Inter-Basin Water Transfer

An inter-basin water transfer deliberately moves water from one river basin to another across the ridge or water divide separating their natural drainage areas. It captures or diverts water in a donor basin and conveys it to a recipient basin, where the water joins a different drainage system or is used for irrigation, domestic supply, industry or other purposes.

How the transfer occurs

Water is commonly intercepted by a dam, reservoir or diversion barrage in the donor basin. It is then carried across the basin boundary through canals, tunnels or pipelines, using gravity where elevations permit and pumping where water must be lifted.

• Storage can regulate seasonal flows before releasing water into the transfer system.
• After crossing the divide, the transferred water may be delivered directly to users or discharged into a river, reservoir or canal network of the recipient basin.

Effect on basin water balances

The transfer increases usable water in the recipient basin, but correspondingly reduces the volume that would otherwise remain in the donor basin or flow downstream. It therefore redistributes existing runoff rather than creating additional water.

• A proposed donor basin is generally identified as having water available beyond assessed in-basin requirements, while the recipient basin faces shortages relative to demand.
• The designation of surplus and deficit basins depends on seasonal flows, storage, present and future needs, environmental requirements and hydrological variability.
• Losses through evaporation, seepage and conveyance mean that water delivered is less than water initially diverted.

Planning and environmental implications

A transfer can support drought-prone areas, irrigation, urban supply, hydropower or flood moderation, but its viability must be assessed case by case. The National Water Policy, 2012 requires consideration of environmental, economic and social impacts.

• Reduced downstream flow can affect environmental flows, sediment movement, wetlands, fisheries and estuarine conditions in the donor basin.
• Reservoirs and conveyance works may submerge land, fragment habitats and displace communities.
• Assessment must account for basin-wide needs, climate and flow variability, rehabilitation costs and interstate water interests.