淺瀨與深潭的河床底質特性研究—以金瓜寮溪中游河段為例

Abstract

摘 要 淺瀨-深潭序列的研究近十幾年來因河川復育計畫而更加受到重視，在河床底質特性方面，一般認為淺瀨的粒徑較大且淘選度較佳，但並非所有研究都有此結論。台灣在這方面的基礎採樣研究較為缺乏，因此本文的目的是藉由採樣調查來比較淺瀨與深潭的河床底質特性，並討論底質分布與河床地形變化的關係，研究區選擇台北縣坪林鄉金瓜寮溪河段。本研究首先進行河段型態以及兩岸環境的調查，藉以探討兩岸環境對於淺瀨與深潭發育的影響。之後以數目網格採樣法於十個淺瀨-深潭對進行採樣，並同時測量河床地形，藉以探討河床縱剖面與粒徑分布的變化，並比較淺瀨與深潭在b軸粒徑、淘選度、圓度及扁平度等底質特性上的差異。 研究結果顯示兩岸環境局部性地影響了淺瀨-深潭的地形發育，特別是河岸岩盤或河道阻礙物，均有利於深潭的形成與發育。粒徑分布與河床縱剖面變化的結果，顯示潭心的粒徑通常較為細小，延伸至潭尾反而有略增的趨勢，而發育良好的淺瀨與深潭，其縱剖面變化與粒徑大小有較佳的對應關係。底質特性比較方面，有九個樣區的淺瀨粒徑大於深潭，其中有五個達顯著水準 (α=0.05)；淘選度及扁平度則沒有一致的結論，圓度值則是淺瀨較深潭高。雙變數圖的分析結果，以粒徑平均數對應偏態值的圖最能區隔出淺瀨與深潭的特性。粒徑分布累積百分位數圖則顯示淺瀨的φ50分布明顯較深潭集中，顯示不同深潭間的河床底質粒徑分布有蠻大的差異。

Abstract The studies of riffle-pool sequence have developed in the 1960s. In the last few years, because the ideas of river restoration start, the studies of riffle-pool become more important. In this research area, the river bed morphology of riffle-pool sequence and the differences in characteristics of bed materials always interest the researchers. There is concurrently academic and application value in bed materials research. The studies of streams in Taiwan comparatively lack the foundation investigations in bed materials, so this research hopes to understand the differences in bed materials characteristic between riffles and pools by sampling investigation. The purpose of this study is to compare the bed materials characteristic between riffles and pools, and to discuss the relationships between bed materials characteristic and the river bed morphology. The river bed materials characteristic contains the particle size, flatness and roundness. The research area - ChinKuaLiao stream - is in the PingLin Township in Taipei County. The results reveal that the bed longitudinal variations and the particle size have better corresponding relations in well-growth riffle-pool morphology. By the T- test, particle sizes in pools are coarser than riffles in the five of ten sample zones. Flatness is varies along with the river channel characteristic, and roundness in most riffles is bigger than pool. In the bivariate scatter plots results, it is most clear to separate the characteristic of riffles and pools by the mean particle size vs. skewness. In the cumulative size frequency distributions plots, the φ50 distribution in riffles is obviously more convergence than pools. This reveals there are great differences in bed material size distribution between pools.