Orange Water Supply July 2019

KL=1000L,  ML=1,000,000L  GL=1,000,000,000L

The Problem

The population of Orange is about 40,000 (2018) and is increasing by 1% a year. Working on historical summer and winter water consumption (table below) daily usage per person is 183 L. This computes into a daily consumption for Orange of 7.3 ML which amounts to 2.7 GL per year. Full storage capacity is about 24.5 GL but water storage is only 34.6% (July) and declining, which is about 8.5 GL. Level 5 restrictions are due to commence when water reserves fall below 35%. This deteriorating reserve situation has been progressing during the past four years, as illustrated by the records: 2016-100%, 2017-75%, 2018-50%, 2019-34.6% (June).

The Orange water supply relies on a network of small creeks as it is distant from major rivers or dam sites. Average annual rainfall is 900 mm and declining. The several water storages and facilities with capacities (GL) and current reserves (%) are:

Storage/Facility Capacity  GL Reserves  %
Suma Dam 19.8 26
Spring Creek Dam 4.5 68
Macquarie River 7.7 ML/day None
Ploughmans  Creek 1200 ML/year None
Blackmans Creek 1300 ML/year None
Water Bores Unknown Unknown
Gosling Creek Dam Recreation Reserve
Lake Canobolas Recreation Reserve

Historical water consumption litres/person/day reflects summer and winter drawdowns:

Month 2016 2017 2018 2019
March 287 285 349 229
June 170 178 170 137

Averaging the 2019 seasonal variations, consumption is 183 L/p/d or 2.7 GL/year against a declining reserve of 8.5 GL. This may permit consumption until early 2021. Because no data has been sighted for distribution loss, agricultural entitlement, evaporation or black (undrinkable) water,  the reserve will be less than quoted.

Water Resources and Facilities

The Orange City Council has generated several reserves and collection facilities, however, there is no large storage to draw upon. Declining water reserves might possibly be augmented by capricious rainfall cells or from bores into a basalt aquifer. Details are:

Suma Dam or Suma Park Reservoir

The dam is located 4 km east of Orange. It was constructed in 1962 with a capacity of 17.3 GL and was later upgraded in 2016 with a capacity of 19.8 GL for a cost of $18 million. By June 2019, storage had declined to 5.2 GL – 28% capacity. Suma dam replaced the aging Spring Creek reservoir.

Spring Creek Reservoir

This is a minor embankment dam located 2 km east of Orange. It was completed in 1931 with a capacity of 4.7 GL. By June 2019, storage had declined to 3.2 GL – 68% capacity and falling.

Macquarie River Pipeline

The 39 km pipeline was completed in 2016 by Geotechnical Engineering Ltd at a cost of $26 million. The facility is designed to transfer water to the Suma dam using pumps delivering 7.7ML/day. In 2017, the Macquarie river flowed at a modest 506 ML/day; for a short time discharge into the dam was 13.4 ML/day. Since early 2019 the water level has been too low for the pumps to operate.

Ploughmans Creek Water Harvesting

This facility in the Orange urban area directs 10-20% of storm water run-off to holding wetlands from where it is pumped to the Suma dam. The installation was constructed in 2009 for a project cost of $4 million. This project was a new initiative and a national first for augmenting water supply. Since commissioning, results have been disappointing and for the year ending June 2019 off-take was only 4.6 ML.

Blackmans Creek Water Harvesting

This facility collects urban run-off for storage in a 2000 ML wetland before transfer to Suma dam. It was completed in 2009 for $5 million. Run off was anticipated to be 1300 ML/year, however for the first six months of operation, only 260 ML was obtained.

Water Bores

There is extensive use of bore water for domestic and agricultural purposes but records have not been sighted. Orange City Council indicated that NSW Water is the authority to approach, information is awaited. The water source is fractured Tertiary basalt that underlies Orange; water is also obtained from the Macquarie alluvials. NSW Water states ground water in the Orange region is of good quality and extraction rates are sustainable but there are signs of extraction stress about the urban area.

In 2011, the Council applied to NSW Water to supplement the urban supply by extraction from the basalt aquifer; an extraction licence has apparently been granted with the proviso that existing users and entitlements will not be affected.

Two issues require clarification:

  • There appears to be no accounting for bore water in the consumption figures; this implies domestic usage is higher than stated.
  • Storage reserves could be higher if ground water was included.

Gosling Creek Dam

This is an embankment dam 4km south of Orange. It was constructed in 1890 with a capacity of 0.4 GL. It was decommissioned in 1962 with the opening of the Suma dam. In 2007 Cadia Mine was granted use of this resource for mining purposes.

Lake Canobolas, formerly Meadow Creek Dam

The Meadow Creek dam, 10km south of Orange, was constructed in 1918 with a capacity of 4.5 GL. The dam was decommissioned in 1962 and renamed Lake Canobolas. It is now within a recreation reserve with water transferred from the Suma dam to maintain water level. The name originates from Wiradjuri language. cona-shoulder and booloo-two which relate to the two peaks of Mt Canobolas.

Future Water Supplies

The backdrop to future water supplies for Orange is a meeting in February 2019 between Central West mayors of Bathurst, Orange and Dubbo with Government representatives and the recent installation of desalination plants in Walgett and Bourke to treat salty bore water. The looming water shortage in NSW is becoming a National issue.

The Orange urban area is located in the headwaters of a river system with no extensive catchments upstream and no nearby large dam sites available. The current water security plan is to increase local storage capacity by 20 GL by implementing the following actions:

  • Drill five bores into the fractured basalt aquifer near the Macquarie river; extraction tests will determine the degree of water security.
  • In and around the urban area, use seven existing and yet to be drilled holes to extract water from the basalt aquifer and pump it to the Suma dam.
  • Pump storm water from the urban area via a borehole array into Tertiary basalt and Palaeozoic aquifers to serve as a storage and retrieval system.
  • Drill a number of bores designed to produce 1 ML/day for discharge into the Suma dam.
  • Investigate a future dam site at Lake Rolands,  45km south of Orange.
  • Investigate storage potential in adjacent valleys.

Discussion

A second and longer term backdrop to already identified water shortage, is a 15% decline in rainfall over south-east Australia which has been confirmed by a consequent slow drying out of the landscape.

The proposed initiatives for short-term water security by extraction from Tertiary and Palaeozoic aquifers must be finite particularly with declining rainfall. It is relevant to note that for Australia, water from aquifers constitute 17% of accessible water and 30% of consumption. On current trend, both figures will increase with only one predictable result. The move toward larger storage dams is logical but construction will be to the detriment of echo systems and agriculture downstream.

Part of a solution will be to evaluate the Israeli system of water management and to consider the transfer of water from East Coast rivers. There are mutterings of extracting water vapour from the air, carried out on a large scale might precipitate unintended consequences.

The Last Drop

With quoted declining water reserves of 8.5 GL and an annual consumption of 2.7 GL, not including distribution losses and undrinkable anoxic water, there appears to be barely a two-year supply – this is against a trend of declining rainfall and increasing temperature.

The short-term solution proposes water bores in and around the urban area but this is not a long-term solution. NSW Water has observed there are signs of extraction stress in the basalt aquifer. The projected Rolands dam site cannot be part of the short-term solution.

The Orange water shortage is part of a State-wide problem that is part of an emerging National problem. Individual solutions may vary but a National management program will be required.

References

  • Orange City Council, 3 May ’05, Lake Canobolas Sanctuary
  • Orange City C0uncil,3 Dec ’07, Spring Creek Reservoir
  • Geologyse PL, Nov. ‘09, Ploughmans Creek Storm Water Scheme
  • National Reserves Commission, Nov. ’10,  Central West Ground Water
  • Orange City Council, 2010, Storm Water Harvesting
  • Orange City Council, 2011, Gosling Creek Reserve
  • Dept. Primary Industry, 2012, Young Granite Ground Water Source
  • Central Western Daily, April ’13, Our Most Precious Reserve
  • Orange City Council, June ’16, Hydrology Monitoring Program
  • WIN News, 6 July  ’16, Suma Park Dam
  • Geotechnical Engineering, 2016, Suma Park Dam Upgrade
  • Orange City Council,  7 July  ’16, Managed Aquifer Reserve
  • Earth First, 9 March ’18,  Ground Water Australia Week
  • Clear Water, June ’18, Orange Storm Water
  • Central Western Daily,  3 April ’19, Level 4 Restrictions
  • Central Western Daily, 30 June ’19, Orange Water Supplies

John Hugh Hill

lurgashall@westnet.com.au

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