Month: February 2019

Elevations of Locations in Bradfield Scheme

The experts say it can’t be done, but a close look at the elevations of the sources, storages and destinations for the Bradfield Scheme says otherwise.

The ideal gradient for an open gravity-fed irrigation channel is 1:5000 or 100m per 500 km. Any flatter and the flow slows and steeper risks damage. This is the typical gradient for the Roman aqueduct system totaling over almost 1000 km delivering 10,000 GigaLitres of fresh water to Rome per day.

In an eastern Bradfield Scheme, the elevation goes from 430m at Niall near the Burdekin River to Lake Buchanan over the 500km to the main storage at 340m at Lake Buchanan and 280m on Lake Galilee. This is an average gradient of 1:5000.

The water could potentially be distributed throughout the whole of the fertile black soil plains area of Central West Queensland, from Barcaldine at 267m and Aramac at 226m, to Longreach and Richmond at around 200m, as far as Julia Creek at 132m about 500 km from Barcaldine (light blue polygon). Again 1:5000.

The topography starts to rise towards Hughenden at 318m and Blackall 284m and so would set the furthest extent for a gravity-fed supply. However, the land continues to fall towards Birdsville 48m and Innaminika 16m and so could continue to be fed in a south-western direction.

The Tully Falls near Cairns at 670m elevation and Herbert River are viable sources of gravity-fed inflow to the scheme.

The black soil plains of Central West Queensland currently support mainly low intensity grazing due to the irregular water availability. However, they are well located to supply communities to the north, south, east and west with higher value agricultural products, including irrigated cotton, wheat, and horticultural products. This would be enabled by a well established infrastructure of rail and road connections.

Water from the scheme would also augment town water supplies, many of which are under extreme pressure, where the drought-hit town of Ilfracombe has even imported a temporary desalination plant.

Water from the eastern portion of the scheme may largely flow to the Muttaburra, Aramac, Longreach and Barcaldine area, while from the western portion of the scheme fed by Gulf rivers may supplement areas such as Richmond and Julia Creek.

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Categories: Book Bradfield Scheme

Is the Bradfield Scheme Viable?

In assessing viability, the value of any project has two components – capex and opex. An operating expense or opex is an ongoing cost for running a project, a capital expenditure (capex), is the cost of developing the project.

CAPEX can be compared with similar project to determine if it provides value for money. For comparison, the Paradise Dam across the Burnett River with a 300,000-megalitre or 300GigaL capacity cost $240 million to build. A cost of $1000 per GL of water storage which is typical of large scale water storages.

The large Bradfield Scheme proposed by Leon Ashby would store 60,000 GigaL and is estimated to cost $52 billion including upgrades of existing dams, new dams, pipelines, tunnels and aqueducts. This $820 per GL of storage capacity – comparable to similar large storages.

The scheme put forward by Sir Leo Hielscher for an enhanced Hell’s Gate Dam with 120m headwall, augmented by tapping waters from the Tully, South Johnstone and Herbert rivers and a tunnel to the west is $15 billion. Hell’s Gate Dam alone could hold 40,000GL for a capex of $375 per GL. While this capex is considerably lower than Ashby’s scheme, the Ashby scheme includes infrastructure to Richmond and down into Muttaburra and many storages en route such as Lake Buchanan.

Thus other measures such as potential area under irrigation, and value of production also need to be compared. For the opex or operating expenditure, the most most vital being the annual offtake of water, and its cost to irrigators.

For comparison the MDB produces $22 billion of produce each year from around 10,000 GL of irrigation water. Leon estimates the annual potential is for a total of 21,000 GL of irrigation to be possible from the Eastern and Western Systems (8,000 GL each) and another 5,000 GL from the Burdekin Dam. Once developed, these three systems could increase National GDP by another 20 – 40 Billion dollars per year.

I don’t yet have the estimates for the Sir Leo Hielscher plan.

Leon estimates the cost of water for the Burdekin Dam enhancement with some delivery charges & pump costs of $12 per megalitre, the cost would be around $39.50 per ML. This compares to $50 per megalitre for water in the MDB system.

I expect the cost of water for the entirely gravity fed portions of the scheme would be considerably less – of the order of $10 per ML. The delivery of 20,000 GL at a cost of $200 million to produce (conservatively) $20 billion of produce.

Add in the cost of financing the capital works as 5% of $50 billion or $2,600 million per annum we are looking at around $3 billion in annual costs. If interest costs were borne entirely by the irrigator, the finance costs would boost water costs to $130 per ML. At a rate to support rapid development of end uses – the farmers would pay say $25 per ML – the annual return on the infrastructure expenditure would be $500 million or 0.5 billion. However, the figures for this project are similar to other large scale water infrastructure project. Clearly, suitable financing arrangements are crucial to their success.

Various plans have been put forward, such as development bonds, development banks, superannuation funds and so on, and clearly a lot of work would need to be done in this area in order for the project to be self-financing.

These rough figures of $3 billion annual expenditure for $20 billion are at peak development which may take 20 years. Increasing the costs of finance to 10% to cover the dip would be $5 billion which gives an opex over capex of 10. From a public project point of view, these figures need to be compared with alternatives such as road, rail and port construction.

It’s hard to imagine an alternative infrastructure with a more favourable opex/capex at the present time.

Categories: Book Bradfield Scheme

Designing an aqueduct to carry flood flows

The flows in North Queensland Rivers can vary enormously, up to 1000GL per day on an annual average flow of a few GL per day. The design of an aqueduct to accommodate both regular flows and yet capture significant flood flows presents a challenge.

As the aqueduct constitutes the most costly component of the scheme, simplifications and cost reductions over 1000km or more would be significant. Above is my suggestion for a simple flood flow aqueduct that also accommodates regular flows.

The image shows the transverse cross-section of aqueduct consisting of the channel and levee, and a longitudinal cross-section shows the100km sections with a flat gradient and hydropower and roads in the gaps.

The levee is constructed with a simple cut and fill operation where soils are suitable, transferring the soil from the trench, which is the low flow channel, to the compacted levee bank. A height of about 6m should be sufficient, allowing a peak depth of 10m. The shapes of the channel and levee could be trapezoidal but are shown as triangles for ease.

The low flow cross-section would be around 25m2 and lines with high-density polyethylene liner (HDPE). The slope is very low in most parts, with an extent of 500 to 1000m on a 5m head. The cross-section of the flood flow would, therefore, be around 1250 to 2500m2.

By my calculations, a maximum flow rate of 1m/s or 3.6 km/hr (not too fast as the gradient is very low and avoids scouring) would convey around 2GL per day in the low flow channel and 110 to 220GL per day in the high flow channel. This is more than adequate to capture significant flood flows accounting for variable flow rates as well. The actual detailed design needs to be done to refine these ballpark specifications, including estimates of realistic losses.

An approach favored by Leo Ashby is for the levee to be constructed on the contour for 100km lengths, with each section joined by 10m falls. The levee would act as a combined storage weir while transferring water by hydraulic flow over long distances at gradients as low as 1:10,000.

The gaps between the section could be located at important infrastructure points like major roads, with appropriate low pressure hydropower stations sited on them. This would minimise the disruption of existing infrastructure while providing access to power lines along roads.

Categories: Book Bradfield Scheme

SCHEMES

Bradfield. Leon Ashby. Sir Leo. David Stockwell

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