集水區險峻值(Melton Ratio, MR)可用於界定土砂災害類型，本研究以ESRI所開發的地理資訊系統(Geographic Information System, GIS) ArcGIS 分析數值地形模型(Digital Elevation Model, DEM)，萃取集水區地貌參數，將主流上任一點之Melton Ratio 值與集水面積值無因次化，分析變化趨勢並將其分類成六種類型，討論各種類型之特性。本研究以新北市平廣溪、南投縣塔羅灣溪及加走寮溪、新竹縣泰崗溪及花蓮縣三棧北溪及魯丹溪作為主要研究之集水區，並以蘭陽溪及陳有蘭溪內部分集水區作為補充討論。本研究將高程差(ΔH)、坡度(S)及形狀係數(F)無因次化後與險峻值比較，得到不同分類下各地貌因子之間的關係。第三類通常為面積較大之集水區，且該分類之集水區數量最多；當集水區形狀係數較小時，通常會分類在第二類。現今可取得精度越來越高的DEM 數據，本研究探討不同 解析度對分析結果之影響，證實精度越高偏差越少，而上游對精度的敏感性很高，隨著下游集水區面積增加，其影響遞減。本研究將原始資料(5m×5m 之DEM)的MR′值作為基準，將粗化後的MR′結果(10m×10m、20m×20m 及40m×40m)與其相減，以MR′差值<0.1 作為判斷的分界，大型集水區偏差集中於√A′ <0.20，小型集水區集中於√A′ <0.35。;The Melton Ratio (MR) of watersheds is used to define the types of slopeland hazards. This study analyses Digital Elevation Model (DEM) with ArcGIS, a Geographic Information System (GIS) developed by ESRI. The geomorphological factors of the watershed were extracted first, then the MR and the drainage area along the main streams would be scaled by the values at the downstream end. The changes between them were classified into six types in order to determine the characteristics of each type. In this study, Pingguang Creek in New Taipei City, Yayung-Truwan River and Jia-Tzou-Liau Creek in Nantou County, Thyakan River in Hsinchu County, and Yayung-Pratan River and Ludan River in Hualien County were used as the main watersheds for the study. Lanyang River and Kunhukan River were used as additional watersheds. In this study, the relationships between geomorphological factors in different classifications were found out by comparing the dimensionless values of watershed relief (H), slope (S) and form factor (F) with MR. The majority of watersheds belongs to Type 3, which depicts a wide distribution in watershed area. When the F value of the watershed is smaller, it is usually classified into Type 2. In order to obtain the higher resolution with less bias, this study investigates the effect of different grid resolution on the morphometric parameter, i.e. the MR value. The upstream reach is more sensitive to the grid resolution, while the influence of grid resolution gradually decreases toward the downstream reach.
