The greenish line in the following chart shows trends in the
number of global free-flowing rivers greater than 1,000 kilometers in length. The
number has declined from 160 in 1900 to approximately 60 today and is projected
to fall further to 2020.
The bars in the chart show the number of big rivers damned in each decade of
the last century. Notable is the big surge in the decades after World War II
and the revival projected over the next decade.
The chart comes from a 2006 report by the World Wildlife
Fund, from which Desdemona Despair provides a few excerpts:
The rapid development of water
management infrastructure – such as dams, dykes, levees, and diversion channels
– has left very few rivers entirely free flowing. Of the approximately 177
rivers greater than 1,000 kilometers in length, only around a third remain free-flowing
and without dams on their main channel.
While clearly this infrastructure
provides benefits at one level, such as hydropower or irrigation, there is
often a hidden cost to aquatic ecosystems and the wider ecosystem services that
they provide. In order to sustain the wealth of natural processes provided by
freshwater ecosystems – such as sediment transport and nutrient delivery, which
are vital to farmers in floodplains and deltas; migratory connectivity, vital
to inland fisheries; and flood storage, vital to downstream cities – it is
imperative to appreciate the importance of free flowing rivers, and developing
infrastructure with a basin-wide vision.
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