RIASSUNTO
ABSTRACT:
In 2009, a typhoon named Morakot moved onto Taiwan and brought torrential rains that washed down huge amount of driftwood into the sea and accumulation at the coastal areas. By the analysis of satellite images, it is found that 83.2% coastlines of Taiwan were occupied by driftwood after Morakot. The amount of driftwood cleaned-up is 1.03 million tons containing 38.7×104 (37.6%) tons were from coastal harbors, foreshores and backshores. The amount of driftwood left from Morakot is more than 100 times the estimate after historical typhoons and may be the world's great record. The Morakot-induced driftwood has harmed the tourism and fishing industries, endangered the navigation and oceanic activities, brought large impacts to the marine environment and ecosystem, and resulted in huge economic lost.
INTRODUCTION
The features of a typhoon that cause death and destruction are mainly high winds, landslides, storm surges and floods associated with heavy rain. The disasters occur at mountains are in additional linked to the vulnerability of environment such as slopeland conditions, geologic fragility, and the surface soil looseness. Wood is one of the washed materials. Driftwood is the remains of trees, in whole or part that has been washed into the river or ocean by the action of flood or other natural forces. Driftwood can be found on most marine shores of the world, but is generally in highest concentrations along the shores of the middle and higher latitudes in the boreal forest and arctic regions of the world. Treefall due to river bank erosion or landslides are the major causes of driftwood. When the fallen trees enter river channels and be transported down river during high flows, they mainly accumulate in the dead water area of the stream, or nearby river structure subject or lodged in estuaries or flushed directly into the sea.