隨著台灣經濟社會的發展及通訊需求日益增加，一旦海底電纜斷裂，預期會造成難以估計的損失。一般推斷造成海底電纜斷裂因素有兩個:(1)海底崩塌 (2)異重流(hyperpycnal flow)。前者通常與隨機的地震事件有關，後者與高流量所攜帶泥沙濃度有關。本研究利用河川數值模式HEC-RAS以及中尺度海洋數值模式ROMS，基於現地觀測之河川斷面地形、流量歷線、懸沙濃度、海域底質、潮汐及垂向溫鹽分布，進行模式架設以及結果分析說明高屏溪及海底峽谷可產生低濃度異重流，而在峽谷溫鹽場不受前場洪水事件影響下，密度差福祿數大於1，因此流速及海域環境內密度為異重流的形成關鍵，此時最低所需的濃度僅為20g/L，流量約為2970cms，而異重流發生時多為退平潮時刻。另外透過局部理查遜數反應出峽谷內受潮汐作用產生之速度會造成剪力不穩定的現象，漲潮時期潮汐方向與異重流方向相同，局部理查遜數較低，剪力不穩定現象造成泥沙再懸浮的作用較明顯。退潮時刻泥沙有部分淤積在大陸棚兩側，此淤積與泥沙水團在河口及峽谷源頭交接處受潮流影響而被帶往峽谷南北兩側有關，而在峽谷源頭處的大量淤積，則是因為退潮時期峽谷流速為朝向河口；但在高流量時期，無論漲潮或退潮時刻，峽谷內異重流速度均是朝向外海方向，泥沙在大陸棚上的淤積都相當的少，河源的泥沙受異重流影響可被傳輸至更深海處。

Hyperpycnal flow induced by large-scale catastrophic events (earthquakes and typhoons) may cause various potential environmental hazards such as submarine and seafloor equipment damages. Approximately 150 to 200 fiber-optic cable break events are recorded each year in the area between the Gaoping Submarine Canyon (GPSC) and the Manila Trench. However, how hyperpycnal flow was triggered by catastrophic events is not well understood. This study aimed to reproduce the flow field and sediment transport processes of hyperpycnal flow of the 2008-flood events during Typhoons Kalmaegi and Typhoon Phoenix using numerical models. The model results showed that the riverine flow was affected by the tidal currents and descended to the submarine canyon. In the submarine canyon, the hyperpycnal flow was enhanced during flood tides and attenuated during ebb tides. The river discharge and SSC required for the occurrence of hyperpycnal flow were approximately 2000~3000 cms and 20 g/L. The density Froude number exceeds the critical value of 0.8, but the concentration is much lower than the critical concentration for the occurrence of the hyperpycnal flow.

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