total 3,927 ML of which 3,640 ML is for winter storage and 287 ML for direct pumping during the irrigation period (December to April).
2.2. Site Selection
Bovee (1982) describes a study site as a location on a stream where some characteristics of the habitat is measured. The study site on the Swan River was established to measure microhabitat characteristics, which provided a basis for determining a relationship between the total amount of habitat (available to key species) and the discharge in the reach of the river represented by that study site (Bovee, 1982).
Site selection was considered along the entire length of the Swan River channel. With the exception of the uppermost reach above Hardings Falls, the main channel and several tributaries throughout the whole catchment are affected by water abstraction. Three reaches were identified, based on instream habitat diversity, channel morphology, sediment supply, bank materials, riparian vegetation, flow regime and discharge. The upstream reach of the Swan River extends from the source down through steeper slopes to Snow Marshes and through to Hardings Falls. Throughout this reach the instream habitat is typified by a substrate dominated by cobble, interspersed with irregular bedrock platforms and a relatively steep bed slope. The middle reach of the river extends from Hardings Falls down to the point where the Tasman Highway crosses the river. This reach is characterised by regular pool/riffle/run sequences with a substrate largely dominated by cobble and boulder with bedrock platforms present in isolated areas. The lower reach of the river extends downstream from the Tasman Highway to the discharge point at Moulting Lagoon. This section has an instream habitat of smaller substrate size dominated by cobble, pebble and silt.
The upper and lower reaches were not considered significant enough to warrant separate study sites due to the lack of water abstractions in the upper reach and the low number of abstractions in the lower reach. The inaccessibility to the river in many sections within the upper reach and the dominance of pools containing a high degree of siltation in the lower reach, in addition to the low number of summer water offtakes in these reaches, meant that the middle reach was considered most appropriate to study. One study site was chosen within the middle reach of the river, which appeared to contain adequate representation of the channel morphology, habitat diversity and discharge that was present throughout the whole reach. Details of the site selected are given in section 2.2.1.
2.2.1 The Swan River at Waters Meeting
The study site was approximately 861m long and was located approximately 2km downstream of the confluence of the West Swan and Swan Rivers (TASMAP grid reference 5356500 590000). This site was selected for its representation of the river from Hardings Falls down to the point where the Tasman Highway crosses the river (see Figure 1). The river here is dominated by sequences of short riffles interspersed with longer runs and pools over a cobble and boulder substrate with some exposed bedrock present.
10 3. Values
3.1 Community Values
A meeting was held at the Swansea Council Chambers on the 15th November 1999 where community values for determining environmental water requirements for the Swan River were identified. Draft Protected Environmental Values (PEVs) for determining water quality objectives were set earlier for the upper catchment through the Southern Midlands Council. The Water Management values identified and prioritised by representatives of various interest and stakeholder groups for the catchment are shown in Table 1.
Table 1. Community Water Values for the Swan River. Those values of highest priority were assigned the number 1 with lower priority values given a 2 or 3. Values not prioritised were considered to be equally of least importance. Values marked with an asterisk in the opinion of the Water Assessment unit will not be affected in terms of maintenance or enhancements by changes in quantity of water flow in the catchment and will not be discussed further in this report. These values have been retained for future reference for values setting under any PEV process or integrated catchment management community consultation.
SPECIFIC WATER VALUES BROAD WATER PRIORITISATION VALUE OF VALUES CATEGORIES 1. Ecosystem • Improve Galaxias fontanus populations. 2 • Provide fish ladder at weir.* 2 • Maintain known and unknown aquatic values (lack of information). • Protect feeding and breeding habitat for water birds. • Retain/Maintain existing natural riparian vegetation 2 and replace vegetation.* • Maintain summer flows and periodic flushing flows. 1 • Maintain Hardings Falls Forest Reserve and above it. • Maintain and protect Snow Marshes. • Maintain freshwater and estuarine native fish populations in Moulting Lagoon. • Maintain and improve water quality in catchment. • Prevent stock access to the main river and it’s 2 tributaries.* • Improve road network maintenance, in particular, 1 stream crossings.* • Provide water for Moulting Lagoon estuary. 1
2. Consumptive • Maintain and improve domestic town water supply 1 and non- and storage. consumptive • Maintain riparian rights. 1 use • Maintain irrigation rights. 1 • Improve stock watering methods.* 2 • Improve methods of irrigation storage.* 3 • Maximum harvest of water during flood events into 2 offstream storages.* • Protect aquaculture values in Swan River 1 (consumptive)* • Improve community awareness of the value of water 1 through education.*
3. Recreational • Maintain Bream fishery. 1
11 • Maintain Estuarine fishery. 1 • Maintain popular swimming holes - Cranbrook 2 bridge, Hardings Falls, Waters Meeting. • Provide education through signage on minimal 2 impact use on swimming holes.* • Duck shooting.* 2 • Boating in Estuarine areas.* 3 • Water skiing in Estuarine areas.* 3 • Camping at Greasy Pole, Yellow Sandbanks, Bagot 3 Point and River and Rocks. (all estuarine).* • Bird Watching.* 2
4. Physical • Maintain diverse landscape value of river and Landscape Moulting Lagoon catchment. • Maintain variable flows regime. • Maintain riparian vegetation.* • Maintain beauty of Snow Marshes. • Maintain natural geomorphological form. 5. Aesthetic • Clear, clean water. 1 • Control of gorse and willows.* • Protect native riparian vegetation.* • Replace/regenerate native riparian vegetation.* • Control bank erosion.* • Encourage the establishment and maintenance of riparian buffers.* • Appropriate buffer widths to filter out contaminants.* • Maintain Hardings Falls.
3.2 State Technical Values
The scientific values for a catchment are identified at the State level using technical experts to identify scientific and technical issues such as endangered species, fisheries and wetlands protected under legislation/agreements. The State Technical Committee for Environmental Flows was set up in order to determine scientific values on a catchment by catchment basis. The committee includes representatives from DPIWE, who provide advice on aquatic ecology, wetlands, geomorphology, riparian vegetation, and estuarine ecology, fisheries biology and ecology. In addition, committee members include environmental representatives from the Hydro-Electric Commission and a researcher from the University of Tasmania with relevant expertise in environmental flows. The committee's term of reference specifically relating to the identification of scientific values is:
• Identify water values for catchments from a technical and scientific perspective including the non-negotiable values, which are implicit in various local, national and international agreements and legislation.
The values that the committee decided warranted consideration for the ecological requirements for flow in the Swan River are provided in Table 2.
12 Table 2: Swan catchment scientific values
Ecosystem Values (all are of equal priority)
• Protect the endangered Swan galaxias (Galaxias fontanus). • Maintain suitable flow for shortfinned eel (Anguilla australis) populations and for the protection of Australian grayling (Prototroctes maraena) and the eastern freshwater lobster Astacopsis franklinii which are both listed in the Tasmanian Threatened Species Act 1995 as vulnerable and of high conservation significance respectively. • Maintain fish stocks, including Australian grayling, Swan galaxias, freshwater flathead (Pseudaphritis urvillii), spotted galaxias (Galaxias truttaceus), common jollytail (Galaxias maculatus), and brown trout (Salmo trutta). • Maintain rearing and/or spawning habitat for Swan galaxias, freshwater flathead, spotted galaxias, common jollytail, and brown trout. • Maintain instream woody debris as habitat for native fish populations. • Maintain sufficient flows to ensure the hydraulic/ecological requirements for the Moulting Lagoon estuary are met.
For further information on the importance of these values refer to Section 6: Discussion.
3.3 Endangered species
Current listings for endangered species in the Swan catchment are provided in Table 3 (Bryant and Jackson, 1999). Bryant and Jackson (1999) also identify suitable habitat in the lower catchment where endangered species may occur. A species is regarded as endangered if it is in danger of extinction because long-term survival is unlikely while the factors causing them to be endangered continue operating. These species may be directly or indirectly affected by alterations to the natural flow regime of the river.
Other species that are listed as threatened in the Tasmanian Threatened Species Act 1995 include the eastern barred bandicoot (Perameles gunnii) and the spotted tailed eastern quoll (Dasyurus maculatus maculatus) which are listed as vulnerable under the Commonwealth Endangered Species Act. Significant avian fauna found to inhabit the Swan catchment include the wedge-tailed eagle (Aquila audax fleayi), swift parrot (Lathamus discolor) and forty-spotted pardalote (Pardalotus quadragintus). Various coastal birds including the fairy tern (Sterna striata), which is listed as rare in the Tasmanian Threatened Species Act 1995, hooded plover (Thinornis rubricollis) and migratory waders, little penguin (Eudyptula minor) and short tailed shearwater (Puffinus tenuirostris) are all listed as high conservation significance.
Many of these species rely on terrestrial riparian habitat that may be indirectly influenced by excessive de-watering. However, the influence of altered flow regimes on riparian vegetation and associated faunal communities are beyond the scope of this report. This issue would need to be addressed if changes to the flood flow regime of the river were contemplated. Those birds that utilise the Moulting Lagoon estuary as habitat for migratory patterns, breeding and foraging may, however, be impacted upon if the natural regime of the Swan River is modified to the extent that the hydrological inputs needed to maintain the delicate balance of the estuarine environment are lost.
13 Table 3. Threatened species that may occur, or are listed as occurring in suitable habitat in the Swan catchment.
Species Listing Habitat/occurrence Swan Galaxias (Galaxias Endangered Endemic to the Swan River (headwaters in particular), fontanus) including a few other localities in eastern Tasmania. Preferring slow to moderately fast-flowing rocky streams containing abundant shelter and where natural barriers (eg. waterfalls and marshes) prevent invasion of predatory exotic fish species (eg. trout and redfin perch). Eastern freshwater lobster High Occurs in the Swan catchment. Typically found in (Astacopsis franklinii) conservation well-vegetated catchments of several stream sizes, significance where snags, pools and undercut (not eroding) banks are present and water temp. <18oC, high dissolved oxygen levels and clear of sediment. Australian Grayling Vulnerable May potentially occur in lower and middle reaches of (Prototroctes maraena) the Swan River. Green and gold frog Vulnerable May occur in permanent or temporary water bodies (Litoria raniformis) with surrounding vegetation.
In addition to threatened faunal species, there are several floral species that occur within the Swan catchment and Moulting Lagoon estuary that are listed under the Threatened Species Protection Act, 1995. They include Acacia axillaris, Brachyscome rigidula, Cryptandra amara, Epacris acuminata, E. grandis, E. limbata, Lasiopetalum micranthum, Pultenaea prostrata, P. selaginoides, and Spyridium microphyllum. Moulting Lagoon contains some endemic species and some species found to be under threat of extinction in Tasmania. These include the endangered golden spray (Viminaria juncea) which is listed as endangered, the endemic spreading stenanthemum (Stenanthemum pimeleoides) which is considered vulnerable at a state and national level, and prickly woodruff (Asperula scoparia), swamp wallaby grass (Amphibromus neesii), ruppia (Ruppia megacarpa) and spreading water-mat (Lepilaena patenifolia) which are all considered rare in Tasmania (Schedule 5, Threatened species Protection Act 1995).
3.4 Moulting Lagoon Estuary
Moulting Lagoon is a listed Ramsar site and is also listed as a Game Reserve under the National Parks and Wildlife Act (NPWA, 1970). Moulting Lagoon encompasses King Bay (where the Swan River discharges) and Great Swanport estuary, and discharges into Great Oyster Bay. Great Swanport estuary has been classified by Edgar et al. (1999) as a class B estuary of high conservation significance. This is defined as being an estuary and associated catchment area remaining relatively pristine or containing an unusual range of species including high fish diversity and significant waterfowl habitat.
Moulting Lagoon is considered an important area for waterbirds and as many as 60 species are found to inhabit the area (Blackhall, 1985). Common waterbirds feed and nest in the lagoon and include black swans (Cygnus atratus), ducks (most numerous being Australian shelduck and chestnut teal), white-faced herons, silver and pacific gulls, masked lapwings and great and little pied cormorants. Nine species of migrating waders use the area during the summer and sometimes in the winter months, for brief stopovers or more extended periods of time. Many of these migratory waders are listed on the Japan/Australian Migratory Bird Agreement (JAMBA) and the China/Australia Migratory Bird Agreement (CAMBA), which are treaties signed by the three governments to protect migratory birds and their
14 environments. Although little information is available on the aquatic vertebrates of Moulting Lagoon, the estuary and coastal wetlands have long been recognised as critical nursery areas for a myriad of marine species. A large number of fish have been recorded in the estuary and some of these also occur in the lower reaches of the Swan River including black bream.
3.5 Values Assessed
It should be noted that while water quality was identified as a community value it was not assessed within this report. There has not been a consistent collection of water quality parameters recorded for the whole of the Swan catchment, rather one-off spot recordings have been taken over the period from 1984 to late 2000 and this data is stored within a Hydrol database. A summary of water quality data sampled over a wide range of flow conditions from 1984 to 1993 was completed by Fuller & Katona (1993) and this indicated that although the number of samples taken were low, they did however cover a wide range of water quality parameters. As such, the lack of comprehensive data does not give a clear indication of water quality conditions in the Swan catchment in relation to current flow conditions. Although these water quality indices have direct implications for acceptable environmental water requirements, it is beyond the scope of this study to address these issues. In addition it should be noted that Davies and Humphries (1996) found that nutrient and turbidity levels in the South Esk river basin were primarily determined by flood flows and were not related to low flows, and the same applied to dissolved oxygen levels in pools. As such the water quality risks associated with declining flows during the irrigation season were therefore not considered significant and would be addressed in the future if a more comprehensive assessment of the catchment was required.
In summary, the ecological values that were considered by DPIWE during the assessment of ecological requirements for flow in the Swan River include:
• Maintain enough water for stream habitat for aquatic animals; • Maintain suitable flows for shortfinned eel (Anguilla australis) populations and for the protection of the Swan galaxias (Galaxias fontanus), Australian grayling (Prototroctes maraena) and the Eastern freshwater lobster (Astacopsis franklinii); • Maintain rearing and/or spawning habitat for freshwater flathead (Pseudaphritis urvillii), spotted galaxias (Galaxias truttaceus) and the common jollytail (Galaxias maculatus); • Maintain fish stocks, including Australian grayling, freshwater flathead, spotted galaxias, and common jollytail, and • Maintain instream woody debris as habitat for native fish populations.
Recreational values considered by DPIWE as part of this study include:
• Maintain suitable flows and rearing and spawning habitat for brown trout (Salmo trutta).
Values that were targeted for detailed and specific assessment include:
• Maintain shortfinned eel, common jollytail and brown trout populations • Maintain macroinvertebrate populations
Those values not specifically targeted are discussed in detail in section 6.
15 4. Methodology
The method used to assess the flow requirements of key species (see Table 6.) was the Instream Flow Incremental Methodology (IFIM), originally described by Bovee (1982). In this process, the preferences of key species for velocity, depth and substrate parameters are combined with transect-derived hydrological data at specific discharges. This data is then incorporated into a suitability index, which is a function of available depth, velocity and substrate. This suitability function is then summed over the study reach to give the Weighted Usable Area, or WUA (Jowett, 1992).
Hydraulic simulation is used to generate velocity and depth data for each transect at the discharges for which data are not available. The outcome is a plot of WUA against discharge for each species or lifestage (see Figure 3). An analysis of the flow levels that will provide varying degrees of risk to the ecosystem is then possible. The software package used for this process was the RHYHABSIM (River HYdraulics and HABitat SIMulation) program developed by Jowett (1992).
4.1 Physical Habitat Data
Transects were established at the site, according to the protocol detailed by Bovee (1982). Within the study reach, a number of distinctive sub-reaches were identified on the basis of hydraulic characteristics and substrate (Bovee, 1982). Transects were established within each of these sub-reaches, perpendicular to the channel.
At each transect, a semi-permanent datum (or header peg) was established by driving a mild steel star picket deep into the upper section of the bank. All measurements were taken perpendicular to the direction of flow, to a point on the opposite bank at a similar height above water level. Water surface elevation relative to the elevation of the header peg was recorded at each transect.
On the initial visits from the 13th-15th April 1999, depth, average water velocity and substrate composition were measured and recorded at regular intervals evenly distributed across the channel with a minimum of 10-15 wetted points. In this way each transect was divided into regular ‘cells’ by collecting all data at the same distances from the header peg. Depth and velocity at 0.6 of the depth from the surface were recorded at each of these points using a pre- calibrated Pygmy current velocity meter and wading rod. Percentage substrate composition was also recorded at each location using the following categories: aquatic vegetation; mud; sand; gravel; pebble; cobble; boulder and bedrock. Substrate particles were characterised by the following modified Wentworth scale: R = Bedrock B = Boulder >256 mm C = Cobble 64 - 256 mm P = Pebble 8 - 64 mm G = Gravel 2 - 8 mm S = Sand 0.06 - 2 mm M = Silt/Mud <0.06mm
Two calibration gaugings were carried out at a suitable location within the study reach to determine discharge. The height of the water surface from the datum peg was measured at each transect at the same time.
16 4.2 Biological Data
4.2.1 Invertebrates
A total of twenty biological samples were taken at Waters Meeting site on the Swan River. The sampling occurred on the 15th April 1999.
Sampling effort was stratified in order for a full representation of the range of depth, velocity and substrate at the sites. Stratification was carried out on the combined habitat data from both sites sampled, using the methodology described by Davies et al. (1997). Sampling for macroinvertebrates was carried out by disturbing the substrate within a 1m2 quadrat upstream of a 250µm kick net. The preserved samples were later sub-sampled to 20% (or a minimum of 200 animals) and invertebrates were identified to the lowest taxonomic level possible using the most current taxonomic keys.
The resulting habitat preference information was used for the creation of WUA-Q curves for key fish and macroinvertebrate species. Key species were selected on the basis of:
• not having rare or patchy abundance; and • exhibiting clear preferences for depth, velocity and substrate
4.2.2 Fish
An electrofishing survey was conducted along the Waters Meeting reach of the Swan River on the 14th and 15th April 1999. The fish species sampled included freshwater flathead (Pseudaphritis urvillii), spotted galaxias (Galaxias truttaceus), common jollytail (Galaxias maculatus), shortfinned eel (Anguilla australis) and brown trout (Salmo trutta). Habitat preference data including depth, velocity and dominant substrate were recorded for each fish sampled as well as fish length and details of aquatic macrophyte and woody debris presence. There was, however, not enough information gathered to be able to accurately develop habitat preference curves for the fish species sampled within the Swan River and so previously developed habitat preference curves were used for the risk assessment.
Habitat preference curves used for brown trout early young of the year, or 0+, were developed from data collected in March 1990 - 1993 by Davies and Diggle (unpublished data) and preference curves for brown trout adults were developed by Bovee (1978). Habitat preference curves were also taken from Jowett and Richardson (1995), who collected habitat preference information for shortfinned eels, and common jollytail.
The transfer of habitat preference curves between different catchments is regarded by many ecologists as an acceptable practice for the above species. Examination of curves for brown trout by previous workers has generally found that these curves are similar in their rise and fall between rivers both in Australia and overseas (Dr Peter Davies, Freshwater Systems, pers. comm.). Similarly, the habitat requirements for shortfinned eels and common jollytails are also regarded as comparable between rivers (Jowett and Richardson, 1995). Given the agreement among ecologists in the transfer of such curves, these preference curves have been adopted for use in this assessment.
4.3 Hydraulic Simulation
From the habitat data of collected at the site and the biological samples collected, values of WUA were generated in m2/m of stream channel for each species or lifestage at a range of discharges. The protocol for generating these WUA-Q curves using the RHYHABSIM
17 hydraulic modelling and simulation package is described by Jowett (1992),. where a data set contained: • velocity, depth and substrate data at every offset for each transect; • locations of all water edges ; • inter-transect distances; and • stage-discharge relationships for each transects.
This information was used to generate velocities and depths at discharges from 0.2 to 1.2 cumecs. Davies and Humphries (1996) describe the protocol used for the hydraulic simulation. Jowett (1992) describes the WUA-Q curve generation in detail. Habitat preference data were combined with simulated velocity and depth data and the measured substrate data, so as to calculate habitat suitability for each cell. The values for all cells from all transects were combined to generate a species total habitat area (WUA) in m2/m or % of stream area for the whole site for each discharge value. This process was used to generate WUA curves for both sites, for all the key species and life stages.
4.4 Risk Analysis
The risk analysis used in this study is a modification of that developed by Davies and Humphries (1996). Risk is based upon changes in useable habitat (∆WUA) relative to a reference flow. In this study the reference flows used (Qm) were the median monthly flows at each site for the period 1964-2000 adjusted to account for irrigation takes (ie. the median monthly flows at each site that would have occurred without abstraction). In this case there are three risk categories (see Table 4), and six variables. The variables include:
WUA for brown trout adults. WUA for brown trout early young of the year. WUA for shortfinned eels. WUA for jollytails. WUA for key individual macroinvertebrate taxa (see Table 6 for a list of these species). WUA for macroinvertebrate taxon diversity.
Table 4. Criteria for assigning risk levels to different values of change in habitat (∆WUA) relative to the reference flow (Qm) for the key ecological variables in this study. Derived from Davies and Humphries (1996). Risk Category I II III Variable No Risk Moderate Risk High Risk ∆WUA for trout, jollytail and eels >85% WUA cf Qm 60-85% WUA cf Qm 30-60% (variables 1-4) WUA cf Qm ∆WUA for individual <10% taxa with <75% ≥10% of taxa with >25% of taxa with macroinvertebrate taxa and taxon WUA cf Qm <75% WUA cf Qm <75%WUA diversity & <25% of taxa cf Qm (variables 5 & 6) with <75% WUA
The risk assessment was conducted as follows for each of the above variables:
• WUA as it varies with Q is normalised so that the maximum (WUAm) is 100% • Qn can then be read directly from the relevant percentage of WUAn on the graph (the appropriate percentage for each risk level is indicated in Table 4) where
WUAn = Weighted Useable (habitat) Area for month of concern WUAm = Weighted Useable Area for pre-offtake median flows Qn= Boundary flow for risk level during month of concern ( n ) (See Figure 3 for worked example)
18 5. Results
5.1 Physical Habitat Data
Hydrological and substrate information was initially collected at the site for the discharge of 0.48 cumec. Two subsequent gauging visits were carried out on 11th December 1999 and 8th August 2000 when the discharge was 1.18 cumecs and 0.23 cumecs respectively. Ranges of depth, velocity and substrate at the site are presented in Table 5.
Table 5. Ranges of depth, velocity and substrate at the Waters Meeting site on the Swan River.
Variable Waters Meeting Depth (m) 0-1.35m Velocity (m/s) 0-1.22m/s Silt (%) 0-100% Sand (%) 0-5% Gravel (%) 0-40% Pebble (%) 0-95% Cobble (%) 0-90% Boulder (%) 0-80% Bedrock (%) 0-60%
19 5.2 Biological Data
Twenty (20) invertebrate samples were successfully taken across the IFIM reach at Waters Meeting on the Swan River. WUA-Q curves were developed for each of the key taxa listed in Table 6. These curves are provided in Appendix 1.
Table 6: Selected taxa for which WUA curves were developed
Type Common name Taxon Lifestage (s) Fish Brown trout Salmo trutta adults and late 0+ Jollytail Galaxias maculatus adults Shortfinned eel Anguilla australis adults Invertebrates Mayflies Baetid Genus 2 spp. larvae Insects Baetid Genus 1 sp. MV4 larvae Atalophlebia spp. larvae Tillyardophlebia spp. larvae Tasmanocoenis tonnoiri larvae Nousia spp. larvae Stoneflies Austrocercoides spp. larvae Caddisflies Hydroptila spp. larvae Hellyethira simplex larvae Oxyethira mienica larvae Ecnomus spp. larvae Helicopsyche murrumba larvae Ecnomina spp. larvae Agapetus spp. larvae Conoesucus spp. larvae Notalina spp. larvae Midges Chironominae larvae Orthocladiinae larvae Podonominae larvae Tanypodinae larvae Flies Austrosimulium furiosum larvae Ceratopogonidae larvae Tipulidae larvae Empididae larvae Beetles Austrolimnius spp. adults and larvae Water penny Sclerocyphon secretus larvae Worms Oligochaeta adults Flat worms Turbellaria adults Freshwater Mites Mites Hydracarina adults Freshwater Crustaceans Amphipods (scuds) Austrochiltoia australis adults Freshwater shrimp Paratya australiensis adults Molluscs Freshwater snails Hydrobiidae adults Freshwater snails Rivisessor gunnii. adults Freshwater limpet Ferrissia tasmanica adults
20 5.3 Risk Analysis
A worked example of the risk assessment process for one variable on the North Esk River is shown in Figure 3. Results of the risk assessment for each month are provided (Table 7), along with curves of the relationship between Weighted Useable Area and Flow for each species investigated (Appendix 1). Note that the highest monthly flow necessary to provide the required quantity of habitat for any variable has been chosen as the flow for each category to ensure that all values are protected.
Figure 3. Worked example of Risk Analysis.
To determine the flow at which there is no risk to adult trout at North Esk River, Watery Plains reach in December (some values excluded for brevity):
1. RHYHAB gives values for WUA as it varies with Q:
Flow WUA (cumecs) (m2/m) 0.05 0.94 0.45 2.95 0.85 3.93 1.25 4.63 1.65 5.31 2.05 5.91 2.45 6.2 2.85 6.37 3.25 6.47 3.65 6.53 3.85 6.55
2. This is then normalised so that the maximum, WUAm, is 100%:
Flow Normalised (cumecs) WUA 0.05 14.35 0.45 45.04 0.85 60.00 1.25 70.69 1.65 81.07 2.05 90.23 2.45 94.66 2.85 97.25 3.25 98.78 3.65 99.69 3.85 100.00
21 Figure 3. cont.:
3. Qn can then be read directly from the relevant percentage of WUAn on the graph where:
WUAd = Weighted Useable (habitat) Area for December WUAm = Weighted Useable Area for pre-offtake median flows Qn= Boundary flow for risk level during month of concern ( n )
WUAm Dec WUA/Q
100 90 85 80 70 60 50 40
Normalised WUA (m2/m) WUA Normalised 30 20 10 0 0.0 0.5 1.0 1.51.8 2.0 2.5 3.0 3.5 4.0
Qn
Flow (cumec)
The Low risk WUA boundary is at 85%, which can be read off the graph as corresponding to 1.8 cumecs. This means that flows below 1.8 cumecs will lead to the WUA dropping below 85% and thereby leading to a Moderate risk to adult trout.
22 Table 7. Flows for each risk category, Waters Meeting (cumecs). Final flows are given to one decimal place for simplicity of application. December Risk Category Low Risk Moderate Risk High Risk Adult S. trutta > 0.36 0.36 – 0.09 < 0.09 0+ S. trutta > 0.42 0.42 – 0.28 < 0.28 G. maculatus > 0.23 0.23 – 0.05 < 0.05 A. australis > 0.18 0.18 – 0.04 < 0.04 Macroinvert. taxa > 0.43 0.43 – 0.35 < 0.35 Taxon diversity > 0.13 0.13 – 0.04 < 0.23 Flow(cumecs) > 0.4 0.4 – 0.3 < 0.3
January Risk Category Low Risk Moderate Risk High Risk Adult S. trutta > 0.16 0.16 – 0.05 < 0.05 0+ S. trutta > 0.15 0.15 – 0.05 < 0.05 G. maculatus > 0.15 0.15 – 0.04 < 0.04 A. australis > 0.10 0.10 – 0.03 < 0.03 Macroinvert. taxa > 0.21 0.21 – 0.15 < 0.15 Taxon diversity > 0.07 0.07 – 0.02 < 0.02 Flow(cumecs) > 0.2 0.2 – 0.1 < 0.1
February Risk Category Low Risk Moderate Risk High Risk Adult S. trutta > 0.08 0.08 – 0.04 < 0.04 0+ S. trutta > 0.08 0.08 – 0.04 < 0.04 G. maculatus > 0.05 0.05 – 0.03 < 0.03 A. australis > 0.05 0.05 – 0.03 < 0.03 Macroinvert. taxa > 0.16 0.16 – 0.09 < 0.09 Taxon diversity > 0.05 0.05 – 0.02 < 0.02 Flow(cumecs) > 0.2 0.2 – 0.1 < 0.1
March Risk Category Low Risk Moderate Risk High Risk Adult S. trutta > 0.10 0.10 – 0.04 < 0.04 0+ S. trutta > 0.09 0.09 – 0.04 < 0.04 G. maculatus > 0.09 0.09 – 0.03 < 0.03 A. australis > 0.06 0.06 – 0.03 < 0.03 Macroinvert. taxa > 0.15 0.15 – 0.11 < 0.11 Taxon diversity > 0.05 0.05 – 0.02 < 0.02 Flow(cumecs) > 0.2 0.2 – 0.1 < 0.1
April Risk Category Low Risk Moderate Risk High Risk Adult S. trutta > 0.27 0.27 – 0.06 < 0.06 0+ S. trutta > 0.42 0.42 – 0.28 < 0.28 G. maculatus > 0.21 0.21 – 0.05 < 0.05 A. australis > 0.15 0.15 – 0.04 < 0.04 Macroinvert. taxa > 0.35 0.35 – 0.24 < 0.24 Taxon diversity > 0.11 0.11 – 0.03 < 0.03 Flow(cumecs) > 0.4 0.4 – 0.3 < 0.3
23 6. Discussion
Before discussing the implications of the risk analysis results, it is important to reiterate the caveat stated at the beginning of the report: that the flows are only appropriate for the individual months for which they have been recommended. However, hydrological processes operating throughout the year dictate the ecological integrity of rivers, and if there is further development of the water resource the issue of non-summer flows will require attention and further assessment.
It should also be stressed that an essential part of setting an environmental flow is the monitoring of compliance and environmental benefit. Further assessment may need to be undertaken in the future if monitoring highlights values that are not being met by the negotiated flow regime.
Any risk assessment must be made relative to some reference period. In this study the reference flows used were the median monthly flows at each site for the period 1964 - 2000, adjusted to account for irrigation takes. (In other words, the flows used were estimations of the median monthly flows that would have occurred at each site without abstraction). Medians have been used for the risk analysis rather than means due to the effect of high flow events skewing means upward and away from a true measure of the central tendency of the data.
The risk analysis (section 5.3) relates to the values specifically considered, including:
• Maintain shortfinned eel (Anguilla australis), jollytail (Galaxias maculatus) and brown trout (Salmo trutta) populations. • Maintain macroinvertebrate populations found in the Swan River.
The risk analysis also indirectly assesses other values nominated by the community, and these were interpreted as: • Maintenance of summer flows. • Maintenance of river flows to protect recruitment of larval and juvenile native freshwater fish populations in Moulting Lagoon.
Other values not specifically targeted are discussed in detail below.
6.1 Fish
6.1.1 Galaxias fontanus
The Swan galaxias (Galaxias fontanus) is endemic to the Swan River and a few other eastern Tasmanian rivers and lives exclusively in freshwater streams (Crook & Sanger, 1997). Its limited distribution has more recently been attributed to the spread and predation pressure from brown trout (Salmo trutta) and redfin perch (Perca fluviatilis) and as such populations are confined to the headwaters of those streams that are inaccessible to the introduced fish species. The Swan galaxias spawn in spring within shallow sections of the river near the normal home range, where abundant instream and riparian cover is present (Fulton, 1990). The larval development occurs over approximately five weeks, where the juveniles occupy shallow, slow flowing water in small groups or schools. Adult colouration begins to develop when the larvae grow to around 35mm in length. Typically three-year classes are present in each population. There is a comprehensive recovery plan currently in place (Sanger, 1993) and the actions include translocation of populations, construction of artificial barriers to
24 introduced fish, monitoring of natural populations, establishment of captive populations and an information and public education campaign. The Tasmanian Galaxiid Recovery Team established in 1996 (Crook & Sanger, 1997) is currently guiding conservation efforts for the threatened species
As there is a lack of habitat preference information available for any lifestages of Galaxias fontanus and the fact that the species is restricted in distribution within the Swan River to headwaters above Hardings Falls, their flow requirements were considered to be outside the present scope of this study. In addition, the establishment of an intensive recovery plan and program of regular monitoring has ensured that the future prospects of the species will be managed with the intention of restoring native and relocated populations to acceptable levels.
6.1.2 Galaxias truttaceus and Galaxias maculatus
Both the spotted galaxias (Galaxias truttaceus) and the common jollytail (Galaxias maculatus) are native to Tasmania. Spotted galaxias prefer to inhabit quiet stream areas, especially amongst submerged logs, and the jollytail prefers to school in the lower reaches of coastal streams. The spotted galaxias is similar to the common jollytail in that both species have a marine juvenile stage and a diadromous life cycle (McDowall & Fulton, 1996). Non land-locked populations migrate downstream to estuaries during autumn-spring tides where spawning and hatching occurs. The newly hatched larvae are swept out to sea and the juveniles eventually migrate back to shore and enter freshwater streams during late winter or spring (Fulton, 1990). Both species form a large part of the whitebait runs at this time. Flow requirements have not been assessed for the whitebait run since it occurs outside of the irrigation season. In addition, habitat preference information is not available for any lifestages of Galaxias truttaceus and therefore the assessment of their flow requirements is outside the scope of this study.
6.1.3 Pseudaphritis urvillii
The sandy or freshwater flathead as it is commonly known is native to lowland streams throughout coastal Tasmania, the Bass Strait islands and southern areas Australia and can tolerate both freshwater and salt water environments. Few details of the life history of freshwater flathead (Pseudaphritis urvillii) are available, but the adults appear to migrate downstream to spawn in estuaries from late April to August (Andrews, 1996). Their preferred freshwater habitat is usually slow flowing water around log snags, under overhanging banks or among leaf litter. As little is known of the spawning requirements of the freshwater flathead, the assessment of the influence of flow on their spawning was beyond the resources of this study.
6.1.4 Prototroctes maraena
The reproductive period for the Australian grayling (Prototroctes maraena) is from late summer to early autumn although Fulton (1990) suggests that spawning in Tasmania may take place from late spring to early summer. Each female produces about 25,000 to 68,000 eggs that sink to the bottom just downstream of the spawning site (McDowall, 1996). Newly hatched larvae are thought to be swept down to estuaries where they remain for about 6 months before returning to freshwater to complete their lifecycle. As little is known of the spawning requirements of the grayling, the assessment of the influence of flow on their spawning was beyond the resources of this study.
25 6.1.5 Salmo trutta
Brown trout (Salmo trutta) are a former native species of Europe and were introduced to Tasmania in 1864, and are now widespread throughout lakes and rivers in the State (Fulton, 1990). Brown trout spawn in late autumn and eggs are deposited in gravel nests or egg pockets (redds) in streams and take at least 28 days to hatch. The spawning of brown trout was not investigated as this occurs outside the irrigation period, between April and August (Davies and McDowell, 1996).
While woody debris is indeed important as habitat for trout, it is beyond the capacity of this assessment to ensure its maintenance. Davies and Humphries (1996) examined the relationship between flow and wetted area of woody debris and found that only small changes in the amount of woody debris inundation occur within the flow ranges typical of the irrigation season. Other issues outside the management of water quantity, such as riparian zone management and woody debris removal, will have greater influence on this value.
6.2 Crayfish
6.2.1 Astacopsis franklinii
The Eastern freshwater lobster (Astacopsis franklinii) occurs throughout eastern Tasmania and although it has not been listed as endangered it is considered to be of high conservation significance and as such maintenance of its habitat, breeding and feeding requirements need to be ensured (Bryant and Jackson, 1999). Ideal lobster habitat encompasses intact catchments of several stream orders including rivulets and headwaters. These should be relatively undisturbed and well-vegetated with woody debris, pools and undercut (but not eroding) banks. Water temperature of less than 18oC, high oxygen content and low sedimentation is also preferential. Breeding of the species occurs in autumn and eggs are carried throughout the winter. Larval development takes place in spring and newly hatched young are found attached to the female during late spring and summer. Although little is known of juvenile requirements, it is suspected that they migrate into smaller stream zones, including semi-permanent creeks and runnels lined with overhanging vegetation (Bryant & Jackson, 1999). As little is known of the spawning requirements of the eastern freshwater lobster, the assessment of the influence of flow on their spawning was beyond the resources of this study.
6.3 Flow Recommendations
This section offers a summary of the flows that provide defined risks to the maintenance of ecological values in the Waters Meeting reach. The Environmental Water Requirements are those flows that ensure "Low risk" to the ecological values for Swan River. Given the low water demands within the Swan catchment and the fact that spawning and rearing of the above fish species is largely outside the summer low-flow period, these values are unlikely to be affected at present. However, substantial reductions in flows may cause dewatering of the preferred habitats of many of these fish species, making the fish more vulnerable to predation. In addition, although the spawning of the above fish and crayfish species occurs during Spring, Autumn and into Winter, at times that are largely outside of the irrigation season, provisions should also be made to ensure adequate flows to enhance the recruitment success of these species. This may mean ensuring that minimal offtakes into offstream storages occurs during these non-irrigation times. It is however outside the scope of this study to address these issues with accuracy for determining specific Environmental Water Requirements for the non-irrigation periods.
26 For the Waters Meeting reach the flow recommendations resulting from the risk analysis are considerably influenced by the water requirements for macroinvertebrate species found to occur in the river. These were identified as a prominent value within the community values and by DPIWE in ensuring that adequate water was provided to maintain instream habitat for aquatic animals. It should also be noted that healthy macroinvertebrate populations provide an essential and highly significant portion of the diets of many game and forage fish and serve a crucial role in the processing of energy in lotic ecosystems (Gore, 1987). In addition, many macroinvertebrates have been shown to have narrow ranges of tolerance to changes in flow (Gore, 1977). Therefore ensuring flow regimes that protect habitats is an integral step in maintaining the perpetuation of both fish and macroinvertebrate populations, and the maintenance of ecological values in the Swan River.
It should also be noted that the Swan River discharges into King Bay, of Moulting Lagoon, which holds significant conservation status as a Ramsar listed wetland. Therefore the defined flows for the Swan River should encompass the natural hydrograph as closely as possible to ensure minimal impact on the estuarine environment. Erosion, sedimentation and eutrophication are primary concerns for the Moulting Lagoon ecosystem and intensive land use activity within the Swan catchment can and has resulted in increased sedimentation levels within the lagoon (Moulting Lagoon Game Reserve, Draft Management Plan, 1999). Bobbi et al. (1996) indicate that these factors are predominantly affected by flood flows. These effects can cause declines in seagrass communities, with concomitant deterioration of the aquatic community, which rely on and utilise the grasses. While historical evidence is not available to suggest a comparable change in the natural aquatic flora and fauna, it should be noted that biotic and abiotic factors affecting the health of the Swan catchment also encompass the estuarine environment. Although essential components of a wetland's water regime include the quantity of water, timing, duration and frequency of inundation (McCosker, 1998), it was outside the scope of this study to address the environmental water allocation needs for Moulting Lagoon.
The flows defined for the study reach are outlined in section 6.3.1.
6.3.1 Waters Meeting
Table 8. provides a summary of Environmental Water Requirements that will provide certain, defined risks to the maintenance of ecological values in the Waters Meeting reach. These risks only apply to this reach (see section 2.2.1 for details of the extent of the reach). We strongly recommend that flows in the "Low risk" range should remain in the river for maintaining instream habitat for aquatic animals including Swan galaxias populations.
Table 8. Flows for each risk category, Swan River at Waters Meeting.
Risk Category I II III Low risk Moderate risk High risk Month flow (cumecs) flow (cumecs) flow (cumecs) Dec > 0.4 0.4 – 0.3 < 0.3 Jan > 0.2 0.2 – 0.1 < 0.1 Feb > 0.2 0.2 – 0.1 < 0.1 Mar > 0.2 0.2 – 0.1 < 0.1 Apr > 0.4 0.4 – 0.3 < 0.3
27 7. References
Andrews, A.P., (1996). Family Bovichtidae: Congolli. In: McDowall, R.M. (Ed.) Freshwater Fishes of South-Eastern Australia. Reed Books, Hong Kong.
ANZECC, (1992). Australian Water Quality Guidelines for Fresh and Marine Waters. National Water Quality Management Strategy.
ARMCANZ and ANZECC, (1996). National Principles for the Provision of Water for Ecosystems, Sustainable Land and Water Resources Management Committee, Subcommittee on Water Resources, Occasional Paper SWR No. 3.
Arthington, A.H., King, J.M., O'keefe, J.H., Bunn, S.E., Day, J.A., Pusey, B.J., Bludhorn, D.R. and Tharme, R., (1992). Development of an holistic approach for assessing environmental flow requirements of riverine ecosystems. In: Pigram, J.J. and Hooper, B.P. (Eds.), Proceedings of an International Seminar and Workshop on Water Allocation for the Environment. Centre for Water Policy Research, Armidale, 69-76.
Beumer, J.P., (1980). Hydrology and fish diversity of a North Queensland tropical stream. Australian Journal of Ecology, 5:159-186.
Blackhall, S.A. (1985). Moulting Lagoon Proposed Game Reserve, Stage 2 – Planning for the reservation and management of a wetland of international importance. Draft Planning Document for Discussion, National Parks and Wildlife Service, Tasmania. Hobart. 86pp.
Bobbi, C., Fuller, D.A. and Oldmeadow, D. (1996) South Esk Basin ‘State of River Report’. Technical Report of Data Collected between 1992 and 1995. Department of Primary Industry and Fisheries internal publication, WRA 96/02.
Bovee, K.D., (1978). Probability -of-use criteria for the family Salmonidae. Instream Flow Information Paper 4. U.S. Fish and Wildlife Service.FWS/OBS-78/07. 80 pp.
Bovee, K.D., (1982). A guide to stream habitat analysis using the instream flow incremental methodology. Instream Flow Information paper No.21, Co-operative Instream Flow Group, US Fish and Wildlife Service, Colorado.
Bryant, S.L. and Jackson, J., (1999). Tasmania’s Threatened Fauna Handbook: what, where and how to protect Tasmania’s threatened animals. Threatened Species Unit, Parks and Wildlife Service, Hobart.
Crook, D. & Sanger, A., (1997). Recovery Plan for the Pedder, Swan, Clarence, swamp and saddled galaxias. Inland Fisheries Commission, Hobart.
Davies, J., (1988). Land Systems of Tasmania, Region 6: South, East and Midlands – A Resource Classification Survey. Department of Agriculture, Tasmania.
Davies, P.E., and Humphries, P., (1996). Final Report: An Environmental Flow Study of the Meander, Macquarie and South Esk Rivers, Tasmania.
Davies, P.E. and McDowall, R.M., (1996). Family Salmonidae: Salmons, trouts and chars. In: McDowall, R.M. (Ed.) Freshwater Fishes of South-Eastern Australia. Reed Books, Hong Kong.
28 Davies, P.E., (1997). Coal River Weir Proposal Environmental Issues. Consultancy Report to Water Management Branch, DPIWE.
Davies, P.E., McKenny, C. and Cook, L., (1997). Mersey River Environmental Flow Study: Report to the Hydro-Electric Corporation Tasmania for the Mersey River Study Committee.
Edgar, G.J., Barrett, N.S. & Graddon, D.J., (1999). A Classification of Tasmanian Estuaries and Assessment of their Conservation Significance using Ecological and Physical Attributes, Population and Land Use. Technical Report Series Number 2, Tasmanian Aquaculture and Fisheries Institute, University of Tasmania.
Fuller, D.A. & Katona, G.G., (1993). An Overview of Water Quality Data in Tasmania. Resource Assessment Branch, Department of Primary Industries and Fisheries, Hobart, Tasmania.
Fuller, D.A. & Read, M., (1997). Environmental Flows Assessment and Allocation. Department of Primary Industries and Fisheries, Hobart, WRA 97/07.
Fulton, W., (1990). Tasmanian Freshwater Fishes. Fauna of Tasmania handbook 7. University of Tasmania and Inland Fisheries Commission, Hobart, Tasmania.
Gore, J.A., (1977). Reservoir manipulations and benthic macroinvertebrates in a prairie river. Hydrobiologia, 55: 113-123.
Gore, J.A., (1987). Development and applications of macroinvertebrate instream flow models for regulated flow management. In Craig J.F. and Kemper J.B (Eds) Regulated Streams, Advances in Ecology. Plenum Press, New York.
Jones, B.G., Martin, G.R. and Senapati, N., (1993). Riverine-tidal interactions in the monsoonal Gilbert River fandelta, northern Australia. Sedimentary Geology, 83: 319-337.
Jowett, I.G., (1992). River hydraulics and instream habitat modelling for river biota. Chapter 14 in ‘Waters of New Zealand’. New Zealand Hydrological Society Inc.
Jowett, I.G. and Richardson, J., (1995). Habitat preferences of common, riverine New Zealand native fishes and implications for flow management. New Zealand Journal of Marine and Freshwater Research, 29, pp17-23.
Loneragan, N.R. and Bunn, S.E., (1999). River flows and estuarine ecosystems: Implications for coastal fisheries from a review and a case study of the Logan River, southeast Queensland. Australian Journal of Ecology, 24, 431-440.
McCosker, R.O. (1998). Methods addressing the flow requirements of wetland, riparian and floodplain vegetation. In Arthington, A.H. & Xalucki, J.M. (eds.), (1998) Comparative Evaluation of Environmental Flow Assessment Techniques: Review of Methods. P.47-65. Land and Water Resources Research and Development Corporation, Canberra.
McDowall, R.M., (1996). Family Prototroctidae: Southern graylings. In: McDowall, R.M. (Ed.) Freshwater Fishes of South-Eastern Australia. Reed Books, Hong Kong.
McDowall, R.M. and Fulton, W., (1996). Family Galaxiidae: Galaxiids. In: McDowall, R.M. (Ed.) Freshwater Fishes of South-Eastern Australia. Reed Books, Hong Kong.
Moulting Lagoon Game Reserve Management Plan (Draft), (1999). Parks and Wildlife Service, Department of Primary Industries, Water & Environment, Hobart.
29 Sanger, A.C., (1993). The Swan Galaxias Recovery Plan: Management Phase. Inland Fisheries Commission, Hobart.
Thomas, D., Davis, J., Froend, R., Hamilton, D., Horwitz, P., McComb, A. and Oldham, C. (2000) How much water do wetlands need? 39th Annual Congress of the Australian Society for Limnology, Darwin, 7-10th July. ASL Inc.
Threatened Species Act (1995). Government of Tasmania, Hobart.
Whitfield, A.K., (1996). Fishes and the environmental status of South African estuaries. Fisheries Management Ecology, 3: 45-57.
30 Appendix 1. WUA graphs for the Swan River at Waters Meeting for the month of December.
Waters Meeting Reach
120
100
Galaxias maculatus (Jowett 80 & Richardson 1995) Anguilla australis ((Jowett & Richardson 1995) 60
WUA Salmo trutta adults (Bovee ∆ 1978) 40 Salmo trutta 0+ (Davies & Diggle unpub. Data)
20
0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Discharge (cumec)
200 Austrocercoides sp.' 180 160 Baetid Genus 2 sp.' 140 Baetid Genus 1 sp.MV4' 120 Atalophlebia sp.' 100
WUA Nousia sp.'
∆ 80 60 Tillyardophlebia sp.'
40 Tasmanocoenis 20 tonnoiri' Agapetus sp.' 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Discharge (cumec)
31 Waters Meeting Reach cont.
250
200 total Hydroptila sp.' Hellyethira simplex' Oxyethira mienica' 150 Ecnomus sp.' Ecnomina sp.' WUA ∆ 100 Conoesucus sp.' Helicopsyche murrumba' total Notalina sp.' 50 Tanypodinae'
0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Discharge (cumec)
250
Podonominae'
200 Orthocladiinae' Chironominae'
Ceratopogonidae' 150 Austrosimulium furiosum' WUA
∆ Empididae' 100 Tipulidae sp.'
total Austrolimnius sp. 50 (larv)' Austrolimnius sp. (ad'
0 0 0.10.20.30.40.50.60.7 Discharge (cumec)
32 Waters Meeting Reach cont.
180 Sclerocyphon secretus 160 (larv)' Turbellaria' 140 Hydrobiidae sp' 120 Rivisessor gunnii' 100 Ferrissia tasmanica'
WUA 80 ∆ Oligochaeta'
60 Austrochiltonia australis'
40 Hydracarina' Paratya australiensis' 20
0 0 0.10.20.30.40.50.60.7 Discharge (cumec)
120
100
80
T otal Abundance' 60
WUA Taxon abundance' ∆
40
20
0 0 0.10.20.30.40.50.60.7 Discharge (cumec)
33