八卦臺地山麓沖積扇形態之研究

The Study of Alluvial Fans Morphometry along Pakua Tableland Piedmont

孫稜翔(Leng-Hsiang Sun)

《地理學報》 61期 (2011/04) Pp. 81-104

https://doi.org/10.6161/jgs.2011.61.04

摘要

根據地形圖、航空照片以及像片基本圖之判釋，八卦臺地東北側與西南側山麓地帶分布許多沖積扇。本研究以集水區面積對沖積扇面積及坡度之2迴歸式為沖積扇分類之依據，以顯示不同形態沖積扇之空間分布，並探討集水區地形指標對其之影響及其背後之可能原因。研究結果顯示：(1)沖積扇面積與集水區面積之相關性低，可能為臺地東北側多末端受限扇，而西南有側面受限扇所致。若將沖積扇分成北段與南段，則各自沖積扇面積與集水區面積相關性可提升。依二關係式劃分之2集群（集群Ⅰ、集群Ⅱ），其差異主為沖積扇坡度與集水區面積關係之差異，且集群Ⅰ（沖積扇坡度相對於集水區面積較小者）多為臺地東北側之扇，集群Ⅱ（沖積扇坡度相對於集水區面積較小者）多為臺地西南側之扇；(2)八卦臺地東北側集水區之地勢落差以及平均河谷邊坡坡度均較臺地西南側為小，因此較多沖積扇被歸類為集群Ⅰ，反之，臺地西南側之沖積扇對被歸類為集群Ⅱ。換言之，即集水區之落差與平均河谷邊坡坡度對於沖積扇之分類結果（沖積扇坡度相對於集水區面積之大小）具關鍵影響；(3)八卦山背斜西南側抬升速率較高，其於集水區地形（集水區高差與邊坡平均坡度）以及沉積物堆積之影響，可能為西南側「沖積扇坡度相對於集水區面積」較東北側者為高之原因。

關鍵字

沖積扇 ； 集水區 ； 地形指標 ； 八卦臺地

並列摘要

By interpreting topographical maps, aerial photographs and orthophoto base maps, we mapped numerous alluvial fans along the northeastern and southwestern Pakua Tableland piedmont. The study carried out analyse on empirical relationships of geomorphic features from the alluvial fans and related watersheds. The drainage basin areas are promoted as independent variables showing the distribution of alluvial fans in different morphometries. My findings include the following. First, the relationship between fan area and drainage basin area is minimal. This is due to two types of fans in the Pakua Tableland: ”distally confined fans” in the northeastern region and ”laterally confined fans” in the southwestern part. The distinction between cluster I and cluster II, differentiated by two equations is mostly attribute to the fan gradient and drainage basin area. Furthermore, cluster I (with lower fans gradient) is distributed mainly in the northeastern region of the tableland, while cluster II (with higher fans gradient) is distributed mainly in southwestern. Second, since the relief and mean valley-side slope of drainage basins in northeast of the Pakua Tableland are lower than those in southwest and most of the northeastern fans are classified as cluster I. The relief and mean valley-side slope of drainage basin are distinct in classifying fans (a fan gradient-drainage basin area relationship) through discriminant analysis. Third, the fan gradient relative to the basin area in the southwest Pakua Tableland is higher than northeast, most likely due to the higher uplifting rate across the Changhua fault in the western side of the Pakuashan Anticline which influences the topography of drainage basin (relief and mean valley slope) and sedimentation of alluvial fans.

並列關鍵字

alluvial fan ； drainage basin ； geomorphic index ； Pakua Tableland

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