離岸流

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離岸流(英语:Rip current),又称裂流,是一種向外海方向快速移動的強勁海流。這些水流的縱向長度可達61~762公尺,但寬度一般不會超過9公尺。離岸流的速度非常快,流速可高達每秒2公尺以上[1]。
離岸流對海邊的人員很危險,因為會將人快速帶離海岸邊,往外海飄流。人員在和離岸流對抗時,容易因體力耗盡,疲倦而發生溺水意外。瘋狗浪也同樣具有威脅性。離岸流常發生於固定沙洲之間,持續時間從幾分鐘到幾星期都有可能,且發生前徵兆通常不明;。離岸流最強的時候是退潮時[2]。在遇到沿岸流時,應沿著平行於海岸的方向朝一側游出,然後藉波浪游回岸邊;如果有風,最好順著風的方向游。
離岸流主要是當海浪沖擊向海岸時,因為遇到阻礙(陸地)而潰散,而大量的海水必須尋找回到海裡的路徑,但由於受到後續海浪的推擠,這些海水初期會沿著與沙灘平行的方向移動,最後匯集成一道或數道的強大水流退回海中,以上的過程循環發生形成離岸流。
離岸流通常會在沿岸海底的低處或人造物如防波堤或碼頭附近形成,寬度、長度與方向因地形而不相同,離岸越遠,離岸流力道越弱。離岸流除了可搬運海底沉積物如砂、石、貝殼等,也會造成沿海地型的改變。
參考文獻
^ 危險!海邊遇到這樣的水流 一定要馬上離開 - 大紀元. 大紀元 www.epochtimes.com. 2015-07-07 [2017-12-14] (中文(台灣)).
^ 海邊戲水 先來認識「離岸流」. 台灣環境資訊協會-環境資訊中心. [2017-12-14] (中文(繁體)).
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