(KL=1000 L, ML=1,000,000 L, GL=1,000,000,000 L)
The population of Tamworth, NSW, and environs number some 45,000. Currently the region is experiencing a prolonged drought. In addition, the Bureau of Meteorology forecast El Niño conditions could continue into 2020. To conserve water Stage 3 restrictions are in place. The Tamworth water supply is principally derived from two dams, now at critically low levels. The Dungowan dam is at 27% capacity – 1.6 GL and the Chaffey dam at 24% capacity – 25 GL.
With no consistent rain forecast the situation is serious since there appears to be approximately a little over a one-year supply. It is unknown if the quoted capacity has taken into account dead water which limits irrigation and also at a lower depth deep undrinkable water. The Tamworth Regional Council is casting around to augment declining reserves.
Details on dams supplying water to Tamworth are:
- Dungowan dam – located 50 km south east of Tamworth – it was built in 1958 with a 6.3 GL capacity. By mid-2014 water supply reserves had declined to 1.6 GL. There are plans to increase capacity to 22.5 GL but progress stalled when feasibility estimates rose to $440 million from an original budget of $150 million.
- Chaffey dam – located 45 km south east of Tamworth – it was opened in 1971 with a 62.8 GL capacity. This was increased to 100.6 GL capacity in 2014. By mid-2019 water supply reserves had fallen to 25 GL. In 2017 there was a proposal to increase capacity to 120 GL but there is no evidence of progress.
The planned consumption proposed by Tamworth Regional Council for 2018-19 and the projected short fall for 2019-20, in giga litres, is summarised:
- Essential Supplies 8.2
- Reserve for 2019-20 14.0
- General Security 4.5
- Horticulture &Disinfection 1.9
- Evaporation & Operation 5.0
- Available Resources 30.6
- Projected Shortfall 3.0
Declining dam reserves of 25.0
plus 1.6 ie 26.6 represents either slippage or
a make good of 4.0 GL from other sources. The estimates indicate Tamworth
may be out of water by mid-2020.
The Chaffey dam provides water to the agricultural industry. There are around 192 irrigation licences with entitlements to 48.3 GL per year along 590 km of the Peel River drainage system. Production includes cotton, wheat, lucerne, vegetables, trees, pasture, sheep and cattle. Entitlements have been reduced to 38% – 18 GL.
At current low dam levels two factors should be considered:
- The lower water layers may become undrinkable. A NSW Government report found the lower levels of the Warragamba dam to be undrinkable – on this basis the remaining water in Chaffey dam might be suspect.
- Depending upon the elevation of the penstocks a proportion of the current low reserves in Chaffey dam could become unavailable to agriculture.
Proposals for Water Security
The Tamworth Regional Council has proposed several measures to augment and provide a more reliable long-term water supply, these are:
- Construct a 62 km pipeline to the Keepit dam north-west of Tamworth. This dam was designed to contain 425 GL but due to the drought and drawdown the dam is at 0.4% capacity – 1.7 GL – this is the lowest level since the drought of 1974. With demands from the Namoi region and the reported long term decrease in rainfall in south east Australia this plan could be ‘dead in the water’.
- Increase the capacity of the Dungowan dam from 6 GL to 25 GL. Owing to the estimated construction cost of $440 million this project may remain shelved unless the Commonwealth Government intervenes.
- Construct a 10-15 GL storage adjacent to the Peel river upstream from Tamworth. With increasing evaporation (1.8 m/year at Dubbo) shallow storage could be ineffective.
- Reopening the Peel river (Paradise) Drift Wells. These wells penetrate the Peel river alluvials. They provided water for Tamworth until the 1950s. Pumping tests between 1977-1980 produced a maximum of 12 ML per day and an equilibrium output of 7 ML per day. Planned pumping tests will attempt to achieve a consistent 10 ML per day over a six months trial. Rehabilitation costs are estimated at $2.25 million which will be funded by the NSW Emergency Drought Relief Fund. This initiative is not a solution, it can only augment a reliable supply. The problem facing the Drift Wells is the combination of prolonged and more frequent droughts combined with a climate induced declining rainfall. River systems under stress will no longer be able to recharge the flood plain alluvials.
- Water bores are planned for alluvials 26 km down stream from Tamworth. Similar limitations to those for the Drift Wells apply.
Impediments to the near term resolution for the Tamworth water supply are:
- Water resources from alluvials can only augment, not replace, storage from large dams.
- There is no guarantee rain will recharge the dams within the next twelve months.
- The past two decades have witnessed a 15% decrease in annual rainfall across south eastern Australia resulting in an almost imperceptible decline in surface run off, declining river flow and a slow drying out of soils and alluvials.
- Longer hotter summers will increase evaporation from water storage while livestock and human consumption will increase.
- Infrastructure funding of massive water storage will become an increasing problem as the changing climate creates water shortages across south east Australia.
The above is not just a Tamworth problem, or a New South Wales problem –it is an Australian problem. Climate trends and modelling predictions indicate the tropical north will become wetter while the not so temperate south will become hotter, drier and subject to damaging rain cells.
To secure future reliable water supplies major infrastructure projects will have to be considered:
- The construction of very large dams since the Chaffey and Keepit dams and others in NSW are no longer fit for purpose. An example of a water storage capable of providing increased security is the Argyle dam, WA, capacity 10,705 GL. Any dam location would require an extensive distribution system to service agriculture and population centres.
- Construction of pipelines from eastward flowing rivers of New South Wales and Queensland into central New South Wales.
- Deep drilling at depths beyond the near surface aquifers to tap into porous limestone, basalt and other permeable formations. This water might be at elevated temperature and contain chemical contaminants.
- By mid-2020 the Tamworth water supply will be essentially exhausted and water may have to be bought in by rail noting however, that the principal Sydney supply, Warragamba dam, is at 40% capacity and declining.
Tamworth is facing a serious water shortage, which by Tamworth Regional Council estimates will result in a shortfall during 2019-2020 of about 3 GL. Rainfall might alleviate this situation in the short term, it cannot solve it. The proposed water from bores into alluvial sediments, deep bores or pipelines can only augment dwindling supplies, they cannot replace large storages. The observed ‘drying out’ of south eastern Australia will play out in declining river flows and water deficient alluvials.
The solution to ensuring water security will involve feasibility into major infrastructure projects. This is not a Tamworth problem, this is a problem involving south-east Australia.
News Ltd., 2006, Sydney’s deep water supply undrinkableWater Industry Assoc. of Aust., 3 April 2009, Paradise Drift Wells, Third Report.Tamworth Regional Council. October. 2018, Water and Dam Information.Northern Daily Leader, 6 March 2019, Dungowan Dam.NSW Government, 8 March 2019, Peel Valley Water Allocation Statement.Water NSW, 10 June 2019, Regional Water Availability Report.Tamworth Council, 2019, Long term options for bulk water.
JOHN HUGH HILL firstname.lastname@example.org
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EXTENT AND INTENSITY OF DROUGHT OVER SOUTH EAST AUSTRALIA