42 WATER SECURITY – MAJOR PROJECTS FEBRUARY 2009 2.2 Existing Cotter Dam (history) The promise of abundant water from the Cotter River was a key factor in the selection of Canberra as the site for the federal capital of Australia. Prominent NSW Chief Engineer for Rivers, Water Supply and Drainage, Ernest de Burgh, claimed that ‘the flow of the Cotter was twice as much as the water consumption of 650,000 people in Sydney’. Construction of the Cotter Dam, designed by Henry Connell, began in March 1912. The dam was a gravity concrete structure, with a straight wall and an overshot spillway that sent water down the face of the wall. The Cotter Dam was completed in 1915 to a height of 18.3m. A royal commission in 1917 criticised the cost of the Cotter Dam’s construction, although the dam had not been constructed to its planned height of 30.5m, and at £75,000 it cost less than was estimated. Canberra’s growing post–World War II population meant an increased demand for water. In 1947–48 it was decided to raise the dam to increase its storage capacity, and in 1949 work commenced. It was hampered by faults in the old wall, and by a big flood in March 1950 that halted work for a month. By 1951 the dam had been raised to 25.8m. An access road constructed in the course of enlarging the Cotter Dam opened up the Cotter River area to visitors, and contributed to its reputation as a beautiful natural setting and a key recreational area for the growing city of Canberra. Water from the Cotter Reservoir needed to be raised 250m to Mount Stromlo Reservoir, so that it could be gravity-fed to Red Hill Reservoir. The Cotter Pumping Station, comprising two single-storey buildings of rendered brick, was designed by the architect of Old Parliament House and the Kingston Power Station, John Smith Murdoch. Construction of the pumping station, began on the right bank of the Murrumbidgee River in 1914, and two Gwynne pumps were ordered from the UK. By October 1918 the Cotter Pumping Station was pumping water to Mount Stromlo Reservoir. At first the Cotter Pumping Station operated for only several days a month, but as Canberra’s population grew, six more pumps were added—one in 1935, one in 1942, two in 1955, and two in 1963, when a two-storey extension was built to accommodate their vertical orientation. The Cotter Pumping Station was no longer required after water from Bendora and Corin reservoirs became available in 1967, and it did not operate again until 2004, after the 2003 Canberra bushfires. Water from the Cotter Reservoir travels to the Cotter Pumping Station through cast iron pipes running along the left bank of the Cotter River to a tunnel on the left bank of the Murrumbidgee, through another tunnel under the Murrumbidgee River, then up to the Cotter Pumping Station on the right bank of the river. Construction of the tunnel was difficult, and it was regarded as a marvel of engineering at the time. As a result of a revision of the flood hydrology of the Cotter River system in 1988 it was determined that an upgrade of the existing Cotter Dam was required. This upgrade was as a consequence of the renewed hydrology (information) that indicated that in the event of an Imminent Failure Flood on Cotter River, coupled with the failure of the two upstream dams of Corin and Bendora, the existing Cotter Dam would fail. In view of these findings and considering the age of the Cotter Dam (build in 1912), material deterioration and inadequate capacity of its spillway, ACTEW undertook a program of remedial work in January 1999. Upgrade works were aimed at improving the stability of the dam against extreme flooding scenarios and earthquakes and consisted of replacing the top 1.8m of the dam with a reinforced concrete load distribution beam and anchoring the dam to the rock foundation using 45 modern anchors. The remedial work was undertaken at a cost of $5.5 million. The work was concluded prior to the commencement of any investigations relating to the Enlarged Cotter Dam proposal (as described in section 1 of this report). This expenditure and the resulting upgraded dam was considered in reviewing the options for the ACT’s next water source, which was conceived in response to the protracted drought experienced in the ACT since 2001. The upgrading of the existing dam was one of more 30 options that were considered as potential new water sources for the ACT. A more detailed review of the options considered is given in section 1 of this report.
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42 WATER SECURITY – MAJOR PROJECTS
FEBRUARY 2009
2.2 Existing Cotter Dam (history)
The promise of abundant water from the Cotter River was a key factor in the selection of Canberra as the
site for the federal capital of Australia. Prominent NSW Chief Engineer for Rivers, Water Supply and
Drainage, Ernest de Burgh, claimed that ‘the flow of the Cotter was twice as much as the water consumption
of 650,000 people in Sydney’.
Construction of the Cotter Dam, designed by Henry Connell, began in March 1912. The dam was a gravity
concrete structure, with a straight wall and an overshot spillway that sent water down the face of the wall.
The Cotter Dam was completed in 1915 to a height of 18.3m. A royal commission in 1917 criticised the cost
of the Cotter Dam’s construction, although the dam had not been constructed to its planned height of 30.5m,
and at £75,000 it cost less than was estimated.
Canberra’s growing post–World War II population meant an increased demand for water. In 1947–48 it was
decided to raise the dam to increase its storage capacity, and in 1949 work commenced. It was hampered by
faults in the old wall, and by a big flood in March 1950 that halted work for a month. By 1951 the dam had
been raised to 25.8m.
An access road constructed in the course of enlarging the Cotter Dam opened up the Cotter River area to
visitors, and contributed to its reputation as a beautiful natural setting and a key recreational area for the
growing city of Canberra.
Water from the Cotter Reservoir needed to be raised 250m to Mount Stromlo Reservoir, so that it could be
gravity-fed to Red Hill Reservoir.
The Cotter Pumping Station, comprising two single-storey buildings of rendered brick, was designed by the
architect of Old Parliament House and the Kingston Power Station, John Smith Murdoch. Construction of the
pumping station, began on the right bank of the Murrumbidgee River in 1914, and two Gwynne pumps were
ordered from the UK. By October 1918 the Cotter Pumping Station was pumping water to Mount Stromlo
Reservoir. At first the Cotter Pumping Station operated for only several days a month, but as Canberra’s
population grew, six more pumps were added—one in 1935, one in 1942, two in 1955, and two in 1963,
when a two-storey extension was built to accommodate their vertical orientation. The Cotter Pumping Station
was no longer required after water from Bendora and Corin reservoirs became available in 1967, and it did
not operate again until 2004, after the 2003 Canberra bushfires.
Water from the Cotter Reservoir travels to the Cotter Pumping Station through cast iron pipes running along
the left bank of the Cotter River to a tunnel on the left bank of the Murrumbidgee, through another tunnel
under the Murrumbidgee River, then up to the Cotter Pumping Station on the right bank of the river.
Construction of the tunnel was difficult, and it was regarded as a marvel of engineering at the time.
As a result of a revision of the flood hydrology of the Cotter River system in 1988 it was determined that an
upgrade of the existing Cotter Dam was required. This upgrade was as a consequence of the renewed
hydrology (information) that indicated that in the event of an Imminent Failure Flood on Cotter River, coupled
with the failure of the two upstream dams of Corin and Bendora, the existing Cotter Dam would fail.
In view of these findings and considering the age of the Cotter Dam (build in 1912), material deterioration
and inadequate capacity of its spillway, ACTEW undertook a program of remedial work in January 1999.
Upgrade works were aimed at improving the stability of the dam against extreme flooding scenarios and
earthquakes and consisted of replacing the top 1.8m of the dam with a reinforced concrete load distribution
beam and anchoring the dam to the rock foundation using 45 modern anchors. The remedial work was
undertaken at a cost of $5.5 million. The work was concluded prior to the commencement of any
investigations relating to the Enlarged Cotter Dam proposal (as described in section 1 of this report). This
expenditure and the resulting upgraded dam was considered in reviewing the options for the ACT’s next
water source, which was conceived in response to the protracted drought experienced in the ACT since
2001. The upgrading of the existing dam was one of more 30 options that were considered as potential
new water sources for the ACT. A more detailed review of the options considered is given in section 1 of
this report.
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 43
Figure 2.6 The Cotter Dam and the Reserve have been a recreational destination for generations of
Canberrans and visitors
Figure 2.7 Building the original Cotter Dam between 1912 and 1915–16
44 WATER SECURITY – MAJOR PROJECTS
FEBRUARY 2009
Figure 2.8 The Cotter Pumping Station in its original configuration, before a two-storey extension was built to
house the vertical pumps
Figure 2.9 The Cotter Dam after the wall was raised in 1951
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 45
Figure 2.10 Tunnel and pipeline to Cotter Pumping Station on the banks of the Murrumbidgee River
2.3 Project specifications
The Enlarged Cotter Dam proposal includes both the main dam and associated infrastructure as well as
works associated with site establishment and gaining of on-site materials.
2.3.1 Main dam, saddle dams and associated infrastructure
The project consists of a main dam located on the Cotter River in the Lower Cotter catchment, with two
saddle dams to the right abutment. The Full Supply Level of the reservoir will be approximately 550m AHD.
The dam will be approximately 80m high. Design optimisation is in progress to determine the preferred dam
configuration by comparing traditional spillway arrangements and gate combinations. The adjacent saddle
dams will be built to an approximate height of 11m and 16m. The main dam will be constructed of RCC and
the saddle dams will be constructed of earth and rock-fill if an appropriate source of clay material can be
identified (including onsite options). If this material cannot be economically sourced, then the saddle dams
may be constructed of RCC or a combination of earth rock fill with a conventional concrete face. This is yet
to be determined.
46 WATER SECURITY – MAJOR PROJECTS
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Figure 2.11 Artist’s impression of the Enlarged Cotter Dam
The dam outlet works will incorporate provision for drawing water from multiple depths in the reservoir. The
Enlarged Cotter Dam will also require valving and pumping arrangements to allow for a variety of water
extraction arrangements to respond to changing operational and environmental requirements. These
arrangements will require modifications to pipework and augmentation of existing pumping facilities at Cotter
Pumping Station. These modifications will enable:
•• A blend of Cotter Reservoir and Murrumbidgee River water to be treated at Mount Stromlo Water
Treatment Plant.
• 100 per cent of Cotter Reservoir water to be treated at Mount Stromlo Water Treatment Plant.
• 100 per cent of Murrumbidgee River water to be treated at Mount Stromlo Water Treatment Plant.
• Murrumbidgee River water to be used for Cotter River environmental flow via recirculation pipework.
• Cotter Reservoir water to be used for Cotter River environmental flow.
A small temporary dam and diversion culvert will be constructed between the existing dam and the new dam
to ensure that the existing dam remains operable throughout the construction period and for protection of the
work site. The location of a quarry to supply construction material for the main dam and associated saddle
dams has been identified to the south-west of the right abutment.
The design of the main engineering infrastructure is still to be finalised. A copy of the latest concept design is
included in Appendix D.
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 47
2.3.2 Associated works and on-site materials
In considering the logistics and materials requirement for constructing the main infrastructure ACTEW is
investigating opportunities to source and use onsite sources of rock, sand and clay. The location of the
quarry sites are shown in Figures 2.3 and 2.4.
The quarry will be developed to extract approximately 800,000 tonnes of rock for use in concrete and
pavement materials. ACTEW is actively investigating the opportunity to manufacture sand from materials
gained from this quarry to use or supplement the aggregate requirements for batching of both RCC and
conventional concrete. Pending the outcome of the crushing trials and suitability of materials manufactured
there may be a need to further import aggregate materials (including sand) as required.
Rock will be extracted from the quarry using conventional quarrying methods (including blasting). Rock from
the quarry will be crushed, graded and stockpiled within the construction area for use in batching operations
and other construction uses.
In the construction of the saddle dams core material is required to create a water proof entre. Early design
estimates indicate a requirement of approximately 50,000 m3 of clay. ACTEW is investigating opportunities to
source clay within the construction and inundation footprint of the Enlarged Cotter Dam. Desktop
assessment and surface investigations during field visits resulted in the identification of three potential clay
borrow areas (see Figure 2.4). Although the areas under consideration are approximately 11ha in total the
actual borrow area required is dependant on the results from detailed geotechnical investigations and the
usefulness of materials found. These studies are yet to be completed.
Sourcing clay will involve excavation utilising a selection of the following machinery – scrapers, excavators,
dozers. Useful material will be carted to the construction site by truck primarily along existing forestry access
tracks with a possible need to use short sections of Brindabella Road or Bullock Paddock Road. Where
required, tracks will be upgraded and widened to allow for the increased use and ensure that no adverse
impacts are created from sediment run-off into the catchment. It is anticipated that no upgrading of local
roads (Brindabella Road or Bullock Paddock Road) will be required.
Clay material gained will be stockpiled within the construction area (adjacent to the proposed saddle dams)
and treated prior to being placed. Treatment of clay material may involve drying out and the addition of a
benign material such as lime or bentonite.
The main driver for investigating and sourcing onsite materials (clay, sand and rock) stems directly from the
opportunities associated with reduced traffic impacts on public roads (less hauling of materials from off-site
sources) and associated reduction in wider noise and traffic safety impacts, reduction in emissions and
greenhouse gases emitted given the reduced haulage requirements and some economics of scale (Detail on
likely delivery requirements are at section 5.1).
The location of the quarry and borrow areas are dependant on finding useful materials but in considering
likely site opportunities ACTEW has been conscious of the likely impacts of these works on the environment.
The locations proposed have been chosen to be primarily within the inundation area of the future Enlarged
Cotter Dam to minimise their impacts on visual amenity, terrestrial flora and fauna, heritage and other
matters. The likely impacts of these structures are discussed under the relevant section of this EIS.
Stripping of the overburden at the main dam and saddle dam sites is expected to produce approximately
400,000m3 of spoil. This material will be stockpiled in separate topsoil and general material piles. This will
allow the re-use of topsoil for rehabilitation and other works during and at the end of the project.
Part of the rock that is to be removed from the construction sites may be suitable for use in the construction
of the engineering infrastructure and investigations are ongoing to confirm its re-use potential. This material
(if suitable) will be blended with the general stockpiles and used in the preparation of construction materials.
ACTEW is also investigating other opportunities for beneficial re-use of the general material. The
opportunities include upgrading and maintenance of haul roads and access roads, build-up and levelling of
construction and works areas, reshaping of landforms during rehabilitation of the construction site and/or
filling of erosions gullies in the inundation area or as determined in consultation with the land custodian
48 WATER SECURITY – MAJOR PROJECTS
FEBRUARY 2009
Parks, Conservation and Lands (PCL). Further details will be provided for consideration at the DA stage of
the project.
The use of these materials is also earmarked by expert consultants for the creation of artificial habitats for
both terrestrial and aquatic species. Any strategies that include use of this material outside the “Extent of
works” will be discussed with the land custodian PCL and the Environment Protection Authority (EPA) prior
to such work being undertaken.
2.3.3 Project scope
In summary, the scope of the works includes:
•• Detailed geotechnical investigation for all associated works (including main infrastructure, quarry and
borrow areas).
• Design and construction of the main dam, the spillway and the saddle dams.
• Design and construction of protection works; that is, flood diversion around site works.
• Design and construction of dam outlet works, including flow control valves, control instrumentation
and gauging.
• Establishment of temporary use the construction site including set out of site compounds, batching and
crushing plants, and erecting of all fencing. (Note that Figure 2.3 provides the latest construction site set-
out. This is yet to be optimised and may change depending on actual construction methodology chosen.
This will be finalised for the Development Assessment.).
• Design and construction of upgrade works required for site access routes, haul roads and forestry tracks.
• Development and implementation of a community and stakeholder engagement program and provision of
community education and visitors services.
• Investigation, design and installation of power supply and communications infrastructure (likely to be
wireless) to service construction and ongoing operational requirements.
• Design and installation of a system to mix the water in the reservoir to maintain water quality.
• Implementation of the Cotter Reservoir Fish Management Program, which includes a range of ecological
studies as well as artificial habitat design and construction.
• Assessment into and ultimately the decommissioning of the old Cotter Dam
• Vegetation clearance (as required) from within the inundation area (mainly large trees)
• Rehabilitation works as required
2.3.4 Project design
The project design will be based on environmental conditions, planning issues related to the local area and
its uses, technical matters such as geology, and ongoing operational requirements.
The design of the dam structure and outlet works will also take into account the appearance of the dam and
its integration into the local Cotter recreational area.
Design will also address the possible progressive impoundment of water during construction and ensure the
ability to meet ongoing abstraction license conditions, including mandated environmental flows.
Additional details of the proposed works are presented in Table 2.1.
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 49
Table 2.1 Details of the proposed works
Element Description of works
Main dam wall—RCC structure.
Integrate the dam wall aesthetically and thematically into the wider Cotter Precinct
landscape and recreational plan.
Dam axis to be located approximately 125m downstream of existing Cotter dam
wall. Final location subject to geological and geotechnical assessment regarding
the adequacy of abutment and foundation conditions.
Width of main dam approximately 260 m.
Height of main dam wall approximately 80 m.
Storage capacity of approximately 78GL (at 550.8 mAHD).
Access to top and base of dam wall, for maintenance personnel and the public (if
permitted).
Multi-level intake tower capable of drawing water down to 5 per cent of storage
capacity.
Main dam
Internal access to drainage and inspection galleries.
Provision of shutters, trash and fish screens and gantry cranes at the intake tower
and associated electrical works.
Provision of surveillance instrumentation of the dam structure including
piezometers, tilt meters, inclinometers and remote monitoring.
Power supply and communications to intake and outlet structures.
Mechanical and electrical
works, instrumentation and
power supply
Dam plug valve to permit draining of the dam reservoir.
Quarry site Investigation and analysis of the quarry site, including suitability, quantity and
proximity of in-situ material.
Clay borrow areas Investigation and analysis of clay borrow areas, including suitability, quantity and
proximity of in-situ material.
Saddle dams Two separate embankments preferentially constructed of earth/rock-fill.
Service spillway for floods, designed in response to risk assessment.
Overflow crest and apron for flood events designed in response to risk
assessment.
Energy dissipating structure.
Variable level intake capacity with an approximate range between 5ML/d and
1,200ML/d for environmental releases with the dam at 60 per cent full.
The pipework required for the delivery of raw water from the river discharge point
to the suction side of the existing tunnel be sized to 1,500 mm.
Manual and remote controlled valve operation.
Spillway, intake and outlet
Intake tower to allow environmental flows and town demand to be sourced from
separate levels within the water column.
50 WATER SECURITY – MAJOR PROJECTS
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Element Description of works
Online water quality sampling for dissolved oxygen, turbidity, and temperature at
intake tower valves. Ability to take physical samples from intake valve levels using
the online water quality system.
Trash racks and fish screens on the intake tower to prevent material being sucked
into river discharge valves and Cotter pumps. Motorised rake arm to clear debris
off the trash racks.
Heavy lift ability for maintenance of intake valves.
Low-level intake to access deep storage and allow for flushing.
Water supply and environmental release pipelines to be fitted with appropriate
meters to measure flow for operational and licence requirements.
The discharge point of the stilling basin to incorporate a river flow gauge (wide V
notch crest), to allow measurement of the flow below the dam, whether it be
overflow or environmental flow release.
Spillway flow measurement.
Provision of additional (and/or replacement of) mixers and de-stratifiers to
maintain water quality in larger reservoir (subject to findings of hydrodynamic
modelling).
Extended boat ramp to allow reservoir access over the full range of drawdown.
Mixers operation to be linked to weather station at the dam wall.
Implementation of fish habitat management plan.
Aquatic real-time management system building on hydrodynamic model.
Quarry and borrow sites to be left to agreed standard and profile. Preference for
the location of sites is below Full Supply Level for use as fish habitats.
Provision of river diversion works.
Design must consider implementation sequencing to permit continued operational
use during construction.
Upgrading and continuous management of access and forestry tracks used to
ensure protection of the catchment and water quality
Vegetation clearing (inside the extent of works and within the inundation area)
as required.
Decommissioning of the old Cotter Dam
Catchment and precinct
management
Revegetation and rehabilitation of affected land (in liaison with PCL)
Optimisation of the progressive impoundment of water taking account of the
continued operational use of the Cotter Dam, including access for ActewAGL
maintenance personnel for the duration of construction.
Obtain all construction works permits and approvals required to execute
the works.
Ability to meet ongoing abstraction licence conditions, including e-flows.
General construction
Relocation of existing services as necessary.
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 51
2.3.5 Design process
An alliance has been developed between the owner, the designer and the constructor of the proposed dam
to benefit from their collective experiences and to ensure constructability of the final design.
The design process will involve the following key aspects:
•• Undertaking hydraulic modelling of dam and spillway and assessment in accordance with
ANCOLD guidelines.
• Revising existing geotechnical investigations and defining the scope for additional investigations (including
dam site, foundation grouting, quarry, saddle dams, access roads).
• Assessing potential quarry materials and carry out physical and chemical analysis together with crushing
trials and preliminary RCC mix designs.
• Assessing the extent of foundation grouting and pinning requirements.
• Assessing main and saddle dam arrangement options for primary and/or auxiliary spillways.
• Developing internal drainage design (optimise the number and location of galleries, determine ventilation,
lighting and operational requirements).
• Undertaking dam stability analysis in accordance with ANCOLD guidelines for normal, unusual and
4. Expanded populations of alien fish Likely Moderate High 6.8 Possible Minor Low
7. Upstream invasion of alien fish
species during construction of new dam
Possible Major High 6.8 Unlikely Moderate Low
Heritage
13. Values—impacts on cultural values Likely Moderate High 6.9 Unlikely Moderate Low
Social
15. Expectations of or misunderstanding
about impacts on water supply and the
need for future restrictions or projects
Likely Moderate High 6.10 Unlikely Minor Very low
14. Recreation loss of recreational
amenity
Likely Moderate High 6.11 Unlikely Minor Very low
Potential impacts on the project
8. Climate change—impact of
unavoidable climate change on the
project
Likely Moderate High 6.12 Unlikely Minor Very low
20. Climate change Likely Moderate High 6.12 Unlikely Minor Very low
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 91
4 Existing conditions
4.1 General
With the exception of a small area to the northwest, the catchment of the Cotter Reservoir is located wholly
within the ACT. The catchment covers approximately 50,000 ha of mostly sharply dissected terrain with a
mixture of sub-alpine, wet and dry sclerophyll forests, perched swamps and valley floor grasslands. The
primary use of the Cotter Catchment since the completion of the Cotter Dam in 1915 is as the water supply
for Canberra and Queanbeyan. Additional land uses have included grazing, forestry, mining and recreational
activities.
The Cotter catchment has been used for a wide range of land uses, many of which have resulted in
degradation of the landscape and subsequent reduction in water quality within the river systems. With the
exception of plantation forestry and some recreational activities, the remaining land use activities (recreation
and research) have only very minor impacts on the landscape and water quality as a whole. Plantation
forestry areas, though not a constraint to the expansion of the Cotter Reservoir, remain a degraded part of
the landscape.
Fire has been a part of the landscape of the Cotter Catchment since before European settlement with major
fires typically occurring during periods of drought. All significant fires within the catchment have resulted in
degradation of the landscape immediately after the fire event with subsequent loss in water quality.
PCL is the custodian and land manager of the Cotter Catchment and have adopted (among other
documents) the Lower Cotter Catchment Strategic Management Plan (ACT Government, 2007b). The
management plan aims to “Restore the lower Cotter catchment to a natural and stable condition that
supports the delivery of clean water and that also allows for a range of activities that are compatible with the
protection of water resources.” The plan recognises the importance of the Lower Cotter Catchment as a
water supply catchment for Canberra and sets out the framework for the management of the catchment and
activities therein in light of a number of strategic requirements, including domestic water supply.
The land immediately surrounding the existing Cotter Reservoir and Enlarged Cotter Dam are a combination
of Native vegetation, pine forest and revegetated land.
A detailed description of the Cotter Catchment is included at Appendix F. The Final Scoping Document
(Appendix A) requires that the EIS specifically describe the existing conditions under the following headings:
•• Climate.
• Geotechnical Conditions.
• Demographics.
• Demand for Water.
• Tenancy and Legal Land Description (Status of the Land).
• Legislative Context and other Statutory Documents (Commonwealth and Territory).
These matters are further are described below.
4.2 Climate
The Australian Capital Territory has a relatively dry continental climate with marked seasonal and diurnal
variations in temperature. As with the rest of Australia, the climate of Canberra is strongly influenced by a
band of high pressure systems located around theGLobe at about 30-40°S, known as the sub-tropical ridge.
As this region moves north and south with the sun, so there are different influences on the climate. During
the summer, the sub tropical ridge is located over southern Australia resulting in warm to hot conditions with
winds generally from the east through to the northwest. During winter this ridge is located across northern
92 WATER SECURITY – MAJOR PROJECTS
FEBRUARY 2009
Australia allowing the westerly winds and associated cold fronts to extend over southern Australia with colder
conditions.
At a latitude of 35.30°S and longitude of 149.20°E, Canberra Airport provides the location by which climatic
details have been collected in the ACT since 1939.
During this time, temperatures have ranged between -10°C and 42.2°C; the daily maximum often exceeds
30°C in summer. During the winter, temperatures are lower, and the higher parts of the mountains are often
covered with snow. The mean annual maximum temperature is 19.7°C and the mean annual minimum
is 6.5°C.
Figure 4.1 Average maximum and minimum temperatures for Canberra
January is the hottest month with a mean daily maximum temperature of 27.7°C and an average of 10 days
of 30°C or more with 2 days of 35°C or more. Canberra’s location being inland and elevated (around 580m
above mean sea level) often results in cool nights. The mean daily minimum temperature in January is
13.0°C. Canberra tends to get cooler easterly winds penetrating from the coast during many summer
evenings which can sometimes bring cloud along with moist air. With the warm to hot conditions during
summer and the effects of the nearby ranges, there is a distinct thunderstorm season during these months
and there are an average of 19 thunderstorm days between October and March compared to an annual
average of 23 days.
By contrast winters are cool to cold with generally westerly winds. Winter is also a time when Canberra can
experience clear, sunny days with light winds and a considerable number of frosts can occur. The
mean daily maximum for July, the coldest month, is 11.2 °C while the mean daily minimum is �0.2 °C.
Over the past 31 years the mean daily sunshine has been calculated at 7.7 hours. Fogs are common on
winter mornings.
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 93
Canberra is not considered a windy city with, on average, 25 days of strong winds a year. Late Winter/Spring
tends to be the windiest time with approximately half of these days (13 days) occurring in the 4 months
between August and November.
The maximum wind speed recorded in the ACT was 128km/h (24 November, 1957). The average annual
wind speed is considerably lower, 17.3km/h (recorded 3pm daily).
Figure 4.2 General wind direction and strength at Canberra Airport
Although it is fairly evenly distributed throughout the year, precipitation is somewhat less in the winter
(approximately 40 mm per month). The average annual precipitation since 1939 is 617.5 mm with the mean
number of rainy days over this same period being 72.5 days. Rainfall is much greater in the mountains,
averaging about 1,525 mm a year.
Rainfall across the ACT varies considerably, with much higher rainfall occurring in the ranges to the west of
the city and less rainfall to the east. During winter, the ranges tend to act as a barrier, and the city itself is in
a relative rain shadow.
94 WATER SECURITY – MAJOR PROJECTS
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Figure 4.3 Average monthly rainfall and number of rain days
Snow at Canberra is a rare occurrence, (only 1 to 2 recordings per annum on average) and most of the time
the snow melts very quickly. Snow tends to fall on the ranges to the west, and during winter this snow cover
can be readily visible from the city.
Average annual evaporation in Canberra is 1677 mm, however this can range from around 8 mm/day in
summer to as low as 1-2 mm/day in winter.
Due to the unreliable nature of local rainfall within the catchments, characterised by periods of drought and
flooding, large storage reservoirs are needed to ensure water supply.
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 95
Section 1 of this EIS provides more information regarding the recent rainfall history which is an important
consideration in determining the need for this proposal.
It is now widely accepted thatGLobal warming is occurring. Long-term studies of the climate confirm that the
increase inGLobal temperature observed since the mid 20th century is unusual. World experts consider it
‘very likely’ that this warming has been caused by emissions of greenhouse gases from human activities
(Intergovernmental Panel on Climate Change, 2007). This may mean that the climate record for Canberra,
which is based on the relatively recent past, no longer adequately represents current or future climate.
The CSIRO summarises the situation as follows:
The average surface air temperature of Australia increased by 0.7°C over the past century—
warming that has been accompanied by marked declines in regional precipitation, particularly
along the east and west coasts of the continent. These seemingly small changes have already had
widespread consequences for Australia. Unfortunately, even if all GHG emissions ceased today, the
Earth would still be committed to an additional warming of 0.2–1.0°C by the end of the century.
Yet the momentum of the world’s fossil fuel economy precludes the elimination of GHG emissions
over the near-term, and thus futureGLobal warming is likely to be well above 1°C. Analysis of future
emissions trajectories indicate that left unchecked, human GHG emissions will increase several fold
over the 21st century. As a consequence, Australia’s annual average temperatures are projected to
increase 0.4–2.0°C above 1990 levels by the year 2030, and 1–6°C by 2070. Average precipitation
in southwest and southeast Australia is projected to decline further in future decades. (Preston &
Jones, 2006)
The ACT Government has accepted the scientific evidence that the use of the planet and its resources has
already, and will continue to change our climate. In response to this, the Government released Weathering
the Change – the ACT Climate Strategy 2007-2025 in 2007 (See section 4.8 for a summary; ACT
Government, 2007d). The strategy provides an overview of the predicted impacts on the ACT and the
Government’s response to climate change. The strategy acknowledges the likelihood of increased
temperatures, more frequent and severe droughts, a decrease in rainfall and an increase in average summer
wind speeds. These are all major issues from a water supply perspective.
4.2.2 Climate variability
Climate variability is the natural variation of climate observed over time; it includes the familiar seasonal
variations, and the less familiar longer-term variations that climate experts are yet to fully understand.
Australia’s climate is highly variable in comparison with other countries; this is largely due to large scale and
long time-frame natural events such as the Pacific Decadal Oscillation, Inter-decadal Pacific Oscillation, and
El Niño Southern Oscillation.
The ACT has only 137 years of recorded historic climate data. Although this period of historic record covers
three major droughts, including the one at present, the ACT can reasonably expect to experience more
frequent or more severe wet or dry periods in the future than have been recorded to date. To address this
possibility, during the Future Water Options study, ACTEW ‘extended’ its historic climate record by using a
standard hydrological methodology to create a longer period of synthetic or stochastic climate data (Sinclair
Knight Merz, 2004).
The generated 10,000 years of stochastic climate data have equivalent average rainfall, evaporation and
variability characteristics to the historic record. The stochastic data also maintain the observed relationships
between rainfall and inflows at various sites, as well as the relationships between rainfall, inflow and
demand. However, the data set includes a greater range of climatic sequences, including more severe
drought events. Because the ‘period of historical record … may not represent the best picture of current
climatic conditions’ due to climate variability over time (Sinclair Knight Merz, 2004) a historic record of 26
years centred on 1990 was selected to generate the median stochastic data with variability based on the full
historic record. The generated stochastic climate data is referred to as the 1990 stochastic climate scenario.
96 WATER SECURITY – MAJOR PROJECTS
FEBRUARY 2009
4.2.3 Step change in climate
WhileGLobal warming progresses proportionally to the build-up of greenhouse gases in the atmosphere, it
can also result in rapid (‘step’) climate changes in a particular region. The reduction in rainfall and run-off
experienced in the Perth region in the past 30 years is often cited as an example of at least one step change
in climate.
It is possible that the recent drought represents a step change in climate for Canberra. The past 5 to 10
years represent the most severe long-term dry period in the 1871 to present extended historic record inflow
sequence. The past few years exhibit inflows that are consistently lower than average, with remarkably
similar low inflows from late summer to early winter. The average system inflows during the past 10 years
are also lower than the average inflows generated with 2030 stochastic data (data that incorporates the
expected 2030 climate change impacts and equates to 88GL per year compared to 105GL per year). On
average, a five-year period worse than the last five years would occur once every 19 years in the stochastic
data. Therefore, the last few years would be a drought even with predicted climate change. The inflows to
Googong reservoir during this period are especially low when compared to the historic record or the
stochastic data. The CSIRO climate change report (2003) comments that:
There is evidence of a shift in the last 20 years, with several locations (Michelago is an exception) near
to Canberra showing a small decline in rainfall and a decrease in interannual variability after the mid to
late 1980s. A similar shift has been well documented in the southwest of Western Australia.
The current drought has the lowest inflows over a long-term period, with 2006 producing the third lowest
inflows of any year on record, behind 1901 and 1982. The 1910s and 1940s also contain long-term droughts
where average inflow is only a little higher than the current period. Figure 4.5 shows the 2-year, 5-year and
10-year average total inflows to Canberra’s water supply system over the period of record. It is noteworthy
that the period from 1950 to 1980 exhibits some consistently high inflows that are not reproduced at other
times in the record. The inflows since 1980, including the current drought, appear relatively similar to the
1871–1950 portion of the period of record.
Figure 4.4 Moving average inflows to Corin, Bendora and Googong Reservoirs
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 97
The aspects of the local climate that are of relevance to this project relate to rainfall and runoff predictions
and their possible changes into the future. These are addressed in detail in section 6.2.
4.3 Geotechnical conditions
A major characteristic of the geomorphology of the Cotter Catchment is the wide range of rock types present
that include marine metasediments, volcanics and granitoids. The rocks of the Cotter consist of Ordovician
and Silurian igneous rocks and marine metasediments from the Adaminaby and Tidbinbilla groups
respectively, Silurian volcanics of the Uriarra and Paddy’s River volcanics, and Silurian to Devonian granitic
rocks. The Ordovician sediments and Devonian granites exist throughout most of the catchment with the
volcanics appearing exclusively within the lower catchment and mostly near the Cotter Reservoir.
Soils derived from these geological units are highly variable in both their physical and chemical properties
and also vary based on land use history. The volcanics are separated from the sedimentary and granitic
rocks by the Winslade fault which passes to the south of the Cotter Reservoir. Unconsolidated sediments
tend to be coarse sands and gravels and are found mainly within the existing creeks, rivers and reservoir
deltas. Finer silts are found in the damp and swampy areas.
A detailed description of the broader geology of the Lower Cotter Catchment is provided in Appendix F.
Preliminary site investigations were carried out in 2007 at the main dam and saddle dam sites and form the
basis of the current geological model for the expected subsurface conditions at the dam sites (Appendix F).
Difficult access conditions to the steep abutment slopes limited the scope of the investigations at the main
dam site to those areas that are accessible by foot and four-wheel drive vehicles.
The preliminary picture has been further completed by ACTEW conducting a range of further investigations
since 2007 that included geological mapping, the establishment of test pits and bore holes, material
sampling, chemical and physical testing of rock, percussion drilling and seismic survey works. More extensive site investigations were completed in 2008 using helicopters to lift small drill rigs onto the steep abutment slopes.
This work was a key recommendation of the Enlarged Cotter Dam Update Report 2007 (Appendix S). The
further investigations undertaken to date include the following work:
Main dam
•• Diamond cored boreholes: 16 diamond cored boreholes, comprising a total length of 948m of rock.
• Seismic refraction survey: 5 seismic refraction survey traverses, comprising a total length of 1160m
including both the main dam seismic line and a number of cross seismic lines.
Saddle dams
• Diamond cored boreholes: 7 diamond cored boreholes, comprising a total length of 544m of rock core.
• Trench excavations: two 21m long trench excavations to investigate the saddle dam foundation conditions
(one in each saddle).
Rock quarry sites
• Diamond cored boreholes: 15 diamond cored boreholes, comprising a total length of 726m of rock core.
• Percussion boreholes: 105 percussion boreholes, comprising a total length of 2,205m of drilling to retrieve
294 rock chip samples.
• Seismic refraction survey: 6 seismic refraction survey traverses, comprising a total length of 1,725m.
• Trial excavation: A trial excavation and rock extraction to a depth of 12m to determine composition and
characteristics of rock for onsite material source.
These investigations form the basis of the current geological model for the expected subsurface conditions at the dam sites.
98 WATER SECURITY – MAJOR PROJECTS
FEBRUARY 2009
All investigations to date have been reviewed by independent experts for quality and the appropriateness of
the extent of investigations performed. A detailed three dimensional geological model has been developed
for the dam abutments to better understand the extent of excavation required and quality of foundation rock.
The information gained from the investigations described above is being used to inform the detailed dam
design and construction methodology.
All three dam sites and the downstream reaches of the storage are located in the Walker Volcanics. Rock
samples from the dam sites have been classified as being mainly a porphyritic rhyolite. Overlying and to the
west of the Walker Volcanic Group and also transecting the storage area is the thin Tarpaulin Creek
Ashstone Member, which is a fine-grained bedded ashstone (Appendix F). The Uriarra Volcanics which
outcrop further to the west, underlies the remainder of the storage area. These are described as consisting
of dark grey to pink rhyodacite ignimbrite and air-fall tuff.
Aerial photographs indicate the presence of a number of well-defined linear gully features within the area of
the dam sites. These features suggest the presence of more fractured or weaker rock, which has eroded,
resulting in the development of stormwater drainage lines.
The main dam site is located within a river valley trending north-west/south-east with steep topography and
limited vegetation. The two saddle dam sites are located about 400m and 800m south-east of the main dam
site at low points on a ridge that will form the right abutment of the main dam. Ground slopes on the left
abutment are in the order of 45 degrees or steeper and on the right abutment slopes range between 35
degrees and 45 degrees. The topography associated with the saddle dams is undulating with slopes in the
order of 10 degrees to 30 degrees from horizontal. Bedrock exposure is common on the left abutment at the
main dam site, with only minor soil cover present. On the right abutment the exposure of bedrock is limited,
with larger areas of soil cover. Geographical mapping identified four major rock mass defect sets on the left
abutment and three sets on the right abutment. In both cases these rock mass defects have exercised
significant control on the stability of the slopes within the valley containing the main dam site. It is expected that intersections of these rock mass defects in the dam foundation will result in some rock mass movements during excavation. The foundation design and construction sequencing will need to cater for this potential.
The slopes at the saddle dam sites mostly have a thin soil cover. The gullies tend to include a higher
proportion of colluvial soil that has eroded from the adjacent slopes. Parts of these gullies are relatively
deeply incised.
The Winslade fault (located to the south and east of the proposed reservoir) at its closest point is about
700m from the dam sites (Detailed description in Appendix F). It does not transect the proposed inundation
area or any of the dam sites and as a result is not likely to have any impact on leakage from the storage. The
further geotechnical investigations (described above) included seismic hazard assessments that confirmed
the suitability of the site for this project.
Rock mass permeability testing has been carried out over selected depth intervals in the investigation
boreholes. The results of the permeability testing at the main dam site generally indicate a low rock mass
permeability with some moderate to high permeability in the weathered zone close to the ground surface, as
well as in isolated locations at depth. Leakage from the reservoir through the dam foundations will be
controlled by the injection of cement grout into any permeable fractures in the bed rock, to form an
impermeable barrier.
The investigations confirmed that a quarry located within the Walker Volcanics, about 700m west of the main
dam site will provide suitable materials for concrete aggregates, filter materials and rock-fill. Potential
borrows for the supply of impervious core for the saddle dams are still under investigation and are described
in section 2.3.
From a geological perspective the site is suitable for the type of dam proposed.
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 99
4.4 Demographics
Canberra is Australia’s national capital and its largest inland city. It is located 280km southwest of Sydney
and 650km north-east of Melbourne. With an estimated resident population at 30 September 2007 of
340,325 people. This represents an increase of 460 people (0.1 per cent) in the three months since 30 June
2007. The ACT Government’s primary policy document the Canberra Plan: towards our second century
(ACT Government, 2008c), has aspirations for the city to grow to approximately 500,000 people.
For the year ending 30 September 2007 the ACT population rose 1.5 per cent, matching the Australian
population rise of 1.5 per cent. The ACT's population increase includes a natural increase of 836 persons, a
net interstate migration loss of 587, and a net overseas migration gain of 211. Natural increase continues to
be the major contributor to population growth in the ACT.
The Canberra Plan examines the option of a higher growth rate scenario for the ACT and region based on
Australian Bureau of Statistics high-end forecasts leading to a population of 500,000 by 2032. This assumes
an annual net migration to the ACT and region of about 2,500, which includes retention of young people
following completion of tertiary training.
Two key points in historical population growth are:
•• Natural increase is by far the largest component of growth for the ACT.
• Volatile migration trends and Federal Government activity drive the swings in the Territory’s
population growth.
Population growth rates in the ACT have been less than national levels and the Australian Bureau of
Statistics estimates confirm a continued low growth scenario that is below the national average. Growth rates
for Canberra and region of around 2,000 to 2,500 per annum would represent a proportionate share of
Australian projected population trends of growth based on net immigration of about 80,000 to 110,000 per
annum but less than replacement fertility rates. These are the parameters necessary to provide for a stable
population base for Australia overall post 2025. Shortfalls in those figures for both Australia and for Canberra
would see an absolute decline in population and increasing aged dependency. For Canberra that decline
would occur by about 2050.
Adequacy and reliability of water supply could contribute to policies to achieve modest growth in the ACT
over the next 30 years or so and longer stability in population levels after that.
The extent of population dependent on the future water supply depends on future policy, particularly with
respect to the population outside Canberra and Queanbeyan. The inclusion of regional supply and
specifically to Yass in future water planning is recommended in Think water, act water (ACT
Government, 2004a).
As the authority responsible for delivering a reliable water supply to the region, ACTEW must ensure
adequate supply is available for the projected future population.
While the ACT Government and ACTEW are targeting reductions in per capita water usage of 25 per cent by
2023, that goal may not be easily achieved. In Future Dilemmas: Options to 2050 for Australia’s population,
technology, resources and environment (CSIRO, 2002) the CSIRO reports that per capita water
consumption tends to rise with increases in real income and with economic growth. The report indicates that
the growth in national water consumption was approximately 4 per cent per annum in the decade to 2001
and predicts that even with achievement of efficiencies in water use of in to order of 30 per cent, usage is
likely to double over the next 50 years for Australia as a whole.
The CSIRO estimates that in the longer term water demand per capita is expected to increase by 5 per cent
to 16 per cent per annum in response to warmer climates. The impact of water as a limiting resource for the
ACT and region could have a range of consequences, difficult to predict but characterised chiefly by human
reactions to uncertainty. The potential consequences may include:
100 WATER SECURITY – MAJOR PROJECTS
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•• Reduced diversity of employment.
• Increases in property pricing (If land development was restricted) and follow-on effect associated with
housing affordability and renting of accommodation.
• Spillover of demand for accommodation deferred to region and surrounding towns with consequential
implications for water demand in those places and likely continuing demand in Canberra for health,
education and like services.
• Reduction in Canberra’s competitiveness as a place in which to establish businesses which would lead to
a declining employment base and an even greater ageing and economic dependency for the population.
• Potential significant adjustments in government investment and outlays, (including its capacity to provide
essential social and community services), private sector investment and employment, and in household
decisions on location.
In current water system performance modelling, all ACT and Queanbeyan population projections begin from
the estimated 2004 water supply population of 360,431. As no further combined projections for Canberra and
Queanbeyan populations have been made since 2003, the numbers provided by the Chief Minister’s
Department are used.
A detailed suburb-by-suburb growth plan and discussion of the growth nodes is included in the ActewAGL
document ACT Population Forecast by Suburb 1998–2018. This forecast is based on key government
policies for urban growth and the ACT Government’s Land Supply Strategy (ACT Government, 2006b).
ACTEW’s Asset Management Plan 2008/09–2027/28 sets out the planning for capital works and the
operations and maintenance of the Canberra water supply, sewerage and reclaimed water system assets in
order to meet to the population projections.
Urban planning policies and trends also require consideration. This includes water efficient sub-division
design, block sizes and densities, and legislative intervention requiring the water efficiency measures in
dwelling design. ACTEW is working closely with relevant ACT Government agencies to ensure these trends
and policies are considered in the appropriate planning for water infrastructure.
4.5 Demand for water
Demand for water and the determining the likely future demand for water in Canberra is a complex matter.
As shown in the Socio-Economic Impact Assessment (Appendix O), increases in water demand are
commonly associated with population growth, increases in housing formation, economic growth and
increases in income. Although Canberra’s population growth rates are expected to be less than the national
average it will be a strong contributor of the likely increases in demand for water.
The Socio-Economic Impact Assessment (Appendix O) references the CSIRO Futures Report (CSIRO,
2002) and states that “…per capita water consumption tends to rise with increases in real income and with
economic growth”. Canberra’s affluent population is expected to demand more water than the average user.
The report further states that “… longer term water demand per capita is expected to increase by 5 per cent
to 16 per cent per annum in response to warmer climates…”, which is a clear indication that climate change
is expected to significantly contribute to Canberra’s future demand for water.
Currently the ACT uses about 65GL of water a year. This usage is out of approximately 494GL of ACT-
controlled water resources, 269GL of which is dedicated to environmental flows. This is based on long term
averages, and the last 7 years has seen a great reduction in use and flows.
Residents in detached houses account for more than half of Canberra’s consumption (see Figure 4.6). The
use of water by commercial users is mostly for workplaces but also for golf course watering and other
irrigation. Of the water used by government users, nearly one third is used for irrigation of parks, playing
fields and school grounds. Queanbeyan uses about 5GL of the water in the ‘Other’ group in Figure 4.5.
ENLARGEMENT OF THE COTTER RESERVOIR AND ASSOCIATED WORKS
ENVIRONMENTAL IMPACT STATEMENT 101
Figure 4.5 Water use distribution for Canberra and surrounds
The ACT Government has outlined a plan to permanently reduce potable water consumption in its Think
water, act water document. This document identified a target per capita reduction of 12 per cent by 2013 and
25 per cent by 2023.
It is intended that a variety of means be used to achieve these targets, including:
•• Education and advertising.
• Permanent water conservation measures.
• Effluent reuse.
• Stormwater harvesting.
• Rainwater tanks.
• Greywater reuse.
• Water efficient appliances and fittings.
• Leakage reduction.
• Government subsidised indoor and outdoor water tune-ups.
• A requirement for new developments to achieve a 40 per cent reduction in water use through water-
sensitive urban design.
• Ongoing pricing reforms.
It is predicted that demand management alone will achieve the 12 per cent target. Indeed, permanent water
conservation measures and a general increased awareness of the need for water conservation may well
have already delivered this saving.
Even with this saving it is expected that source substitution (for example, rainwater tanks, greywater reuse,
effluent reuse, stormwater harvesting) will be required to reach the 25 per cent reduction target. As source
substitution methods are relatively expensive, it is expected that the 12 per cent target by 2013 will be more
easily achieved than the 25 per cent target by 2023.
In April 2008 the Independent Competition and Regulatory Commission (ICRC) released its determination on
water prices for the period 1 July 2008 to 30 June 2013 (see section 5.11). The determination provides a
tariff structure that is based on forecast consumption by the customer base, but one that also provide price
signals for high water use. Further analysis over the regulatory period will be required to assess the
102 WATER SECURITY – MAJOR PROJECTS
FEBRUARY 2009
effectiveness of the price signals leading to behavioural change in terms of water usage. Full details on the
ICRC’s considerations leading to their decision are in Water and Wastewater Price Review – Final Report
and Price Determination (ICRC, 2008).
4.5.2 Permanent water conservation measures
Permanent water conservation measures were introduced in Canberra and Queanbeyan in November 2005.
However, they only applied for a year before temporary water restrictions were reintroduced. The component
of the permanent measures that has the most significant impact on consumption is limiting sprinkler and
other irrigation systems to the hours of 6 pm to 9 am, except during winter. This measure encourages garden
watering in the morning or evening when absorption rates are higher than in the middle of the day. The intent
behind the permanent measures is to discourage inefficient water use through means that should cause very
little inconvenience to the community.
The target reduction for the permanent measures was 8 per cent. A 23 per cent reduction in consumption
was observed during the year that they were introduced, relative to the pre water restriction consumption
pattern. However, this reduction is unlikely to be sustained in the long term because:
•• The permanent measures were applied after a severe drought. Awareness of water conservation was at a
very high level and many gardens that required high water use were adversely affected by the drought and
had not been re-established.
• Many users may be maintaining habits established during the water restrictions scheme, such as only
watering every second day. These patterns may not be maintained indefinitely.
Until the recent drought, very little information was available on how much consumption is reduced by water
restrictions. However, it is now possible to determine the consumption reduction associated with each water
restriction level. It has not been determined how much of the reduction is achieved by the water restriction
event itself and how much is achieved by the ongoing demand management program.
Table 4.1 shows the target and observed consumption reductions for the period from 1 November 2005 to 15
April 2008. As discussed above, the permanent water conservation measures period produced a larger than
expected reduction that can be attributed to a range of factors besides the measures themselves. Stage 2
and Stage 3 have also delivered significant water savings, but have narrowly failed to achieve the targets.
Table 4.1 Target of and observed reductions from water restrictions since November 2005
Restriction
level
Target reduction
relative to PWCM (%)
Target reduction relative to
period before restrictions (%)
Observed reduction relative to
period before restrictions (%)
PWCM* – 8 23
1 10 17 –
2 25 31 26
3 35 40 38
4 55 59 –
*PWCM—Permanent Water Conservation Measures.
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ENVIRONMENTAL IMPACT STATEMENT 103
4.5.3 Conclusions
All water resource modelling used in this EIS assumes that the ACT Government’s 25 per cent reduction
target will be met by 2023. It is assumes that the reduction will occur uniformly from 8 per cent achieved
in 2005.
ActewAGL, on behalf of ACTEW, will continue developing a Canberra End Use Model. The model is
designed to determine how water is used, the impact of water efficient devices, changes in water usage
behaviour and will thus inform water resources modelling and assist with investigating the means required to
meet the ACT Government demand reduction target.
Objective
Gain a greater understanding of water use in the ACT
Commitments
End use model ACTEW, through ActewAGL, will continue developing an effective Canberra End Use
Model.
4.6 The status of the land
All land within the project area is either unleased land owned by the ACT Government under the
custodianship of PCL or leased by ACTEW Corporation.
The following blocks of land, as described in Table 4.2 and Figure 4.6, may be directly affected by
the project:
Table 4.2 Blocks of land that may be affected by the project
District Block Land status Lessee/custodian
Coree 29 Unleased/public land/gazetted park TAMS – Environment