The concept of environmental flows describes the quantity, quality and timing of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these ecosystems. (Brisbane Declaration 2007)
A useful and simple way of thinking about environmental flows is that of ‘ecological water demand’, similar to agricultural or industrial water demands. Environmental Flows seek to strike a balance between water resources development and the protection of freshwater-dependent ecosystems.
A negotiated trade-off
Setting environmental flows requirements may take two fundamentally different approaches depending on the objective in question:
- What ecosystem condition must be maintained, and how much water is needed for this?
- How much water does society allocate to ecosystems?
…and what is the resulting ecosystem condition maintained by this given water allocation?
…and is this condition desirable and sufficient?
Environmental flows support ecosystems that provide a wide range of services to people (Costanza 2003; Emerton and Bos 205; Millenium Ecosystem Assessment 2005; Pearce et al. 2006). Ecosystem services may be categorized mainly as:
Provisioning services: Provision of tangible products to humans such as fresh water, fish, fibre, fuel wood;
Regulation services: indirect services to humans through regulation of hydrological processes that attenuate floods and mitigate droughts, and natural purification capacities of wetlands, lakes and floodplains;
Cultural services: the provision of locations (settings) for religious ceremonies, recreation and aesthetic value.
Ecosystem services sustain human life on earth. Many people in developing countries depend directly on these services in order to generate income and food, to stay healthy and to have a safe place to live.