Geoscience Reference
In-Depth Information
17 DIKE ENGINEERING
A
DELTAS IN THE WORLD
A scan through the world reveals that there are about 75 large delta areas (Africa
13, Asia 26, Australia 9, Europe 8, America 19), which all differ due to the
associated environmental processes. About 500 million people in the world live
and work in these river deltas, and this number is rapidly increasing (Fig 17.1a).
Deltas are centres of nature (wildlife), agriculture and economy. The safeguarding
and sustainable development of these areas should receive the highest priority.
Geotechnical aspects related to the management of a delta region concerns land
subsidence (sinking) and flood protection under changing climate conditions.
dot: major city (more than 1 million)
measuring staff interval is 5 million
Figure 17.1a Large deltas and mega-cities in the world (Waterman)
While the 2007 Intergovernmental Panel on Climate Change (IPCC) report
concluded many river deltas are at risk from sea level rise, recent studies indicates
other factors are causing deltas to sink significantly. The sinking of deltas is
accelerated by the upstream trapping of sediments by reservoirs and dams, man-
made channels and levees that sweep sediment beyond coastal floodplains, and the
compaction caused by the extraction of groundwater and natural gas and oil. One
third of the world's major deltas is sinking and 85 percent regularly experience
severe flooding. Intensive storms, rains and flooding result in temporary
submergence of vast areas with huge damage. Fig 17.1b shows an example of the
global floods in the year 2003, notably not a particular year.
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