霧社水庫集水區土砂生產量與其自然環境和土地利用之關係

Sediment Yield in the Wushed Reservoir Watershed and its Relations to Environmental and Land-use Factors

曾麗綺(Li-Chi Tseng) ； 陳毅青(Yi-Chin Chen)

《農業工程學報》 65卷2期 (2019/06) Pp. 63-77

https://doi.org/10.29974/JTAE.201906_65(2).0006

摘要

霧社水庫位於濁水溪上游，集水區大量崩塌和土石沖刷，造成水庫嚴重淤積。對於霧社水庫的淤積情形，社會大眾紛紛將矛頭指向濁水溪上游支流的崩塌以及清境農場、廬山溫泉的人為開發，但目前尚無研究針對霧社水庫集水區的土砂來源進行完整的量化分析。本研究量化霧社水庫集水區土砂量來源，崩塌土砂量是利用林務局提供的2002－2014年山崩目錄，配合面積－體積經驗公式進行估算，土壤沖蝕量則是以通用土壤流失公式估算。研究結果顯示霧社水庫集水區年平均土砂量為507萬公噸，其中，崩塌土砂量約佔288萬公噸，年平均土壤沖蝕量約佔219萬公噸，兩者比例約為六比四。在2008年以前，集水區土砂量和水庫淤積量相近，說明邊坡和水庫的泥砂系統的連結度良好；在2008年之後，強降雨帶來大量土砂堆積在邊坡和河道上，並未完全進入水庫庫區。進一步分析土砂和自然與土地利用關係示，集水區的崩塌土砂主要受到地質構造影響，與人為開發關係不顯著；土壤沖蝕則受到道路與農地開發的影響。整體來說，地質構造因素造成的崩塌為集水區主要土砂來源，人為開發主導土壤沖蝕的貢獻雖然較少，但仍然不應忽視，可藉由水土保持與植被復育等措施著手，減少農地與裸露地土砂之沖刷。

關鍵字

霧社水庫 ； 坡單元 ； 崩塌 ； 土壤沖蝕 ； 土地利用

並列摘要

Wushed Reservoir, located in the upstream of the Chuoshui River, has serve problem of sedimentation due to large amount of sediment eroded from landsliding and soil erosion in the watershed. The public think that the sediment is mainly from the landslides in the upstream of the Chuoshui River and the over-cultivation in the Chingjing Farm and Lushan warm spring. However, there are no sufficient scientific and quantitative evidences to clarify these debates. This study adopted quantitative approach to estimate the sediment yield in the Wushed Reservoir watershed in 2002-2014. Landslide erosion is estimated by using landslide inventory and a volume-area scaling relationship. Soil erosion is calculated by using the Universal Soil Loss Equation (USLE). The results show that the averaged sediment yield rate is 5.07 Mt yr^(-1) (million tons annually), which landslide and soil erosion contributed 2.88 Mt yr^(-1) and 2.19 Mt yr^(-1), respectively. Before 2008, the sediment yield from watershed is generally consistent with that of reservoir sedimentation, indicating a well connectivity between hillslope and reservoir. After 2008, large amount of sediment triggered by intensive rainfall were trapped in hillslopes and river and did not transport into the reservoir. Moreover, the analyst of the relations between sediment yield and the effects of environmental and land-use suggested that the landslide is controlled by geological structure, instead of land-use; soil erosion is accelerated by road construction and cultivation. In summary, the geological-controlled landslide contributes the major part of total sediment yield. The contribution from soil erosion is relatively minor, but is considerable. This study suggested that the authorities should adopt soil watershed conservation and recovery of forest cover to reduce the surface erosion on the farm and bared hillslopes.

並列關鍵字

Wushed reservoir ； Sediment yield ； Llandslide ； Soil erosion ； Land-use