Environmental Flows

Rio Pascua, Patagonia
Rio Pascua, Patagonia
A river's flow is its heartbeat. Freshwater plants and animals have evolved with, and intimately depend upon, natural patterns of hydrological variability. Naturally high and low water levels create habitat conditions essential to reproduction and growth, and drive ecological processes required for ecosystem health. Specific patterns of freshwater flows also support a range of other services provided by river systems. For example, flood pulses move sediment that maintains the form and function of rivers. Seasonal inundation of floodplains and wetlands supports groundwater recharge. And the flow of freshwater to estuaries prevents saline intrusion into coastal aquifers. We all depend on healthy river flows.

When a river has been dammed, one of the most obvious changes is the disruption to the amount and timing of its flow. “Environmental flows” is a system for managing the quantity, timing, and quality of water flows below a dam, with the goal of sustaining freshwater and estuarine ecosystems and the human livelihoods that depend on them. The most ecologically important aspects of a river’s flow are extreme low flows, low flows, high flow pulses, small floods, and large floods. Environmental flows can be designed to restore any of these, with the goal of improving water quality, restoring sediment deposition, addressing the life-cycle needs of fish and wildlife, and restoring the livelihoods of river-based communities.

Many governments and river-management agencies around the world have developed policies to protect environmental flows, and more are doing so all the time. Yet implementation of these policies remains weak. Learn more about efforts to ensure compliance with e-flow policies .

While more effective management of dams can help to mitigate environmental impacts, it should be noted that many dams around the world presently lack the mechanisms needed to control water discharge.


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