玉峰堰集水區洪峰流量及崩塌潛勢分析

Abstract

中文摘要 本報告研究區域為玉峰堰集水區，第一部份探討集水區的不同人為開發情況下的洪峰流量及河道是否能夠容納洪峰流量，第二部分則為以玉峰堰集水區根據2009年莫拉克颱風後崩塌分布所建構的崩塌潛勢。 在分析玉峰堰集水區在不同人為開發情況下的洪峰流量估算，玉峰堰集水區面積為390.5〖km〗^2，本報告先在玉峰堰集水區取出三個不同面積的集水區，此三個集水區面積分別為107.0 〖km〗^2(佔總面積之27.4%)、204.4 〖km〗^2(佔總面積之52.3%)及262.7 〖km〗^2(佔總面積之67.3%)，本報告估算在現況土地利用與完全未開發情況下之洪峰流量在上述三種不同集水區面積下的洪峰流量差異。本報告統計鄰近雨量站近年年平均降雨量為3515.9 mm，25年頻率60分鐘延時的降雨強度為123.8 mm/hr，在上述三種不同集水區面積下的洪峰流量差異分別為125.5 cms、260.3 cms及351.5 cms，且此流量在河段內的估算都無法通過，都會造成河段兩旁的淹水情況。 而在建構崩塌潛勢部分，玉峰堰集水區在2009年莫拉克颱風後的崩塌面積有6.5 〖km〗^2(崩塌率約為1.67 %)，本研究分別以頻率比法跟不安定指數法建構玉峰堰集水區崩塌潛勢。玉峰堰集水區以頻率比法建構的平均崩塌潛勢0.136，根據崩塌潛勢預估為會崩塌的地區約佔總集水區面積之8.5%，崩塌潛勢正確率約為66.9%。玉峰堰集水區以不安定指數法法建構的平均崩塌潛勢0.129，根據崩塌潛勢預估為會崩塌的地區約佔總集水區面積之2.4%，崩塌潛勢正確率約為54.9%。以正確率之比較，玉峰堰集水區使用頻率比法建構崩塌潛勢會得到比較好的成果。

Abstract The report estimates the discharge under different landuse conditions and the flooding possibility along the river, and discusses the landslide susceptibility based on the landslide inventory after 2009 Typhoon Morakot in the Yu-Feng-Yen watershed. The area of Yu-Feng-Yen watershed is around 390.5 〖km〗^2. This report extracts three different watersheds from Yu-Feng-Yen watershed, and the smallest, middle, and largest area of the three watersheds are 107.0 〖km〗^2 (27.4% of the total watershed area), 204.4 〖km〗^2 (52.3% of the total watershed area), and 262.7 〖km〗^2 (67.3% of the total watershed area). This report estimates the discharge difference under the current landuse condition and the landuse condition before artificial development from the three watershed areas. The mean annual rainfall is around 3515.9 mm and the rainfall intensity with the return period of 25 years and the duration of 60 minutes is around 123.8 mm/hr. The discharge under above-mentioned rainfall and the current landuse condition in the smallest, middle, and largest watershed is larger by 125.5 cms, 260.3 cms, and 351.5 cms than that under the landuse condition before artificial development. The area along the river will be flooding under such rainfall condition in the current landuse condition. The landslide area after 2009 Typhoon Morakot in the Yu-Feng-Yen watershed is around 6.5 〖km〗^2, i.e. the landslide ratio is around 1.67%. This report builds the landslide susceptibility of Yu-Feng-Yen watershed based on the landslide inventory by using Frequency Ratio method and Instability Index method. The mean landslide susceptibility value by using Frequency Ratio method in the Yu-Feng-Yen watershed is around 0.136, the predicted-landslide area occupies 8.5% of the total watershed area, and the correct ratio of landslide susceptibility model is around 66.9%. The mean landslide susceptibility value by using Instability Index method in the Yu-Feng-Yen watershed is around 0.129, the predicted-landslide area occupies 2.4% of the total watershed area, and the correct ratio of landslide susceptibility model is around 54.9%. The performance of landslide susceptibility model by using Frequency Ratio in the Yu-Feng-Yen watershed is better than that by using Instability Index method.