The water strategies of the 20th century helped to supply drinking water, food, flood control and electricity to a large portion of the human population. These strategies largely focused on engineering projects to store, extract and control water for human benefit. Indeed, it is hard to fathom today's world of 6.6 billion people and more than $65 trillion in annual economic output without the vast network of dams, reservoirs, pumps, canals and other water infrastructure now in place. These projects, however, have often failed to distribute benefits equitably and have resulted in the degradation, or outright destruction, of natural freshwater ecosystems that in their healthy state provide valuable goods and services to society.
As water stress and the risks of climate change deepen and spread around the world, policies and strategies designed to meet human needs, while protecting ecosystem health, will become increasingly critical to human well-being. Scientific understanding of the components of freshwater ecosystem health has advanced markedly over the last decade, but incorporation of this knowledge into water policy and management has lagged. A number of nations and regions--including Australia, the European Union, South Africa and the Great Lakes--are pioneering policies that establish boundaries on human degradation of freshwater with an aim of safeguarding ecosystem health. Although imperfect, and facing tough implementation obstacles, these policies offer promising ways of better harmonizing human uses of water with protection of valuable ecosystems.
THE DECLINE OF ECOLOGICAL INFRASTRUCTURE
Water infrastructure typically refers to the collection of dams, levees, canals, pipelines, treatment plants and other engineering works that help provide water services to the human population. There is another class of infrastructure that also delivers valuable services to society: the aquatic ecosystems that perform nature's work. Healthy rivers, floodplains, wetlands and forested watersheds supply much more than water and fish (see Table 1). When functioning well, this "eco-infrastructure" stores seasonal floodwaters, helping to lessen flood damages. It recharges groundwater supplies, which can ensure that water is available during dry, spells. It filters pollutants, purifies drinking water and delivers nutrients to coastal fisheries. Perhaps most importantly, it provides the myriad habitats that support the diversity of plants and animals that perform so much of this work.
For millennia, human societies grew and flourished by relying on this time-tested work of nature. The ancient Egyptians, for instance, thrived for several thousand years on the ecological services provided by the annual flood of the Nile River, which delivered water and nutrients to their farm fields, carried off harmful salts that had accumulated in the soil and supported a diversity of fish. (1) During the 20th century, however, such reliance on nature's services was supplanted by engineering projects that provided hydroelectric power, intensive irrigation, flood control and other benefits demanded by burgeoning populations and economies.
Since most of nature's services lie outside of commercial markets and are not priced in conventional ways, they are grossly undervalued. While the benefits of dams and other water projects are measured in familiar metrics--kilowatt-hours generated and hectares irrigated and populations served--the ecological downsides of these engineering approaches have largely been left out of the cost-benefit calculus. As a result, ecological infrastructure has been dismantled and degraded at a rapid rate. An estimated 25 to 55 percent of the world's wetlands have been drained, 35 percent of global river flows are now intercepted by large dams and reservoirs and more than 100 billion tons of nutrient-rich sediment that would otherwise have replenished deltas and coastal zones sits trapped in reservoirs. (2) River flows are turned on and off like plumbing works, eliminating the natural flow patterns and habitats upon which myriad life forms depend. (3)
It is difficult to place a dollar value on any one piece of eco-infrastructure, but in 2005, scientists participating in the Millennium Ecosystem Assessment estimated that wetlands alone provide services worth $200 to 940 billion per year. (4) Following the Great Midwest Flood of 1993, U.S. researchers estimated that restoration of 5.3 million hectares of wetlands in the upper portion of the Mississippi-Missouri watershed, at a cost of $2 to 3 billion, would have absorbed enough floodwater to have substantially reduced the $16 billion in flood damages that resulted from that one major flood episode. (5) And when Hurricane Katrina struck the U.S. Gulf Coast in August 2005, an important piece of nature's protective infrastructure was partially missing: coastal wetlands and barrier islands that could reduce the power of storm surges. The state of Louisiana alone has lost 492,000 hectares of coastal wetlands since the 1930s, and continues to lose them at a rate of more than 6,200 hectares per year--approximately one football field every forty-five minutes. (6) It is impossible to know how many lives and homes might have been saved had natural protections along the coast remained in place. But surely one of Katrina's lessons is to enlist nature's help in mitigating future disasters rather than simply assigning it blame when disasters occur.
Indeed with climate change impacts unfolding more rapidly than scientists had predicted even five years ago, the value of protecting and restoring ecological infrastructure is rising. Global warming and its anticipated effects on the hydrological cycle will make the robustness and resilience of nature's way of mitigating disasters all the more important, as tropical storms, spring flooding and seasonal droughts increase in frequency and/or intensity.
SOUTH AFRICA AND AUSTRALIA PIONEER ENVIRONMENTAL FLOW POLICIES
To suggest that the maintenance and repair of ecological infrastructure should be a core principle of water policy and planning might sound about as necessary as suggesting a building's foundation be secure before constructing twenty stories on top of it. In reality, however, the systems of water law and policy that guide water allocation rarely give ecosystems the water they need in order to carry out their functions. However, at least two nations--South Africa and Australia--are advancing a new policy framework that places ecological health and the water required to sustain it squarely at the center of water allocation and management.
Simply framed, the old water mindset held that water acquires value only when it is extracted from the natural environment and put to use by a farm, factory or home. The evolving new mindset recognizes water's value when left in place to do its ecological work. Perhaps no nation is working harder than South Africa to shift from the old way of thinking about water to the new, more environmentally intelligent view. After coming to power in 1994, Nelson Mandela's post-apartheid government undertook a rewriting of the country's constitution and laws, and water reform was near the top of the agenda. "There was a desire to reshape water management so as to transform South African society," according to Evan Dollar, a river scientist with South Africa's Council for Scientific and Industrial Research. "We were given a unique historical opportunity to do so." (7)
South Africa's National Water Act of 1998 was the result of that process. (8) The law was grounded firmly in the doctrine of public trust--the recognition that governments hold certain rights and entitlements in trust for the people and are obligated to protect them for the common good. One of the innovative features of the law is the establishment of a water reserve consisting of two parts. The first is a non-negotiable water allocation to meet the basic drinking, cooking and sanitary needs of all South Africans. (9) The second part of the reserve is an allocation of water to support ecosystem functions so as to secure the valuable services they provide to South Africans. Specifically, the act says:
The quantity, quality and reliability of water required to maintain the ecological functions on which humans depend shall be reserved so that the human use of water does not individually or cumulatively compromise the long-term sustainability of aquatic and associated ecosystems. (10) The water determined to constitute this two-part reserve has priority over irrigation and other licensed uses, and only reserve water is guaranteed as a right. What the South African law says, in effect, is that both people and ecosystems must get the water they need to be healthy before other water demands are fulfilled. Not surprisingly, the pioneering law is far easier to express on paper than to implement on the ground. Because the human reserve amounts to little more than 25 liters per person per day (certainly better than no access to safe drinking water at all, but a sparse daily allotment), many poor black South Africans view the law as a perpetuation of historical inequities.
The ecological reserve has solid scientific underpinnings but is difficult to implement. Just as doctors check blood pressure, cholesterol levels and heart rate to see if these values fall within ranges essential for good human health, scientists assess certain ecosystem attributes to determine whether they fall within ranges essential for good ecological health. With sufficient information about a particular river system, scientists can develop an "environmental flow prescription"--a description of the quantity and timing of flows required to sustain an ecosystem's important functions. The approach calls for water managers to sustain or replicate a river's natural pattern of variable flows--the pattern of high and low flows, as well as periodic floods and droughts--that the...