Estuary Processes and Managment - River Dynamics and Integrated River Management - page 527

integrating influences from both the land and the sea in wetland areas. Wetlands along coastal shorelines
serve as natural barriers against flood damage and erosion due to wind, waves and currents. In contrast to
hardened structures such as riprap and seawalls, the construction and/or maintenance of native wetlands
is often the most economical long term solution to shoreline stabilization problems. However, human
activities within coastal shorelines have often removed the native wetlands and installed a variety of
structures, causing problems of shoreline erosion and destabilization. In Louisiana, USA, it has been
estimated that each kilometer of wetland reduces hurricane storm surges by 5 to 7 cm (Stokstad, 2005).
A representative example of the disastrous consequence of loss of wetland habitat can be illustrated by
the well-known 2004 Indian Ocean tsunami. On 26 December 2004, an earthquake of magnitude 9.0 (on
the Richter scale) occurred at the west coast of northern Sumatra, Indonesia, causing a catastrophic
tsunami. A series of devastating waves attacked the coastal shorelines, severely damaging communities
in Indonesia, Thailand, Sri Lanka, and India. The estimated tsunami death toll ranges from 156,000 to
178,000, with an additional 26,500 to 142,000 missing (Liu et al., 2005). Figure 8.70 shows the epicenter
and the affected countries of this tsunami.
This earthquake is the largest ever recorded in the region and in the world since the 1964 Alaskan
quake. Measurements of maximum tsunami wave heights, inshore inundation distances, eyewitness accounts
and serendipitous observations suggest that human activities within coastal shorelines have likely modified
the run-up behavior of the tsunami (Fernando, 2005). For example, coral reefs can provide shoreline
protection in reduced erosion and wave damage; however, in some of the affected regions, coral is often
illegally mined to provide souvenirs for tourists, which significantly increased the amount of destruction
wrought by this tsunami (e.g., along Sri Lanka's coastline, Fig. 8.71). It is observed that the wave heights
in narrow swaths where coral cover has been removed are as much as 5-10 times those with coral-reef
protection. In an area where substantial coral mining had occurred, tsunami run-up in the area was nearly
8 m; a passenger train was derailed and overturned by the tsunami, killing more than 1,000 people (Liu et
al., 2005).
Fig. 8.70 The 2004 Indian Ocean tsunami driven by an oceanic earthquake (from Marris, 2005a )