Environmental flows are the water that is left in a river ecosystem, or released into it, for the specific purpose of managing the condition of that ecosystem. The flows of the world’s rivers are increasingly being modified through infrastructure, water abstractions for agriculture and cities, hydropower, and drainage return flows. These interventions have reduced the flow of many rivers, altered the seasonality of flows, and changed the size and frequency of floods. In many cases, these modifications have adversely affected water ecosystems. There is now an increasing recognition that modifications to river flows need to be balanced with maintenance of essential water-dependent ecosystems. These ecosystems include not just in river fauna and flora, but also the floodplains and wetlands watered by floods, groundwater-dependent ecosystems replenished through river seepage, and estuaries. Ecosystem degradation often hurts the poor the most. Thus better management of ecological flows have had impressive results for the poor. Fishermen in the Senegal River in Mauritania, for example, saw their annual catches increase from 10 tons a year to 110 tons after the operating rules for a hydropower dam were changed to allow for artificial floods. |
Key Challenges
The recognition that modifications to river flows are an important source of ecosystem degradation is relatively recent. Population growth and economic development will increase water demand for agricultural, industrial and human uses in the coming years. The challenge is to define and implement appropriate strategies that blend various types of interventions. For example, well conceived water projects should have components that aim at improving watershed management, with associated benefits for the poor who usually constitute the majority of people living in such degraded environments, develop operating rules that specify ecological flows for the benefit of downstream riparians and implement smart water demand management measures. Successful mitigation, compensation, and restoration of downstream effects are more likely if a thorough flow assessment has been undertaken. Flow assessments can help display the wider costs as well as the benefits of development, allowing more informed tradeoffs to be made. Water policy and should define the need and objectives for the volume and temporal distribution environmental flows. The implementation of an agreed flow regime should allow for adaptive management based on regular monitoring. Back to Top |
World Bank Response
The 1993 World Bank Water Resources Management Policy (pdf) included as an objective that "the water supply needs of rivers, wetlands, and fisheries will be considered in decisions concerning the operation of reservoirs and the allocation of water." World Bank projects address maintenance of environmental flows in the design of new infrastructure, and in re-calibrating of operating rules in river basins. The World Bank is actively engaged in bringing best practice to bear, through knowledge generation, through partnerships and through its operations. The World Bank’s environmental assessment policy (Operational Policy 4.01) is triggered if modifications to river flows lead to adverse environmental risks and impacts. 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 policy (Operational Policy 4.04) in order for a loan to be approved. |
Environmental Flows: Methods & Concepts
RSS