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The amount of water abstracted or developed each year by purpose and drainage division. To manage a resource, we need to know where it is going. In water management, a useful distinction can be made (Pimental et. al. 1997) between water consumption (where water is abstracted once for exclusive ownership) and water use (where at least some water is returned to the hydrological cycle and reuse is possible).
The ABS (2000) estimates that 47.8 million ML of water used for hydro-power generation in Tasmania in 1996-97. Although the Hydro-Electric Corporation is the largest water user in the State, its use is usually categorised as non-extractive. Normally, water is released downstream when the power stations are operating so that water is not lost from the catchment. For example, the water flowing through the Pieman, Derwent, Tamar, and Mersey-Forth power developments can be used by up to eight power stations. Exceptions are when a scheme diverts water between catchments. Hydro-Electric Commission storages change downstream flow patterns by smoothing peaks and increasing low flows. While this is often of benefit to water users, the aquatic environment downstream of dams has changed substantially as a result. Surface water consumption in 1996-97 for other users (excluding in-stream uses) was estimated as 414,170 ML or 701,442 ML including in-stream uses (NLWRA 2001). The following figure compares the relative volume of water use for hydro-power with other uses in Tasmania. Comparison of Hydro-Electric and other water uses Notes: Although the Hydro-Electric Corporation is the largest water user in the State, its use is usually categorised as non-extractive. Source: Fuller 1991 and NLWRA 2001.
The Cressy-Longford, Winnaleah and South-East irrigation schemes are the main State irrigation schemes in Tasmania. These schemes are operated by the Rivers and Water Supply Commission. Water use figures are collected and reported for each financial year. Water use is affected by the wetness or dryness of the irrigation season and also by the economic conditions at the time. The water usage curves shown in the following figure have similar year-to-year variability, and this variability is roughly the mirror image of the year-to-year variability of stream flows in the State.
In 1996-97, an estimated 266,452 ML was consumed for irrigated agriculture (pasture, grapes, fruit, vegetables, and other crops), representing 38% of all water used and 64% of consumptive water use (DPIWE 2001). The total consumption of water for irrigation in Tasmania represents 59% of the total water use in the State. Ninety-seven per cent of the water used for irrigation is sourced from surface water and 3% from groundwater (NLWRA 2001). Comparison of irrigation, industry and domestic water uses Source: NLWRA 2001 Irrigation is the major water user in a number of SWMAs in Tasmania. The Mersey and Tamar SWMAs, in particular, show the majority of water available allocated to irrigation. The situation is similar in the Coal River and Kingston Coast SWMAs. As would be expected in agriculturally important areas, the Burnie-Smithton SWMA also directs a large proportion of available water to irrigation. An anomaly is the apparent consumption of 300 ML irrigation water in the South-West Coast SWMA. It is likely that this is due to the steps taken in allocating or redistributing data collected under ABS statistical boundaries to the SWMAs.
The estimates of water consumed for irrigation in the last SoE Report (SDAC 1997) indicated a strong rise in irrigation demand over the past four decades, with an average growth rate of 6% a year. The amount of water used in irrigation was arrived at by using a range of measured and estimated rates of application per hectare. Estimates from the ABS for 1996-97 show that consumption of water for irrigation grew by about 7% a year since 1993.
A range of irrigation methods are used in the State including:
The last SoE Report (SDAC 1997) noted that different methods of irrigation have good and bad points in relation to environmental effects, economics and feasibility. Flood methods consume a lot of water and can contribute to land salinisation and waterlogging. Flood irrigation is considered to be the least efficient and potentially the most damaging. In comparison, methods such as trickle or drip irrigation are more capital intensive, but use much less water. Various types of spray irrigation (e.g. centre pivot, travelling irrigator and gun irrigation) lie somewhere in between in their environmental impacts. Generally, the greater the intensity of water application the greater the potential risk for causing erosion also, particularly if irrigation of sloping land is occurring. However, there is limited information available on the type of irrigation systems installed on various farms and the resulting environmental and/or production benefits. There is anecdotal information that centre pivot irrigation is an increasingly preferred irrigation system. However, information is required on the extent of adoption of these systems and their impacts. It is possible to collect this information as part of the next Australian Bureau of Statistics Agricultural Census.
The ABS Water Account for Australia (ABS 2000) reported that Tasmania had the lowest mean household water usage of 176 kL/year. Mean water use per household is highest in the Northern Territory (500 kL/year), Queensland (340 kL/year) and Western Australia (320 kL/year). Mean household water use in NSW-ACT, Victoria and South Australia was between 218 and 237 kL/year. However, detailed information and trend estimates regarding the volume of the domestic water supply is fairly limited in Tasmania. In part this is due to household metering only occurring in a few areas. In 1996-97, domestic water usage in Tasmania was estimated as 31,776 ML (ABS 2000). The Derwent and Tamar SWMAs contained the highest proportion of water use for domestic purposes, representing some 60% of all domestic water usage. The following table details the water supplied by councils including both treated and untreated water and estimates of water use by councils outside of water Authority Areas. The water that is supplied is used for a range of purposes including domestic, commercial and industrial (DPIWE 2001). The household sector was a substantial user of mains water, using on average 29% of mains supplied water (ABS 2000). Water supplied by major councils, 1999-00 Council Population(a) ML ML/person(b) Supplier Central Coast 20,380 4,053 0.2 Cradle Coast Water Circular Head 8,108 1,540 0.19 Cradle Coast Water Devonport 23,814 4,491 0.19 Cradle Coast Water Kentish 5,331 312 0.06 Cradle Coast Water Latrobe 7,627 325 0.17 Cradle Coast Water Waratah/Wynyard 13,350 1,601 0.12 Cradle Coast Water George Town 6,653 843 0.13 Esk Water Launceston 62,431 10,353 0.17 Esk Water Meander Valley 16,773 1,229 0.07 Esk Water West Tamar 18,873 2,374 0.13 Esk Water Brighton 12,471 1,801 0.14 Hobart Water Clarence 47,461 8,617 0.18 Hobart Water Glenorchy 43,066 9,760 0.23 Hobart Water Kingborough 26,839 3,847 0.14 Hobart Water Hobart 46,676 11,678 0.25 Hobart Water Remaining Southern Councils (d) 24,976 3,129 0.13 Hobart Water (e) Burnie 19,283 3,500 0.18 Self - Estimate (f) Other councils 55,547 9,500 0.17 Self - Estimate (g) Total 459,659 79,953 0.17 (a) Based on ABS 1996 Census. Source: DPIWE 2001
A few Tasmanian industries-such as some of the pulp mills-have legislatively guaranteed water rights; and most industries are supplied by the metropolitan and regional utilities. As these generally have limited data, details on the breakdown of this class of water users are sketchy. It is known, however, that industrial and commercial users consume just over half of the total supply from the metropolitan and regional water suppliers. Many of the mining operators have developed their own water supply infrastructure. A small part of this water is used for domestic uses, but most is used for cooling, ore washing, dust suppression, and so on. These applications make mining the second largest water consumer. The ABS estimate that 43,071 ML of water was 'self-extracted' for the printing, paper and publishing sector in Tasmania in 1996-97. The wood and wood products sector and the mining industry 'self-extracted' 25,073 ML and 33,168 ML over the same period (ABS 2000). The industry sectors in the table represent about 98% of the total self-extracted water use (excluding water supply and distribution and hydro-electricity). Selected water use, industry comparison, 1996-97 Sector Self-extracted water use 1996-97 Mains water use 1996-97 Mining 33,168 3 Wood and wood products 25,073 2,563 Paper, printing and publishing 43,071 993 Livestock, pasture, grains and other agriculture 54,454 15,260 Vegetables 32,258 8,886 Fruit 1,736 478 Figures are estimates and contain assumptions that are described in the explanations in the ABS Water Account (ABS 2000) Source: ABS 2000
The NLWRA (2001) estimated changes in water use based on snapshot assessments undertaken in 1985 and 2000. The NLWRA points to the difficulties in comparisons between the 1985 and 2000 snapshots due to factors such as seasonality and variability of climate. The comparison shows an overall increase in water use in Tasmania of 126% from 199 GL in 1983-84 to 451 GL in 1996-97. The surface water management areas with the greatest percentage increase over the period were Piper-Ringarooma and the Kingston Coast. The NLWRA assessment of changes in water use is available from the Australian Natural Resource Atlas. The following table summarises the changes in water use between 1983-84 and 1996-97. Changes in water Basin Name Use in 1983-84 (GL/yr) Use in 1996-97 (GL/yr) % Change Tasmania 199 451 126 Arthur River 0 22 no data Coal River 1 4 325 Derwent River 20 75 280 East Coast 4 15 320 Flinders-Cape Barren Islands 1 1 52 Forth River 3 15 401 Gordon River 1 0 -100 Huon River 3 4 34 King Island 1 1 -69 King-Henty Rivers 1 5 524 Kingston Coast 2 7 420 Mersey River 18 20 9 Pieman River 2 9 442 Piper-Ringarooma Rivers 8 53 557 Rubicon River 6 10 85 Sandy Cape Coast 0 0 no data Smithton-Burnie Coast 39 90 133 South-West Coast 1 1 -21 Tamar River 25 92 272 The total surface water use reported for each river basin does not include the water consumption of the 11 major cities. The data for cities and river basins are reported in the State totals. Source: NLWRA 2001 |
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