International Congress on Engineering, Sciences and Innovative Technologies (ICESIT 2020) - Kuala Lumpur - Malaysia (2020-02-13)

Impact Evaluation of Typhoon Disaster on Groundwater Resources in Pingtung Plain, Taiwan
On August 7, 2009, medium-strength typhoon Morakot landed on Taiwan in Hualian County. The typhoon caused severe flooding and landslide disasters in southern and eastern Taiwan because of long-duration and high-intensity precipitation. The typhoon lasted a total of 107 hours and recorded the largest rainfall duration in Taiwan. Moreover, the maximum hourly rainfall reached 123 mm/hr at Alishan station during the typhoon period. The consequence of the catastrophe including 619 deaths, 76 missing persons, the temporary evacuation of 24,950 residents, flooding, and more than US$ 5 billion in economic losses. According to the investigation by Forestry Bureau, Council of Agriculture, Taiwan showed the landslide areas reached 34,757 hectares, and most kerfs of the forest rips were broken or ripped forest fibre structure. The phenomenon showed the trees destroyed by the direct collapse of the landslide [1]. The water resources conservation ability in the forest reduced due to the large-scale landslide on the upper catchment. In addition, the landslide soil flowed into the river and sediment in the river bed and decreased the water recharge from the river into groundwater. All the results decreased the groundwater resources in this area. The Pingtung Plain located in the south of Taiwan and mainly includes three basins: Gaoping River, Donggang River, and Linbian River [2]. This paper collects monthly mean groundwater level data for each of the basins for nine years from around 2009. This study uses statistical tests to analyze the significance of the difference in groundwater levels before and after the disaster. Then, the cloud theory is used to analyze the uncertainty characteristics of groundwater level variation. The results show that there are significant differences in groundwater levels before and after the disaster. The expected values decreased in the upper and middle fan areas and increased in the distal fan area after the typhoon disaster. The entropy values of the monthly average groundwater level increased in the upper fan area and mostly decreased in the middle and distal fan areas after the typhoon disaster. The results indicated that the groundwater level variation in the upper fan area was more sensitive after the typhoon disaster.
Professor Yi-Lung Yeh