Strategy for the Snowy Montane Rivers Increased Flows 2017-18 · Strategy for the Snowy Montane...

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SNOWY WATER INITATIVE: SNOWY FLOW RESPONSE MONITORING AND MODELLING PROGRAM

Strategy for the Snowy Montane Rivers Increased Flows 2017-18

Introduction

The Snowy Water Initiative (SWI) is an agreement for water recovery and environmental flows between the NSW, Victorian and Australian Governments, and Snowy Hydro Limited (SHL) which is set out in the Snowy Water Inquiry Outcomes Implementation Deed 2002 (SWIOID 2002). The SWI provides three main environmental water programs as part of rebalancing the impacts of the Snowy Hydro Scheme on montane rivers. These three programs are increased flows for: (i) Snowy River, (ii) River Murray, and (iii) Snowy Montane Rivers (Figure 1).The NSW Government is responsible for the implementation of the SWI.

The NSW Government has referred the management of River Murray Increased Flows (RMIF) to the Southern Connected Basin Environmental Water Committee (SCBEWC). The SCBEWC is a collective of water manager’s actively and jointly managing environmental water in the River Murray.

The Snowy Montane River Increased Flows (SMRIF) program identifies five montane rivers to receive environmental water (Figure 1 and Table 1). The water availability for SMRIF is linked to the water availability for Snowy River Increased Flows (SRIF) (Williams 2016), which is determined by the water recovery in the western rivers and the preceding climatic conditions. Both SRIF and SMRIF are managed by the NSW Government as part of the SWI.

The SWIOID 2002 provides for SHL to forego up to 150 Giga Watt hours (GWHrs) of electricity generation to allow for environmental releases to be made to SMRIF. This value of 150 GWHrs

is converted into a volumetric allocation, but the conversion factor differs depending on the location of the releases in the Snowy Mountains Scheme, and thus influence the overall volume released. In some locations water released can be re-used to generate electricity so a smaller conversion factor is applied (SWIOID 2002), however, where water is lost to the Snowy Scheme a higher conversion factor is applied.

Figure 1. Location of the Snowy Montane Rivers release points (indicated by green icons). The volumes identified are an upper limit for a full allocation scenario, and thus represent a maximum that could be released in any one year.

This document describes the: (i) environmental water management arrangements in the Snowy

Snowy Montane Rivers Increased Flows 2017-18

Montane Rivers, (ii) ecological principles for environmental water management in montane rivers, (iii) the specific annual water allocation strategies and (v) the intended environmental benefits expected form the strategies. It also proposes new approaches to the use of environmental flows for river rehabilitation based initially on restoring riverine processes, rather than traditional terrestrial based biodiversity management principles.

Ecological process: the basis for flow based river rehabilitation Aquatic biota have adapted life history strategies to local climatic and hydrological conditions (Bunn and Arthington 2002; Baumgartner et al. 2015). Mimicking the varied characteristics of the local hydrology is a key driver to river recovery from flow regulation.

Understanding the flow related river processes that support: (i) habitats, (ii) resource availability and productivity (iii) reproduction and recruitment and, (iv) biotic dispersal form the ecological basis of the strategy and guides the setting of rehabilitation objectives for the Snowy River (Figure 2).

The key riverine processes considered important are stated as a set of overarching ecological principles. These over-arching ecological principles for environmental water management include:

• River dynamics including high daily flow variability and hydraulic diversity are required to meet a wide range of ecological water requirements including aquatic biota and their various life stages.

• River discharge is managed to repair flow related river processes and applied at a whole ecosystem scale rather than for individual species.

• Hydrological disturbance and the repair of instream habitat (Coleman and Williams 2016) provide a template for recovery of aquatic biota and needs to be implemented early in the recovery

process in order for complementary measures (i.e. provision of basal resources via tributary releases) to be successful.

• The repair of instream habitat is important to provide instream nutrient translocation sites to support benthic biofilms (Baldwin et al. 2014) and provide a more efficient flow of energy to higher trophic levels and support third order ecological responses, i.e. recruitment.

• The focus on the type of nutrient translocation site may differ based on the river type, but should focus on dominate hard surface area i.e. montane reaches– cobble substrate, and lowland reaches– large woody debris (LWD).

• The provision of basal resources, such as dissolved organic carbon (DOC) and dissolved silca (DSi) are required to stimulate the food web to maintain viable populations. These types of basal resources are unlikely to be made available via managed dam releases, but rather sourced from unregulated tributaries (Rohlfs et al. 2015; Rohlfs et al. 2016; Williams et al. in prep) or floodplain contributions (Figure 3).

• The landscape is not uniform, and understanding the bio-geochemical processes such as the source and uptake of basal resources (i.e. “hot spots” or “hot moments” (Figure 3)) provides an opportunity to improve productivity and target rehabilitation (McClain et al. 2003; Rohlfs et al. in prep). Understanding river productivity is a major consideration for system wide success using environmental water.

• Consideration of flow related reproduction cues should be considered in conjunction with recruitment requirements and success, when allocating water across a year. Potentially, substantial energy may be consumed by aquatic biota for

2 NSW DPI Water, May 2017


reproduction, but recruitment may not be successful unless basal resources are available post reproduction.

• Provision of increased recruitment opportunities are required to maintain viable populations, but require the provision of basal resources (i.e. DOC and DSi) to maintain the new recruits.

• Consideration of the organisation of populations across multiple spatial scales is required, including functional sites, landscapes and networks (Poiani et al. 2000). Some specific areas of the riverine landscape may be more significant in supporting viable populations (Kiffney et al. 2006).

• Dispersal mechanisms need to be considered if the taxa of interest are absent or in low abundance in the regulated river. Particularly, if the ecological end points require the dispersal of aquatic biota from unregulated tributaries to a regulated river. This requires the:

o active management of tributaries, and the junction of tributaries with regulated rivers.

o consideration and management of hydraulically induced barriers.

o consideration of active re-location of target taxa to the significantly improved habitat condition of the regulated river. This active management should only be considered late in the rehabilitation process, once it’s clear that taxa are unlikely to disperse from tributaries.

• Flow may not always be the primary driver for improvement in ecological function or status. Other factors, such as water temperature, are significant drivers of ecological processes, i.e. decomposition, respiration, production reproduction and movement (Bothwell 1998; Carr et al. 1997; Caissie 2006).

• The management of rare taxa per se does not provide the primary driver for flow strategies, but will be achieved by addressing the above river rehabilitation principles (i.e. river processes rather than the management of a series of rare taxa). The management of rare taxa will be achieved by adopting functional variable flow regime, i.e. akin to functional landscapes/networks described by Poiani et al. (2000).

• A greater understanding of life histories is required than currently available. The limited life-history knowledge provides great uncertainty in the setting of ecological targets, particularly where large investment occurs on limited understanding of basic ecology.

• The sequencing of priorities will be important to implement a long term flow regime and will change as the primary objectives are achieved. Initially, a higher priority will be given to flow objectives that relate to habitat maintenance or improvement. Flow objectives relating to connectivity and productivity are only likely to be achievable/ maximised once in-stream habitat is considerably improved.

• Ecological rehabilitation takes time (i.e. decades). Use the time to experiment with releases and build the scientific evidence that allows future adaption.

• There is a need to focus on holistic river management rather than just water allocation targets and environmental water. The prerequisite conditions (i.e. habitat suitability), need to be in-place for significant environmental water achievements.

Figure 2. Ecological rehabilitation theory and river processes forms the basis of the Snowy River program. The early stages of the program focus on improving hydrology, hydraulics, habitat and biochemical processes rather than expecting immediate biological responses in higher trophic levels (i.e. 1 through 4, rather than 1 and 4).



Understanding the flow related river processes that support (i) habitats, (ii) resource availability and productivity (iii) reproduction and recruitment and, (iv) biotic dispersal forms the basis of the strategy and the setting of rehabilitation objectives for the Snowy River. Over the long term, the sequencing of objectives and emphasis will generally follow the above order for implementation.

Figure 3. Using tributary environmental-water to create bio-chemical “hot spots” and “hot moments” (red) in regulated rivers. A conceptual model of chemical spiralling and processes in a (i) confined montane river and (ii) a floodplain river. Modified from Nilsson and Svedmark (2002).

Ecological outcomes

The SWIOID 2002 sets a series of ecological objectives for the Snowy Montane Rivers but they are broadly defined as follows:

• To protect endangered/ threatened species

• To maintain natural habitats

• To maintain wilderness and national parks values.

The SWIOD 2002 also requires these objectives to be further defined. In developing a more comprehensive set of ecological objectives, the inclusion of rehabilitation ecology theory forms the basis of the approach for the Snowy River and the Snowy Montane Rivers, including the development of a revised set of ecological flow principles. The focus of the strategy is to repair the flow related river processes that support:

• habitats (i.e. hydraulic diversity, substrate condition, channel morphology and thermal regime)

• resource availability (i.e. DOC, DSi) and productivity

• reproduction and recruitment, and,

• biotic dispersal.

Issues relating to aquatic biodiversity outcomes associated with hydrological alteration will be achieved via re-instating these key riverine processes (Williams 2016).

For the Snowy Montane Rivers, it is envisaged that the following ecological benefits will be realised by the release of environmental water:

• To mimic the hydrological characteristics of a smaller montane river.

• To provide substantially increased wetted in-stream habitat and the river channel better reflects the natural hydraulic diversity and geometry of a montane river.

• To provide a thermal regime that better reflects a higher altitude montane river (i.e. cold water).

• To provide regular scour of the river substrate to maintain benthic biofilms and nutrient translocation sites.



• To improve hydrological and ecological connectivity along the water source.

o Hydraulic connectivity between Higher altitude and lower altitude

reaches pools within the regulated river

(Figure 4). o Downstream provision of dissolved

organic carbon, and dissolved silica to provide bio-chemical responses (Figure 3).

o Downstream provision of river bed sediment.

o Downstream provision of plant prologues.

o Downstream drift of aquatic macroinvertebrates and fish.

• To reduce the ingress of terrestrial vegetation in the river channel, such as tea-tree.

• To establish a clear aquatic and riparian vegetation community within the channel of the former river based on the new hydraulic gradient (Figure 5).

• To establish ecological communities (i.e. biofilms, aquatic plants, bugs, and fish) reflecting those of a reference Snowy Montane River.

o To provide flow related opportunities for reproduction and recruitment.

o To provide flow related opportunities for biotic dispersal.

Figure 4. The releases from Falls Creek and the minor diversion structures will improve hydraulic connectivity between isolated pools within the Snowy River below Guthega Dam (Source: Google Earth). Direction of river flow is left to right.

Figure 5. The Geehi River below Geehi Dam (A) in 2009 prior to environmental water and (B) in 2017 with low flow releases via Middle Creek. The releases have seen greater hydraulic diversity, river connectivity, the development of a defined channel, improved benthic condition, provision of basal resources and a more pronounced littoral zone (Source: S. Williams).



Snowy Montane Rivers and flow based river rehabilitation The implementation of the Snowy Montane Rivers strategy comprises the following two components, these being:

• Snowy Montane Rivers weir releases, and

• Snowy Montane Rivers dam releases.

Table 1 outlines the annual water targets for the Snowy Montane Rivers, for 2017-18. This is the first year that an allocation of 212GL to SRIF and results in an allocation 150 GWHrs of foregone electricity generation to the Snowy Montane Rivers. Variations to these targets are discussed later in the strategy, but reflect many of the principles listed previously.

Table 1. Snowy Montane Rivers Increased Flows, SWIOID Target, average yield, and 2017-18 annual targets.

Snowy Montane Rivers Increased Flows (SMRIF)

SWIOID Annual Target

(GL)

Average Annual Yield (GL)

2017-18 Annual Volume

(GL) Murrumbidgee River @ Tantangara 27 27 35.76

Goodradigbee River 12 12 12

Geehi River 19.8 22.7 22.7 Snowy River- Island Bend 29 18.9 18.9

Snowy River- Perisher Range 30 3.4 3.4

Total 117.8 84 92.76

Snowy Montane Rivers -weirs

The Snowy Montane Rivers weirs have historically diverted water from headwaters to the larger dam infrastructure to increase the catchment area, and thus increase the water yield harvested. Selected weirs have been identified to release environmental water as part of the rehabilitation program.

In the Snowy Hydro-Electric Scheme, weirs can be categorised as (i) large, (ii) moderate or (iii) minor. The six weirs that comprise the Snowy Montane Rivers Increased Flows program are categorised as large, but have limited capacity

to actively manage releases (Table 2). Additionally, releases associated with the Falls Creek aqueduct include some minor diversion structures.

Table 2. Snowy Montane Rivers Increased Flows-weirs, and identified release locations.

No SWIOID Snowy Weirs

1 Goodradigbee River

Goodradigbee River Weir

2 Geehi River Middle Creek Weir

Strzlecki Creek Weir

3 Snowy River- Island Bend

Tolbar Creek Weir

Diggers Creek Weir

4 Snowy River- Perisher Range

Falls Creek Weir and minor diversion structures

Typically the releases from these locations reflect the catchment inflows to the weir pool and it is not practical to prescribe a daily flow target. Accordingly, the SMRIF weirs program sets a long term annual yield, rather than daily flow targets (Williams 2014; Williams 2015; Williams 2016). This means that over the long term the annual volume will average the nominated target. The downstream flow will typically reflect the hydrology of the inflows. In wetter years the flow will exceed the long term target and in drier years the annual volume will be less than the target.

To achieve the long-term target each weir has been modified to either (i) allow all water to pass downstream (i.e. ‘transparent releases’) or (ii) in the case of the Goodradigbee River, allow a proportion of the daily inflows to be released (i.e. `translucent’ release). It is anticipated that the hydrological characteristics downstream of the weir under the modified flow regimes will reflect the hydrology of a Snowy montane river / stream.

Each of the Snowy Montane Rivers release locations are presented in Figures 6 to 9. The weirs were selected as release locations rather than dams as they provide (i) alternative ecological benefits not capable of being delivered via large dams, and (ii) a present a simpler method of implementation. This is further described later in the strategy.



Figure 6. Environmental water releases to the (A) Upper Snowy Rivers below Guthega Dam via (B) Falls Creek Weir and (C) associated minor diversion structures. Releases will occur for the first time in the 2017-18 water year by overtopping the structures (Source: S. Williams).

Figure 7. Environmental releases to the Snowy River below Island Bend Dam via (A) Diggers Creek Weir and (B) Tolbar Creek Weir. These releases were commissioned in 2013-14 (Source: S. Williams).



Figure 8. Environmental releases to the Geehi River below Geehi Dam via (A) Middle Creek Weir and (B) the defunct Strzelecki Creek Weir. Releases to the Geehi River were commissioned in 2010-11, with releases from Strzelecki Creek credited to SMRIF from 2016-17 (Source: S. Williams).

Figure 9. Environmental releases to the Goodradigbee River via (A) Goodradigbee River Weir and (B) downstream of weir. Releases to the Goodradigbee River were commissioned in 2005-06 (Source: S. Williams).



Snowy Montane Rivers- Dam- Murrumbidgee River below Tantangara Dam

Releases to the Murrumbidgee River are made from Tantangara dam, a much larger structure than the other release points, for which a gated release structure is available (Figure 10). Accordingly, the daily flow release strategy for the Murrumbidgee River differs from the other SMRIF release points.

The releases comprise two components: (i) the SMRIF and (ii) a Base Passing Flow (BPF). The BPF has some key components, these being:

• A 2GL year volume is targeted over the longer term.

• A 32 ML/day discharge is to be targeted at Mittagang Crossing, near Cooma.

• A maximum of 3.5GL is set for any one year.

The Base Passing Flow releases typically occur during drier weather.

Figure 10. Tantangara Dam on the Murrumbidgee River essentially acts as a large diversion weir and diverts water to the Eucumbene Dam for electricity production. Releases commenced in 2005-06 (Source: S. Williams).

A modified ‘flow scaling’ approach used to set SRIF releases to the Snowy River has also been applied to the SMRIF in the Murrumbidgee River (Williams 2014; Williams 2015; Williams 2016). This modified approach uses the recorded flows in a nearby natural catchment (in a year where similar volumes of flow occurred) to set daily releases. For releases to

the Murrumbidgee River from Tantangara dam, the initial daily flow targets were set using the 1991-92 flow sequence for the Murrumbidgee River above Tantangara (station No. 410535). Daily targets were then amended to account for operational implementation (Figure 11).

Figure 11. The Murrumbidgee River (Station No. 410535) above Tantangara Dam, was used as the hydrological reference condition to develop the release strategy (Source: S. Williams).

The key difference in the application of the method between the Snowy River and the Murrumbidgee River is that the Jindabyne Dam has a greater capacity to release a wider range of discharge rates than Tantangara Dam, and it’s not operationally possible to make the 8hr high flow releases.

The SWIOID 2002 identifies a target of 27GL (i.e. 30% of the Mean Annual Natural Flow- MANF) in a full allocation scenario. In 2017-18, a total of 35.76GL has been allocated to the upper Murrumbidgee River below Tantangara Dam. This is the 2nd largest allocation since 2005-06 (Figure 12), and represents a volume greater than the SWIOID target and larger than the long-term annual median allocation (Figure 12B).

The proposed daily flow pattern (Figure 12) attempts to include hydrological characteristics typical of a smaller mixed snowmelt - rainfall river system typical of the northern Snowy Mountains consistent with the (i) volume available and (ii) the dam outlet capability.

The natural flow pattern of the Upper Murrumbidgee River varies from that of the



upper Snowy River, as there are strong climatic gradients across the Snowy Mountains. Typically, the Upper Murrumbidgee River catchment is lower in elevation than the Snowy River Catchment and has substantially less catchment area above the snow line. Thus, the snow melt signal is not as pronounced as the Snowy River. The unregulated reaches of the upper Murrumbidgee River has a more pronounced winter high flow signal, associated with rainfall rather than snow melt.

Figure 12. Comparison of total annual (A) SMRIF target (black) and actual Base Passing Flow (light grey) and (B) long term median annual allocation to the Murrumbidgee River below Tantangara, 2002-03 to 2017-18.

In a high allocation year, the flow strategy (Figure 13 and Figure 14) attempts to reinstate key montane hydrological characteristics, these include:

• An annual allocation of 35.76GL allows water to be allocated for most days of the water year.

• A monthly flow pattern that reflects a strong seasonal pattern, and includes eight months (i.e. June-January) above 1.5 GL.

• A pronounced winter-spring signal with three months above 3 GL (i.e. July to September) (Figure 13), and a peak month discharge of 12.35GL.

• Daily flow variability across most of the year, with flow varying between 30 and 1,100ML/d, and with discharge above 400 ML/day on 16 days during five events.

• A peak event of 1,100 ML/day to reflect a spring storm event in the Snowy Mountains.

• A base flow of 50 ML/day in late spring- summer, punctuated by seven minor events.

• A transition base flow discharge of 30 ML/day in early autumn and late summer.

• There will be two periods without releases, these being: (i) 1 day in May 2017 and (ii) 34 days in March-April 2018, as there is insufficient water available to maintain flows for every day of the year. It is assumed the BPF allocation will provide some minor base flows during the March-April 2018 period.

• The annual flow sequence differs from the previous year and introduces daily variability between years.



Figure 13. Mean daily discharge pattern for the Murrumbidgee River below Tantangara in 2017-18.

Figure 14. Total monthly discharge in the Murrumbidgee River below Tantangara Dam for 2017-18.

Overall long-term rehabilitation of the upper Murrumbidgee River

The long-term objective for an environmental flow regime based on natural daily flow sequences in the Upper Murrumbidgee River is “To facilitate the rehabilitation and evolution of the Murrumbidgee River below Tantangara Dam into a smaller but healthy river”. Over decadal to century long time scales, environmental water releases scaled to the Upper Murrumbidgee River will allow the Murrumbidgee River to slowly develop a size, shape and perhaps condition, similar to that of a smaller but healthier Snowy montane river. It is expected that the ecological response to the

releases in the upper Murrumbidgee will take longer than the responses in the Snowy River. Particularly given the given the lower annual allocations of water.

The largest hydrological alteration occurred between 1958-60 to 2005-06, with 1% of MANF released to the Murrumbidgee River. Spatially, the largest hydrological impacted has occurred between Tantangara Dam and the junction with Yaouk Creek, the first major perennial tributary with the regulated upper Murrumbidgee River. It is anticipated that flows from Tantangara Dam will support the inflows from these smaller tributaries, and the ecosystem resources provided via tributary contributions (McClain et al. 2003; Dye 2010; Rohlfs et al. 2015). It is expected that in this wetter part of the Snowy Mountains, that the tributaries will be a key mechanism to ecological recovery, but the dam releases will facilitate this ecological recovery.

The long-term SMRIF objective implicitly recognises that: • It is not possible to restore or maintain the

Murrumbidgee River to its former size with one third of its former annual flow volume.

• The in-stream habitat needs to be improvedin order for major secondary (i.e.appropriate bio-geochemical processes) andtertiary (i.e. recruitment) ecologicalresponses to occur. This forms the primaryfocus of the strategy in the early stages ofthe river recovery, where water is available.

• The releases will complement inflows fromthe major downstream tributaries toprovide the opportunity for ecologicalrecovery.

The annual allocation of 35.76GL is seen as a high allocation and hence the primary objective for the strategy is primarily focussed on the re-working the in-channel habitat and the maintenance of the existing improvements (Figure 15) to the river since environmental water via SMRIF commenced in 2005-06.

Key seasonal aspects of the SMRIF-dams strategy are presented below.



Autumn low flows

An autumn minor low flow of 30ML/day is provided to the upper Murrumbidgee River, to represent the autumn low flow typically recorded in the Snowy Mountains. This provides a minor wetting of in-channel features such as riffles and runs, and localised in-channel habitat connectivity.

Winter- spring high flows

The higher winter-early spring base flow interrupted by regular higher events is designed to provide a moderate to high level of physical disturbance in the river bed, including riffle meso-habitats (Figure 16) of the upper Murrumbidgee River.

It is envisaged that the following ecological benefits are likely to be realised via the greater flow variability and peak magnitude flow rates: • Slightly improve the physical habitat

condition of the river riffles due to increased scour of fine sediment and water mixing.

• Improved riffle habitat condition willfacilitate:o Increased opportunities for water and

nutrient exchange in the riffles, andsupport improved heterotrophicprimary productivity.

o Sustain the aquatic macroinvertebratefauna, by maintaining the currentabundances of mayflies, caddies fliesand stone flies.

o Increased utilisation by MacquariePerch (Macquaria australasica).

• Provide minor pulses of dissolved organiccarbon by inundating lower benches andpromoting heterotrophic primaryproductivity (Figure 17).

The annual peak event of 1,100 ML/d is primarily designed to rework the bed of river pools (i.e. scour of fine sediment from the bed of the river). The condition of bed of river pools is expected to take a greater longer time to recover than running water habitats such as riffles, runs and glides.

Figure 15. The Murrumbidgee River below Tantangara Dam, (A) 2009, (B) 2011, and (C) 2016 showing gradual improvement in instream habitat, and complementary management of willows.



Figure 16. The quality of the bed of the Murrumbidgee River below Tanatangara Dam can be improved by the provision of higher magnitude flow events to scour the benthos. A prerequisite to encourage secondary and tertiary ecological responses to the environmental water (Source: S. Williams)

The increased winter-spring daily flow variability is also designed to frequently wet the lower margins of the riparian zone and maintain moisture in the soil profile of the riverbank. It is expected that the proposed daily flow variability will favour the development of aquatic and riparian vegetation within a band just above the low water level of the Murrumbidgee River bank. Additionally, the daily flow variability will attempt to limit the ingress of terrestrial vegetation back into the river channel between the Tanatangara Dam and Yaouk Creek. The regular inundation will disadvantage these terrestrial vegetation types, by increasing the moisture content of the root zone.

Spring low flows

The preservation of the low flow conditions (i.e. 50 ML/day) during spring is designed to provide protection of riffles. Flowing water habitats (i.e. riffles runs and glides) are the first in-stream habitat to be impacted by low flow periods. The protection is provided by maintaining water over the running water habitats such as riffles (Figure 20).

This will provide some protection of riffle dependent biota, such as aquatic biofilms, macroinvertabrates (i.e. mayflies, caddies flies and stone flies) and fish eggs such as Macquarie Perch.

Figure 17. Higher flow events in the Murrumbidgee River will inundate the lower benches and attempt to (i) provide dissolved organic carbon and promote heterotrophic primary productivity and (ii) limit the ingress of terrestrial vegetation in aquatic habitats. (Source: S. Williams).

Spring higher flows The three minor events in spring attempt to provide habitat hydraulic connectivity between pools and riffles for large bodied fish. These events provide an opportunity for Macquarie Perch to move into riffles to lay eggs. Fish such as Macquarie Perch need elevated water levels to gain access to the riffles. The higher flows aim to facilitate this access for the adult fish to reproduce. Macquarie Perch are likely spawn around October (pers. comm. Mark Lintermans 2017).

There is some uncertainty regarding the (i) event magnitude and (ii) event duration to provide adequate inundation of riffles. This is also some further uncertainty relating to the differences in running water habitats based on river grade to support connectivity and access.



Figure 20. The reach of the Murrumbidgee River near Yaouk is an important habitat for Macquarie Perch. Macquarie Perch (“Wanumbic“ ) are reliant on running water in-channel habitats for reproductive success (Source: S. Williams).

Summer low flows

A 50 ML/day summer low flow release, punctuated by five minor discharge events are aim to protect riffles and the flow dependent biota (e.g. the eggs of Macquarie Perch). In perennial systems these are the habitats most at risk to reduced flow. However, there is some uncertainty regarding the duration of base flow to ensure the development of the Macquarie Perch eggs to maturity, but it is expected that fish larva will have developed by December (pers. comm. Mark Lintermans 2017).

The preservation of a very low flow of 30 ML/day in February to March 2017 attempts to provide a transition period to limit hydrological stranding of flow dependant guilds. This very low period is designed to replicate the gradual drying of the river, and may provide the opportunity for flow dependant guilds to transition to remnant pools during the no-flow period. However, there is some uncertainty if this strategy supports the recovery of these flow dependent guilds that typically occur in upland perennial rivers.

Cultural recognition

In recognising the strong cultural connectivity to the waterways of the Australian high country and the upper Murrumbidgee river catchment, the spring high flow event has been named by the Wongalu Aboriginal Nation.

The high flow event is named “Gyack” after the Corroboree Frog (Connolly et al. 2017).

The Corroboree Frog is endemic to the Australian high country. The Northern Corroboree Frog (Pseudophryne pengilleyi ) is located primarily in the upper Murrumbidgee catchment, above Tanatangara Dam. The Corroboree Frog typically occupies seasonal wetlands for breeding, and highly vegetated montane and sub-alpine woodland landscapes for feeding and shelter. Although, not a riverine frog species per sa, the Corroboree Frog is an important totem for the Wongalu Aboriginal Nation in the Upper Murrumbidgee River catchment. Naming the event “Gyack” is a small step in the recognition of the connection of the Aboriginal Nations to aquatic habitats and rivers of the Australian high country.

The Wongalu Aboriginal Nation has requested that in the following year that the high flows are named after the Macquarie Perch (“Wanumbic”).

Variation to SMRIF program

To date, the allocation of water to the SMRIF program has varied each year. This variation has occurred due to: (i) a gradual increase in water entitlements, (ii) climate variability, (iii) operational issues at existing infrastructure, and (iv) optimising use of the available environmental water.

To date insufficient water has been available to meet the SMRIF SWIOID 2002 annual targets, and there is also some uncertainty that the annual targets can be met with a full 150 GWhr allocation. Therefore, a conservative and staged approach has been implemented to ensure sustained long term ecological improvements at each montane location.

The optimisation of water has primarily occurred via two mechanisms, by varying annual allocations to the upper Murrumbidgee River and the stage commissioning of each release location in the weirs program.



Snowy Montane Rivers- weirs

Two variations to the SWIOID 2002 annual targets are being implemented in the Snowy Montane Rivers weirs.

Firstly, in the upper Snowy River catchment lower annual targets are being implemented. This lower target reflects issues associated with the overall available water, and a staged implementation within Perisher Range.

Secondly, a significant variation to the SMRIFs program is being implemented in the Geehi River catchment. For the second year, an additional volume of 5.2 GLy-1 is being released to the Geehi River as a result of infrastructure failure in Strzelecki Creek (Figure 4b). A significant bed load is moving down the Strzelecki Creek attributable to a major landslip in the upper catchment. It is not practical to re-instate the weir and associated infrastructure given the significant bed load moving down the system.

The additional environmental water (i.e. 5.2 GLy-1) will be released to the Geehi River via a tributary release on Strzelecki Creek. The annual SMRIFs volume will increase from 17.5 to 22.7 GL year on a long term annual average, and is expected to provide improved ecological outcomes for the Geehi River given the additional connectivity to higher altitude headwaters.

Snowy Montane Rivers- dams

The ability to actively manage environmental releases from Tantangara Dam to the upper Murrumbidgee River provides the flexibility to accommodate changes in total annual allocation to SMRIF.

In 2017-18, a greater allocation is provided to the upper Murrumbidgee River, as (i) the 35.76GL will allow a better mimicking of the local hydrology across most of the year, and (ii) it will allow greater physical reworking of the river benthos and in-channel habitats during winter and spring. The poor in-channel habitat of the Murrumbidgee River is still deemed a constraint to river recovery. This type of re-working of the in-channel habitats appears to be limited with lower annual allocations.

Ecological constraints to recovery and SMRIF The following have been identified as potential ecological constraints to ecological recovery in the Snowy Montane Rivers: 1. Habitat

• Limited wetted habitat.

• Limited hydraulic diversity.

• Poor substrate condition (i.e. abundant fine sediment, filamentous green algae).

• Thermal regime (i.e. warm water).

• Poor riparian zone condition.

2. Resource availability and production

• Insufficient basal resources (i.e. DOC, DSi).

• Insufficient nutrient translocation sites (i.e. cobbles/ large woody debris).

• Limited opportunities for heterotrophic production

3. Reproduction and recruitment

• Insufficient habitat (see above).

• Insufficient resources and resource competition.

• Insufficient abundance / densities within system.

4. Biotic dispersal

• Limited ability to disperse.

• Limited connectivity to remnant populations of target species.

• Significant hydraulically induced barriers (natural/ built).

Complementary measures and SMRIF Complementary resource management activities are required to support the delivery of environmental water and the SMRIF objectives. These complementary activities potentially include:



• Management of exotic weeds such as willows/blackberry, to allow channel change with the available water.

• Management of large bodied exotic animals to protect in-channel habitats, riparian zones, and headwater streams/ swamps.

• Management of catchment sources of fine sediment.

• Government investment in Infrastructure upgrades at Tantangara Dam to allow greater flexibility in achieving an increased range of daily flow targets between 1 and 100 ML/d. This will allow improved hydrological outcomes with the available water in the upper Murrumbidgee River.

Conclusion

In attempting to repair highly modified aquatic ecosystems, thought needs to be applied to conceptualising and understanding the proposed ecological processes of river recovery provided by the addition of environmental water.

Rather than applying a formal legal terrestrial based biodiversity management approach to the rehabilitation of upland rivers, i.e. focusing on rare or charismatic species or attempting to protect formal land based reserves, this rehabilitation strategy firmly focuses on repairing river processes to aid river recovery.

In a high water allocation year the SMRIF strategy will focus mainly on improving river processes leading to (i) habitat improvement (i.e. substrate /channel condition, thermal regime, riparian condition), (ii) resource availability (i.e. DOC and DSi), and production, (iii) increased opportunities for reproduction and recruitment, and (iv) dispersal of montane aquatic biota.

In the Snowy Montane Rivers (weirs), the physical habitat is reasonably intact and a faster recovery is expected. However, in the upper Murrumbidgee River significant improvement in instream habitat condition is still required prior to substantial tertiary level ecological response can be assessed using community based ecological metrics.

References

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Acknowledgments The document should be cited as Williams, S. (2017). Release strategy for the Snowy Montane Rivers Increased Flows, 2017-18. Snowy Flow Response Modelling and Modelling program, NSW DPI Water, Sydney.

© State of New South Wales through the Department of Industry, Skills and Regional Development, 2017. You may copy, distribute and otherwise freely deal with this publication for any purpose, provided that you attribute the NSW Department of Primary Industries as the owner.

Disclaimer: The information contained in this publication is based on knowledge and understanding at the time of writing (May 2017). However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of the Department of Primary Industries or the user’s independent adviser.

Published by the Department of Primary Industries.


http://dx.doi.org/10.1071/MF14230

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