Interbasin Transfer

Interbasin transfer or transbasin diversion are (often hyphenated) terms used to describe man-made conveyance schemes which move water from one river basin where it is available, to another basin where water is less available or could be utilized better for human development. The purpose of such designed schemes can be to alleviate water shortages in the receiving basin, to generate electricity, or both. Rarely, as in the case of the Glory River which diverted water from the Tigris to Euphrates River in modern Iraq, interbasin transfers have been undertaken for political purposes. While ancient water supply examples exist, the first modern developments were undertaken in the 19th century in Australia, India and the United States; large cities such as Denver and Los Angeles would not exist as we know them today without these diversion transfers. Since the 20th century many more similar projects have followed in other countries, including Israel, Canada and China. Utilized alternatively, the Green Revolution in India and hydropower development in Canada could not have been accomplished without such man-made transfers.

Since conveyance of water between natural basins are described as both a subtraction at the source and as an addition at the destination, such projects may be controversial in some places and over time; they may also be seen as controversial due to their scale, costs and environmental or developmental impacts. While developed countries often have exploited the most economical sites already with large benefits, many large-scale diversion/transfer schemes have been proposed in developing countries such as Brazil, African countries, India and China. These more modern transfers have been justified because of their potential economic and social benefits in more heavily populated areas, stemming from increased water demand for irrigation, industrial and municipal water supply, and renewable energy needs. These projects are also justified because of possible climate change and a concern over decreased water availability in the future; in that light, these projects thus tend to hedge against ensuing droughts and increasing demand. Projects conveying water between basins economically are often large and expensive, and involve major public and/or private infrastructure planning and coordination. In some cases where desired flow is not provided by gravity alone, additional use of energy is required for pumping water to the destination. Projects of this type can also be complicated in legal terms, since water and riparian rights are affected; this is especially true if the basin of origin is a transnational river. Furthermore, these transfers can have significant environmental impacts on aquatic ecosystems at the source. In some cases water conservation measures at the destination can make such water transfers less immediately necessary to alleviate water scarcity, delay their need to be built, or reduce their initial size and cost.