13-11-2012, 05:22 PM
Tsunami Mitigation Strategies
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Introduction
While tsunamis can not be prevented, or their destructive effects entirely avoided, actions can be taken to mitigate the risks of this hazard, thereby reducing the impacts on life, physical structures and livelihoods. The first step in mitigating the tsunami hazard and reducing vulnerability is to gain an understanding of the threat and potential effects should a tsunami occur.
Strategy 1 :Land Use Management
Building Placement
The late seismologist, Ian Everingham conducted extensive research and wrote numerous publications concerning earthquake and tsunami phenomena and their effects in the Pacific Islands. Concerning building placement, he suggests:
•A simple precaution against damage from most tsunamis is for all buildings to be placed 2-3 metres above the high tide level (Everingham, 1976). Special precautions should be made for buildings supplying essential services, however, as is seen by the $300,000 damage caused to a government communications station at Torokima, on the west coast of Bougainville by a 2 metre tsunami following a magnitude 7.7 earthquake in the east Solomon Sea on 20 July, 1975 (Everingham, et al, 1977).
Strategy 2: Planting and Environmental Preservation
Preserve Dunes And Other Natural Barriers
Professor Hugh Davies outlined several environmental mitigation measures in Tsunami PNG 1998 excerpts from Earth Talk:
•Sand dunes and sandy berms topped with shrubs and grasses offer some protection from tsunamis depending upon the height and force of the wave. Once the wave crosses a berm and moves inland it may encounter obstructions or ground features that will cause it to lose energy. Ideally, the ground behind the berm would have an uphill slope to further deter the wave. Conversely, if the ground behind the berm has a gentle or downhill slope, the wave will maintain its energy, and may even gain momentum.
•Mangroves, and stands of dense vegetation can offer some protection from tsunami by not only providing holding capacity for near-shore areas, but by absorbing some of the energy of the waves, catching and holding logs and other debris, and diverting the flow of water.
Ecologist and wetlands specialist Faizal Parish was quoted in a 16 January 2005 article in the New Straits Times:
•During the 26 December 2005 tsunami, the Malaysia Forestry Department found that the “mangrove swamps had acted as an effective buffer zone against the full impact of the tsunami.” Based on observations of this tsunami, “it was estimated that a mangrove belt 100 meters wide with a density of two to three trees every three meters could have reduced the height [of a tsunami] by 70%, assuming the wave was created by a 7.5 Richter earthquake. Instead of a wave, the water would have reached land like a rising flood. Such a green belt would have also reduced the power of the wave by about 90%.”