Impact of Tsunami Disaster on the Water Environment

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ABSTRACT
The earthquake that generated the great Indian Ocean tsunami of 2004 is estimated to have released the energy of 23,000 Hiroshima-type atomic bombs, according to the U.S. Geological Survey (USGS). The earthquake occurred on December 26, 2004 was an undersea earthquake originated in the Indian Ocean off the western coast Indonesia and generated tsunamis that were among the worst disasters in modern history. At a magnitude of 9.0, it was the largest earthquake since the 9.2 magnitude earthquake off Alaska in 1964. The earthquake was the result of the sliding of the portion of the Earth's crust known as the India plate under the section called the Burma plate. Tsunamis have been relatively rare in the Indian Ocean. They are most prevalent in the Pacific. The Indian Ocean tsunami caused waves as high as 50 feet (15 meters) in some places, according to news reports. The resulting tsunamis devastated the shores of Indonesia, Sri Lanka, India, Thailand and other countries even reaching the east coast of Africa some 2800 miles away of the epicenter.

Tsunami waves poisoned the fresh water supplies and the soil by salt water infiltration and deposition of a salt layer over arable land. It has been reported that in the Maldives, 16 to 17 coral reef atolls that were overcome by sea waves are totally without fresh water and could be rendered inhabitable for decades. Uncountable wells that served communities were invaded by sea, sand and earth; and aquifers were invaded through porous rock. Salted-over soil becomes sterile, and it is difficult and costly to restore for agriculture. It also causes the death of plants and important soil micro-organisms.

The flood waters of the Tsunami contaminated water supply systems and in many cases destroyed. Millions of people lack safe water and are at risk of potentially deadly water borne diseases like cholera, diarrhea, malaria and typhoid. With over 150,000 people dead from the Tsunami, waterborne epidemics or out breaks is a major concern (WHO, 2004). After the 2004 Indian Ocean tsunami, contaminated water supplies and infrastructure destruction threatened the lives of many survivors of the disaster. The tsunami impacted water quality by flooding septic tanks and causing their contents to contaminate ground and surface water. Seawater also penetrated into groundwater tables, making the water unfit for human consumption. The tsunami also destroyed rural water supply systems across the region. The impact of the Asian Tsunami related to water environment can be described in three time frames: immediate, medium-term and long-term. Immediate impacts include physical destruction of water and wastewater treatment plants, supply pipes and sewers. Some plants not physically destroyed can be severely affected by power failures and worker unavailability. Immediate impacts include cross contamination of water supplies, salt and silt in supply sources makes water unusable for consumption and possible contaminations from biological (human and animal corpses, dead vegetation etc) sources. Aquifer contamination by salt water is one of the severe long term impacts and also the most difficult to treat. Other long term impacts may include pollution from chemical and oil spills. The United Nations Environment Program (UNEP) estimated that the recent Indian Ocean tsunami extensively damaged Indonesia's coastal environment, causing $675 million in losses to natural habitats and important ecosystem functions.

INTRODUCTION
Drinking water is cited as a health priority in most emergencies. Much of the drinking water response to the Indian Ocean tsunami focused on providing a sufficient quantity of water, with perhaps less focus on quality. Following a disaster, there is enormous pressure on political leaders and public health officials to take disease control interventions mainly spread through contaminated water. The tsunami raised unique challenges for those involved in these efforts.

In most respects the profile of a tsunami resembles that of a flood caused by a hurricane or cyclone. Therefore, disaster response guides consider Tsunamis as floods although the hydrological and engineering issues associated with saline water infiltration are vastly different. Innovative solutions were often necessary to deal with the special circumstances
presented by the aftermath of the Tsunami disaster.

After a Tsunami, subsurface pressure wave precedes the surface wave and causes an upward movement of the freshwater lens. Water levels in wells rise. Previously fresh parts of the aquifer turn brackish. When the area is completely flooded and saline water infiltrates through the unsaturated zone especially in areas with permeable soils. Salt water fills wells and enters the aquifer. Other pollutants present on the surface are spread with the water and will also contaminate the groundwater. When the floodwater recedes and saline water remains in pools and puddles, increasing the duration of the infiltration. The saline water mixes with the fresh groundwater and intrudes the freshwater areas.

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