To dam or not to dam
Today only a third of the world’s 177 large rivers (1,000 km and longer) remain free-flowing, unimpeded by dams or other barriers.
But we have learnt that dams can cause damage as the natural flow of rivers becomes fragmented. Dams can destroy ecosystems and cause people to lose their homes and livelihoods.
In 1998, the World Commission on Dams was established to address what had become one of the most controversial areas of infrastructure development and in the words of Nelson Mandela ‘one of the battlegrounds in the sustainable development arena’.
Agriculture: the greatest user of water
Agriculture wastes 60% or 1,500 trillion litres, of the 2,500 trillion litres of water it uses each year. Between 15–35% of water used by agriculture is estimated to be unsustainable.
The main causes of wasteful and unsustainable water use are:
- Leaky irrigation systems
- Wasteful field application methods
- Cultivation of thirsty crops not suited to the environment
These chemicals don't just stay on the fields they are applied to. Some application methods – such as pesticide spraying by aeroplane – lead to pollution of adjacent land, rivers or wetlands. Fertilizers and pesticides also commonly run-off from fields to adjacent rivers and lakes and contaminate groundwater sources.
Pesticides often don't just kill the target pest. Beneficial insects in and around the fields can be poisoned or killed, as can other animals eating poisoned insects. Pesticides can also kill soil microorganisms.
Unlike pesticides, fertilizers are not directly toxic. However, their presence in freshwater and marine areas alters the nutrient system, and in consequence the species composition of specific ecosystems.
Protecting and restoring freshwater habitats is essential for safeguarding plant and animal species, as well as the communities who rely on them for livelihoods and other services.
However, freshwater habitats in many places are either still under immediate threat or underrepresented in current protected area networks.
In most cases, existing freshwater protected areas are fragmented and disconnected from one another, and not sufficiently large or robust enough to safeguard species and freshwater ecosystem services.
The impacts of climate change are most visible in the dramatic changes occurring to the planet’s freshwater resources according to a WWF report written in 2010 for the World Bank.
The report, Flowing Forward, finds both “visible” water such as rivers, lakes, precipitation, glaciers and snowpack, and water used for crops and livestock, health and sanitation services, hydroelectric and nuclear power as well as manufacturing and business are heavily influenced by climate change.
The very language of climate change — droughts, floods, desertification, famines, tropical cyclones — is the language of water.
We can no longer assume that what is sustainable now will remain sustainable in 10 years, much less 50. So a shifting climate means that the rules for water management must change too. Our current model of ‘sustainable development’ is threatened by climate change. Engineers, policymakers and resource managers need new tools to prepare for more extreme floods and droughts.