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A Study of Vegetation Recovery and Slopeland Sediment Yield of Landslides Caused by 921 Earthquake
Vegetation Recovery Rate
Slopeland Sediment Yield
|摘要:||The 921 earthquake caused not only heavy casualties and extensive damage to building, but also a large number of landslides in Central Taiwan. Due to scattered distribution of the landslides, satellite images were applied to rapidly monitor and evaluate vegetation recovery for the large-scale landslides.
The SPOT images of the Ninety-nine Peak area located at Wu River, the Xueshankeng and Wushikeng watersheds at Daan River and the watershed between Tianlun and Techi dam along Dajia River were chosen to identify the spatial distribution of the landslides. Normalized Difference Vegetation Index (NDVI) of the images was used to calculate vegetation recovery rate (VRR) of the landslides. Universal Soil Loss Equation combined with sediment delivery ratio was used to assess the slopeland sediment yield at watershed scale.
Results show that VRR of the landslides at the Ninety-nine Peak area and in the other investigated watersheds are 36% and —10% respectively. The calculation of NDVI of SPOT image taken at the time of one and a half-year after the quake was used for calculated the soil erosion. Annual erosion depth of the landslides at the Ninety-nine Peak area, the Xueshankeng and Wushikeng watersheds, and the watershed between Tianlun and Techi dam are 4.8 cm/yr., 4.4 cm/yr., and 3.5 cm/yr. respectively. Cluster analysis for VRR of the landslides at the Ninety-nine Peak area can be grouped into three categories (good, ordinary and bad). Terrain analysis shows that the landslides whose VRR belong to bad class were located mostly at steep slope (55~100%) and northern aspect. Besides, site analysis shows that the landslides whose VRR belong to bad class were located mostly at ridge areas.|
921大地震除造成人員大量傷亡與許多房屋毀損之外，亦導致台灣中部地區多處山坡地發生山崩。由於崩塌區位分佈遼闊且零散，利用遙測衛星影像能快速地監測、評估大範圍崩塌區位之植生復育情形。 本研究以九九峰、大安溪支流之雪山坑溪和烏石坑溪集水區及大甲溪上游自天輪起至德基大壩間之集水區等三個地區為對象，利用地震前後期SPOT衛星影像進行崩塌區位判釋，再以地震一年半後之衛星影像進行崩塌區位植生復育率分析，並利用通用土壤流失公式，配合坡面泥砂遞移率分析，來推估崩塌區位於地震前、地震後及一年半後等三個時期植生覆蓋情形下之坡面泥砂產量及平均沖蝕深度。 分析結果得知，地震一年半後，九九峰崩塌區位之植生復育率平均值約達36％，顯示其植被已逐漸生長恢復，而其年平均沖蝕深度約為4.8cm/yr；雪山坑溪、烏石坑溪及天輪至德基大壩間之集水區崩塌區位之植生復育率平均值則皆約為—10％，顯示其植生復育情形有變差之趨勢，其年平均沖蝕深度則分別約為4.4cm/yr及3.5cm/yr。另將九九峰崩塌區位之植生復育率以群集分析法分為優、普通及差三個等級，進一步對等級屬於「差」者之崩塌區位進行坡度、坡向及稜線與濱水區位分析，結果得知其植生復育率等級屬於「差」者之區位主要分佈於坡度55∼100％之間、北坡向及稜線區。
|Appears in Collections:||水土保持學系|
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