平面式及階梯式緩坡海堤之水理特性比較研究

Abstract

緩坡海堤之景觀及親水性良好，且有較佳的降低反射率、溯升及越波量的功能，故已廣被日本海岸工程所採用，成為兼具景觀及海岸保全的新式海岸工法。本研究使用新式平面式及階梯式緩坡海堤護塊於面坡1：4及1：6兩種緩坡，進行一系列反射率、溯升及越波等實驗，並利用波浪尖銳度、碎波相似參數、相對堤頂高…等參數進行分析，以瞭解各種參數對於反射率、溯升及越波量的影響。本實驗採用波高計來量測溯升及越波水量的變化，可以節省人力及提高實驗的精確度。 分析結果發現階梯式緩坡在反射率、相對溯升及越波量等分析結果，皆較平面式緩坡有較佳的水理特性。增加坡度有助於降低反射率及溯升，其中平面式緩坡面坡1：6之反射率約為面坡1：4者之75％。由實驗觀測中發現階梯式緩坡護塊易受到波浪衝擊而移動或翻動，故設計上需加強其鏈結性。平面式緩坡之安定性則較階梯式緩坡為佳。

A mildly sloping seawall provides with better functions of both recreational actions and promenade and reduces the wave reflection, runup and overtopping. The mildly sloping seawalls have been constructed in Japan for last two decades. In this paper, we designed a new kind of plain armouring block for plain-type and step-type mildly sloping seawalls and find its hydrodynamics, such as wave reflection, runup and overtopping by physical model tests. We developed measuring techniques for wave runup and overtopping. The hydrodynamics was related to the wave steepness, surf parameter, and relative freeboard and formulated by suitable regressed formula. The experimental results showed that step-type seawalls reduce more wave reflection, runup and overtopping than plain-type seawall and that the milder seawalls reduce more than steeper ones, especially for plain-type seawalls. The blocks on plain-type seawalls are more stable than those on step-type ones.