ACT Future Water Options

5.4 Environmental impacts/benefits of the Tantangara options

Several of the Tantangara options propose that a section of Porcupine Creek in the Upper Cotter River will have additional flow averaging 11 GL/yr. Porcupine Creek is a small headwater reach, and would be severely impacted by such a delivery. The Tantangara options may have impacts on the landscape, both in the upland areas immediately affected by construction works and in areas downstream. From the perspective of the aquatic ecology study, Tantangara option 5 (release water from Tantangara Dam to flow 100 km down the Murrumbidgee River) has the least impact compared to all other future water supply options. This option avoids construction impacts in a National Park, does not increase fragmentation because the dam already exists, and improves flows downstream of Tantangara Dam, which will benefit the aquatic ecosystem of the Murrumbidgee River. Options c, d and e are likely to have a positive effect on the aquatic flora and fauna in the Murrumbidgee River between Tantangara Dam and Yaouk. However, unless the Canberra water supply needs are piggy-backed onto the planned environemental flow releases, the benefit to the aquatic system will be minimal. Tantangara options 1, 2, 3 and 4 (water pumped to upstream of Corin Dam) have much greater impact on stream geomorphology, water quality, hydrological disturbance and habitat availability, particularly in Porcupine Creek and the upper Cotter River, than the other options. Modifications that may have less of an impact include piping the water supply directly into the Corin Reservoir (Tantangara option 6). However, Tantangara option 6 still has risks associated with an Inter-Basin Transfer. Provided they are designed carefully, the Tennent and Cotter options appear to have much less impact on stream geomorphology and sediment movement.

If the design of an Inter-Basin Transfer scheme to the upper Cotter River proceeds, we advise that it should include possible safeguards to help prevent transfer of aquatic organisms, such as physical barriers, electrical barriers, and/or channel screens, which must be capable of screening eggs of both vertebrates and invertebrates and plant propagules. A study should also be carried out to provide baseline data on Porcupine Creek and the upper Cotter River so that future impacts of an Inter Basin Transfer on the aquatic ecosystem can be assessed.

6 Regional overview

6.1 Aquatic biota

6.1.1 Vulnerable, threatened or endangered species There are currently 29 threatened species and ecological communities listed in the ACT. Excluding fish, there are two threatened aquatic species (Table 6.1). They are the Murray River Crayfish and the Northern Corroboree Frog (Environment ACT, http://www.environment.act.gov.au/nativeplantsandanimals/thrtspecinfo.html, Last updated 18 August 2004). Table 6.1. Listing of threatened aquatic species in the Australian Capital Territory Common name Scientific name Declared status Murray River Crayfish Euastacus armatus Vulnerable Northern Corroboree Frog Pseudophryne pengilleyi Endangered

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6.1.2 Amphibians In Australia there has been little specific research on the impact of dam construction, river regulation, and associated hydrological infrastructure on amphibian communities. However, based on a broader understanding of the ecology of each species, and direct inference from field observations (e.g. Gillespie 2001), the likely impacts of such developments have been considered in recovery planning for several species of endangered frogs in the region (NSW NPWS 2001, 2002). Similar criteria were used in the present study in relation to considering the impact of each option. The frog fauna of the ACT region is described by Rauhala (1997) and Lintermans and Osborne (2002). Most of these are common pond-breeding species that do not breed in flowing rivers and streams. Specific surveys for amphibians have been conducted as part of detailed flora and fauna surveys conducted in the Mt Tennent – Blue Gum Creek area (Gilmour et al. 1987) and the Upper Cotter River above Corin Dam (Helman et al. 1988). Very detailed information is available on the distribution of the Northern Corroboree Frog in the ACT region (Osborne 1989; Osborne et al. 1999). The frogs found along parts of the Cotter River below Corin Dam have also been surveyed (Osborne et al. 1994; W. Osborne pers. observations; P. Ormay Environment ACT pers. comm.).

Based on this information, and other unpublished records, we consider that ten species are likely to occur in areas that will be affected by the various water supply proposals (Table 6.2). Table 6.2. Species of frogs likely to occur specifically at investigation sites Species Location code UM YA CAB CBC CD C TD Whistling Tree Frog Litoria verreauxii verreauxii UM YA CAB CBC Emerald-flecked Tree Frog Litoria peroni CD C TD Leaf-green Tree Frog (Cotter River Form) Litoria nudidigitus CAB CBC Rocky River Frog Litoria lesueuri UM CAB CBC CD C TD Smooth Toadlet Uperoleia laevigata CAB CD C TD Southern Toadlet Pseudophryne dendyi YA CAB Eastern Banjo Frog Lymnodynastes dumerilii UM YA CAB CBC CD C TD Common Froglet Crinia signifera UM YA CAB CBC CD C TD Alpine Tree Frog Occur higher in catchment on the Bimberi Range Litoria verreauxii alpina Northern Corroboree Frog Occur higher in catchment on the Bimberi Range Pseudophryne pengilleyi

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Description of location codes UM Upper Murrumbidgee below Tantangara YA Yaouk – Porcupine Creek CAB Cotter River above Bendora Dam CBC Cotter River between Bendora and Corin dams CD Coree Dam C Cotter Dam enlarged TD Tennent Dam

6.1.2.1. Frog species of concern for conservation Five species of frogs in the region are listed as threatened species under appropriate State or Territory legislation (Table 6.3). One additional species, referred to as the Cotter River Frog, is also included here, because it represents a particularly unusual colour form of the widespread Leaf Green Tree Frog (L. nudidigitus) and may in future be listed as an endangered population. The Southern Corroboree Frog (P. corroboree), Boorolong Frog (L. boorongensis) and Spotted Tree Frog (L. spenceri), do not occur specifically in the area being considered in this report and will not be discussed further.

Table 6.3. Species of conservation concern in the ACT and region Species marked with an # occur within the general region that encompasses the water supply proposals. CRE = critically endangered; END = endangered; VUL = vulnerable. Species Conservation status Commonwealth ACT NSW Southern Corroboree Frog (Pseudophryne pengilleyi) CRE Not present END Northern Corroboree Frog # (Pseudophryne pengilleyi) VUL END VUL Alpine Tree Frog # (Litoria verreauxii alpina) END Not listed END Cotter River Frog # (A form of Litoria nudidigitus) Not listed Not listed Not listed Booroolong Frog (Litoria boorolongensis) END Not present END Spotted Tree Frog (Litoria spenceri) CRE Not present END

6.1.2.2. Likely impacts of stream impoundments on amphibian communities, particularly for obligatory stream breeding species At certain times of the year anuran larvae (tadpoles) may occur in high densities in streams, contributing significantly to stream ecology as primary consumers and as prey for aquatic invertebrates and fish (Alford 1999; Flecker et al. 1999). The likely impacts on stream amphibians of hydrological changes associated with impoundments are reviewed briefly below.

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1. Direct inundation of habitat The construction of dams on streams is likely to directly inundate suitable in-stream habitat. This may include, for example, the inundation and removal of river cobble, rock outcrops, in- stream log debris piles, and streamside vegetation (Gillespie and Hines 1999; Gillespie and Hollis 1996). 2. Alteration of downstream water flow and temperature regimes Alteration of downstream water flow and temperature regimes may affect the viability of eggs and tadpoles and influence populations of invertebrates that adult frogs feed on. In particular, increased stream flows during the warmer months, are likely to have severe impacts upon riverine frog populations. This is because substantial rises in water level and velocity are likely to flush eggs and larvae downstream (Gillespie and Hines 1999; Gillespie and Hollis 1996). The reduced temperatures of some releases of water from dams during summer months are likely to inhibit the growth and development of larvae. Some surface waters may also be anoxic and have different pH and higher concentrations of activated heavy metals (Doeg 1987; Ligon et al. 1995; Erskine 1996). Reduced peak flows resulting from dams may allow build up of sediments and colonisation of the stream channel by vegetation. Increased sediment retention in the bed of the river will reduce availability of oviposition (egg-laying) sites and cover for larvae by blanketing the streambed and infilling of crevices between rocks, litter and cobble (Gillespie and Hines 1999; Gillespie 2001). This may result in greater vulnerability to predation or flushing effects from flood events (e.g. Welsh and Ollivier 1998). Increased shading from establishment of vegetation in the streambed may lower stream temperatures, which may have an influence on tadpole growth. 3. Loss of semi-detached streamside breeding pools during periods of artificially high flow. Increased access by trout to previously shallow areas, increased predation risk on tadpoles. The abundance of riverine frogs can vary quite markedly between streams, and the factors involved in this are poorly known. Predation by trout on tadpoles has been put forward as one factor explaining differences in the abundance of riverine frog species. Trout are known to prey heavily on tadpoles of the spotted tree frog L. spenceri and the leaf Green Tree Frog L. nudidigitus (Gillespie 2001; D. Hunter CRCFE pers. comm.). The highest abundance of those species of frogs occur in streams that do not contain trout. Semi-detached streamside pools (pools that are only connected to the main stream during peak flows) are important in-stream breeding sites for many species of frogs. When inundated, these pools may be occupied by trout. Juvenile trout are capable of entering shallow water (D. Hunter and M. Lintermans pers. comm.) that affords some protection from adult trout.

6.1.3 Macroinvertebrates Aquatic macroinvertebrates (animals without backbones that can be seen with the naked eye) are commonly used biological indicators for freshwater resources (Rosenberg and Resh 1993). Macroinvertebrates are good biological indicators because they are found in most habitats, they have generally limited mobility, they are quite easy to collect using well established sampling techniques and they are sensitive to various changes in water and habitat quality. Information about an organism’s preferred habitat and tolerances to certain types of pollution are used to interpret habitat quality and degree of water pollution (ANZECC & ARMCANZ 2000).

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The major taxonomic groups are the insects (including mayflies, stoneflies, caddisflies, true flies, beetles and bugs), crustaceans, molluscs, and worms. Most macroinvertebrates are important components of ecosystems. They graze periphyton (and may prevent blooms in some areas), assist in the breakdown of organic matter and cycling of nutrients and, in turn, may become food for predators such as fish (ANZECC & ARMCANZ 2000). In 1992 the Australian Federal Government initiated a nationwide program of biological assessment of river health. In the ACT, the First National Assessment of River Health (FNARH), previously called the Monitoring River Health Initiative (MRHI), was coordinated by the Cooperative Research Centre for Freshwater Ecology (CRCFE). Under the MRHI, the Australian River Assessment System (AUSRIVAS) predictive models for the biological assessment of river health were developed. 6.1.3.1. Habitat needs The habitat in aquatic systems is determined by the complex interaction of water quality, energy sources, physical channel structure and the flow regime (Maddock et al. 2004). Macroinvertebrates cover a diverse assemblage of organisms that live on, or in, the solid substrates at the bottom of rivers, wetlands and lakes. Suitable habitat includes wood, aquatic plants, fine organic sediments and inorganic substrata such as sand, gravel and cobbles (ANZECC & ARMCANZ 2000).

The composition of aquatic macroinvertebrates is strongly influenced by physical habitat. If the physical habitat of a river is in poor condition, then the macroinvertebrate communities are likely to be adversely affected (Norris and Thoms 1999). Changes to the flow and sediment regimes of rivers can alter the physical nature of the channel and consequently the habitats that support macroinvertebrates (Norris and Thoms 1999). The riparian zone and floodplain also have an influence on macroinvertebrates through organic matter inputs, shade and nutrients (Norris and Thoms 1999). 6.1.3.2. Migratory/nomadic patterns Recolonization mechanisms are essential to the functioning of stream ecosystems, which would otherwise become depleted of macroinvertebrates that are important for nutrient cycling and carbon processing (Hershey et al. 1993). Invertebrates are able to re-establish populations using four main recolonization pathways; adult flight and oviposition, upstream migration by swimming or crawling, vertical migration from refuges in the streambed, and drifting downstream in the water column (Williams and Hynes 1976a; Boulton and Brock 1999). Macroinvertebrates have preferred directions in the recolonization of depleted areas and this may lead to the establishment of separate and distinct faunal assemblages, if one of these directions is excluded (Williams and Hynes 1976a). The ability of macroinvertebrates to recolonize recently opened stream habitats may vary depending on regional life histories, position within the stream network, and dispersal abilities (Wallace 1990). Rapid colonization will occur of any newly available habitat that is within the dispersal range of species living in nearby lakes or rivers (Williams and Hynes 1976b). Many insects are capable of flight during their adult stages and have little difficulty in recolonizing stream habitats (Williams and Hynes 1976b). Some animals do not occupy all their potential range even though they are able to disperse into the unoccupied areas. Thus, the distribution of a species may be limited by the behaviour of individuals in selecting their habitat (Krebs 1994). Experiments on site selection by aerially colonizing invertebrates show that water current and food availability largely determine the qualitative and quantitative nature of the fauna that colonizes a water body (Williams and Hynes 1976b). The recolonization of aquatic invertebrates

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may also be influenced by many resource factors such as the presence of organic matter and substrate composition (Coysh 1998). Many studies have dealt with benthic recolonization (Schmid-Araya 2000), predominantly targeting invertebrate drift (Bergey and Ward 1989). Drift is generally thought to be the most important of all the recolonization pathways (Townsend and Hildrew 1976; Williams and Hynes 1976a; Brittain and Eikeland 1988; Mackay 1992), although recent studies have found other sources of colonists are of equal importance to drift (Coysh 1998). The dominant source of colonizers appears to be taxon-specific and may change over time (Williams and Hynes 1976; Coysh 1998). Aquatic macroinvertebrates are generally considered to have high dispersal capabilities and given the extensive geographic distribution of some taxa, it is apparent that effective mechanisms for dispersal do exist, or at least have existed in the past (Bunn and Hughes 1997). 6.1.3.3. Major habitat and Water Quality Issues in the ACT region based on macroinvertebrate sampling in the First National Assessment of River Health The major impacts affecting the rivers and streams of the Upper Murrumbidgee River catchment include chemical pollutants, trace metal contamination, nutrient enrichment, rural runoff, habitat degradation, sedimentation and river regulation. With the exception of river regulation, all the described impacts are directly related to land use practices. In addition to the above, low flows have also had a major effect on the biological condition of the rivers and streams within the region.

Low flows Low flow conditions experienced during autumn 1997, 1998 and 1999 resulted in a regional reduction in biological condition, with nearly 40% of the reference sites sampled in autumn assessed as below reference conditions compared to only 25% in spring. Impacts identified during the First National Assessment of River Health (FNARH), which resulted from low flows, include high organic load from allochthonous (leaf litter) and autochthonous (periphyton/filamentous algae) organic matter which covered stream substratum. Invertebrate samples from sites affected by low flows were numerically dominated by Oligochaetes and or Chironominae midge larvae, which are both tolerant of low flows and high organic loads. During more normal flow conditions, organic material would be regularly flushed from the system preventing the build up that caused such impairment. Chemical Pollutants

Impacts from chemical pollutants were restricted to urban areas, specifically the rivers and creeks receiving runoff from stormwater drains. Urban runoff can contain a variety of pollutants including fertilizers, pesticides and petroleum products that impact on a large proportion of the aquatic invertebrate community. Many of the sites subject to urban runoff sampled during FNARH (e.g. Yarralumla Creek and Weston Creek) were assessed as having impoverished biological condition and were characterized by the absence of nearly all taxa predicted to occur there. Yarralumla Creek also had strong petroleum odours indicating that chemical pollutants may be the main cause of biological impairment at this site. Thus, urban runoff may be responsible for the reduced biological condition at some sites sampled within the urban area of the ACT. The effects of urban run-off are like to be increased if downstream dilution is reduced through water abstraction.

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Trace Metal Contamination Trace metal contamination within the Upper Murrumbidgee River catchment occurs along the Molonglo River, downstream of the abandoned Captains Flat mine. The effects of trace metal pollution on the macroinvertebrate assemblages of the Molonglo River have been examined in several studies (Weatherly et al. 1967; Nicholas and Thomas 1978; Norris 1986). These studies found both the number of taxa and abundance were markedly reduced downstream of the mine in comparison to macroinvertebrate communities upstream of Captains Flat. The depauperate fauna downstream of the mine was attributed to the direct influence of metal toxicity, and the indirect influences of reduced food availability, unstable substrate during high flows, and smothering by fine floc precipitate of metal oxides (Weatherly et al. 1967; Nicholas and Thomas 1978). The FNARH study clearly shows that there has been little improvement in biological condition downstream of the mine since the last of these studies in 1982 (Norris 1986). Thus, trace metal contamination from the Captains Flat Mine is still adversely affecting the biological condition of the Molonglo River. While not directly related to the water supply options, the poor water quality, contaminated sediments and depauperate fauna of the Molonglo River mean that this catchment is effectively unavailable as a source of colonists or refuge in the ACT region. Nutrient Enrichment

Nutrient enrichment in the ACT region is likely to come from treated sewage effluent and fertilizers from agricultural practices, stock and urban runoff. Nutrient enrichment can have several consequences, including increased periphyton cover, which alters habitat and food resources (Petts 1984). This may favour pollutant tolerant taxa such as Oligochaeta, Chironomiinae, and Orthocladiinae, and disadvantage sensitive taxa such as mayflies (Jolly and Chapman 1966; Gaufin 1973). Water chemistry analysis throughout the FNARH detected several sites with higher than recommended levels of phosphorus. Reductions in flow are likely to exacerbate the biological effects of nutrients through lack of dilution. Habitat Degradation and Sedimentation

Aquatic habitat degradation and sedimentation are related problems, with sediment input resulting in the degradation of instream habitat. Addition of sediment to streams can prevent feeding, respiration and movement and fill substrate interstices thus adversely affecting many taxa such as pollution sensitive mayflies and caddisflies (Swanson 1980; Lemly 1982; Minshall 1984). Many sites in the FNARH study were found to be suffering from habitat degradation and sedimentation, for example Uriarra Creek, Condor Creek and Woden Creek were suffering from erosion of agricultural land, forestry activities and unstable river banks, respectively. In general, these sites were numerically dominated by oligochaetes and chironomid larvae, which are often associated with shifting sandy substrates. Therefore, unfavourable habitat conditions and sedimentation at many of the sites sampled for the FNARH may be responsible for the impaired biological condition at these sites. River Regulation River regulation was concluded to have adversely affected the fauna at some of the sites sampled for FNARH. For example, downstream of Scrivener, Bendora and Cotter Dams were all assessed as having biological condition well below reference (Band C) in autumn. Generally, these sites were numerically dominated by oligochaetes and/or orthocladiinae and chironominae and had much (35-90%) of the sampled habitat covered by periphyton and or filamentous algae. Thus, the impaired biological condition found at sites downstream of these

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dams is likely to be a result of reduced flow, build up of organic matter (especially algae), reduced oxygen levels and the barrier to invertebrate drift. Conclusion from FNARH The major impacts affecting sites within the Upper Murrumbidgee River catchment appear to be chemical pollutants, trace metal contamination, nutrient enrichment, rural runoff, habitat degradation, sedimentation and river regulation. With the exception of river regulation, all of the impacts are directly related to land use practices. Low flows may have contributed to the impaired biological condition at many of the test sites within the Upper Murrumbidgee Catchment during autumn 1997, 1998 and 1999. However, despite the effect of low flows during these sampling occasions the condition of rivers and streams in the Upper Murrumbidgee River has been less than desirable with the majority of sites indicating some form of impact.

6.1.4 Crayfish In the southern hemisphere, all the freshwater crayfish belong to the family Parastacidae. The family contains nine genera and approximately 100 species. The two largest genera are Cherax, which contains the Common Yabby (Cherax destructor); and Euastacus, which contains the spiny crays (ACT Government 1999). The Murray River Crayfish (Euastacus armatus) is listed as Vulnerable in the ACT. 6.1.4.1. Habitat needs Murray River Crayfish (Euastacus armatus) has the largest geographic range of any of the spiny crayfish in Australia (ACT Government 1999). While most spiny crayfish are restricted to the cooler, montane streams, the range of E. armatus extends into the warmer, lower reaches of the Murray-Darling Basin (ACT Government 1999). E. armatus inhabits large and small streams in a variety of habitats including cleared pasture and dry and wet sclerophyll forests at altitudes from close to sea level to over 700 m ASL. The species prefers faster flowing, cool water habitats of the main river channels (ACT Government 1999). Murray River Crayfish are omnivorous, eating mainly vegetation, scavenged fish and other animals. In upland rivers with stony beds the species tends to use the interstitial spaces between boulders and cobbles of the riverbed for shelter (ACT Government 1999). In the Murrumbidgee River, there has been a decline in the quality and quantity of crayfish habitat because of sedimentation filling in spaces between rocks. Locally, E. armatus uses these spaces as refuges because the banks are generally not suitable for constructing burrows. Increased turbidity and sediment loads also have detrimental effects on submerged aquatic weed beds through reductions in light penetration, thus reducing an important food source (ACT Government 1999).

6.1.5 Reptiles Aquatic areas, particularly rivers, provide important habitat for reptiles (Lintermans and Osborne 2002). In the ACT, the types reptiles that use rivers and their associated riparian zones (Table 6.4) are not threatened by the proposed future water options.

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Table 6.4. Native reptiles found in the Australian Capital Territory Abundance is assessed subjectively as common, uncommon or scarce. Distribution is described as widespread (W) or localised (L) (Source: ACT State of the Environment Report, 2000) Common name Scientific name Distribution Abundance Eastern snake-necked turtle Chelodina longicollis Widespread Common Eastern water dragon Physignathus lesueurii Localised Common Alpine water skink Eulamprus kosciuskoi Localised Uncommon Murray turtle Emydura macquarii Localised Scarce

6.1.6 Mammals - Platypus 6.1.6.1. Conservation status The platypus is now considered to be common, but may be vulnerable to potential human threats such as river regulation and water extraction. Platypus are still sighted below many of the major storages in the Murray-Darling Basin, however, further studies are needed to determine whether river regulation has caused a significant impact on abundance (Scott and Grant 1997). The platypus is protected by legislation in all States in which it occurs (Grant and Temple-Smith 2003). Its conservation is of considerable importance not only because of its unique features, status and niche but also because it is the only living representative of a significant lineage of platypus-like animals with a 60 million year fossil history (Grant and Temple-Smith 2003).

As a result of its specific habitat requirements, the platypus is affected by many of the widely recognized threatening processes operating in Australian river systems. This has lead to the fragmentation of local platypus distributions within the Murray-Darling Basin. Although the platypus is still widespread, the animals occur at low population densities in much of their habitat, and thus even in big streams, platypus populations are unlikely to be big enough to persist in isolation from others. This emphasises the importance of conserving platypus habitat throughout catchments, and not just in isolated sections of streams (Scott and Grant 1997). With the exception of the deep waters of large storage dams, the platypus has continued to occupy aquatic systems and habitats throughout the remainder of its historical distribution, including ecosystems where various threatening processes are having major impacts on aquatic and riparian habitats. The platypus has continued to inhabit and reproduce in considerably degraded ecosystems, although differences in abundance before and since these systems were modified are largely unknown (Grant and Temple-Smith 2003). The concern is that, although many populations appear to be largely unaffected at present, they may show rapid and severe changes in response to degrading processes in the future. The fragmentation of platypus populations found in some river systems suggests the possibility that apparently secure local platypus populations may quickly become threatened or locally extinct because of the effects of one or more threatening process arising from human activities (Grant and Temple-Smith 2003). 6.1.6.2. Habitat The platypus is known to occupy a wide range of habitats, including streams at all elevations, coastal and inland rivers, swamp lagoons, artificial impoundments, glacial lakes, backwaters and billabongs, and isolated ponds filled by floods (Serena et al. 1998). Ideal habitat for the platypus is a fairly shallow river or stream with relatively steep earth banks consolidated by the roots of native vegetation and branches overhanging the bank. The river should have a diversity

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of habitats for macroinvertebrates (the main food source), including aquatic vegetation and logs, and consist of a series of distinct pools of less than 5 metres depth, with little sand accumulation and separated by cobbled riffle areas (Scott and Grant 1997). Riparian vegetation is an important component for several reasons. First, the roots help consolidate the banks and hence protect the platypus burrows from collapsing, and second, the overhanging vegetation provides cover from predators when they enter or leave their burrows. Riparian vegetation also creates suitable habitat in the stream for macroinvertebrates by providing shade, food material and habitat diversity. Platypuses can also inhabit natural and artificial lakes, particularly if they are connected to a nearby stream and are not too deep. Most large water storages within the Murray-Darling Basin do not provide suitable habitat since they tend to be too deep for the platypus to dive to the bottom for food (Scott and Grant 1997). Preference has been shown for cobbled substrate and avoidance of gravel. Platypuses have been observed foraging most frequently in water deeper than 1 metre. These observations have implications for catchment, stream and riparian management, where activities leading to sedimentation and reduced flushing flows may reduce depths and/or alter the distribution of preferred foraging substrates (Grant 2004). Sedimentation tends to reduce the quality of the instream habitat for benthic invertebrates and could impact on the abundance of platypuses. Most of their diet consists of insect larvae such as caddis fly (Trichoptera), fly (Diptera) and mayfly (Ephemeroptera), along with other bottom dwelling macroinvertebrates such as shrimps and molluscs. They tend to be opportunists to the extent that their diet varies depending on the availability of different food types (Scott and Grant 1997). 6.1.6.3. Movement and dispersal Most platypuses have a definite home range, which may include one or a number of adjacent pools along a stretch of river. On occasions, however, adults have been found to move outside their normal home range, with distances of up to 15 km having been recorded. Small weirs (with wall heights of 3 metres or less) do not prevent the dispersal or movement of platypuses, as shown by studies on the Barnard River in NSW. Platypuses are capable of moving around the wall by walking overland, although they are more prone to predation and risk of injury as they detour around these weirs (Scott and Grant 1997; Grant and Temple-Smith 2003). Larger structures, however, such as Burrinjuck Dam on the Murrumbidgee River, create a significant barrier that platypuses find difficult to negotiate and these inhibit both the movement of adults and the dispersal of juveniles (Scott and Grant 1997). 6.1.6.4. Effects of river regulation The downstream effects of river regulation may be complex and vary according to the type of habitat and changes in flow patterns, sediment input, water quality and thermal regime (Boulton and Brock 1999). Removing water from streams has the potential to impact on platypus populations (Grant and Bishop 1998). Release of cold water from below the thermocline in impoundments, forces platypus living downstream of dams to spend extra energy maintaining body temperature (Scott and Grant 1997). Platypus are physiologically well adapted to living under cold conditions in winter over much of its current distribution but raised metabolic demand, coupled with changes to benthic food availability, must impose additional stress on animals inhabiting waters downstream of large dams (Grant and Temple-Smith 2003).

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Upstream increases in water levels, associated with dam construction and operation, that change relatively shallow and productive river environments into deep, less productive lake-like ones may cause the main impact on platypus populations. Platypuses appear to be unable to forage successfully for small food items at depths greater than about 5–10 metres and are only occasionally reported from deep areas of water storage impoundments. Increased proximity of burrows to the water or the flooding of burrows by rising water levels are also potential impacts that have not yet been studied in impoundments or in regulated streams. Throughout Australia, much more consideration is now being given to the provision of environmental flows and the implementation of operational procedures for existing structures to reduce their downstream impact. Currently, it is unknown what environmental flow strategies are necessary for the maintenance of platypus populations in regulated rivers (Grant and Temple- Smith 2003). However, it is likely that to ensure suitable habitat for platypus breeding, extended periods of bankfull flow in late spring and summer should be avoided whenever possible. Bank collapse can be minimised by avoiding sudden falls in water level. There should be sufficient calm water so that the platypuses are not continuously swimming against a strong current. The flow regime should also be designed to ensure an abundance of invertebrates for food (Scott and Grant 1997). The regulation of many rivers within the Murray-Darling Basin has changed the natural flow conditions and many sections of rivers immediately below large water storages now experience very low flows each year from late autumn through to early spring, rather than during summer. These low flow conditions over the cooler months result in a reduction in foraging area for the platypus at a time when invertebrate abundance is also low. Ideally a minimum flow should be released through the winter months to cover the riffle areas of streams to maintain invertebrate productivity and to increase the foraging area for the platypus. The flow should also provide enough water so that the platypus can swim up through the riffle areas without having to come out of the water. This allows it to move safely between pools and provides a continuity of habitat (Scott and Grant 1997).

Releases from the lower levels of water storages can result in depressed water temperatures downstream. Although the platypus can tolerate very cold water, it does force the animal to spend extra energy maintaining its body temperature. Also, the sudden release of cold water might have indirect effects by reducing the abundance of benthic invertebrates and hence the availability of food for the platypus. For the rivers of the Murray-Darling Basin there is considerable natural variation from year to year in both the floods and low flows, and these variations are essential if diversity is to be maintained. Environmental flow releases should be close to the natural pattern of flows.

6.1.7 Mammals – Water rat The water rat (Hydromys chrysogaster) is an amphibious rodent, which is widely distributed throughout Australia. In the Murray Darling Basin it is found in permanent water bodies across a wide range of habitats from upland streams along the Great Dividing Range to lowland rivers and wetlands in the west (Scott and Grant 1997). In the past, populations declined in certain areas following its exploitation for fur. Destruction as vermin in irrigation areas may have also contributed to the decline. Legislation now protects the species and populations have recovered (Scott and Grant 1997).

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The overall distribution of the water rat does not seem to have changed much since European settlement. On a national scale, water rats have recently been assessed as 'secure' but with an overall decline in abundance estimated at 10 - 50% (Scott and Grant 1997). 6.1.7.1. Habitat The water rat usually lives in the vicinity of permanent bodies of fresh or brackish water and even on some marine beaches. The highest numbers of water rats are generally seen in irrigation canals and permanent wetlands, but appear to be less common along inland rivers. It is also an occasional vagrant to temporary waters. It has been suggested that the water rat may be one of the few native mammals to have profited from human activities in some areas. Although it is usually found close to water, the water rat is able to survive on dry land and may range far from water in search of prey. Nests are made at the end of tunnels in banks or occasionally in logs (Scott and Grant 1997) Most food is gathered from the water with movements being primarily along the shoreline. Water rats will also collect food from the land if it is readily available. Water rats are largely carnivorous, mainly eating invertebrates and fishes (Watts and Kemper 1989). Versatility and broad resource utilisation would appear to ideally suit the water rat to the changing waterways of Australia (Scott and Grant 1997). Rivers are only one type of waterbody occupied by water rats. Large numbers are also found in permanent wetlands, lakes and in irrigation areas. Therefore, while river regulation might have negative impacts on some water rat populations, they do not pose a serious threat to the survival of the species as a whole. 6.1.7.2. Movement and dispersal The water rat maintains a home range and has no migratory patterns. For adult males, home ranges may vary from less that a metre to several kilometres. Dispersal of young to surrounding waterbodies presumably occurs after each successful breeding season. Dams and weirs would not inhibit the dispersal of water rats since they can move considerable distances across dry land. They are however, more prone to predation while moving around these structures (Scott and Grant 1997). 6.1.7.3. Effects of river regulation Water rats do not require the flow in a river to be maintained above some minimum value. Even if the river ceases to flow, they can move across land to gain access to upstream or downstream pools, although this places them at higher risk to predation. Releases from lower levels of water storages can result in depressed water temperatures downstream. Since the water rat cannot maintain its body temperature in cold water, such releases would reduce the amount of time it could hunt for food instream. The release of cold water might also have indirect effects on the water rat's food supply by altering the abundance or composition of aquatic invertebrates. However, the water rat is known to be a readily adaptable animal and it could probably change its feeding patterns to compensate any negative impacts. No studies addressing this topic have yet been published (Scott and Grant 1997). The water rat is an opportunistic and highly adaptable species, capable of occupying a wide range of habitats from small inland waterways to swamps and lakes and coastal estuarine waters. Within the Murray-Darling Basin it is common in areas where there is suitable habitat, and appears to have benefited from the increase in permanent waterbodies associated with irrigation areas. It is an opportunistic predator and will consume a wide range of foods including

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crustaceans, fish, large insects, frogs and even domestic garbage or carrion. Throughout most of its distribution, breeding is on a seasonal basis and does not appear to be triggered by any change in water regime such as flow rate or water depth. In arid areas however, where the amount of suitable habitat declines; during dry periods, breeding might be delayed until sufficient water (and hence food) are available. The adaptability of the water rat to conditions in a wide range of habitats and the high level of transience are of primary significance in ensuring the survival of the species (Scott and Grant 1997).

6.1.8 Riparian vegetation and macrophytes 6.1.8.1. Habitat needs The composition of the vegetation in the riparian zone is influenced by factors such as climate, topography, frequency and duration of inundation. The habitat needs of a healthy riparian zone include: ¾Protection from vegetation clearing, because bank slumping may occur and cause altered composition of aquatic plants; ¾Natural river flows and floods, because modifying natural water and sediment regimes may cause the banks downstream of a dam to be eroded as the channel readjusts to the change in flow regime. Changes to inundation frequency may also kill riparian plants through flooding and drowning or excessive drying; and

¾Weed control, because exotic species such as willows and blackberries can smother and destroy natural riparian vegetation (Boulton and Brock 1999).

6.1.9 Significant wetlands Wetlands include both natural and artificial water bodies and may be either static or flowing, fresh, brackish or saline, permanent or temporary. Wetlands generally include swamps, marshes, billabongs, lakes, saltmarshes, mudflats, mangroves, coral reefs, fens, peatlands, as well as rivers and streams (Environment Australia 2001). Wetlands of international importance (Ramsar sites) are listed under the Ramsar Convention, and the nationally important wetlands are listed in A Directory of Important Wetlands in Australia in the Australian Wetlands Database (see http://www.deh.gov.au/water/wetlands/database/index.html). The ACT currently has 1 wetland of International importance (Ginini Flats Wetland Complex), and 13 nationally important wetlands (Table 6.5) recognized as meeting the criteria for inclusion in the Directory (Environment Australia 2001). There are also several nationally important wetlands in the region surrounding the ACT, such as Yaouk Swamp in NSW (Environment Australia 2001). The ACT is located within two biogeographic regions, with the majority of important wetlands being found in the Australian Alps bioregion, and all others located in the South Eastern Highlands. Most of the significant high altitude wetlands of the ACT are located in the Cotter and Gudgenby River catchments (Environment Australia 2001). Locations of each of the wetland sites are shown in Figure 6.1. Nature reserves and national parks protect the majority of remaining wetlands in the ACT. Approximately 52% of the ACT is managed for nature conservation purposes with the largest

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reserved area being Namadgi National Park, covering 105,900 ha. The Namadgi National Park contains all the wetlands within the Australian Alps bioregion (Environment Australia 2001).

Table 6.5. Nationally important wetlands in the Australian Capital Territory Wetland Reference Area Criteria for name No. Region (ha) inclusion Big Creamy Flats Deleted Cotter Flats ACT001 Australian Alps 41 1 Ginini and Cheyenne Flats ACT002 Australian Alps 125 1, 2, 4, 5, 6 Rock Flats ACT003 Australian Alps 12 1 Rotten Swamp ACT004 Australian Alps 30 1, 6 Scabby Range Lake ACT005 Australian Alps 5 2 Snowy Flats ACT006 Australian Alps 35 5 Upper Cotter River ACT007 Australian Alps 600 1, 6 Upper Naas Creek ACT008 Australian Alps 56 1 Bendora South Eastern Reservoir ACT009 Highlands 81 5 Horse Park South Eastern Wetland ACT010 Highlands 40 1, 3, 6 Jerrabomberra South Eastern Wetlands ACT011 Highlands 174 3, 6 South Eastern Nursery Swamp ACT012 Highlands 53 1, 6 Cotter Source Bog ACT013 Australian Alps 5 1, 2, 6

6.1.9.1. Wetlands Types The wetland classification system used in the Directory identifies 40 different wetland types in three categories: A - Marine and Coastal Zone wetlands; B - Inland wetlands; and C - Human- made wetlands. 6.1.9.2. Criteria for determining important wetlands The criteria for determining nationally important wetlands in Australia, and hence inclusion in the Directory, are those agreed to by the ANZECC Wetlands Network in 1994 and used in the second edition of the directory. A wetland may be considered nationally important if it meets at least one of the following criteria: 1. It is a good example of a wetland type occurring within a biogeographic region in Australia. 2. It is a wetland which plays an important ecological or hydrological role in the natural functioning of a major wetland system/complex. 3. It is a wetland which is important as the habitat for animal taxa at a vulnerable stage in their life cycles, or provides a refuge when adverse conditions such as drought prevail.

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4. The wetland supports 1% or more of the national populations of any native plant or animal taxa. 5. The wetland supports native plant or animal taxa or communities which are considered endangered or vulnerable at the national level. 6. The wetland is of outstanding historical or cultural significance.

6.1.9.3. Ramsar Criteria for Inclusion A wetland is identified as being of international importance if it meets at least one of several criteria relating to the site’s uniqueness, rarity, or representativeness, or the flora, fauna or ecological communities it supports. The current criteria, agreed upon by Contracting Parties at the seventh Conference of Parties held in Costa Rica, May 1999 have been applied to sites designated since that time and to any sites where the Ramsar Information Sheet (RIS) has been reviewed and updated (Environment Australia 2001).

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Figure 6.1. Wetlands of the ACT Source: Environment Australia 2001

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6.2 National Land and Water Resources Audit summary of the condition of ACT streams

The National Land and Water Resources Audit (Norris et al. 2001) concluded that over 56 percent of the river length assessed in the Australian Capital Territory had damaged biological communities with around 28 percent of the river length assessed in significantly impaired condition indicating that 20-50 percent of the different kinds of animals expected to occur have been lost. Around 84 percent of the river length assessed in the Australian Capital Territory was degraded as assessed by environmental features. Seventy-one percent of the river length assessed was in moderately modified condition and 13 percent was in substantially modified condition. Changes to hydrological regimes, nutrient loads and suspended sediment loads contribute to most of this damage. Over 40 percent of the river length assessed in the Australian Capital Territory was affected by disturbed catchments, which was attributed to effects of run-off from the surrounding land use. All of the river length assessed in the Australian Capital Territory had altered hydrological regimes. Thirty-five percent of the river length assessed was in severely modified condition being affected by changes to the mean annual flow and seasonal amplitude indicating that the hydrological regime has been extremely modified from natural. Fifty-seven percent of the rivers assessed had substantially modified flow durations. However, only 32 percent of the total river length was assessed.

Around 45 percent of the river length assessed in the ACT had altered habitat resulting from changes to the connectivity and riparian vegetation. Ninety-seven percent of the river length assessed in the ACT had altered nutrient and suspended sediment loads. Moderate to high loads of total phosphorus occurred at 58 percent of the river length assessed and elevated levels of suspended solids and total nitrogen occurred at 73 and 47 percent of river length assessed, respectively.

It was concluded in the NLWRA that the key issues affecting the rivers of the Australian Capital Territory are changes to all aspects of the hydrological regime including substantial changes to the quantity, timing and duration of flow. High loads of total phosphorus and elevated levels of suspended solids are also problems for the rivers of the Australian Capital Territory.

6.3 Overview of issues surrounding dam enlargement

Reservoir size plays an important role in determining downstream river impacts (Cassidy 1989). The environmental and social effects of dams are generally scalable. That is, the larger the dam, the greater the environmental effects, and the more difficult it becomes to avoid, mitigate, or compensate for those effects (Bizer 2001). Shallow lakes and reservoirs have greater surface areas exposed during lake level fluctuations and are generally more biologically productive than deep lakes (Battaglene and Callanan 1991). Increases in the depth of Cotter Dam may potentially change the productivity of the reservoir, because deeper water can become cold, deoxygenated and possibly lethal to aerobic organisms. The baseline Cotter option will also reduce the quantity of water allocated for environmental flows, which are important for maintaining the health and function of river and floodplain environments (Poff et al. 1997).

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Corin Dam in the upper Cotter catchment has a greater impact on macroinvertebrate communities than the two downstream dams (Bendora and Cotter). Barlow (2001) suggests that this may be partly explained by the larger size of Corin Dam. Corin Dam has 7 times the capacity of Bendora Dam and 16 times the capacity of Cotter Dam. Water from Corin dam is generally released from 6 to 9 metres depth, which is below the thermocline in summer. The smaller size of the existing Cotter Dam allows it to be operated transparently (inflows = outflows) and most discharge is generally over the top of the dam wall. The purpose of a dam, structural features and the mode of operation (e.g. amount and timing of releases, off-take level) have potentially different downstream effects on aquatic biota (Finlayson et al. 1994; Marchant and Hehir 2002). A regulated-river hydrograph may show a decrease in the median annual flow of the river or changes to the timing and magnitude of high and low flows (King et al. 2003). Flow and water quality changes have the potential for detrimental effects on river ecosystems (Poff et al. 1997; Richter et al. 2003). There is a substantial amount of literature on the effects of dams and other regulating structures, but despite this there are few multi-disciplinary studies on serial impoundments (Nichols et al. in press). A common concept is that the downstream river ecosystems will ‘recover’ from the effects of regulation with increasing distance downstream from the impoundment. By adding another dam (Coree Dam) to the Cotter River, which already has multiple dams, this restarts the recovery process, and removes a stretch of river that provides good aquatic habitat. Abstraction for Canberra’s water supply has altered the riverine environment of the Cotter River and any future dam construction on the Cotter River would probably exaggerate this situation (Nichols et al. in press). On the other hand, an effective way to avoid widespread adverse effects to environmental resources across the ACT is to initiate a development strategy that commits a single catchment to development while limiting development in other catchments. This is a particularly effective strategy in areas where there are several undeveloped river basins, some of which have more environmental significance than others. By adopting a strategy whereby multiple dams are concentrated in a few selected catchments, the ecological resources located in the other catchments may be conserved (Bizer 2001). The problem with applying this strategy at this time is that locations need to be selected where significant ecological resources do not occur or significant adverse effects are not anticipated. This may not be the case for the Cotter catchment. The enlargement of the Cotter Dam or construction of Coree Dam may have environmental impacts on fish; cumulative impacts on downstream flow regime and associated aquatic, riparian and floodplain habitats; impacts on the foreshore environment and potential impacts of increased recreational use of the reservoir. The degree of environmental impact will depend on several factors including the volume of increased dam capacity; changes in water quality; depth of stratification; flooding of riparian areas; and the release strategy during flood events and at all other times. Increase in dam capacity will take water from the peak of large floods, thereby reducing the translucency of larger events. Increased storage may affect threatened fish populations within the storage, such as Macquarie perch, because of changes to the depth of stratification, which influences water quality. These changes may potentially disrupt breeding and alter food resources. Permanent increase of the Cotter Dam capacity would affect available habitat in the upper portion of the reservoir and upstream in the Cotter River. Cotter Dam has had little impact on the largest freshes and floods, because these water volumes are too large to store. Increased storage capacity will allow the storage to hold larger floods. Consideration needs to be given as to how floods will be regulated in the future. Natural

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river flows are important for protecting aquatic ecosystems. The enlargement of Cotter Dam has the potential to impact aquatic and riparian habitat through reduced environmental flows and water quality effects. Measures that could be implemented to mitigate the downstream effects of the dam include: ¾installing a multi-level off-take to prevent cold water pollution or other water quality effects; ¾providing appropriate environmental flows; and ¾provide fish passage where appropriate (e.g. Coree Dam) and maintain barriers needed to isolate native and exotic fish populations (e.g. Cotter Dam).

6.4 Overview of issues surrounding dam construction

6.4.1 Dam construction Changes to aquatic ecosystems after river impoundment may result from both direct and indirect effects of dam construction (Penczak et al. 1998). Few studies have looked at changes that occur during the construction of reservoirs (Doeg et al. 1987) therefore, it is unknown whether this may cause long-term impairment, irrespective of the continued river regulation following dam completion. Potential activities during dam construction may include bank revetment, clearance of trees and shrubs, water diversion or manipulation, and changes in sediment load (Doeg et al. 1987; Penczak et al. 1998). Doeg et al. (1987) found that sedimentation resulting from dam construction activity in the Thomson River, Australia, lowered the total numbers of species and the density of macroinvertebrates below the dam site. For the Thomson Dam project, a sediment-settling pond was built below the crushing plant, and sediment dams were constructed in nearly all the gullies in the cleared impoundment area. These procedures were mostly inadequate, however, the effects of the Thomson Dam were not as severe as those reported from the Mitta Mitta River during construction of Dartmouth Dam where few environment protection measures were conducted (Doeg et al., 1987). Changes to the abundance and composition of primary sources of food downstream of dams, such as decaying organic material or algal films on rock surfaces, may also have profound effects on benthic populations but the magnitude and consistency of these changes is not well known. The time scale over which all these changes take place is uncertain. It seems most changes occur rapidly during and soon after dam construction but the more subtle changes, such as to the food supplies, may take longer to develop.

6.4.2 Fragmentation Dam construction has serious consequences for aquatic ecosystems, and one of the most serious is the “barrier effect”, the prevention of aquatic organism dispersal and migration throughout a system (Gore 1980; Fagan et al. 2002; Morita and Yamamoto 2002). Rivers are among the most intensively fragmented ecosystems that exist, because it is easy to accomplish. A single damming event can isolate adjacent river segments and obstruct avenues of organism dispersal (Jager et al. 2001). Rivers are important pathways for the flow of energy, matter and organisms through the landscape. Among organisms, river continuity is important for migrating fish, drifting invertebrates and plant dispersal along riparian corridors (Andersson et al. 2000). There have been limited published studies on the influence of habitat fragmentation in biodiversity loss and river health degradation. Most studies of river fragmentation by dams have

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focused on disruptions to migratory fish (Jansson et al. 2000), and the majority are international research projects, which may not apply to Australian fish fauna. Dispersal constraints are especially detrimental for fish because they are entirely aquatic species (Fagan 2002). Many stream insects have the advantage in adult life stages that they can disperse over land. However, dams can also substantially reduce the potential for macroinvertebrate recolonization, and result in changes to community composition. The Cooperative Research Centre for Freshwater Ecology (CRCFE) is currently undertaking a research project on fragmentation and connectivity in Australian river systems (Milligan 2003). Preliminary results show that populations of shrimp and crayfish are very fragmented, even on very small spatial scales, indicating very limited dispersal between streams. This implies that dispersal within and between catchments may not be as extensive as previously thought and has major implications for the likely recovery of disturbed systems (Milligan 2003). In contrast, the insect species all showed very high levels of connectivity, both within and between catchments, indicating flight is the major dispersal mechanism (Milligan 2003). In a regulated river the habitat conditions are changed downstream of dams. Therefore, although adult flight may be a satisfactory dispersal mechanism, successful recolonization may depend on the suitability of the habitat invaded. Ecological continuity in regulated rivers is lost not only for the river channel, but also for the adjoining riparian corridor. Dams act as barriers to plant dispersal and conditions within impoundments may result in the development of different riparian floras (Andersson et al. 2000; Jansson et al. 2000). Vegetation changes following hydrological alterations have been documented for both vascular plants and bryophytes that disperse by water (Andersson et al. 2000). Dams affect many structures and functions of rivers and this may contribute to changes in the redistribution of drift material, including diaspores (e.g. seeds and buds). River regulation reduces the occurrence of flood events that are considered to be essential for the persistence of riverine systems. The absence of floods eliminates the lateral (riparian–aquatic) movement of drift material, both to and from the riverbank, as well as the transport of drift along the river. Also, the redistribution of sediment and organic debris is a key process of free-flowing riparian corridors, which are obstructed along regulated rivers (Andersson et al. 2000). In impounded rivers, current velocity is low and floating diaspores either sink or become swept ashore by winds. A few diaspores may pass dams through turbines or spillways. Long floaters are more likely to pass, because passages are hard to hit, and long floating-times increase the probability of success. Short floaters may be absent from impoundments because they fail to recolonize after local extinction (Jansson et al. 2000). The isolation of remaining populations is likely to cause deterioration, both in the number of individuals and in the genetic diversity of riparian vegetation (Andersson et al. 2000). Habitat fragmentation, both in the surrounding terrestrial habitat and within the river channel itself, can alter riverine food webs via effects upon dispersal, metapopulation dynamics and gene flow (Woodward and Hildrew 2002). Habitat fragmentation resulting from water abstraction may affect habitat availability, spatial distribution, movement, fitness and survival. In order to maintain and restore ecological integrity of river systems, the preservation of intact flow conditions is one of the key issues for river management (Fischer and Kummer 2000). Habitat fragmentation in river systems has different and more severe consequences on fragment size than other landscapes, resulting in both smaller fragments and higher variance in fragment size (Fagan 2002). Habitat fragmentation has rarely been studied in rivers; therefore, it is unknown whether there exists a critical minimum habitat size required for population persistence. In rivers, this concept translates into a minimum segment length required for

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population persistence (Jager et al. 2001). There is some evidence, however, that supports the idea that population viability is improved by providing longer reaches (Jager et al. 2001). Studies also suggest that increased fragmentation produces an exponential decline in the likelihood of persistence, but there is no known extinction threshold to suggest a minimum viable length of river (Jager et al. 2001). Theoretical efforts and small-scale experiments have found that the fewer occurrences a species has or the more fragmented its distribution is, the more vulnerable that species is to extinction (Fagan et al. 2002). Davies et al. (2000) predicted that isolated, rare, or predaceous species will be lost first from fragmented forest landscapes in Australia. It is unknown whether these traits would apply to aquatic insects.

6.4.3 Sediment loads Large dams create significant changes in flow regime and sediment load of the river downstream (Sherrard and Erskine 1991). Following river regulation, the magnitude and frequency of peak discharges is often lowered because of the effects of water storage and use. Dams also trap inflowing sediment, resulting in the release of water with little suspended sediment downstream. The sediment trap efficiency of dams may lead to erosion and degradation problems immediately downstream by increasing the rivers competence to transport bed and bank materials. The erosion may cause degradation of the river channel, but is often limited by an armoured layer of particles too large to be transported by the reduced flow conditions (Simons 1979; Brookes 1994). The effect of the reduced silt deposits, and the consequent armouring, may alter the variety of habitat available for riverine biota (Holden 1979). Bank erosion impacts are not limited to the immediate site of erosion with eroded material being deposited downstream, resulting in siltation of pools and floodplain wetlands. Sediment may also be introduced from non-regulated tributary sources (Petts 1988). Increases of fines into permeable gravel substrates may result in decreased quality and extent of habitat, leading to a reduction in biota diversity and abundance, and significant effects on aquatic biota (McCartney et al. 2001). The effects of the likely flow regime on armouring and fine suspended sediment transport were investigated for each of the future water supply options.

6.5 Overview of issues surrounding interbasin transfer

Inter-basin water transfers (IBTs) are developments aimed at redistributing water from areas with sufficient water supply to those with high demand or perceived water deficits (Wishart and Davies 2003). It is now well recognised that large dams can have major environmental effects on rivers and landscapes (Hart 1999). In contrast, less is known about the ecological consequences of inter-basin water transfer through natural stream systems (Davies et al. 1992; Matthews et al. 1996; Gibbins et al. 2000).). The major issues surrounding inter-basin transfer schemes include the loss of biogeographical integrity, the loss of endemic biotas, the frequent introduction of alien and often invasive aquatic and terrestrial plants and animals, the genetic intermixing of once separated populations, the implications for water quality, the alteration of hydrological regimes, climatic effects, and the spread of disease vectors (Davies et al. 1992). Any transfer of water within or between basins will have physical, chemical, hydrological and biological implications for both donor and recipient systems. This demands a serious appraisal of current planning of IBTs and determination of strategies to minimize their impacts.

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Impacts on rivers where water is removed Environmental impacts on rivers from which water is removed include loss of aquatic biodiversity, degradation of the channel and associated wetlands (Hart 1999). In the Snowy River, large interbasin water transfers for hydroelectric power generation have substantially changed the hydrology. Annual, monthly, mean daily and peak instantaneous flows have been significantly reduced and flood variability greatly increased along 352 km of channel (Erskine et al. 1999). Reduced flows in the upper Murrumbidgee River have also resulted in significant degradation, especially in the reach immediately downstream of Tantangara Dam. The river now has extensive sand and gravel deposits, partly because of poor management of rural catchments and partly because of a lack of flushing flows, and this has caused an apparent decrease in biodiversity (Hart 1999). Impacts on receiving systems Several rivers in the Snowy Scheme (e.g., Tumut, upper Snowy, upper Murray) now have massively changed flow regimes from natural, because they are used as channels to transfer water from one reservoir to another or receive large pulses of water as part of the operation of hydro power plants. The impact of these changes has been little studied, but it is likely they have significantly affected the riverine biota (Hart 1999). The Tumut River is intensively managed to maximize capacity; channel sections are engineered to minimize flow resistance and, as a consequence, all in-channel vegetation is removed. During the summer irrigation period, flows are maintained at bankfull capacity, which has important implications for channel stability (Davies et al. 1992). Since shifts in flow regime are common to all IBTs, it is logical to assume that all IBTs will have impacts on the biota, with potentially serious implications as far as invasive species and human disease vectors are concerned (Davies et al. 1992).

Impacts on receiving systems – Overseas In the River Wear England, velocity changes were found to be variable following interbasin water transfer (Gibbins et al. 2000). Some parts of the river channel were subjected to order of magnitude increases in near-bed velocity, whereas others suffered no perceptible change. Losses of fine particulate organic material were associated with the areas of greatest velocity increase (Gibbins et al. 2000). Riffle invertebrate communities were found largely to be resistant to the effects of periodic transfers into the River Wear. However, for flow sensitive taxa, even relatively minor flow changes may be considered as disturbance events when viewed at the patch or reach scales (Gibbins et al. 2000). Losses were variable within the 250 m reach monitored, with some areas gaining animals because of patches of the stream bed acting as flow refugia (Gibbins et al. 2000). Snaddon and Davies (1998) report on the implications for discharge and invertebrate community structure in the receiving reaches of a small IBT in the Western Cape of South Africa. Transfers occur during summer and lead to greatly elevated summer discharges in the recipient river (Snaddon and Davies 1998). The major perturbation caused by the IBT in the receiving reach of the Berg River, was hydrological ‘reversal’. They also found that the IBT was a major input of fine particulate organic matter (FPOM) in the form of both living and fragmented plankton: primarily Cladocera and Copepoda, and the dipteran family Chaoboridae from the source reservoir. Transfer impacts depend on the design and operational use of the scheme in question. Critical determinants are the nature of the transfer pipeline (e.g. open canal versus underground tunnel) and the magnitude, frequency and duration of transfers. If donor and receiving catchments are

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far apart, their water chemistries are likely to differ. Biological differences between donor and receiving catchments are also likely to increase with distance, so increasing the possibility that any organisms transferred through the system may be non-native. Impacts tend to be greatest where the physical and chemical characteristics of donor and receiving systems differ and where there are large flow changes associated with transfers (Gibbins et al. 2000). Preliminary studies have shown that small numbers of live macroinvertebrates enter the River Wear from the transfer tunnel, despite the screening mechanisms installed at the intake point. High levels of genetic differentiation have been found between invertebrate populations within and between catchment areas (Hughes et al. 1996, Australia); therefore, there are concerns over the effects of transfers on genetic diversity. Before use of a transfer scheme, detailed research and careful design are needed (Gibbins et al. 2000). The kinds of fishes in a stream, and variability of the fauna, may depend largely on schedules of stresses or disturbances, life histories of organisms or their ability to withstand disturbance, the size or discharge of the stream at a given location, habitat complexity or heterogeneity, or chemical composition of the water. The degree to which water transfer changes physical features or flow schedules of a natural stream should influence its effect on the existing fish fauna (Matthews et al. 1996). Also of concern is the potential for the transfer of toxic algal blooms from the source reservoir to the receiving River (Snaddon and Davies 1998).

A decrease in taxon richness of the invertebrate communities was observed below the transfer outlet, compared to the river above the transfer. Some sensitive families of Ephemeroptera and Trichoptera were not recorded below the outlet during transfer months. Collector-predators such as the Hydropsychid Trichopterans showed large increases in numbers during the same transfer months, when compared against above-outlet samples. This change was probably because of the introduction of live zooplankton to the receiving river from the source reservoir (Snaddon and Davies 1998). Diversion of Lake Texoma water through Sister Grove Creek in summer and autumn resulted in abrupt increases in discharge, well above average natural flows for those months, and in at least a doubling of conductivity of water in the stream. Although the artificial high flows in Sister Grove Creek were brief in ecological time, they probably represented an unusually long period of sustained high flow (Matthews et al. 1996).

In South Africa, the introduction of several non-indigenous fish species to the Great Fish River from the Orange River, via IBT, has been documented, even though it was thought impossible, given the nature of the draw-off system (Davies et al. 1992). Snaddon and Davies (1998) show that the transfer of living organisms from one basin to another is not only possible, but also that it can be significant, despite the rigours of the transfer route. Living organisms are remarkably robust; therefore, it cannot be assumed that transfer pipelines, valves, high-pressure releases and tunnels will prevent genetic transfers. Such problems are unresolved because there has been relatively little research on this issue, and current technology does not guarantee prevention of organism transfers (Snaddon and Davies 1998). Major projects must include adequate environmental planning Retrofitting of large dams, for example to add a multi-level offtake, bigger capacity release pipes, or fish ladders, is extremely expensive. It is much more sensible to undertake adequate initial planning, and to include these at the time of construction (Hart 1999). A range of catchment activities can influence the quality of rivers and wetlands, and integration of catchment and waterway management is essential if the quality of Australia’s water resources is to be sustained in the future. The whole river basin must be the management unit.

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Five environmental lessons are identified from the way water has been managed over the past 50 years: ¾community values change over time requiring flexible and adaptable management agencies; ¾large dams can cause major environmental problems; ¾major projects must include adequate environmental planning from the early stages; ¾all organisations must be subject to the relevant environmental legislation; ¾knowledge improves over time - management agencies must be knowledge-based (Hart, 1999).

7 Acknowledgements

Thanks to the ACTEW future water options project team, particularly; Ian Wallis, Richard Barratt, Laslo Nagy, Kirilly Dickson, Anthony Nagle, Chris Webb, Bob Harvey. Also thanks to: Ecowise Environmental, Andy Cumming; Environment ACT, Peter Liston, and Mark Lintermans.

8 References

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Hero, J-M. and Gillespie, G. (1993). The Tadpole of Litoria phyllochroa (Anura: Hylidae). Proceedings of the Royal Society of Victoria, 105: 31-38. Hero, J-M., Littlejohn, M.J. and Marantelli, G. (1991). Frogwatch Field Guide to Victorian Frogs. Department of Conservation and Environment, Melbourne. Hershey, A.E., Pastor, J., Peterson, B.J., Kling, G.W. (1993). Stable Isotopes Resolve the Drift Paradox for Baetis Mayflies in an Arctic River. Ecology, 74: 2315-2325. Holden, P. (1979). Ecology of Riverine Fishes in Regulated Stream Systems. In The Ecology of Regulated Streams (Eds J. Ward and J. Stanford). Plenum Press, New York. Holloway, S. (1997). Survey Protocols for the Stream-breeding Frogs of Far East Gippsland: The Application of Habitat Modelling and an Assessment of Techniques. Master of Applied Science thesis, Applied Ecology Research Group, University of Canberra. Hughes JM, Bunn SE, Hurwood DA, Choy S, Pearson RG. (1996). Genetic Differentiation among Populations of Caridina zebra (Decapoda: Atyidae) in Tropical Rainforest Streams, Northern Australia. Freshwater Biology, 36: 289–296. Hunter, D. and Gillespie, G. R. (1999). The Distribution Abundance and Conservation Status of Riverine Frogs in Kosciusko National Park. Australian Zoologist, 31: 198-209. Jager, HI; Chandler, JA; Lepla, KB; Van Winkle, W. (2001). A Theoretical Study of River Fragmentation by Dams and its Effects on White Sturgeon Populations. Environmental Biology of Fishes, 60 (4): 347-361. Jansson, R; Nilsson, C; Renoefaelt, B. (2000). Fragmentation of Riparian Floras in Rivers with Multiple Dams. Ecology, 81 (4): 899-903.

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Ligon, F.K., Dietrich W.E. and Trush, W.J. (1995). Downstream Ecological Effects of Dams. Bioscience, 45: 183-192. Lintermans, M. and Osborne, W. (2002). Wet and Wild. Field guide to the Freshwater Animals of the Southern Tablelands and High Country of the ACT and NSW. Environment ACT, Canberra. Lintermans, M. (1998). The Status and Distribution of the Platypus (Ornithorhynchus anatinus) in the Australian Capital Territory with Notes on Some Local Declines. Australian Mammalogy, 20: 306. Mackay, R.J. (1992). Colonization by Lotic Macroinvertebrates: A Review of Processes and Patterns. Canadian Journal of Fisheries and Aquatic Sciences, 49: 617-628. Maddock, I. (1999). The Importance of Physical Habitat Assessment for Evaluating River Health. Freshwater Biology, 41:373-391. Maddock, I., Thoms, M., Jonson, K., Dyer, F., Lintermans, M. (2004). Identifying the Influence of Channel Morphology on Physical Habitat Availability for Native Fish: Application to the Two- spined Blackfish (Gadopsis bispinosus) in the Cotter River, Australia. Marine and Freshwater Research, 55: 173 – 184. Maini, N., Dudgeon, S., Acaba, Z. and Bowling, L. (1997). Nutrient Investigation and Water Quality in the Murrumbidgee Catchment Above Cooma. DLWC Centre for Natural Resources, and Catchment Monitoring Services, Murrumbidgee Region. Marchant R. and Hehir G. (2002). The Use of AUSRIVAS Predictive Models to Assess the Response of Lotic Macroinvertebrates to Dams in South-east Australia. Freshwater Biology, 47: 1033–1050. Matthews, WJ; Schorr, MS; Meador, MR. (1996). Effects of Experimentally Enhanced Flows on Fishes of a Small Texas (U.S.A.) Stream: Assessing the Impact of Interbasin Transfer. Freshwater biology, 35 (2): 349-362. McCartney M.P., Sullivan C., and Acreman M.C. (2001). Ecosystem Impacts of Large Dams. Background Paper Nr 2. Prepared for IUCN/UNEP/WCD (www.iucn.org/webfiles/doc/archive/2001/IUCN852.PDF). MDBC. (2004). Pilot Audit Technical Reports and Supporting Information – Sustainable Rivers Audit. MDBC Publication 28/04, CD.

Meffe, G. and Sheldon, A. (1988). The Influence of Habitat Structure on Fish Assemblage Composition in Southeastern Blackwater Streams. American Midland Naturalist, 120: 225-240. Milligan, A. (2003). Cooperative Research Centre for Freshwater Ecology Annual Report 2002– 03. Goanna Print, Australia. Minshall, G. W. (1984). Aquatic Insect - Substratum Relationships. Pp. 358-400. In: Resh V. H. and Rosenberg, D. M. The Ecology of Aquatic Insects, Praeger Publishers, New York. Morita, K, and Yamamoto, S. (2002). Effects of Habitat Fragmentation by Damming on the Persistence of Stream-Dwelling Charr Populations. Conservation Biology, 16 (5): 1318-1323. NCA. (2002). Consolidated National Capital Plan. National Capital Authority, Australia. http://www.nationalcapital.gov.au/planning/NCP/NCP_download.htm#download_2.

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NCDC. (1983). The Gudgenby Area. Draft Policy and Development Plans Incorporating an Evaluation of Planning and Environmental Issues. Draft Only, To be published in November 1983. National Capital Development Commission, Canberra Australia. Nicholas, W.L., and Thomas, M. (1978). Biological Release and Recycling of Toxic Metals from Lake and River Sediments. Australian Water Resources Council Technical Paper No. 33. Nichols, S., Norris, R. N., Maher, W. and Thoms, M. C. (in press). The Ecological Effects of Serial Impoundment on the Cotter River, Australia. (Hydrobiologia). Norris, R., Chester, H. and Thoms, M. (2004). Ecological Sustainability of Modified Environmental Flows in the Cotter River during Drought Conditions January 2003-April 2004. Final Report August 2004. Cooperative Research Centre for Freshwater Ecology, University of Canberra, Canberra 2601. Norris, R.H. (1986). Mine Waste Pollution of the Molonglo River, New South Wales and the Australian Capital Territory: Effectiveness of Remedial Works at Captains Flat Mining Area. Australian Journal of Marine and Freshwater Research, 37: 147-57. Norris, R.H. and Thoms, M.C. (1999). What is river health? Freshwater Biology, 41: 197-209. Norris, R.H. Prosser, I., Young, B., Liston, P., Bauer, N., Davies, N., Dyer, F., Linke, S., and Thoms, M., (2001). The Assessment of River Condition (ARC). An audit of the Ecological Condition of Australian Rivers. Report submitted to the National Land and Water Resources Audit Office, May 2001. NSW National Parks and Wildlife Service (2001). Approved Recovery Plan for the Spotted Tree Frog (Litoria spenceri). NSW National Parks and Wildlife Service, Hurstville, NSW.

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Oliver, R. L. and Ganf, G. G. (1999), 'Freshwater Blooms' in Whitton, B. A. and Potts, M. (eds.) The Ecology of Cyanobacteria: Their Diversity in Time and Space, Kluwer Academic Publishers. Olley, J. M. and Wasson R.J. (2003). Changes in the Flux of Sediment in the Upper Murrumbidgee Catchment, SE Australia, since European Settlement. Hydrological Processes, 17: 3307-3320. Osborne, W. S. (1989). Distribution, Relative Abundance and Conservation Status of Corroboree Frogs Pseudophryne Corroboree Moore (Anura: Myobatrachidae). Australian Wildlife Research, 6: 537-547. Osborne, W., Hunter, D. and Hollis, G. (1999). Population Declines and Range Contraction in Australian Alpine Frogs. Pp 145-157 In A. Campbell (ed.) Declines and Disappearances of Australian Frogs. Environment Australia, Canberra. Osborne, W.S., Gillespie, G.R. and Kukolic, K. (1994). The spotted tree frog Litoria spenceri: An Addition to the Amphibian Fauna of the Australian capital Territory. Victorian Naturalist, 111: 60- 64. Ovington, P. (1973). A Resource and Management Survey of the Cotter River Catchment. Department of Forestry, Australian National University, Canberra, Australia. Penczak, T., Glowacki, L., Wanda Galicka, W., Koszalinski, H. (1998). A Longterm Study (1985–1995) of Fish Populations in the Impounded Warta River, Poland. Hydrobiologia, 368: 157–173.

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Schmid-Araya, J.M. (2000). Invertebrate Recolonization Patterns in the Hyporheic Zone of a Gravel Stream. Limnology and Oceanography, 45: 1000-1005. Schnaffer, W.R. and Oglesby, R.T. (1978). Phosphorus Loadings to Lakes and Some of their Responses. Part 1: A New Calculation of the Phosphorus Loading and its Implication to 13 New York Lakes. Limnology and Oceanography, 23: 120-134. 1978. Scott, A. and Grant, T. (1997). Impacts of Water Management in the Murray-Darling Basin on the Platypus (Ornithorhynchus anatinus) and the Water Rat (Hydromys chrysogaster). Technical Report 23/97. CSIRO Land and Water, (Australia). Serena, M., Thomas, J.L., Williams, G.A. and Officer, R.C.E. (1998). Use of Stream and River Habitats by the Platypus, Ornithorhynchus anatinus, in an Urban Fringe Environment. Australian Journal of Zoology, 46: 267–282. Sherrard J. J. and Erskine W. D. (1991). Complex Response of a Sand Bed to Upstream Impoundment. Regulated Rivers: Research and Management, 6: 53-70. Simons, D. (1979). Effects of Stream Regulation on Channel Morphology. In The Ecology of Regulated Streams (Ed. J. Ward and J. Stanford). Plenum Press, New York. Snaddon, C.D., Davies, B.R. (1998). A Preliminary Assessment of the Effects of a Small South African Inter-basin Water Transfer on Discharge and Invertebrate Community Structure. Regulated Rivers: Research and Management, 14 (5): 421-441.

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Swanson, F.J. (1980). Geomorphology and Ecosystems. In Waring, R.H. (Ed) Forests: Fresh Perspectives from Ecosystems Analysis, Proceedings of the 40th Annual Biology Colloquium, Oregon State University Press, Oregon. Townsend, C.R. and Hildrew, A.G. (1976). Field Experiments on the Drifting, Colonization and Continuous Redistribution of Stream Benthos. Journal of Animal Ecology, 45: 759-772. Upper Murrumbidgee Expert Panel. (1997). Expert Panel Environmental Flow Assessment of the Upper Murrumbidgee River. Report to the NSW Environment Protection Authority. Wallace, J.B. (1990). Recovery of Lotic Macroinvertebrate Communities from Disturbance. Environmental Management, 14: 605-620. Watts, C. and Kemper, C. (1989). Muridae. In Fauna of Australia Volume 1B Mammalia. D.W.Walton and B.J.Richardson (eds). Published by Australian Government Publishing Service Canberra. Available at http://www.deh.gov.au/biodiversity/abrs/publications/fauna-of- australia/pubs/volume1b/47-ind.pdf Weatherley, A.H., Beevers, J.R., and Lake, P.S. (1967). The Ecology of a Zinc Polluted River. In: Australian Inland Waters and their Fauna: Eleven Studies. (Ed. A. H. Weatherley) pp. 252- 278. (A.N.U. Press: Canberra.) Welsh, H.H. Jr. and Ollivier, L. M. (1998). Stream Amphibians as Indicators of Ecosystems Stress: A Case Study from California's Redwoods. Ecological Applications, 8: 1118-32.

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Woodward, G. and Hildrew, A.G. (2002). Food Web Structure in Riverine Landscapes. Freshwater Biology, 47 (4): 777-798. Young, W.J., Chessman, B., Erskine, W., Jakeman, A., Raadik, T., Tilleard, J., Varley, I., Wimbush, D. and Verhoeven, J. (1988). Environmental Assessment Method for the Rivers in the Area of Interest of the Snowy Water Inquiry. In: Anon. (1988) Resource Materials – Appendix to the Final Report of the Snowy Water Inquiry, 44pp. (http://www.snowywaterinquiry.org.au/documents/appendix/appendix.htm).

8.1 Web Links

http://www.actew.com.au/futurewateroptions/Cotter.aspx http://www.actew.com.au/futurewateroptions/Tantangara.aspx http://www.actew.com.au/futurewateroptions/Tennent.aspx

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8.2 Personal communication

M. Lintermans personal communication, September 2, 2004. Senior Aquatic Ecologist Wildlife Research and Monitoring Environment ACT Ph (02) 6207 2117 Fax (02) 6207 2122 Email [email protected]

I. Wallis personal communication, 2004. Environmental and Consultation Manager ACTEW corporation [email protected]

P. Ormay Wildlife Research and Monitoring Unit

Environment ACT Ph (02) 6207 2115 Fax (02) 6207 2122

Email [email protected]

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A P P E N D I C E S

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Appendix A – Methods

9 ARC and SRA methods

9.1 Assessment of River Condition (ARC)

The Assessment of River Condition (ARC) is based on the premise that ecological integrity, as assessed by the aquatic biota, is the fundamental measure of river health. Impacts to biota are usually the final point of environmental degradation and pollution, making the biota good indicators of disturbance to rivers and their catchments. The biota are also components of, or critical to, the goods and services provided by rivers that are valued by society. Thus, the biota are important both as critical elements of river systems, and as indicators of degradation of other key elements. The function of the ARC is to bring together in an assessment several related elements of river condition, all of which affect, or are influenced by, ecological condition. The approach adopted has been informed by our understanding of the links between catchments, riverine habitats and the aquatic biota. Elements other than the aquatic biota need to be included in a comprehensive ARC for several reasons. These are: ¾The available or selected group of biological indicators may not be sensitive to all forms of riverine degradation; ¾There may be a lag between environmental disturbance and biotic response; and ¾Assessing the biota only may tell us that the biota are impaired, but not the reasons why they are impaired. A comprehensive assessment of river condition that can guide management decisions requires information about both extent of impact and the causes of degradation. Consequently the ARC is based on a hierarchical model of river function (Fig. 2.1) in which broad-scale catchment characteristics affect local hydrology, habitat features and water quality, which in turn influence the aquatic biota; our ultimate indicator of river health. This model is a refinement of the model underpinning the assessments made in the Snowy Water Inquiry (Young et al., 1998).

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Catchment character influences a river by large-scale controls on hydrology, sediment delivery and chemistry (Allan and Johnson 1997). If catchments are disturbed or unhealthy, then rivers will also be unhealthy. Much of the degradation in Australia’s rivers results from land use practices in surrounding catchments (Boulton and Brock 1999). Thus, assessing catchment condition may provide information about the ultimate causes of any observed biological impoverishment, and may highlight potential impacts that have not yet caused biological degradation within rivers but that are likely to do so. The ARC includes assessments of potential diffuse and point source impacts from surrounding catchments. Available habitat, and the local physical, chemical and biological features that provide living space and resources determine the types and numbers of plants and animals that can potentially live in an area. The quantity and quality of available habitat affects the structure and composition of resident biological communities (Meffe and Sheldon 1988, Boulton and Brock 1999, Maddock 1999), and are thus critical elements of ecological condition. Habitat assessment provides information about the likely proximal causes of impoverished biological states, and may be used as surrogates for biological condition where these latter data are unavailable. Aspects of habitat assessed in the ARC include water quantity and quality, geomorphology, riparian condition, and the longitudinal and lateral connectivity of the stream.

9.1.1 Sustainable Rivers Audit (SRA) The Sustainable Rivers Audit (SRA) Pilot project (MDBC 2004) addresses stream health across five themes:

¾Fish; ¾Macroinvertebrates; ¾Hydrology;

¾Physical Habitat; and ¾Water Quality. Of these five themes, the hydrology, macroinvertebrate, physical habitat and water quality themes are relevant to this study. The macroinvertebrate assessments used in the Pilot SRA were similar to those used in the ARC, therefore, the approach used in the ARC was used for the Assessment of ACT Water Supply Options. At the conclusion of the Pilot SRA, it was recommended that the physical habitat and water quality themes undergo further refinement before a set of indices and methods is approved for use in riverine assessments. The hydrology theme used in the Pilot SRA built on that used in the ARC and the indices used in the SRA are therefore also used in this study.

9.1.2 ARC and SRA indices and Methods used in this assessment The indices that were initially considered for use in the assessment of the ACT water supply options are shown in Table 9.1. Of the initial list of indices provided in Table 9.1, only the biota and hydrology indices were calculated in their entirety. Investigation of the various water supply options indicated that many of the sub-components of the other indices (nutrient and suspended sediment load, habitat index, catchment disturbance index) would not change as a result of the water supply options. Therefore, it was decided to only assess the components of the indices that were expected to change as a result of implementation of any of the ACT water supply options.

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The components assessed were: ¾Biota; ¾Hydrologic disturbance; ¾Suspended sediment load; ¾Bed (coarse) sediment load; and ¾Connectivity.

Table 9.1. Indices to be used in this study - Assessment of Water Resource Options Index Description Pros and Cons Reference condition Biota (ARC) ƒAssessment of ƒBiota are usually the final point ƒNear pristine macroinvertebrates of degradation, making them or minimally good indicator. impacted ƒCan only be used to benchmark the current condition – no predictive capability. ƒPotential effect of each water resource option on the aquatic biota could be predicted from other modelled indices based on physical and chemical characteristics, but only if sufficient data available. Hydrologic ƒAssessment of effects of ƒRequires information on ƒModelled Disturbance regulation and abstraction on extraction. natural flows (SRA) river flows. ƒOften limited to main trunk (pre regulation ƒSub-indices: streams. and extraction) High flow ƒPredictive capability, as based Low and zero flow on modelling. Variability Seasonality Flow Volume. Nutrient ƒAssessment of changes in ƒDoes not include toxicants and ƒModelled pre- and Total N, P and SS. salinity, because of sparse data European Suspended for river reaches. levels Sediment ƒSub-indices: Load Index - Total N ƒCan provide comparative assessments, but not absolute. (ARC) - Total P - Suspended sediment. Habitat ƒAssessment of key Index components of aquatic habitat. (ARC) ƒSub-indices: - Bed condition - Riparian vegetation - Connectivity

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Index Description Pros and Cons Reference condition Catchment ƒDetect or provide a measure of ƒCould be used to show the ƒUndisturbed Disturbance human changes that ultimately effect of new infrastructure (e.g. catchment Index impact the river condition and pipelines and associated (pre-European) (ARC) the biota. access tracks) ƒSub-indices: - Infrastructure - Land use - Land cover change.

9.2 Assessment limitations and assumptions

There were several assessment limitations and assumptions of this aquatic ecology study. The evaluation of each of the proposed water supply options was based on existing data and information, which was lacking in some areas. To assess the likely effects of the altered hydrologic regimes posed by the various options on the aquatic ecology, it was necessary to synthesise hydrographs for the various water supply options. Several assumptions were made including: ¾release patterns from the dams; ¾evaporative losses from the dams and calculation of safe yield;

¾transmission losses in the Murrumbidgee River; ¾rate of inflow from Lower Molonglo Water Quality Control Centre; and ¾losses from Queanbeyan River system imposed by Googong Dam.

10 Indices considered for use in ACT water supply options assessment

10.1 Biota Index (AUSRIVAS)

O BiotaIndex E

O = Observed number of taxa E = Expected number of taxa

10.2 Hydrologic Index

SRA uses sigmoid function to combine individual indicators into indices as relationship believed to be non-linear. Linear function used here for simplicity, using the SRA weights.

HI HIlz HIhf HIv HIs 07.013.020.028.033.0 uuuuu HIvol

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High Flow Events Sub-Index

§  ARIARIARI 1052 · HIhf ¨ ¸ © 3 ¹

Where:

ARIn = 1:2,1:5, 1:10 year ARI flood indicator (HFEN)

min( NN ), HFEN cn max( NN cn ),

Nn, Nc = number of event exceedences (1:2, 1:5, 1:10) under natural and current conditions. An event is defined as independent if it is separated by 5 days or more of lower flows.

Low Flow and Zero Flow Sub-Index

HIlz 5.0 LFEN 3.0 LFED 2.0 uuu Zd

Where: LFEN = Low flow event number indicator: min( NN ), LFEN cn max( NN cn ),

th Nn, Nc = number of event exceedences < the natural 90 percentile of non-zero flows under natural and current conditions.

An event is defined as independent if it is separated by 5 days or more of lower flows.

LFED = Low flow event duration indicator:

min( NN ), LFED cn max( NN cn ),

th Nn, Nc = mean duration of event exceedences < the natural 90 percentile of non-zero flows under natural and current conditions.

An event is defined as independent if it is separated by 5 days or more of lower flows.

Zd = difference in proportion of zero flow days indicator:

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§ § Z Z ·· Z 1 ¨ ABS¨ c  n ¸¸ d ¨ ¨ ¸¸ © © days days ¹¹

Zc, Zn = number of zero flow days under current and natural conditions Days = total number of days in record

Flow Variability Sub-Index

HIv SA u 4.06.0 AV

Where: SA = Seasonal Amplitude: h l c  c h l SA n n 2 h = highest mean monthly flow l = lowest mean monthly flow for current ( c ) and natural ( n ) conditions.

Note: denominator is always larger of c and n. AV = Annual Variation AVC AV n AVCc

AVCn, c = Annual coefficient of variation, under natural and current conditions.

Seasonality Sub-Index

­ª 1 º ª 1 º½ 1 HIs ®« ¦ MIN ;YHNYHC ii »  « ¦ MIN ;YLNYLC ii »¾ ¯¬M i 1 ¼ ¬M i 1 ¼¿ 2

Where: YHC/ YHN = number of years the ith month has the peak annual flow under current / natural conditions YLC/ YLN = number of years the ith month has the minimum annual flow under current / natural conditions M = number of years in flow data set.

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Flow Volume Sub-Index

HIvol Med A 2.03.05.0 uuu AAPFD

Where: Med = Median Annual Flow:

§ Q50n · Med ¨ ¸ © Q50c ¹

Q50n,c = Median annual flow under natural and current conditions

Note: denominator is always greatest of Q50n,c. A = Mean Annual Flow: § Q · ¨ n ¸ A ¨ ¸ © Qc ¹

Q ,cn = Mean annual flow under natural and current conditions

Note: denominator is always greatest of Q ,cn .

AAPFD = Amended Annual Proportion of Flow Deviation (sum of the ratio of change in monthly flow (current to natural) to average monthly flow):

2 12 §  nc · ¨ ijij ¸ p ¦¨ ¸ i 1 © ni ¹ AAPFD ¦ j 1 p

p = years in the simulation period cij = modelled existing flow for month i in year j. nij = modelled natural flow for month i in year j.

ni mean natural flow for month i across p years.

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Value of AAPFD between 0 for fully unregulated river to 3.46 where there is a 100% increase or decrease in flow. It is also responsive to seasonal changes. The scores are compressed between 0 and 1 using the following rating table developed for the ISC.

AAPFD Rating <0.1 1 0.1 0.9 0.2 0.8 0.3 0.7 0.5 0.6 1.0 0.5 1.5 0.4 2 0.3 3 0.2 4 0.1 >5 0

10.3 Nutrient and suspended sediment load index (using SEDNET)

The nutrient and suspended sediment load index was determined from the SS, TP, and TN measures by taking the worst of the three measures as the overall index. The philosophy underpinning this approach is that if one of the three measures indicates poor condition, then the reach is in poor condition regardless of whether the other two measures have been impacted or not.

Total N and P Indices (TNI and TPI)

55.0 § TNnat · TNI ¨ ¸ © TNcurr ¹

TNnat = Natural Total Nitrogen Load (t/yr)

TNcurr = Current Total Nitrogen Load (t/yr) Same applies for Total Phosphorus.

Suspended Sediment Index (SSI) § NSS · SSI  33.01 log10 ¨ ¸ © CSS ¹ NSS = Natural Suspended Sediment Load (t/yr) CSS = Current Suspended Sediment Load (t/yr) A logarithmic scale was used because of the highly skewed frequency distribution of the CSS/NSS ratio. It remains a partly arbitrary scale because there are few data available that define ecosystem sensitivity to precise levels of suspended sediment.

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10.4 Habitat Index (HI)

10.4.1 Bed Load Condition Sub Index

BCI  33.033.0 log10 CDEP)(

Where: CDEP is the predicted historical accumulation of sand and gravel on the bed. This information can be gained from SEDNET modeling. The bed sediment index varies from a value of 1 for CDEP = 0, through 0.67 for 1 m of deposition, to 0 for 10 m of deposition. A logarithmic transformation of the bed deposition values was used because of the greater impact of initial deposition and because of the distribution of the results, which produced a high frequency of low values of deposition and very few cases above 5 m deposition.

10.4.2 Riparian Sub Index

¾Not expected to change between scenarios Æ will just be used to derive habitat index.

§ Awv250 · RSI ¨ ¸ © Lr uu 210 ¹

(Where RSI = riparian sub-index, Awv-250 = area of woody cover within 250 m of the reach, Lr = length of the link).

10.4.3 Connectivity Sub Index Longitudinal connectivity is important for the migration and breeding of many fish species, and lateral connectivity for movement of water, biota and material across the floodplain.

The connectivity sub-index was calculated as the sum of the deviations of each measure from a pristine condition (see equation below). This approach was taken because the two measures tend to represent connectivity impacts on different parts of the catchment and so should be combined in an additive way.  LongICS LatI  1

(Where CS = connectivity sub-index, LongI = longitudinal connectivity, LatI = lateral connectivity. CS is limited to a minimum of 0). 10.4.3.1. Longitudinal Connectivity Longitudinal connectivity was calculated at the river link level for greater accuracy, and then aggregated to the river reach level. Taking a precautionary approach, the effect of structures up to 40 km upstream and downstream were considered. In this process the algorithm used to calculate connectivity downweighted structures depending on their remoteness from the link being determined. The more remote the structure the lower the influence.  )*()*(  )*()*(  wbwbwbwbwbwb )*()*( LongI wb )*0((1  1 1  2 2 ... 4 4 ) 2 3 5

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(Where LongI = dam impact, b0 indicates a the barrier in the reach, b1 a barrier in the next reach

upstream, b-1 a barrier in the next reach downstream, and wn is the appropriate weight. LongI is limited to a minimum of 0) The structures used were weighted (major structures, weight = 1, locks/sluice gates, weight = 0.5). Weights were based on a judgement of the relative impact of these structures on fish movement. 10.4.3.2. Lateral Connectivity ¾Not expected to change between scenarios Æ will just be used to derive connectivity sub-index. L LatI  (1 l ) Lr 2*

(Where LatI = Lateral connectivity measure, Ll = length of levees in reach, Lr = length of reach. LatI is limited to a minimum of 0).

10.4.4 Catchment Disturbance Index (CDI) CDI = I +LU+ LC - 2 (Where CDI = catchment disturbance index, I = infrastructure measure, LC = land cover change measure, LU = land use measure) In most catchments the land cover change measure is quite small relative to the other two measures. Thus, for the calculation of the catchment disturbance index we required a minimum of the land use and infrastructure measures. Infrastructure Sub Index:

uu 1 wIwII 2211 uu ... (Where I = infrastructure measure, I1 = fraction of the catchment of infrastructure category 1, w1 = the weight for infrastructure category 1 etc) Category ARC infrastructure weights Main sealed road 0.70 Other sealed road 0.70 Railway 0.22 Unsealed road 0.55 Vehicle track 0.55 Utilities (power, pipes) 0.07 Walking track 0

Land Use Sub Index: ¾Not expected to change between scenarios Æ will just be used to derive catchment disturbance index.

LU 1 wFwF 2211 uu ... (Where LU = land use measure, F1 = fraction of the catchment that is category 1 land use, w1 = weight associated with land use 1, etc)

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Audit land use categories ARC categories ARC weights Horticulture, orchards, legumes, cotton, Intensive and irrigated 0.70 rice, non-cereal forage crops agriculture Transport Utilities Urban 0.68 Urban uses Institutional uses Cropping not included in intensive and Dryland cropping 0.48 irrigated agriculture

Production forests Forestry – Eastern 0.20 Farm forestry Australia Plantations Grazing Grazing 0.33 Wilderness area; Protected landscape; Conservation 0 National park; Habitat/species management; Area Strict nature reserve; National monument; Managed resource protected areas; Unmanaged land; Water

10.4.5 Land Cover Change Index ¾Not expected to change between scenarios Æ will just be used to derive catchment disturbance index.

Area u w LCC 1 d Areat

(Where LCC = land cover change measure, Aread = area of catchment in which woody vegetation decreased, Areat = total area of catchment for which there are data, w = weight (0.68))

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11 Hydrology calculations

This appendix describes the methods used to: ¾derive streamflow hydrographs for each of the dam options; ¾derive the current and natural streamflow hydrographs for the selected assessment reaches; and ¾assess the likely impact of the altered hydrology imposed by each of the options on the aquatic ecology.

11.1 Synthesis of Streamflow hydrographs for ACT Water Supply Options

The Water Supply Options assessed are listed below. 1. Cotter Dam Options a. Increase capacity of Cotter Dam to 45 GL b. Increase capacity of Cotter Dam to 76 GL c. Construct Coree Dam upstream of Cotter Dam with 78 GL capacity d. Reduce minimum environmental flows to 90th percentile. 2. Tennent Dam Options a. Construct 45 GL dam b. Construct 76 GL dam c. Construct 164 GL dam d. Virtual dam – measure Gudgenby flows and pump an agreed proportion (35%) from Murrumbidgee River at a downstream site (near Tharwa). 3. Tantangara Dam Options a. Pump water via a pipeline across the Bimberi Range at Murrays Gap to discharge into the Cotter River upstream of Corin Dam. b. Run water for 17 km beside river to Yaouk, then for 10 km along Yaouk Valley and via 1km long tunnel leading into Porcupine or Cribbs Creek, upstream of Corin Dam. c. Run water for 10 km down Murrumbidgee River, then pump through 11 km tunnel leading into Porcupine or Cribbs Creek, upstream of Corin Dam. d. Run water for 17 km down Murrumbidgee River to Yaouk, then for 10 km along Yaouk Valley and via 1 km long tunnel leading into Porcupine or Cribbs Creek, upstream of Corin Dam. e. Release water from dam to flow 100 km down Murrumbidgee River. Then pump through 20 km pipeline from Murrumbidgee River in the ACT to Googong Dam.

11.1.1 Synthesis of streamflows from Cotter and Tennent dams This procedure was used for all the Cotter and Tennent Dam options, except Tennent option 2d (virtual dam) and Cotter option 1d (90 percentile flow releases). 11.1.1.1. Assumptions 1. Minimum environmental flow release from dam would be the 80 percentile, as for existing Bendora and Corin dams. 2. Pan evaporation of 1600 mm / yr with pan evaporation co-efficient of 0.7 (Lawrence 2004).

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3. Yearly evaporation was varied seasonally as follows: Season Evaporation (mm) Annual 1575 Summer 626 Autumn 329 Winter 184 Spring 436

Data Source: CSIRO (2003). Note: daily evaporation was calculated by dividing the seasonal evaporation by the number of days in the season. 4. 100 percent of the inflows to the dam are passed through if the inflow is less than the 80th percentile of inflows. 5. At all other times, a minimum environmental release of the 80th percentile is maintained. 6. The first few years of the record were used to calculate the time taken to fill the dam (likely to be a reasonable approximate). 7. When filling the dam, all flows over and above the 80th percentile of inflows were captured.

8. The pattern of the inflow hydrograph was mimicked for the dam releases. 9. Design probability of failure for the dam = 2% (Lawrence 2004) 10. Daily usage from dam is constant throughout the year (i.e. 11,000 ML per year / 365 days = 30.1 ML/d). 11. Two options for supply from the dams were analysed: (a) Dams are operated such that only supply 11 GL/yr is supplied for consumptive use. Any water available beyond this limit is released as an environmental flow. (b) For Tennent dams only, dams operated for a greater consumptive use equivalent to 80% of the safe yield. This option investigated the effects of possible increases in future demand on the hydrologic variables and associated effects on aquatic ecology.

11.1.1.2. Procedure 1. 80 percentile of inflows computed. 2. Minimum release from dam calculated (= 80th percentile or if inflows < 80th percentile then 100% of the inflows). 3. Time taken to fill dam calculated. Table 11.1 shows the time taken to fill each of the dams identified in the Cotter and Tennent options.

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Table 11.1. Time taken to fill dams, assuming minimum 80% flow release during filling period. Option Description Time taken to fill dam (mths)* 1a Cotter 45 GL dam 9 ++ 1b Cotter 78 GL dam 12 ++ 1c Coree 68 GL dam 11 2a Tennent 45GL dam 14 -- 2b Tennent 76GL dam 23-- 2c Tennent 164GL dam 48-- * Using first few years of record. ++ Assuming existing dam already at capacity (4.7GL) -- Assumes zero evaporation whilst dam is filling 4. The proportion of average annual flow that occurred for each day of the record was calculated for the natural flow regime. This proportion was later used to apportion the dam releases across the year to follow a natural pattern. 5. Average annual volume of water available for release from the dam (over and above the consumptive requirements, evaporative losses and environmental flow requirements was calculated). The Gould – Gamma formula was used (Lawrence 2004).

2 2 >z p Cv @ 2 D 1 >@W u d 4 Cv Where: D = safe draft expressed as a ratio of mean annual flow

Zp = standardised normal variate for the design probability of failure

Cv = Coefficient of variation of annual flows W = storage / mean annual flow ratio d = correction factor

p = probability of failure

The following table was used to determine ‘zp’ and ‘d’: Table 11.2. Correction factors and standardised normal variates Probability of failure Standardised normal Correction factor ‘d’ (p%) variate (zp) 1 2.33 1.5 2 2.05 1.1 5 1.64 0.6 ¾The mean annual flow for use in the calculation of W was defined as the mean annual inflow minus the average 80 percentile of the inflows (i.e. the minimum environmental flow release).

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¾The yield for the dam (Y) is therefore equal to the Draft x Mean annual flow (reduced by the environmental flow)

¾The safe yield for the dam (Ys) was calculated as the Yield minus the Evaporation. ¾The average annual volume of water available for release from the dam was calculated as:

Qavailable = Y – E – C Where:

Qavailable = Average annual volume of water available for release from the dam Y = Yield E = average annual evaporation C = consumptive requirement from dam (~11GL/yr) The Tennent options were also tested for higher consumptive rates (equal to 80% of the safe yield) to determine the sensitivity of the indices calculated to increased use. Table 11.3 shows the Safe Yield and volume available for release as estimated for each of the dam options.

Table 11.3. Safe Yield and Release Volume for Dam options

Option Description Safe Yield [Ys] Volume (GL) available for environmental release [Qavailable] (GL) 1a Cotter 45 GL dam 42.4 31.4 1b Cotter 78 GL dam 50.8 39.8 1c Coree 68 GL dam 42.5 31.5 2a Tennent 45GL dam 29 18.0 2b Tennent 76GL dam 33.9 22.9 2c Tennent 164GL dam 37.7 26.7 2a (C = Tennent 45GL dam 29 5.8 23 GL) 2b (C = Tennent 76GL dam 33.9 6.8 27 GL) 2c (C = Tennent 164GL dam 37.7 7.5 30 GL)

1. The volume of water available for release from the dam was calculated for each day of the record. If the flow into the dam was greater than the 80 percentile of the inflows, then the amount released from the dam was equivalent to the volume available for environmental release multiplied by proportion of natural average annual flow represented by the inflow (calculated in step 4) minus daily evaporation and consumptive use. (It was assumed that daily consumption was constant throughout the year and was equal to 30.1 ML/d). This computation was necessary to ensure that the flow released from the dam resembled the pattern of the natural inflow hydrograph.

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2. The cumulative volume in the dam was calculated for each day of the record. If the cumulative volume was calculated to be within 3ML of the full supply level of the dam, all inflows were allowed to pass through the dam. This rule was put in place to simulate spilling of the dam. The limit of 3ML was selected, as this was the maximum daily inflow recorded at each of the dam sites. If the dam were operated transparently when the capacity was within 3ML of full supply capacity, this would ensure that the dam would not overtop under any conditions and a controlled spilling pattern could be simulated. Figures 11.1.1 to 11.1.9 show the simulated hydrographs for each of the dam options. 3. Natural hydrographs for Cotter Dam options were calculated from summing Gingera gauge inflows, Bendora sub-catchment inflows and Cotter sub-catchment inflows.

Cotter Dam Outflow Hydrograph Cotter Dam Outflow Hydrograph (45 GL dam) (78 GL dam) 9000.00 Cotter Natural inflows 9000.00 Cotter current inflows Cotter Natural inflows 8000.00 Volume released from dam (Cotter 45 GL) Cotter current inflows 8000.00 Volume released from dam (Cotter 78 GL) 7000.00 7000.00

6000.00 6000.00

5000.00 5000.00

4000.00

Flow (ML/day) Flow 4000.00 Flow (ML/day) Flow 3000.00 3000.00

2000.00 2000.00

1000.00 1000.00

0.00 0.00 18-Feb-82 14-Nov-84 11-Aug-87 7-May-90 31-Jan-93 28-Oct-95 24-Jul-98 18-Feb-82 14-Nov-84 11-Aug-87 7-May-90 31-Jan-93 28-Oct-95 24-Jul-98 Date Date

Corree Dam Outflow Hydrograph Tennent Dam Outflow Hydrograph (68 GL dam) (45 GL) 18000.00 9000.00 Tennent Dam Natural Inflows Cotter Natural inflows 16000.00 Volume released from dam (45 GL) Cotter current inflows 8000.00 Volume released from dam (Corree 68 GL) 14000.00 7000.00

12000.00 6000.00

10000.00 5000.00

8000.00 4000.00 Flow (ML/d) Flow (ML/day) 6000.00 3000.00

4000.00 2000.00

2000.00 1000.00

0.00 0.00 18-Feb-82 14-Nov-84 11-Aug-87 7-May-90 31-Jan-93 28-Oct-95 24-Jul-98 18-Feb-82 14-Nov-84 11-Aug-87 07-May-90 31-Jan-93 28-Oct-95 24-Jul-98 Date Date

Tennent Dam Outflow Hydrograph Tennent Dam Outflow Hydrograph (76 GL) (164 GL)

18000.00 18000.00 Tennent Dam Natural Inflows Tennent Dam Natural Inflows Volume released from dam (76 GL) Volume released from dam (164 GL) 16000.00 16000.00

14000.00 14000.00

12000.00 12000.00

10000.00 10000.00

8000.00 8000.00 Flow (ML/d) Flow (ML/d) Flow

6000.00 6000.00

4000.00 4000.00

2000.00 2000.00

0.00 0.00 18-Feb-82 14-Nov-84 11-Aug-87 07-May-90 31-Jan-93 28-Oct-95 24-Jul-98 18-Feb-82 14-Nov-84 11-Aug-87 07-May-90 31-Jan-93 28-Oct-95 24-Jul-98 Date Date

Tennent Dam Outflow Hydrograph Tennent Dam Outflow Hydrograph (45 GL with 23GL/yr consumptive use) (76 GL with 27GL/yr consumptive use)

18000.00 18000.00 Tennent Dam Natural Inflows Tennent Dam Natural Inflows Volume released from dam (45 GL) Volume released from dam (76 GL) 16000.00 16000.00

14000.00 14000.00

12000.00 12000.00

10000.00 10000.00

8000.00

Flow (ML/d) Flow 8000.00 Flow (ML/d)

6000.00 6000.00

4000.00 4000.00

2000.00 2000.00

0.00 18-Feb-82 14-Nov-84 11-Aug-87 07-May-90 31-Jan-93 28-Oct-95 24-Jul-98 0.00 Date 18-Feb-82 14-Nov-84 11-Aug-87 07-May-90 31-Jan-93 28-Oct-95 24-Jul-98 Date

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Tennent Dam Outflow Hydrograph (164 GL with 30GL/yr consumptive use)

18000.00 Tennent Dam Natural Inflows Volume released from dam (164 GL) 16000.00

14000.00

12000.00

10000.00

8000.00 Flow (ML/d)

6000.00

4000.00

2000.00

0.00 18-Feb-82 14-Nov-84 11-Aug-87 07-May-90 31-Jan-93 28-Oct-95 24-Jul-98 Date

Figures 11.1.1 – 11.1.9: Simulated outflow hydrographs for Cotter and Tennent Dam options

11.1.2 Synthesis of streamflows from Tantangara Dam 11.1.2.1. Assumptions 1. Losses between Tantangara Dam and Tharwa pumping station total 10 cusecs (this included evaporation, groundwater loss, water pumped by farmers and Cooma town water supply) (SMHEA 1968). This is equivalent to 0.283 m3/s or 8.9 GL/yr. This is likely to be a conservative estimate, as the losses were calculated under drought conditions. 2. Planned environmental flow releases of 28 GL/year from Tantangara Reservoir would occur from 2006, and these would be additive to any water supplied for Canberra consumption. 3. Water released from Tantangara dam for environmental flows is consistent with the pattern for natural inflows to the dam.

4. Water released from Tantangara Dam to supplement Canberra’s water supply could either be released in accordance with the environmental flow release seasonal patterns or released at a constant rate each month. Both scenarios have been modelled. 11.1.2.2. Procedure a. The proportion of average annual flow that occurred for each month of the record was calculated for the natural inflows. This proportion was used to apportion the environmental flows and seasonal ACT water supply options across the year to follow a natural pattern. b. Several different scenarios for flow releases from Tantangara were synthesised:

¾Environmental flow release only (corresponding to 28 GL/yr) ¾Environmental flow release + 11 GL/yr required to supplement Canberra Water supply released seasonally using the proportions calculated in step a (i.e. outflow hydrology for Tantangara options 3c and 3d) ¾Environmental flow release + 11 GL/yr required to supplement Canberra Water supply released at a constant rate throughout the year (i.e. outflow hydrology for Tantangara options 3c and 3d) ¾Environmental flow release + 11 GL/yr required to supplement Canberra water supply + 8.9GL/yr required to overcome maximum losses between Tantangara dam and Tharwa, released seasonally using the proportions calculated in step a (i.e. outflow hydrology for Tantangara option 3e) ¾Environmental flow release + 11 GL/yr required to supplement Canberra water supply + 8.9GL/yr required to overcome maximum losses between Tantangara dam and Tharwa,

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released at a constant rate throughout the year (i.e. outflow hydrology for Tantangara option 3e) c. Natural hydrographs for Tantangara were derived from modelled data developed in NLWRA1. Figures 11.2.1 – 11.2.5 show the outflow hydrographs for each situation described in b above.

Tantangarra Dam Outflow Hydrograph Tantangarra Dam Outflow Hydrograph (28GL/yr environemental flows only) (28GL/yr environemental flows + 11GL/yr Canberra water supply released seasonally) 140 Natural 140 Current Natural Total monthly flow (Eflow only) Current 120 120 Total monthly flow (Opt 3c,d) - seasonal

100 100

80 80 Flow (GL) Flow 60 (GL) Flow 60

40 40

20 20

0 0 18-Feb-82 14-Nov-84 11-Aug-87 7-May-90 31-Jan-93 28-Oct-95 24-Jul-98 18-Feb-82 14-Nov-84 11-Aug-87 7-May-90 31-Jan-93 28-Oct-95 24-Jul-98 Date Date

Tantangarra Dam Outflow Hydrograph Tantangarra Dam Outflow Hydrograph (28GL/yr environemental flows + 11GL/yr Canberra water supply + Losses between Tantangarra and Tharwa) (28GL/yr environemental flows + 11GL/yr Canberra water supply released at constant rate)

140 140 Natural Natural Current Current 120 Total monthly flow (option 3e) 120 Total monthly flow (Opt 3c,d) - const

100 100

80 80 Flow (GL) Flow Flow (GL) Flow 60 60

40 40

20 20

0 0 18-Feb-82 14-Nov-84 11-Aug-87 7-May-90 31-Jan-93 28-Oct-95 24-Jul-98 18-Feb-82 14-Nov-84 11-Aug-87 7-May-90 31-Jan-93 28-Oct-95 24-Jul-98 Date Date

Tantangarra Dam Outflow Hydrograph (28GL/yr environemental flows + 11GL/yr Canberra water supply released at constant rate + Losses between Tantangarra and Tharwa)

140 Natural Current Total monthly flow (option 3e) - const 120

100

80

Flow (GL) Flow 60

40

20

0 18-Feb-82 14-Nov-84 11-Aug-87 7-May-90 31-Jan-93 28-Oct-95 24-Jul-98 Date

Figures 11.2.1 – 11.2.5: Simulated outflow hydrograph for Tantangara Dam Options

11.2 Synthesis of streamflow hydrographs for assessment reaches

11.2.1 Location Key reaches along the Murrumbidgee, Gudgenby and Cotter rivers were selected for the aquatic ecology assessments (as shown in Figure 11.3). These reaches were: Site A: Murrumbidgee River downstream of Tantangara Dam to Yaouk; Site B: Murrumbidgee River – Mittagang Crossing to Numeralla River confluence; Site C: Murrumbidgee River – confluence of Gudgenby River to Tharwa; Site D: Murrumbidgee River – confluence of Cotter River to confluence of Molonglo River; Site E: Murrumbigee River – confluence of Molonglo River to Hall’s Crossing; Site F: Cotter River downstream of Cotter Dam;

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Site G: Gudgenby River downstream of Tennent Dam; and Site H: Porcupine Creek. Note: The methods used to determine the hydrographs for assessment reaches A, F and G are outlined in sections 11.1.1 and 11.1.2.

Figure 11.3. Reaches selected for ecological assessment

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11.2.2 Assumptions Several assumptions were necessary to enable computation of monthly hydrographs for each of the assessment reaches. All data, with the exception of natural Tantangara outflows and natural Lobbs Hole flows, were estimated from observed gauge data. The gauging stations, which were used to calculate the streamflow hydrographs, are also shown in Figure 11.3. The assumptions used for these calculations are listed below: 1. Site B: a. Losses between Tantangara Dam and Mittagang Crossing total 3 cusecs (SMHEA 1968). This is equivalent to 0.085 m3/s or 2.64 GL/yr. This is also likely to be a conservative estimate. b. Losses were apportioned in a similar seasonal pattern to natural flows. c. Natural flow at Mittagang Crossing is equal to current flow + natural outflows from Tantangara Reservoir – current outflows from Tantangara Reservoir. 2. Site C: i. Flow = Lobbs Hole flow + Gudgenby inflows. ii. Modelled natural flow for Lobbs Hole calculated during NLWRA1. 3. Site D:

i. There are negligible losses between Gudgenby confluence and Molonglo confluence. ii. Travel time from the Gudgenby confluence to Molonglo confluence is less than 1 day (necessary for calculating natural flows at Mt McDonald from Lobbs Hole).

iii. Flow = Murrumbidgee River @ Mt McDonald flow + Paddys River @ Riverlea flow + Cotter Releases. iv. Current and natural flows in Paddys River are similar (i.e. there are low levels of extraction and consumptive use in the Paddys River catchment). v. Natural flow = modelled natural flow at Lobbs Hole + Paddys River @ Riverlea flows + Cotter natural flows.

4. Site E: i. Flow = Flow at site D + Molonglo inflows (Coppins Crossing Flows + inputs from Lower Molonglo Water Quality Centre). ii. The Lower Molonglo Water Quality Centre currently discharges 90ML/d into the Molonglo River downstream of Coppins Crossing. iii. Discharges from the LMWQC are constant throughout the year and will remain so with implementation of any of the ACT water supply options. iv. An additional 6GL/yr (2.2 ML/d) will be discharged from the LMWQC for any of the ACT water supply options. v. There are negligible inflows into the Molonglo River downstream of Coppins Crossing. vi. Flow captured by Googong dam can be approximated by subtracting outflows (410701) from inflows (410781).

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vii. There are negligible flow losses from the Molonglo River beteween the confluence of the Queanbeyan River to the confluence with the Murrumbidgee River. (i.e. there are negligible evaporative losses from Lake Burley Griffin and extraction of water along the Molonglo River for stock and domestic use). viii. There are negligible flow losses from the Queanbeyan River from Tinderry gauging station to the confluence with the Molonglo River (excluding water captured by Googong Dam). Assumptions f and g are necessary to enable calculation of natural flows at Coppins Crossing. (i.e. there is negligible extraction of water along the Queanbeyan River for stock and domestic use). ix. The monthly volume of water harvested by Googong Dam is equal to the difference in volume flowing past the gauge upstream of Googong Dam (410781) and the gauge downstream of Googong Dam (410701). An inherent assumption is that the inflows and extractions between the gauging stations and the dam are negligible. x. There are linear relationships between the flows at the two gauges downstream of Googong Dam (410701 – Queanbeyan River d/s Googong Dam and 410760 – Queanbeyan River at Wickerslake Lane). This enables the gauge record from 410701 to be infilled using a regression relationship with measured flows at 410760. xi. There are linear relationships between the flows at the two gauges upstream of Googong Dam (410781 – Queanbeyan River u/s Googong Dam and 410766 – Queanbeyan River upstream of Tinderry). This enables the gauge record from 410781 prior to 1990 to be calculated using a regression relationship with measured flows at 410766.

xii. There is a linear relationship between the flow recorded at Coppins Crossing (410756) and the Oaks (410729) on the Molonglo River. This enables the gauge record from 410756 to be estimated for1976 and 1977 using a regression relationship with measured flows at 410729.

5. Site H: i. The rainfall and runoff characteristics of Porcupine Creek are similar to those of the Upper Cotter River, enabling a linear relationship between catchment area and mean annual flow to be used to predict flows in Porcupine Creek. ii. The seasonal flow pattern in Porcupine Creek is identical to that of the Cotter River at Gingera gauging station.

11.2.3 Procedure It was necessary to determine both the natural and current monthly streamflow hydrographs for each assessment reach to enable calculation of the hydrology indices that relate changes in hydrologic regime to aquatic ecology outcomes. 1. Site B: Mittagang Crossing Three streamflow hydrographs were computed for Mittagang Crossing (Figures 16-20): ¾natural flow; ¾flow from implementation of Tantangara option 3e released seasonally + environmental flow releases from Tantangara; ¾flow from implementation of Tantangara option 3e released at a constant rate throughout the year + environmental flow releases from Tantangara;

¾flow from implementation of environmental flow releases from Tantangara only.

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The second, third and fourth hydrographs were computed by adding the Tantangara Dam releases to the current flows and subtracting losses between Tantangara Dam and Mittagang Crossing (assumption 1a). The losses were apportioned in a similar pattern to the streamflow. This resulted in greater losses during the higher flow months, which, although not observed in practice, was the only assumption that could be made with the data available at the time of the assessment. It should be noted that the losses are relatively small in comparison to the average annual discharge predicted to occur with the proposed environmental flow releases and Canberra water supply (1.4 %). This assumption is therefore unlikely to affect the hydrology indices calculated in the section below.

2. Site C: Murrumbidgee River – Gudgenby confluence to Tharwa. Nine streamflow hydrographs were computed for this reach: ¾natural flow (NLWRA1 Lobbs Hole modelled natural flow + current Gudgenby inflows); ¾current flow (Lobbs Hole measured flows + Gudgenby measured flows); ¾flow from implementation of Tennent option 2a – 11 GL use;

¾flow from implementation of Tennent option 2b – 11 GL use; ¾flow from implementation of Tennent option 2c – 11 GL use; ¾flow from implementation of Tennent option 2d;

¾flow from implementation of Tennent option 2a – 23 GL use; ¾flow from implementation of Tennent option 2b – 27 GL use; ¾flow from implementation of Tennent option 2c – 30 GL use.

The last seven hydrographs were computed by summing the Lobbs Hole observed flows with the dam outflows computed for the various options.

3. Site D: Murrumbidgee River – Cotter confluence to Molonglo confluence. Thirteen streamflow hydrographs were computed for this reach: ¾natural flow (NLWRA1 Lobbs Hole modelled natural flow + current Paddys River inflows + Modelled natural Cotter River flows); ¾current flow(Mt McDonald measured flows + Cotter measured flows); ¾flow from implementation of Tennent option 2a – 11 GL use; ¾flow from implementation of Tennent option 2b – 11 GL use; ¾flow from implementation of Tennent option 2c – 11 GL use; ¾flow from implementation of Tennent option 2d; ¾flow from implementation of Tennent option 2a – 23 GL use; ¾flow from implementation of Tennent option 2b – 27 GL use; ¾flow from implementation of Tennent option 2c – 30 GL use; ¾flow from implementation of Cotter option 1a – 11 GL use;

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¾flow from implementation of Cotter option 1b – 11 GL use; ¾flow from implementation of Cotter option 1c – 11 GL use; ¾flow from implementation of Cotter option 1d. The hydrographs for both the Cotter and Tennent options were computed by subtracting the difference between current and predicted flows in the Cotter and Gudgenby rivers from the current flows measured at Mt McDonald on the Murrumbidgee River. For example, for Cotter

option 1a, the flow for Site D (QSiteD) is:

SiteD QQ MtMcDonald  (QCotter _ current  QCotter GL _45_ Dam )

4. Site E: Murrumbigee River – confluence of Molonglo River to Hall’s Crossing. Fourteen streamflow hydrographs were computed for this reach: ¾natural flow (Estimated natural flow at Site D + Current flow at Coppins Crossing + estimated flows captured by Googong Dam); ¾current flow(Site D measured flows + estimated Molonglo River inflows); ¾flow from implementation of Tennent option 2a – 11 GL use;

¾flow from implementation of Tennent option 2b – 11 GL use; ¾flow from implementation of Tennent option 2c – 11 GL use; ¾flow from implementation of Tennent option 2d;

¾flow from implementation of Tennent option 2a – 23 GL use; ¾flow from implementation of Tennent option 2b – 27 GL use; ¾flow from implementation of Tennent option 2c – 30 GL use;

¾flow from implementation of Cotter option 1a – 11 GL use; ¾flow from implementation of Cotter option 1b – 11 GL use; ¾flow from implementation of Cotter option 1c – 11 GL use;

¾flow from implementation of Cotter option 1d; ¾flow from implementation of any of the Tantangara options.

i) Natural Flows: As there was no natural flow data available for the Molonglo River downstream of Coppins Crossing, a method for synthesising this data was derived: ¾It was assumed that natural flows would be equivalent to current flows minus any flow captured by Googong Dam. This assumption is likely to result in an underestimation of the natural flows, as it does not take into account other extractions, which currently occur along the Molonglo or Queanbeyan Rivers. ¾The flow captured by Googong Dam was calculated as the difference in monthly flow between the inflow gauge (410781) and the outflow gauge (410701). ¾A continuous flow record between 1975 and 1999 was required, as this was the gauge period used for hydrologic computations at the other assessment sites. The gauge site

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upstream of Googong Dam (410781) did not have a continuous record until 1990, however the gauge further upstream (410766) had a record extending from before 1975 until present. The record for 410781 was extended from 1990 to 1975 using the gauge data from 410766 as follows: i. For the overlapping period of the two gauges, the proportion of flow recorded at the upstream gauge relative to the downstream gauge was computed. ii. This series of monthly flow proportions was then copied to corresponding months for the missing period of record for gauge 410781. iii. The monthly flow for 410781 was then calculated by dividing the flow recorded at 410766 by the estimated monthly flow proportion calculated in (i) and (ii). A similar procedure was used to infill the gauging record for the site immediately downstream of Googong Dam (410701) using measured flows from Wickerslake Lane (410760) and two years of overlapping records. The record at Coppins Crossing (410756) was also extended, using the above procedure, from 1978 to 1975 using gauging data from the Oaks gauge (410729) further upstream.

ii) Current Flows:

¾The current flows in the Murrumbidgee River downstream of the Molonglo River

confluence (Qds_Mol) were calculated as follows:

_ Molds SiteD  (QQQ Coppins Cros _sin_ currentg  QLMWQC _ inf low )

iii) Water supply options:

The hydrographs the various water supply options were computed adding the additional inflows from the LMWQC to the flows calculated for Site D. For the Tantangara options, the LMWQC flows were added to the estimated current flows at Site D.

5. Site H: Porcupine Creek Three streamflow hydrographs were computed for this reach: ¾natural flow (Estimated using area – volume relationship from flows measured in the Cotter River @ Gingera); ¾flow from implementation of Tantangara options 3a – d, assuming a constant rate of supply of the 11GL required for Canberra’s water supply; ¾flow from implementation of Tantangara options 3a – d, assuming a variable rate of supply of the 11GL required for Canberra’s water supply based on the pattern of natural flows to Tantangara Reservoir; a) The catchment area of Porcupine Creek was calculated from a 1:25,000 topographic map coverage (12km2).

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b) The catchment area of the Cotter River upstream of Gingera gauge was obtained from the gauge site description (129km2). c) The mean annual flow for Gingera gauge was determined as a proportion of the catchment area (178 ML/yr/km2) d) Mean annual flow for Porcupine Creek was estimated by multiplying the value calculated in ‘c’ above, by the catchment area of Porcupine Creek, calculated in ‘a’ above [4537ML/yr] e) A monthly time series for flow in Porcupine Creek was developed from the recorded flows in the Cotter River at Gingera. The recorded flow at Gingera was multiplied by the average annual flow in Porcupine Creek relative to the Cotter River at Gingera:

MAFPorcupineCk QPorcupineCk Gingerra xQ MAFGingerra

Where: Q = monthly flow (ML/d); MAF = Mean Annual Flow (ML/d) f) The second and third hydrographs were calculated by adding the predicted releases from Tantangara Dam for the ACT water supply to the estimated current flows in Porcupine Creek.

11.3 Calculation of Hydrology Indices

Several hydrology indices were developed for the Assessment of River Condition component of the first National Land and Water Resources Audit (NLWRA). These indices comprised the elements of the flow regime that were considered important to aquatic biota, and as such the indices provide a direct indication of the likely effect of changes to hydrologic regime on the aquatic biota. These indices and the individual measures that comprise them were further refined during the Pilot phase of the Sustainable Rivers Audit (SRA). An assessment of the likely affect on aquatic biota caused by changes to the hydrologic regime imposed by the various ACT water supply options has been undertaken. This assessment included a comparison between the SRA and NLWRA indices. Although the SRA indices are considered to more effectively describe the likely hydrologic impacts on the biota, two of the five indices rely on the existence of daily data. Daily data has not been available at all of the assessment sites, therefore, the indices requiring computation from daily data have been calculated using monthly data. It was unclear whether the use of the indices in this way, using this lower resolution data, would affect the overall assessment of the impact of the altered hydrologic regimes on the aquatic ecosystem. Therefore, the NLWRA1 indices, which used only monthly data, were also calculated for each assessment site to enable comparison and identification of any errors caused by using the monthly data in the SRA daily indices. Both the SRA and NLWRA hydrology indices provide an indication of the current or future hydrologic condition relative to natural. Natural hydrographs were therefore calculated for each of the assessment reaches using the procedures outlined in sections 1 and 2. The assessments were generally undertaken for the period between 1975 and 1999. This period was restricted by the availability of current and modelled natural streamflow data. For the Cotter options, assessments were undertaken using hydrographs from 1965 to present, as the length of continuous record was sufficient to permit this. It is unlikely that the difference in period used for calculation of the hydrology indices will affect the value of the indices themselves.

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11.3.1 Procedure (a) SRA Indices The hydrology component of the Sustainable Rivers Audit consists of: ¾An overall index; ¾5 sub-indices which describe key components of the hydrologic regime; ¾13 individual measures that comprise the 5 sub-indices. These indices are further described below.

Overall Hydrologic Index

For the Pilot SRA, a sigmoid function was used to combine individual indicators into indices as the relationship was believed to be non-linear. For the assessment of the ACT Water Supply options, a linear function was used for simplicity. This linear function uses the weightings developed in the SRA for the various indices and is represented by:

HI HIlz 28.033.0 HIhf HIv HI s 07.013.020.0 uuuuu HIvol

Where: HIlz = low and zero flow sub-index HIhf = high flow events sub-index HIv = flow variability sub-index HIs = seasonality sub-index HIvol = flow volume sub-index

i) High flow events sub-index §  ARIARIARI 1052 · HIhf ¨ ¸ © 3 ¹ Where:

ARIn = 1:2,1:5, 1:10 year ARI flood indicator (HFEN)

min( NN ), HFEN cn max( NN cn ),

Nn, Nc = number of event exceedences (1:2, 1:5, 1:10) under natural and current conditions. An event is defined as independent if it is separated by 5 days or more of lower flows. ii) Low flow and zero flow sub-index

HIlz 5.0 LFEN 3.0 LFED 2.0 uuu Zd

Where: LFEN = Low flow event number indicator: min( NN ), LFEN cn max( NN cn ),

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th Nn, Nc = number of event exceedences < the natural 90 percentile of non-zero flows under natural and current conditions. An event is defined as independent if it is separated by 5 days or more of lower flows.

LFED = Low flow event duration indicator:

min( NN ), LFED cn max( NN cn ),

th Nn, Nc = mean duration of event exceedences < the natural 90 percentile of non-zero flows under natural and current conditions. An event is defined as independent if it is separated by 5 days or more of lower flows.

Zd = difference in proportion of zero flow days indicator:

§ § Z Z ·· Z 1 ¨ ABS¨ c  n ¸¸ d ¨ ¨ ¸¸ © © days days ¹¹

Zc, Zn = number of zero flow days under current and natural conditions Days = total number of days in record iii) Flow variability sub-index

HIv SA u 4.06.0 AV

Where: SA = Seasonal Amplitude: h l c  c h l SA n n 2 h = highest mean monthly flow l = lowest mean monthly flow for current ( c ) and natural ( n ) conditions. Note: denominator is always larger of c and n.

AV = Annual Variation AVC AV n AVCc

AVCn, c = Annual coefficient of variation, under natural and current conditions. iv) Seasonality sub-index ­ª 1 º ª 1 º½ 1 HIs ®« ¦ MIN ;YHNYHC ii »  « ¦ MIN ;YLNYLC ii »¾ ¯¬M i 1 ¼ ¬M i 1 ¼¿ 2

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Where: YHC/ YHN = number of years the ith month has the peak annual flow under current / natural conditions

YLC/ YLN = number of years the ith month has the minimum annual flow under current / natural conditions M = number of years in flow data set. v) Flow volume sub-index

HIvol Med A 2.03.05.0 uuu AAPFD

Where: Med = Median Annual Flow:

§ Q50n · Med ¨ ¸ © Q50c ¹

Q50n,c = Median annual flow under natural and current conditions

Note: denominator is always greatest of Q50n,c. A = Mean Annual Flow:

§ Q · ¨ n ¸ A ¨ ¸ © Qc ¹

Q ,cn = Mean annual flow under natural and current conditions

Note: denominator is always greatest of Q ,cn .

AAPFD = Amended Annual Proportion of Flow Deviation (sum of the ratio of change in monthly flow (current to natural) to average monthly flow):

2 12 §  nc · ¨ ijij ¸ p ¦¨ ¸ i 1 © ni ¹ AAPFD ¦ j 1 p

p = years in the simulation period cij = modelled existing flow for month i in year j. nij = modelled natural flow for month i in year j.

ni mean natural flow for month i across p years.

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The value of AAPFD varies between 0 for fully unregulated rivers and 3.46 where there is a 100% increase or decrease in flow. It is also responsive to seasonal changes. The scores are compressed between 0 and 1 using the following rating table developed for the Victorian Index of Stream Condition.

AAPFD Rating <0.1 1 0.1 0.9 0.2 0.8 0.3 0.7 0.5 0.6 1.0 0.5 1.5 0.4 2 0.3 3 0.2 4 0.1 >5 0

b) NLWRA Indices The hydrology component of the Assessment of River Condition used in the first NLWRA consists of:

¾An overall index; ¾4 sub-indices which describe key components of the hydrologic regime; ¾12 individual measures that comprise the 4 sub-indices.

These indices are further described below. Overall Hydrologic Index

SP 2 SA 2 111 FDC 2 1 A 2 HI 1 4

i) Seasonal Period Indicator (SP) This indicator uses the mean flow for each of the 12 months of the year over the entire time series. The indicator was defined as the difference from one of the sum of the differences between the numerical values of the months with the highest mean monthly flow (H) and the numerical values of the months with the lowest mean monthly flow (L) for current and natural conditions (subscript c and n respectively), divided by 12:

1 SP 1 if HH d 6 then  HH else, lookuptable if LL d 6 then  LL , else lookuptable 12 nc nc nc nc

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Lookup table: if then = 7 5 8 4 9 3 10 2 11 1

ii) Seasonal Amplitude Indicator (SA) The seasonal amplitude index (SA) assesses the change in amplitude of the seasonal pattern of monthly flows. It is defined as the average of two current to natural ratios, firstly, that of the

highest monthly flows (hc:hn), and secondly, that of the lowest monthly flows (lc:ln) based on calendar month means. Each of these ratios is defined as being less than or equal to 1, so in each case the denominator is the larger of current and the natural value.

h l c  c h l SA n n 2

h = highest mean monthly flow

l = lowest mean monthly flow for current ( c ) and natural ( n ) conditions. Note: denominator is always larger of c and n. iii) Flow Duration Curve Difference Indicator (FDC)

The flow duration curve difference index (FDC) is the difference from 1 of the proportional flow deviation, averaged over p monthly flow percentile points. FDC gives equal weighting each percentile flow from the lowest flow to the highest flow and provides a measure of the overall difference between current and natural flow duration curves.

1 p c 1 p n If n > c FDC ¦ i else FDC ¦ i p i 1 ni p i 1 ci

Where: P = Number of percentiles (11 evenly spaced percentiles were used for this assessment – 0%, 10%, 20% … 100%)

ci = Current flow at the ith percentile (ML/month)

ni = Natural flow at the ith percentile (ML/month)

iv) Mean annual flow indicator (A)

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§ Q · ¨ n ¸ A ¨ ¸ © Qc ¹

Q ,cn = Mean annual flow under natural and current conditions

Note: denominator is always greatest of Q ,cn .

Results: The component sub-indices and overall hydrology indices were calculated for each assessment reach using both the SRA and NLWRA1 methods described above. Table 11.4 shows the results. Note: SRA high flow and low/zero flow indices have been used with monthly data, but originally developed for daily data --> may not be valid in all cases.

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Table 11.4. Summary of Hydrology Indices for each Assessment Reach

Site G - Gudgenby River d/s Tennent Dam

Tennent Dam Tennent Dam Tennent Dam (45GL) - (76GL) - 27 GL (164GL) - 30 GL Tennent Dam Tennent Dam Tennent Dam 22 GL demand (80% demand (80% of demand (80% of Index (45GL) (76GL) (164GL) of safe yield) safe yield) safe yield) SRA (high flow) 0.92 0.83 0.68 0.68 0.40 0.36 SRA (low/zero flow) 1 1 1 1.00 1.00 1.00 SRA (variability) 0.85 0.84 0.86 0.72 0.69 0.70 SRA (seasonality) 0.59 0.6 0.6 0.46 0.41 0.41 SRA (volume) 0.69 0.68 0.67 0.50 0.47 0.45 SRA (overall) 0.88 0.86 0.82 0.76 0.67 0.66 NLWRA1 (Seas Period) 1 1 1 0.83 0.92 0.83 NLWRA1 (Seas Amp) 0.83 0.81 0.82 0.65 0.57 0.55 NLWRA1 (Flow dur. Cve) 0.84 0.86 0.88 0.73 0.70 0.69 NLWRA1 (Mean Ann. Flow) 0.82 0.82 0.81 0.66 0.60 0.56 NLWRA1 (overall) 0.69 0.69 0.69 0.56 0.52 0.50

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Site F - Cotter River downstream of Cotter Dam

Cotter Cotter Dam Dam Corree Dam (68 Cotter dam (with Cotter Dam Index (45 GL) (76GL) GL) 90% eflows) (current) SRA (high flow) 0.46 0.29 0.29 0.68 0.96 SRA (low/zero flow) 1 1 1 1 1 SRA (variability) 0.53 0.55 0.55 0.46 0.6 SRA (seasonality) 0.5 0.46 0.46 0.54 0.67 SRA (volume) 0.36 0.38 0.38 0.39 0.52 SRA (overall) 0.65 0.61 0.61 0.71 0.72 NLWRA1 (Seas Period) 0.92 0.92 0.92 0.92 0.92 NLWRA1 (Seas Amp) 0.43 0.43 0.43 0.37 0.5 NLWRA1 (Flow dur. Cve) 0.36 0.36 0.35 0.22 0.42 NLWRA1 (Mean Ann. Flow) 0.47 0.47 0.47 0.45 0.56 NLWRA1 (overall) 0.38 0.38 0.38 0.33 0.43

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Site A - Murrumbidgee River downstream of Tantangara Dam to Yaouk Tantangara Dam with Tantangara Dam Tantangara Dam Tantangara Dam eflows + with eflows + with eflows + with eflows + Canberra water const Canberra const Canberra Canberra water supply (Opt3c, Tantangara water supply water supply supply (Opt3e) d) flow to dam with Tantangara (Opt3e) flow to (Opt3c,d) flow to Index flow to Tharwa Yaouk eflows Dam (current) Tharwa Yaouk SRA (high flow) 0.00 0.00 0.00 0.00 0.00 0.00 SRA (low/zero flow) 0.27 0.24 0.19 0.10 0.00 0.41 SRA (variability) 0.61 0.58 0.54 0.09 0.45 0.44 SRA (seasonality) 0.91 0.90 0.77 0.04 0.87 0.87 SRA (volume) 0.18 0.15 0.11 0.03 0.18 0.15 SRA (overall) 0.34 0.32 0.28 0.06 0.22 0.35 NLWRA1 (Seas Period) 1.00 0.92 0.92 0.33 0.92 0.92 NLWRA1 (Seas Amp) 0.25 0.22 0.17 0.01 0.37 0.28 NLWRA1 (Flow dur. Cve) 0.32 0.27 0.20 0.00 0.35 0.31 NLWRA1 (Mean Ann. Flow) 0.19 0.16 0.11 0.01 0.19 0.16 NLWRA1 (overall) 0.29 0.27 0.24 0.07 0.33 0.30

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Site C - Murrumbidgee River - confluence of Gudgenby River to Tharwa

Tennent Dam Tennent Dam Tennent Dam (164GL) - 30 Tennent (45GL) - 22 GL (76GL) - 27 GL GL demand Tennent Dam Tennent Dam Dam demand (80% demand (80% of (80% of safe Index Current (45GL) (76GL) (164GL) of safe yield) safe yield) yield) SRA (high flow) 0.95 0.94 0.94 0.95 0.83 0.81 0.81 SRA (low/zero flow) 0.94 0.94 0.97 1.00 0.94 0.94 0.94 SRA (variability) 0.95 0.91 0.91 0.92 0.90 0.89 0.88 SRA (seasonality) 0.63 0.63 0.63 0.63 0.63 0.60 0.63 SRA (volume) 0.80 0.75 0.74 0.74 0.72 0.72 0.71 SRA (overall) 0.90 0.89 0.90 0.91 0.85 0.84 0.84 NLWRA1 (Seas Period) 0.83 0.83 0.83 0.83 0.83 0.83 0.83 NLWRA1 (Seas Amp) 0.88 0.88 0.88 0.89 0.87 0.85 0.84 NLWRA1 (Flow dur. Cve) 0.95 0.95 0.95 0.95 0.93 0.92 0.92 NLWRA1 (Mean Ann. Flow) 0.98 0.98 0.98 0.98 0.96 0.95 0.94 NLWRA1 (overall) 0.86 0.86 0.86 0.86 0.82 0.80 0.79

Document No: 4682 - Aquatic Ecology 134 Final ACT Future Water Options

Site B - Murrumbidgee River - Mittagang Crossing to Numeralla River confluence

Tantangara Dam Tantangara Dam with eflows + Tantangara Dam with eflows + constant with eflows (opt Canberra water Canberra water Index Current 3e) supply (opt 3e) supply (opt 3e) SRA (high flow) 0.03 0.04 0.04 0.04 SRA (low/zero flow) 0.34 0.39 0.45 0.48 SRA (variability) 0.56 0.60 0.65 0.72 SRA (seasonality) 0.74 0.81 0.81 0.81 SRA (volume) 0.30 0.35 0.39 0.39 SRA (overall) 0.35 0.39 0.42 0.45 NLWRA1 (Seas Period) 1.00 1.00 1.00 1.00 NLWRA1 (Seas Amp) 0.40 0.43 0.48 0.55 NLWRA1 (Flow dur. Cve) 0.34 0.42 0.49 0.50 NLWRA1 (Mean Ann. Flow) 0.34 0.40 0.45 0.45 NLWRA1 (overall) 0.35 0.39 0.42 0.44

Document No: 4682 - Aquatic Ecology 135 Final ACT Future Water Options

Site D - Murrumbidgee River - confluence of Cotter River to confluence of Molonglo River

Tennent Tennent Tennent Dam Dam Dam (45 GL - (76 GL - (164 GL - 22 GL) 27 GL) 30 GL) Cotter demand demand demand Cotter Cotter Dam (with Tennent Tennent (80% of (80% of (80% of Dam (45 Dam 90% Dam Tennent Dam safe safe safe Index Current GL) (76GL) eflows) (45GL) Dam (76GL) (164GL) yield) yield) yield) SRA (high flow) 0.93 0.92 0.93 0.92 0.93 0.93 0.93 0.90 0.93 0.90 SRA (low/zero flow) 0.58 0.58 0.58 0.50 0.60 0.60 0.60 0.58 0.58 0.58 SRA (variability) 0.86 0.82 0.82 0.81 0.82 0.82 0.82 0.81 0.82 0.80 SRA (seasonality) 0.74 0.67 0.67 0.65 0.74 0.72 0.74 0.74 0.70 0.74 SRA (volume) 0.76 0.73 0.72 0.73 0.73 0.73 0.73 0.72 0.71 0.72 SRA (overall) 0.77 0.75 0.76 0.72 0.77 0.77 0.77 0.75 0.81 0.75 NLWRA1 (Seas Period) 0.83 0.83 0.83 0.83 0.83 0.83 0.83 0.83 0.83 0.83 NLWRA1 (Seas Amp) 0.86 0.80 0.80 0.80 0.81 0.81 0.81 0.79 0.78 0.77 NLWRA1 (Flow dur. Cve) 0.76 0.75 0.75 0.69 0.75 0.75 0.75 0.73 0.93 0.72 NLWRA1 (Mean Ann. Flow) 0.95 0.93 0.93 0.93 0.93 0.93 0.93 0.91 0.91 0.90 NLWRA1 (overall) 0.77 0.74 0.74 0.73 0.74 0.74 0.74 0.72 0.75 0.71

Document No: 4682 - Aquatic Ecology 136 Final ACT Future Water Options

Site E - Murrumbidgee River - confluence of Molonglo River to Hall's Crossing

Tennent Tennent Tennent Tantangara Dam Dam Dam Options (45 GL - (76 GL - (164 GL - (increase Cotter 22 GL) 27 GL) 30 GL) in Dam demand demand demand discharge Cotter Cotter (with Tennent Tennent Tennent (80% of (80% of (80% of from Dam (45 Dam 90% Dam Dam Dam safe safe safe LMWCC Index Current GL) (76GL) eflows) (45GL) (76GL) (164GL) yield) yield) yield) only) SRA (high flow) 0.92 0.96 0.96 0.90 0.91 0.91 0.95 0.95 0.76 0.95 0.92 SRA (low/zero flow) 0.68 0.46 0.46 0.54 0.46 0.46 0.46 0.46 0.36 0.46 0.46 SRA (variability) 0.88 0.85 0.85 0.85 0.85 0.85 0.86 0.84 0.86 0.84 0.87 SRA (seasonality) 0.80 0.80 0.78 0.83 0.74 0.74 0.70 0.80 0.76 0.80 0.74 SRA (volume) 0.80 0.80 0.80 0.78 0.80 0.79 0.79 0.78 0.77 0.78 0.81 SRA (overall) 0.82 0.75 0.75 0.76 0.73 0.73 0.74 0.75 0.66 0.75 0.74 NLWRA1 (Seas Period) 0.92 0.92 0.92 0.92 0.92 0.92 0.92 0.92 0.92 0.92 0.92 NLWRA1 (Seas Amp) 0.87 0.83 0.83 0.83 0.84 0.84 0.84 0.81 0.82 0.81 0.85 NLWRA1 (Flow dur. Cve) 0.79 0.77 0.78 0.77 0.77 0.77 0.77 0.77 0.78 0.77 0.78 NLWRA1 (Mean Ann. Flow) 0.97 0.96 0.96 0.96 0.96 0.96 0.96 0.94 0.95 0.94 0.98 NLWRA1 (overall) 0.83 0.80 0.80 0.80 0.80 0.80 0.80 0.77 0.78 0.77 0.83

Document No: 4682 - Aquatic Ecology 137 Final ACT Future Water Options

Site H - Porcupine Creek Constant Seasonal Canberra Canberra supply from supply from Index Tantangara Tantangara SRA (high flow) 0.08 0.08 SRA (low/zero flow) 0.00 0.14 SRA (variability) 0.28 0.56 SRA (seasonality) 0.90 0.80 SRA (volume) 0.23 0.22 SRA (overall) 0.21 0.30 NLWRA1 (Seas Period) 1.00 1.00 NLWRA1 (Seas Amp) 0.29 0.33 NLWRA1 (Flow dur. Cve) 0.21 0.26 NLWRA1 (Mean Ann. Flow) 0.28 0.27 NLWRA1 (overall) 0.28 0.31

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12 Ecological risk assessment for amphibians

The ecological risks of the proposed water supply options to amphibians (frogs) was assessed using two different components of the amphibian fauna: (1) the risks to species of conservation concern (e.g. listed threatened species such as the Northern Corroboree Frog and Alpine Tree Frog); and (2) the risks to any obligatory riverine species (species that breed only in streams, and that are a conspicuous seasonal component of the stream biota).

12.1 Listing of species in areas likely to be affected

A complete listing of all frogs known to occur at specific locations in the study area was assembled from published and unpublished reports as well as from information provided by: Wildlife Research and Monitoring Unit, Environment ACT; Environment Protection and Regulation Division, Department of Environment and Conservation (NSW); the Australian Museum, Sydney; and Museum of Victoria, Melbourne.

12.2 Assessment of conservation status of amphibians occurring in the study area

The formal conservation listing for each species known to occur in the study area was recorded by reference to the appropriate State, Territory and Commonwealth listing (ACT Nature Conservation Act 1980; Environment Protection and Biodiversity Conservation Act 1999 – Commonwealth EPBC Act; NSW Threatened Species Conservation Act 1995).

The following steps were involved in risk assessment for species of conservation concern: ¾Geographic information for each species was collated and prepared as a GIS layer at a 1:25,000 scale (existing topographic maps). Maps were prepared showing known and likely distributions. ¾Any species that do not occur, or are not expected to occur, within the region under consideration were deleted from further consideration.

¾Information on critical life history features of each species was collated, i.e. life history, reproduction, broad habitat associations of larvae and adults. ¾Known threats were summarised. ¾The likely risk to each species was determined based on their known field ecology. This involved an evidential (weight-of-evidence) approach.

13 Assessment of risk of nuisance algal growth, Tennent Reservoir

As part of the ecological risk assessment of the Tennent Dam ACT water supply augmentation option, algal blooms were identified as a possible threat to the security of supply. A preliminary assessment of the potential for nuisance algal growth was undertaken. Three Tennent Dam options were assessed, in accordance with the options being developed by ACTEW (Table 13.1).

Document No: 4682 - Aquatic Ecology 139 Final ACT Future Water Options

Table 13.1. Tennent Dam Options assessed Option Volume (Gl) Surface area (ha) Average depth (m) 1 45 407 11.06 2 76 616 12.34 3 164 1125 14.58

13.1 Outline of algal assessment method

For the purposes of the preliminary assessment, a lumped predictive model, based on the Vollenweider Eutrophication Model, was used. The application of the Vollenweider Model to Australian reservoirs and lakes has consistently over predicted in-lake TP and algal levels, by as much as four to five times observed levels (Cullen et al. 1978; Lawrence 1993; Harris 1994). Research by Schaffner and Oglesby (1978), identified several significant modifiers limiting the potential for full release of nutrients discharged to lake waters, and limiting the potential for algae to fully utilise the released nutrients. They included limited light availability in the case of turbid lakes, and nutrients in particulate form and therefore not immediately available to algae. Drawing on empirical analysis of modelled and observed algal biomass levels (Chlorophyll ‘a’) for Burrinjuck Reservoir and Lake Burley Griffin from 1976 to 1980, Lawrence and Lansdowne (1981) established a ‘biological availability’ factor for exported P of 10% in the case of nature reserves and low level agriculture across the Southern Tablelands, 30% for urban stormwater discharge, and 90% for sewage effluent. Application of the Vollenweider Model to the ‘effective P’ load then provided a good fit (R2 = 0.93) of predicted with observed ‘in-lake TP’ and algal levels, across Burrinjuck Reservoir, Lake Burley Griffin and Lake Ginninderra. P in-lake = (L’/q)/(1 +(z/q)0.5) (mg/m3)

Chlorophyll ‘a’ = 0.367 x (in-lake P)0.91 (mg/m3) Where L’ = annual loading of TP x ‘biological availability’ factor (mg/m2)

q = hydraulic loading (m) = Qan/A Q = annual inflow to lake (m3) A = surface area of lake (m2) z = mean depth of lake (m) Australian research since that time has demonstrated that the predominantly particulate (adsorbed P) composition of P loads for Australian streams results in deposition of the bulk of P and burial in the river and lake sediments. The presence of relatively high levels of Ferric iron in Australian streams (0.1 to 0.5 mg/L) is a further factor binding P to the particles of suspended sediment in streamflow. The analysis of the Burrinjuck data in the late 1990s (Lawrence et al. 2000) identified organic loading (Biological Oxygen Demand and Chemical Oxygen Demand) as the primary driver of reducing conditions in lake sediments, and release of ortho-phosphate in lake waters for take-up by algae. That is, organic loading is the primary driver of P release for algal growth in Australian lakes and reservoirs. The P load, modified by a ‘bio-availability’ factor, provides a surrogate measure of the Biological Oxygen Demand (BOD) loading.

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Research by Oliver and Ganf (1999), the Burrinjuck research, and the modelling of physical processes by CSIRO, identified the key factors determining algal composition in lakes and reservoirs. In the case of deep stratified water storages, the thermocline creates a barrier to water mixing

between the epilimnion and hypolimnion, and to the diffusion of O2 to the hypolimnion. Organic material and adsorbed P on particulates continue to settle to the sediments post storm event. Typically, storm inflows are colder than lake surface waters, with the inflow ‘diving’ to the colder hypolimnion waters. During the months of stratified conditions (September to March), the bottom water progressively become de-oxygenated, with the potential for onset of reducing conditions and re-mobilisation of P as Dissolved Reactive Phosphorus (DRP). Following the remixing of top and bottom waters in the autumn, the hypolimnion P is available for algal growth in subsequent months. In the case of discharges high in organic material, reducing conditions may also be experienced in the upstream inlet depositional zone. DRP remobilised under these conditions is directly available to the surface waters, promoting algal growth during summer periods. This condition is extremely unlikely in the case of Tennent Reservoir.

Document No: 4682 - Aquatic Ecology 141 Final