Environmental flows can be described as ‘the quality, quantity, and timing of water flows required to maintain the components, functions, processes, and resilience of aquatic ecosystems which provide goods and services to people ‘.The flows of the world’s rivers are increasingly being modified when water is withdrawn for agriculture, urban use, and hydropower and when it is not returned to the river through drainage or groundwater flow. Thus the flow of many rivers has been reduced or seasonally altered changing the size and frequency of floods, the length and severity of droughts, and adversely affecting ecosystems. Indeed, a number of rivers run dry before they reach their destination, including, among others, the Aral Sea, and the China Hai River. The Hai River Basin is among the most polluted and depleted river systems in China. Groundwater extraction in Hai Basin is estimated at about 50 percent greater than the sustainable yield. To address some of these problems in the Hai Basin, the World Bank has committed to helping the Government of China develop and implement an integrated approach to water and environmental management.
Modifications to river flows and storage for flood protection, hydropower production or irrigation may have significant positive development impacts. At the same time the World Bank recognizes that modifications to river flows need to be balanced with due consideration of the viability of water-dependent ecosystems, which provide goods and services to people. These ecosystems include not just fauna and flora that live in the river, but also those that live in the floodplains and wetlands watered by floods, as well as groundwater-dependent ecosystems, which are replenished through river seepage, and estuaries.
World Bank projects address the maintenance of environmental flows in the design of new infrastructure. Projects must also consider the water supply needs of rivers, wetlands, and fisheries when making decisions about the operation of reservoirs and the allocation of water.
According to the Bank’s Operational Policy 4.01 aproposed project must have an environmental impact assessment if it is likely to have significant adverse environmental impacts that are sensitive, diverse, or unprecedented. Even projects with less adverse (but non-minimal) impacts must have an environmental impact assessmentalthough the scope of the EIA in this case may be narrower. If changes in flow have the potential to cause significant loss or degradation of natural habitats, borrowers must also comply with the Bank’s Natural Habitats (Operational Policy 4.04) in order for a loan to be approved.