SPEAKER : 黃政鴻

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Abstract

The Ardesen( 地名 ) area is prone to landslides because of the climate conditions, geologic, and geomorphologic characteristics of the region.

In this study, the analytical hierarchy process (AHP), the statistical index (Wi), and weighting factor (Wf) methods were used to produce and later compare three susceptibility( 敏感性 ) maps.

The results showed that the AHP method gave a more realistic picture of the actual distribution of landslide susceptibility, than the Wi and Wf methods.

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Introduction A landslide susceptibility map depicts areas( 地滑坡敏感性地圖 )

likely to have landslides in the future by correlating some of the principal factors that contribute to land slides with the past distribution of slope failures

The AHP developed by Saaty(1980) provides a flexible and easily understood way of analyzing complicated problems( 靈活和易於理解的方式分析複雜的問題 ).

It is a multiple criteria decision-making technique( 多重標準決策技術 ) that allows subjective as well as objective factors to be considered in the decision-making process

Early attempts defined susceptibility classes by qualitative overlaying of geological( 定性敏感度類 ) and morphological slope-attributes to landslid ein ventories ( 疊加地質和地貌坡滑坡屬性 )

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Quantitative methods( 量化分析 ) are based on numerical expressions of the relationship between controlling factors ( 控制因子 )and landslides ( 山體滑坡 )

Bivariate statistical analysis( 二元統計分析 ) deals with one dependent variable( 獨立的變量 ) ( in this case the occurrence of mass movements )and one independent variable

Each factor map( 各個因素圖 ) is combined ( 結合 ) with the landslide distribution map,( 地滑分佈圖 )and weighting values( 加權值 ) based on landslide densities are calculated for each parameter

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Bivariate statistical analysis( 二元統計分析 ) deals with one dependent variable( 獨立的變量 ) ( in this case the occurrence of mass movements )and one independent variable

each factor map( 各個因素圖 ) is combined ( 結合 ) with the landslide distribution map,( 地滑分佈圖 )and weighting values( 加權值 ) based on landslide densities are calculated for each parameter

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The development of Geographic Information Systems (GIS) has enhanced the capabilities for susceptibility assessment of large regions( 增加敏感度分析的能力 )

the extraction of morpho metrical and hydrological parameters( 型態計量學和水文參數 ) from Digital Elevation Models (DEM) that would otherwise have been difficult to obtain

Parameters such as slope gradient( 坡度 ), slope aspect( 坡向 ), slope convexity( 坡凸 ) watershed area ( 流域面積 ),and drainage network order( 河網秩序 ) can be easily included for susceptibility analyses. ( 敏感度分析 )

Complete overviews of the use of GIS for landslide susceptibility assessment

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General situation of the region

The study area, in Rize province, covered around 50 km2 on the a Standard Topographic Map in a 1/25,000 scale, in the Artvin F46-d1 and Artvin F45-c2 section of the map, and in Ardesen town which is between 41°09’54” and 41°12’04” latitudes, 40°57’17” and on 41°06’39” longitude (Fig. 1).

Very intense precipitation episodes also occur, causing disastrous flash floods in river basins and many landslides on slopes. Rize is the rainiest city in Turkey

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Materials and methods

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Ardesen 省地滑發生區

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-Landslide influencing data layers

Digital photogrametric data By testing the results, obtained by evaluating( 評估 ) the aerial

photos( 航拍圖 ), with land controls, it was determined that the data obtained matched with the data of the land. The landslide area and related data for the properties of landslide were obtained quickly and accurately by evaluating the aerial photos. It was much easier to discern( 辨識 ) the landslide by evaluating the aerial photos taken before and after the years 1996 and 2002 (Fig. 3).

Aerial photographs are a more efficient( 有效的 ) and practical way to identify( 確認 ) land cover types. In this study, aerial photos are evaluated using digital photogrametric methods and the land cover boundaries were determined in conformity with land state. As a result of the evaluation, five different land cover are described including tea gardens( 茶園 ), forests, rocky areas, hazelnut fields ( 榛子區 ), and residential areas ( 住宅區 ). To show the relationship between the existing land cover and landslides, the landslide inventory( 編製 ) map was evaluated with land cover maps. As a result of these evaluations the percentage distribution of land cover was calculated according to the landslides (Table 1).

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Lithology-weathering( 岩性風化 ) The degree of weathering ( 風化 ) the rocks was determined by

using the classification of weathering method suggested by ISRM( 國際岩石力學協會 ) and the weathering map was produced according to the data obtained.

It was verified that approximately 95% of the landslides occurred in high degrees and among the completely weathered rocks.

Slope The landslide percentage in each slope group class is presented in

Table 1. This table indicates that most of landslides occur at aslope angle of less than 40°.( 發生在安息角小於 40 度 )

Aspect Aspect related parameters( 參數 ) such as exposure to sunlight ( 暴

曬於陽光下 ), drying winds, rainfall (degree of saturation), and discontinuities( 不連續性 ) may control the occurrence of landslides.

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Distance to streams An important parameter that controls the stability of a slope is the

saturation degree of the material on the slope. The closeness of the slope to drainage structures is another important factor in terms of stability.

The landslide percentage in each buffer zone( 緩衝帶 ) is given in Table 1 and shows that most of the landslides are closely located within the first 150 m buffer zone.

Drainage density( 河網密度 ) Drainage density is the ratio of the total length of the stream to

the area of the drainage basin; the higher the drainage density, the lower the infiltration and the faster the movement of the surface flow.

The study area was split into 7 drainage basins using ArcView 3.2. and ARC/INFO Hydro module. The landslides are mainly observed in zones E and B (Table 1).

Distance to the road Similar to the effect of the distance to streams, landslides may

occur on the road and on the side of the slopes affected by roads.

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註： andesite( 安山岩 ) dancite( 英安岩 ) granite( 花崗岩 )

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-Analytical hierarchy process (AHP) 層級分析法 (AHP) 為 1971 年 Thomas L.Saaty 所發展出來，主要應用在

不確定情況下及具有多數個評估準則的決策問題上。 AHP 發展的目的，就是將複雜的問題系統化，由不同的層面給予層級分解，

並透過量化的方法，覓得脈落後加以綜合評估，以提供決策者選擇適當的方案。 AHP 評估尺度的基本劃分包括五項，及同等重要、稍重要、頗重要、極重要

及絕對重要等，並賦予名目尺度 1 、 3 、 5 、 7 、 9 的衡量值；另有四項介於五個基本尺度之間，並賦予 2 、 4 、 6 、 8 的衡量值。有關各尺度所代表的意義，如表 1 所述。 AHP 在處理認知反應的評估得點時，則採取比率尺度的方式（從名目尺度產生）。

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AHP 的敏感度分析圖

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WI 分析

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WI 敏感度分析圖

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WF 分析

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WF 敏感度分析圖

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結果示意圖一

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結果示意圖二

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Discussion and conclusion( 結論與建議 ) The Wi and Wf maps show 62.5% and 68.8% of the landslide zones

AHP, Wi, and Wf derived susceptibility maps with the AHP map gives the better results than the Wi and Wf maps (AHP 的方法優於其他兩者 )

The landslide inventory map was prepared in such a way that it included shallow landslides. Besides, it also considered that lithology-weathering, slope gradient and land cover of materials as parameters important for susceptibility mapping.( 地滑坡敏感圖以岩性風化 坡度和土地覆蓋作為重要的參數 )

The AHP method predict higher percentage of in the landslide area.

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報告到此謝謝指教

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