Go with the Environmental Flow

The overuse of freshwater resources is limiting the ability of aquatic ecosystems to purify wastewater flows and, in the case of wetlands, to reduce flooding -- both of which are services that benefit people. Overexploiting freshwater damages the health of rivers, lakes, wetlands and coastal lagoons. It also harms rural communities that depend on these resources for drinking water, irrigation and fishing.

Overexploitation of freshwater damages the health of rivers, lakes, wetlands and coastal lagoons. It also harms rural communities who depend on these resources for drinking water, irrigation and fishing. Photo credit: Sharmani Gunawardena

Decision makers need to strike a balance between allocating water for human use in agriculture, industry and homes, and water for indirect use such as in ecosystem services. They need to safeguard environmental flows -- the flow regimes needed to keep freshwater ecosystems healthy and productive -- and to maintain the services they provide. The International Water Management Institute (IWMI) has conducted the first ever global assessment of environmental water needs, which showed that in many parts of the world environmental flows are not being met.

Water Stress Indicator Map: This water stress indicator (WSI) map takes into account environmental water needs, which is the amount of water needed to keep freshwater ecosystems in a fair condition. It was developed using global models of hydrology and water use. Red areas show where environmental water needs are not being satisfied because too much water is already being withdrawn for other uses. (click on map for larger image)

Various methods of assessing environmental flow have been developed over the past decade, but the detailed hydrological data needed to apply them is often lacking in developing countries. Meanwhile, IWMI has successfully applied hydrology-based "desk top" assessment methods in, for example, India and Nepal.

Research shows that the cost of not maintaining environmental flows is high. There are risks to public health, as reduced river flows mean less drinking water and more concentrated pollution. There is also loss of food security and damage to livelihoods as lower water availability means less water for agriculture and fisheries. The livelihood of the poor often relies on common resources such as rivers or wetlands. The loss of biodiversity and resource degradation prevents countries from taking advantage of the revenue-earning options offered by recreation and tourism. As different users compete for water to satisfy their needs, conflicts arise.

Water managers must take into account the needs of all sectors including agriculture, industry and the environment, and they must recognize the importance of allocating water to maintain environmental flows. They should first identify the desired environmental status of a river and then use modeling to establish the amount of water and the timing, frequency and duration of flow needed to achieve this status. They should implement the required flow regimes by controlling discharges and withdrawals and monitor the resulting flows and their environmental effects.

If a river is to be maintained close to its pristine state, as much as 60-80% of its total annual flow may be required. In highly developed river basins where reallocating water is difficult, an environmental flow component of as little as 15-20% may be acceptable. However, allocating only 10% of total natural flow to environmental flow will not ensure a healthy river ecosystem.

Delivering environmental flows may require dams, channels or pumps to add or remove water. Water can be released into rivers to augment dangerously low flows. Dams and pumps can regulate flows into other environments by, for example, stimulating natural floods that flush out salty coastal lagoons.

The environmental flows concept is already being applied in some form in more than 70 countries worldwide. Australia and South Africa are two countries with a wealth of practical experience that decision makers can tap into. A database of methods and summaries of studies conducted by IWMI is available at www.lk.iwmi.org/ehdb/EFM/efm.asp.