曾文溪流域豪大雨事件的流量及輸沙量

The Discharge and Sediment Load of Heavy Rainfall Events in the Tsengwen River Basin, Southern Taiwan

陳翰霖(Han-Lin Chen) ； 張瑞津(Jui-Chin Chang)

《地理學報》 48期 (2007/06) Pp. 43-65

https://doi.org/10.6161/jgs.2007.48.03

摘要

曾文溪流域豪大雨造成主流下游近三百多年來多次河流改道及洪水災害，影響當地居民生活。本研究蒐集1959至2004年的雨量及流量資料，分析豪大雨（單日雨量≧50mm）對河流流量及輸沙量的影響。研究成果得知，曾文溪上游豪大雨頻率平均每年11日佔全年平均雨量49%(1,303mm)；後崛溪流域豪大雨頻率平均每年16日佔全年平均雨量60%(1,757mm)；菜寮溪流域豪大雨頻率平均每年13日佔全年平均雨量52%(1,249mm)。豪大雨事件集中於五至九月份，日數佔全年95%，主要由颱風及梅雨滯留鋒所引發。山地區發生災難性的大豪雨事件(≧200mm)頻率均較丘陵區高，前者約1.5day/yr，累積雨量佔全年約20%；後者約1 day/yr，佔全年平均雨量約10%。
流量分析顯示豪大雨造成下游流量暴增，豪大雨逕流量佔年平均逕流量比例，主流下游約40%（4.3億立方公尺）、後崛溪約45%（1.4億立方公尺）、菜寮溪約52%（1.0億立方公尺）。1981年艾妮絲颱風引致豪大雨事件，造成主流下游最大瞬時流量曾高達7,820 CMS。輸沙量推估顯示豪大雨輸沙量佔年平均輸沙比例，主流下游約68%（806萬噸）、後崛溪約70%（102萬噸）、菜寮溪約81%（691萬噸），五月至九月期間佔全年比例高達99%。曾文溪主流上游雖有曾文水庫攔沙，但因水庫下游支流菜寮溪輸沙量佔總量70%，水庫雖可蓄洪攔砂，但颱風期間水沙放流以及壩下菜寮溪的高輸沙量，均是主流下游輸沙量依然偏高的原因。若加計水庫豪大雨淤積量，則主流下游、後崛溪、菜寮溪的豪大雨輸沙比例將分別提升爲72%、80%、88%。豪大雨事件對不同地質區造成的輸沙量影響有所不同，菜寮溪流域多泥岩地質區，故豪大雨輸沙量佔全年平均比例較高，充分證明豪大雨對泥岩地質區的影響十分顯著。

關鍵字

豪大雨 ； 流量 ； 輸沙量 ； 曾文溪

並列摘要

Based on historical data, the Tsengwen River has experienced four times channel avulsion over last three hundred years due to abundant sediment supply caused by heavy rainfall events. The channel morphology is controlled by the huge volume of water and sediments. This paper attempts to analyze the proportion of precipitation, discharge and sediment induced by the heavy rainfall events to the annual amount. The data of precipitation and discharge collected from Central Weather Bureau and Water Resource Agency respectively over last 45 years (1959-2004). The amount of sediment load was estimated by the rating curve method.
The result shows that heavy rainfall events (≧50 mm/day), which occurred only 11 days per year on average accounted for about 49% (1,303 mm/yr) of precipitation, 40% (435×10^6 m^3/yr) of runoff and 68% (8.1×10^6 MT/yr) of sediment load to total annual amount. The heavy rainfall occurred in the ”Mei-yu” (stationary front) and typhoon season from May to September. The frequency of disastrously torrential rain (≧200 mm) in mountainous areas, 1.5 days per year, is higher than 1 day in hilly areas. The highest daily amount of discharge 4,070 CMS and maximum peak of discharge 7,820 CMS have been recorded for Typhoon Agnes, 1981. And the highest daily sediment was larger than 20 million tons induced by Typhoon Herb in 1996, which occupied 70% of total sediment, mainly supplied mainly from the tributary Tsailiao River, due to the easily eroded silt. This study highlights that the heavy rainfall events have vital influence on the discharge and sediment load in the Tsengwen River.

並列關鍵字

heavy rainfall ； discharge ； sediment load ； Tsengwen River

參考文獻

Bull, L. J.,Kirkby, M. J.,Shannon, J.,Hooke, J. M.(1999).The impact of rainstorms on floods in ephemeral channels in southeast Spain.Catena.38,191-209.

Crawford, C. G.(1991).Estimation of suspended-sediment rating curves and mean suspended-sediment loads.Journal of Hydrology.129,331-348.

Ferguson, R. I.(1987).Accuracy and precision of methods for estimating river loads.Earth Surface Processes and Landforms.12,95-104.

中央氣象局(1983)。民國七十年颱風調查報告。臺北市:中央氣象局。

林孟龍、林俊全(2003)。颱風對於蘭陽溪上游集水區懸移質生產特性的影響。地理學報。33，39-53。