Extending water resources
Extending water resources

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Extending water resources

1 Water transfer

Water transfer is the transfer of water from one river catchment to another. Transfer can take place by river diversion, pipeline or even by sea tanker. There is often a surplus of water in one area and too little in another — both on a small scale within a country, on a larger, continental scale and even on a global scale. Water transfer is one method of increasing the supply to areas with too little water. For example, Manchester is supplied with water piped from reservoirs in the Lake District (Figure 1) and the industrial cities of South Yorkshire are supplied with water from rivers to the north through the Yorkshire Grid Scheme, which uses rivers and large mains to transfer water from one river catchment area to another.

Figure 1 Haweswater reservoir in the English Lake District, which provides water for Manchester.

On a larger scale, water is transferred between major river catchments in the south-western USA by means of large canals, pumping stations and tunnels. An enormous quantity of water, around 5.5 × 109 m3 a year, is transferred 300 km or so from the Colorado River basin to California, where it is used mainly for irrigation in the agricultural areas of southern California, but also for public water supply in Los Angeles, San Diego and other cities. Half of all the water used in southern California comes from the Colorado, and California would like even more but the river is unable to supply it.

On an international scale, the southern USA would like to transfer water from Canada. Every few years, plans to divert massive amounts of Canadian water to water-scarce areas of the United States by tanker, pipeline, or rerouting of the natural river systems, are considered. One of the largest proposed diversion projects was called the GRAND Canal — the Great Recycling And Northern Development Canal. It originally called for the building of a dam across James Bay at the Hudson Bay entrance to create a giant freshwater reservoir out of James Bay and the twenty rivers flowing into it. This water would then be diverted south by river and canal through the Great Lakes to the south of the USA.

The North American Water And Power Alliance (NAWAPA) was a similar scheme. The general idea of NAWAPA was to collect surplus water from areas of high precipitation in the north-western part of the North American continent and distribute it to water-scarce areas of Canada, the USA and northern Mexico.

A series of dams and power stations in Alaska and northern British Columbia would collect water and provide power to pump this water up to a reservoir in the Rocky Mountains in south-eastern British Columbia. From the Rocky Mountains reservoir, water would be pumped to another reservoir in Idaho. From there, the water would flow by gravity to the western States.

None of the North American diversion and pipeline schemes were implemented nor look likely to be in the future. The most obvious reason for this is the capital cost of the schemes, due to the massive engineering works involved in diverting water on a continental scale. The value of the water, especially if used for irrigation, is insufficient to repay or justify the construction cost. The second reason is the difficulty of reaching international agreement to go ahead with the scheme, and there is also an unwillingness to depend on another country for water. The final reason is environmental: the schemes attracted massive opposition on environmental grounds, for drowning land and towns, destruction of wildlife habitats and even the possibility of changing the climate.

Box 1 The Snowy Mountains Scheme

One of the world's largest-scale national water transfer schemes in existence is the Snowy Mountains Scheme in Australia, where water is lacking in the vast, low-lying interior, but the eastern rim of highlands has plentiful rainfall. Unfortunately the rivers of the highlands flow eastward into the Pacific Ocean mainly unused. The Snowy Mountains Scheme traps part of the flow of two of these rivers in reservoirs (Figure 2). This water is then pumped through tunnels and aqueducts to the west side of the Snowy Mountains, to the Murray and Tumut River systems, increasing the water available to Australia's interior. Because of the difference in altitude between the intake in the highlands and the outlet in the interior, the Scheme generates enough hydroelectricity to pay for the operating costs.

Figure 2 (a) The Snowy Mountains Scheme in Australia. (b) A diagrammatic cross-section (not an accurate section). Some of the reservoirs have been lettered (A-E) so that you can identify the same reservoirs in (a) and (b).

The Scheme was completed in 1974, taking 25 years to build, at a cost of £400 million. It diverts an average of 2.36 × 109 m3 of water a year to the interior, and the hydroelectric power output is 3754 MW (equivalent to the power output of almost four nuclear power stations). The system has the flexibility to allow water to be released from reservoirs only when needed during the dry season, or to allow water to be transferred between reservoirs.

Although the discharge of the Murray and Tumut Rivers was successfully increased, there have been large environmental impacts associated with the scheme; land drowned by reservoirs, higher water tables, increased leaching of salts into rivers, and ecological changes in the river basins.

Although large-scale international water transfers by diversion and pipeline have not yet been implemented, international transfer on a smaller, more flexible scale is being used (Box 2).

Box 2 Tankering, towing water and icebergs

Among other schemes, Canada is transporting water to the Bahamas using ships as water tankers, Alaska has sent water to Japan and Turkey sends water to Cyprus. Water could also be towed, as well as tankered, in large plastic bags. There is little capital cost involved, and transport by sea is cheap. The environmental effects are minimal: no land need be drowned.

A large proportion of the Earth's fresh water is in the polar ice caps, but so far this has not been used for water resources. Ice is formed in both polar regions, but 90% of it is in Antarctica and most of the rest is in the Greenland ice cap. The problem with using these frozen assets is that the ice is in the wrong place. To be of use as a water resource, it would have to be transported large distances to lower-latitude water-deficient areas such as western South America and Australia, or even across the Equator from the Antarctic to southern California or the Middle East. The most convenient ice to transport would be floating icebergs.

Antarctic icebergs are flat slabs 200-250m thick and a kilometre long on average, which have broken off from the floating ice shelves that surround the Antarctic land area. Greenland icebergs form by breaking off from valley glaciers where these glaciers border the sea; they have a wide range of sizes, but are generally smaller than the Antarctic icebergs and more irregular in shape. Icebergs float with most of the iceberg beneath the sea surface, which gives them a draught much greater than that of ships and prevents them travelling in shallow water. It is technically possible to tow icebergs; offshore oil rig operators have moved them short distances when there has been the possibility of collision with oil rigs.

The cost of water from icebergs is difficult to estimate, because of uncertainties about the energy required for towing and the rate of melting, and icebergs have not yet (2004) been used as a water source. Iceberg water will probably never be cheap, but it could prove to be less expensive than water from desalination or from long-distance water transfer.

Water used to be regarded as a resource with a high place value, but international water transfers indicate that it can at times be a low place value resource. Large-scale water transfer is a very expensive way of increasing water resources, but may be necessary when there are no alternative local sources. The cost can be comparable with that of desalination, and while desalination may be a preferable alternative in many areas, it is energy-intensive and restricted to coastal areas.

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