Inter-Basin Water Transfer

An inter-basin water transfer deliberately moves water from one river basin to another across the water divide separating their natural drainage areas. Water captured in a donor basin is conveyed to a recipient basin for irrigation, domestic supply, industry or other uses, thereby redistributing existing runoff rather than creating additional water.

How water is transferred

Water is commonly intercepted by a dam, reservoir or diversion barrage and carried across the basin boundary through canals, tunnels or pipelines. Gravity is used where elevations permit, while pumping is required where water must be lifted.

• Storage can regulate seasonal flows before water enters the transfer system.
• Transferred water may be delivered directly to users or discharged into a river, reservoir or canal network.
• Evaporation, seepage and conveyance losses make delivery smaller than the volume initially diverted.

Changes in basin water balances

A transfer increases usable water in the recipient basin, but reduces water that would otherwise remain in or flow downstream through the donor basin. The designation of surplus and deficit basins depends on seasonal flows, storage, present and future needs, environmental requirements and hydrological variability.

• Transfers may support drought-prone areas, irrigation, urban supply, hydropower or flood moderation.
• Assessment must include climate and flow variability, basin-wide needs, rehabilitation costs and interstate water interests.

Effects on ecological integrity

By altering the quantity, timing and route of water flows, a transfer can change the connected basins as functioning ecosystems. The National Water Policy, 2012 requires environmental, economic and social impacts of such transfers to be evaluated.

• Reduced downstream flow can impair environmental flows, sediment movement, wetlands, fisheries and estuarine conditions in the donor basin.
• Transferred water can alter water quality and seasonal flow patterns in the recipient basin, affecting habitats and native aquatic communities.
• Canals and linked reservoirs can create dispersal corridors through which non-native organisms, pathogens or parasites enter a previously separate basin; some may become invasive species and disrupt food webs through competition, predation or disease.
• Reservoirs and conveyance works may submerge land, fragment habitats and displace communities.
• Ecological assessment should therefore examine both basins and their downstream reaches, rather than treating transferred water only as an additional supply.