Geoscience Reference
In-Depth Information
The use of satellite mapping, along with Global Positioning Systems (GPS), to establish
accurate source locations will continue to improve our ability to study river systems in
their entirety, but subjective decisions about the scale of study and which tributaries to in-
clude and exclude will continue to mean that it is effectively impossible to say definitively
which river holds the 'world's longest' title. The Amazon and the Nile have been the main
contenders for centuries as knowledge has improved and conventions have changed. The
Scottish explorer John Hanning Speke thought he had solved one of the great mysteries of
19th-century world geography when he claimed in 1858 to have discovered that the source
of the Nile was Lake Victoria. For much of the 20th century, most authorities recognized
the Nile as the world's longest river, having added the longest tributary leading into Lake
Victoria from the south. However, since the 1990s several credible claims have been made
for the Amazon to be longer, following a number of expeditions in search of its source in
the mountains of southern Peru. These claims put the length of the Amazon at some 6,850
kilometres, at least 150 kilometres longer than the Nile, but the debate is unlikely to end
there.
River flow
Two particularly important properties of river flow are velocity and discharge - the volume
of water moving past a point over some interval of time, although confusingly this may also
be called simply the flow. A continuous record of discharge plotted against time is called a
hydrograph which, depending on the time frame chosen, may give a detailed depiction of a
flood event over a few days, or the discharge pattern over a year or more.
