Delineation of Optimal Subdivisions for Watershed Sediment Disaster Management Using Environmental Variables

• Main Authors: Yu-Ching Chien, 錢郁晴
• Other Authors: 林昭遠
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/73xgjm

碩士 === 國立中興大學 === 水土保持學系所 === 106 === Taiwan is an island located at the junction of the tectonic plate. There is a large amount of sediment yield in the watersheds due to fragile geological property, and the watershed also suffers extreme climate impacts in recent year which results in increases of extreme rainfall events. Typhoons usually cause massive sediment disasters in Taiwan. Chenyoulan Creek is the longest tributary of Taiwan''s longest river. The distribution of its riverbed and fault zone is close to coincidence, and it shows that the geology along the riverbed is fragmented. Because of the gentle gradient of the riparian areas in Chenyoulan watershed, the agricultural development behavior and human activities along the river bank are frequent. The sediment disasters caused by extreme rainfall event are threating the protected object in the watershed. To avoid repeated occurrence of the disasters, the watershed should be managed effectively. Prediction of a watershed disaster rate should be made according to the topography, landform or characteristics of the watershed prior to debris disaster occurrence and delineate the management subdivisions in advance. In addition, added the extreme rainfall indicator can predict the corresponding disaster rating of each subdivision within the watershed if encountering the extreme event in future. As a management basis, it is possible to strengthen management or increase preventive measures for those with high disaster rates, and to concentrate resources on subdivisions that do need to be managed. The most notorious sediment disaster in the Chenyoulan watershed is Typhoon Herb event in 1996. In this study, a hotspot scanning system was applied to select the interested watershed, and an automatic watershed division system (WinGrid) was used to delineate the subdivisions of the watershed. The optimal subdivisions were determined from the curve of the accuracy-subdivision number. The results show that the optimal number of subdivisions of Chenyoulan watershed is 23, and the accuracy could up to 87.0%. The methods developed in this study can be as references of the related authorities.