Ord River Irrigation Area - Stage 2
How Goomig Farmlands Development
allows for an Expanding Future
Background
Development of the Ord River Dam and the first stage of the irrigation development
(Ivanhoe Plain and Packsaddle areas - M1 development area) were initially
undertaken in the 1960s. Since that time, there have been a number of attempts at
getting a second stage of this development underway. These have been without
success until now.
The second stage was originally envisaged as involving the development of
approximately 30,000ha of new farmland, with the main broad acre areas straddling
the WA and NT borders. These areas included the Weaber, Keep and Knox Plains
which comprised the M2 area. Stage 2 development also targeted further riverside
development for horticultural purposes.
The preliminary designs for the development of these areas were undertaken in
1997 and, subsequent to this, a consortium of Wesfarmers and Marubeni was
awarded the mandate to develop the total broad acre areas. Unfortunately, after
considerable effort and consideration, this consortium withdrew.
Development of the M2 area was made possible through the resolution of Native
Title issues in 2005, with the signing of the Ord Final Agreement. State level
environmental approvals are in place for the full M2 area, however only the first
phase of the M2 development on the Weaber Plain (now called Goomig Farmlands
and comprising about 8,000 ha) has Federal Government (EPBC) approval at this
time.
The WA government provided funding in excess of $300m for the Goomig
Farmlands through its Royalty for Regions scheme. Detailed design commenced in
mid 2009 and construction commenced in mid 2010.
A key requirement of the Goomig Farmlands development is the delivery of
indigenous employment and business development for the traditional owners, the
MG people.
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One of the major challenges of the new Goomig Farmlands development was
providing for the approved development, while still preserving the full development
option potential and at the same time minimising capital investment.
The intention was to be in a position to progressively release lands and develop
further lands, depending on the market demands.
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New Development - Overview
The existing Stage 1 development is supplied by an existing main channel (M1) and
a number of subsidiary channels. The M1 channel originates at the Kununurra
Diversion Dam and has a total length of approximately 23km. The Preliminary
Design of the Stage 2 development allows for the construction of a new main
channel (M2) for the full length of the existing M1 channel.
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The M2 channel continues in a north-easterly direction through Cave Springs Gap
for a further 7kms, before branching into two channels to supply the Weaber Plains
area.
The construction of M2 channel for the first 23km where it parallels the M1 channel
will require a very significant capital investment, and a number of studies have
focused on the potential for staged construction to delay the investment in this
section of channel.
The approved new development (Goomig Farmlands) is centred on the western end
of the Weaber Plain, which is some 10-15km north east of the existing irrigation
area. The initial phase is targeting approximately 8,000ha of new farmland. This
area was based on assessments undertaken in 2002 of a cost effective upgrade of
the existing M1 channel, to delay the high cost of the new M2 channel.
Stimulating development at an affordable cost was a major objective of the project.
The Weaber Plain is bounded by ranges in the west, north and south (Weaber/Cave
Springs) and the Keep River in the east. However, not all of the Weaber can be
readily developed, as the eastern extent is within the Northern Territory which, to
date, has not been participating in this Project.
The Weaber Plain is a remanent alluvial flood plain of the Ord River, with the soils
being a uniform cracking clay and very flat grades (less than 1:5000), generally
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sloping to the north east. The main feature of the area is Folly Rock which is a
protrusion of the bedrock. In order to supply the individual lots, a system of channels
to the north (M2N) and south (M2S) of Folly Rock was necessary.
Design Scope
The design of the works to supply the new farmlands was undertaken by an
association of GHD and SunWater. The scope of the designs included:
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Subdivisional Layouts
Channels and Structures – 40 km
Roads and structures – 35 km
Farm Drainage – 54 km
Protection Levees – 33 km
Hillside drainage – 30 km
This paper primarily concentrates on the supply works, since these are impacted
most by provisioning for further stages. Where other aspects are impacted, these
are also noted.
Channels
In addition to the 37km of M2, there were some 18.5km of other channels required to
supply the individual lots. These channels vary in capacity and are all earth and
earth-lined, with regulating points to control water levels. Structures include siphons
to cater for access and allow overland flow, wasteways for overflow and drainage
and metered outlets to individual blocks.
Rubicon Water has been awarded the contract to supply and commission the control
system for the channels.
The M2S channel will be constructed to within 9km of the NT/WA border.
Roads
The design criteria are in accordance with current Main Roads Western Australia
(MRWA) and Austroads standards, with MRWA taking precedence.
Pavement designs catered for future lands being developed and took into account
the anticipated ESAs generated by these developments.
Area Drains
Drains are being provided to cater for storm water runoff and prevent excessive loss
to crops due to inundation.
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A key environmental approval requirement was to ensure that the first flush of 25mm
for annual crops and 12mm for sugar was retained on farm, and gated drainage
inlets have been included to assist individual farms achieve this outcome.
Flood Protection Levees
A system of levees will be constructed to prevent the farm areas been flooded during
large external runoff events. Given the high rainfall intensities and the significant
size of the outer catchments, a major consideration was the provision of Flood
Protection Levees, to avoid flooding of the development area and potential damage
to crops. These Levees have been design for a 1:20 year event.
The Flood Protection Levee (FPL1) will ultimately extend through to the Keep River
with an additional 20km of levee. A smaller levee has been constructed to link into
the existing Weaber Plains Road.
Hill Side Drains
There is a significant catchment area between the surrounding ranges and the
irrigation development. A system of hill side drains will be constructed to manage
the runoff from these areas.
Scope Exclusions
A significant exclusion for the initial phase of development was any of the originally
proposed balancing storages. The design of the supply system originally included
two balancing storages, to even out any fluctuations in supply and demand, as well
as provide capacity to capture any rain rejection flows. As the balancing storages
were designed to cater for the total Stage 2 demand, it was not proposed to
construct any balancing storages as part of this initial phase. A critical aspect of the
design was the provision of mechanisms to manage the supply to the new area
within the prescribed efficiency limits, which were aimed at achieving less than 15%
losses.
This target would be a challenge in any open channel system, but even more so in
one with such a long distance between the water source and supply areas (some
37km in the initial development area). Being able to combine the M1 and M2
demands, in part, has enabled these targets to be achieved.
Staging Options
M1 versus M2
While the approval of the Goomig farmlands was based on the use of the
M1 channel as the supply mechanism for the development, the detailed design reexamined this aspect and developed the final arrangement.
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A hydraulic model was developed to allow assessment of the water surface profile in
the M1 channel. The model is a steady state backwater analysis tool capable of
representing a range of flow conditions. It uses stepped calculations within an Excel
spreadsheet and models open channels, concrete control structures and piped
sections. The model has the capability to vary channel dimensions and design
criteria such as bed width, flow depth, bank height and Manning’s roughness.
The combined flows for the existing M1 channel and the proposed new development
were modelled and the optimal arrangement of bed widening and deeper flow
sections was determined. Given that this was to be a “short term” solution, it was
argued that some minor encroachment on the existing freeboard allowances would
be acceptable.
Various methods to increase the capacity of this channel were considered, such as:
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Increasing bed width;
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Raising bank height (and structures);
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PE lining; and
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Combinations of the above.
This assessment concluded that a combination of upgrading M1 to 17.3km, and a
new M2 channel beyond that point, would be the most cost effective solution for a
development of up to about 8,000ha.
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This varied slightly from the 2002 assessment, in that the section of M2 channel from
17.3km to 23km was included in the Stage 2 scope for the following reasons:

Relatively short section;
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This section of the existing M1 channel was originally constructed as a
temporary channel and to lower standards;

There was evidence that this section of channel was susceptible to
intermittent overtopping.
The proposed supply to the new development for this initial phase includes:

Upgrade (through a 3.0m bed widening) of the existing M1 channel to the
control structure at M1C3 (about 17.3km);

Construction of the M2 channel from 17.3 to 37.2km;
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Decommissioning of M1 from 17 to 23km;
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M1 downstream of 23km to be supplied by the new M2 channel.
The above arrangement will be a challenge from a water accounting perspective.
There is currently a water meter at the start of M1 channel, and a new meter has
been installed in M2 at about the Drain D4 crossing (23km), in order to account for
the existing supplies and new development supplies. Negotiation of the share of
losses between the existing Ord Cooperative and the new M2 Service provider is still
to be negotiated.
The current design of the M2 channel is based on flow control being via upstream
controlled regulators. To set flows as accurately as possible to achieve the target
efficiencies, a system of water ordering will need to be introduced. Given that the
existing area will also be supplied by the same channel, this water ordering system
will also need to be introduced into the existing area.
M2 and M2S Design Standard
The M2 and M2S channels are the main conduit to supply the land which will
potentially be developed in future stages of this project, namely the Knox and Keep
Plains areas.
Options to stage the construction of these channels were examined. It was
concluded to not be cost effective to attempt staging of the channel earthworks.
Accordingly, the designs for the Goomig area provided channel sections that will
ultimately cater for the full development.
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An examination of staging options for the structures also concluded that this would
be impractical for the concrete works. However, only sufficient control gates and
siphon capacity has been installed to supply farmlands in WA in the initial
development.
Management of Flows
Balancing storages offer a simple mechanism to manage any mismatch between
supply and demand within a channel system. Storages can be located at any
convenient location, however the closer they are to the actual demands, the quicker
changes in demand can be managed and losses minimised.
While balancing storages, as envisaged in the Stage 2 preliminary design, are not
provided for in the Goomig area design, specific features such as the over-capacity
of the main supply channels (as provided for future stages) and the allowable
operating ranges of specific sections, were worth examining, to see if any worthwhile
in-channel storage was available. The options for storage potential vary depending
on the channel and vertical alignment. Each channel has been examined for
potential storage options.
Channel M2
There is opportunity to use the bay between M2C3 and M2C4 as a temporary
Balancing Storage, until such time as any future lands to be served come on line.
There is the potential to create a 200ML in-line storage, provided all 4 gates at the
M2C4 structure are installed. These gates will be needed to get the Weaber Plains
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flow (approximately 1,000ML/day) through this structure at a lower operating level
(refer the following diagram).
Hydraulic Model of Channel M2
34.00
33.00
32.00
Elevation (m)
31.00
30.00
29.00
28.00
27.00
26.00
20000
22000
24000
26000
28000
30000
32000
34000
36000
38000
40000
Distance (m)
Bed Elevation (m)
Bank Elevation (m)
DFL (m)
Modelled Water EL
Pool (m)
Lower Pool (m)
Nat Surface
Having this inline storage would eliminate the need to change the flow settings at the
M2C3 regulator (23km) other than for major changes in demand. Daily adjustments
could be managed by control of the M2C4 regulator (30km).
Channel M2S
The M2S channel is sized to supply the potential development of the remainder of
the Weaber Plain, as well as the Keep and Knox Plains. The actual demand on M2S
in this phase of the Project is about 550ML/day, as opposed to the design capacity of
close to 2,800ML/day. As a consequence, there will be very little fluctuation in water
levels in the channel bays due to demands on the system. The design for the full
capacity will detail a channel freeboard of 0.95m. Given the small demands on this
system from the Goomig development, it is feasible to allow an encroachment on this
freeboard for this interim development.
A 500mm encroachment on the last bay of Channel M2S (6.0-12.3km) provides a
potential operational volume of approximately 90ML. If the system was being
operated in a standard upstream control mode, a 45ML operating storage would be
available, which would provide approximately a 12 hour reaction time for the system
to change when an outlet (maximum outlet on system is 89ML/day) turns on or off.
If the system was being operated under Total Channel Control (TCC), then the total
90ML would be available, with a resulting 24 hour reaction time being provided.
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Channel M2N
Some operational storage could also be built into the last bay of the M2N channel;
however, as the freeboard is only 600mm, some additional earthworks would be
necessary to provide for the channel fluctuations. Allowing for the Pool level to be
300mm higher in the last bay of M2N, provides an in-line storage of about 15ML,
however the cost of the additional earthworks is not as cost effective as adopting an
advanced control system such as TCC.
Progress to Date
The current status of the Project is that almost 70% of the works have been
constructed, with the balance expected to be completed by the end of this year.
Construction is being undertaking by Leighton Contractors. To date, 20% of the
direct labour force has been indigenous. It is forecast that about $4m will be spent
with local indigenous business.
WA undertook a land sales process, which included Goomig and the balance of the
farmlands within WA, totalling in excess of 15,000ha. The WA Government is
currently negotiating with the preferred proponent, Kununurra Agricultural
Investments Pty Ltd (KAI), a subsidiary of the Chinese Zhongfu-group, with a view to
completing negotiations and finalising lease conditions in mid 2013. KAI expects to
start developing farms in the Goomig area in the latter half of 2013 for sugar
production. One cornerstone of the KAI proposal is to construct a sugar mill near the
NT/WA border.
As the main water supply channel is now only 9km from the NT border, the NT
Government has indicated a willingness to investigate farmland development within
the NT and has commenced development investigations.
Some further staging options to supply these lands through the M1 channel are now
being considered.
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