荖濃溪流域的河階地和地形演育

River Terraces and Landscape Evolution of Laonong Drainage Basin

齊士崢(Shyh-Jeng Chyi) ； 黃美璇(Mei-Hsuan Huang)

《環境與世界》 5期 (2001/11) Pp. 123-140

https://doi.org/10.6304/EAW.2001.5.6

摘要

荖濃溪流域河階地特徵顯示，更新世末期，河川由一相當廣闊，覆有薄層沉積層的夷平坦面開始加速下切，之後則經過三次的加積與再下切，總共形成六階河階地。大致說來，早期河階地的前期河川下切規模較大，隨之的河谷加積規模亦較大，同期階地面與河床的高差及沈積積厚度，則大致自上游向下游逐漸減小。河川持續下切的原因，應是持續且上洲較快的構造上昇運動，和全新世較暖濕的氣候，造成的河川水文地形特徵必變。本流河川加積的原因，應是全新世氣候轉變為較乾冷時，迅速回春的支流形成沖積扇。河階地主要是由環境變動造成的，但也受流域地形、地質特性影響，使流域上、下游或不同的支流域有不同的地形演育史，整體呈現穿插侵蝕的過程。

關鍵字

沖積扇 ； 河階地 ； 地形演育 ； 環境變遷 ； 複雜反應

並列摘要

There are six terrace flights developed along the main valley of Laonong drainage basin. The sequencef of terraces and their sediments reveal Laonong River have been incised from a planated surface and aggraded subsequently three times in different scale since the end of Pleistocene. The height of terrace scarp and thickness of terrace deposits or the scale of river incision and aggradation are larger in upstream area. continuing uplift of landmass, which faster in upstream area, and the more humid climate should be the major factor that caused incision. Laonong River The average downcutting rate is about 5mm/year. Some tributaries developed alluvial fans which caused the aggradation of main valley. It is suggested that the dryer and cooler events during Holocene are the main trigger causes. However, the main controls are drainage systems themselves, which have different characteristics and sensitivities, then responses to environmental changes in different ways.

並列關鍵字

alluvial fan ； river terrace ； landscape evolution ； environmental change ； complex response