中華防災學刊/Journal of the Taiwan Disaster Prevention Society
中華防災學會,正常發行
選擇卷期
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本文應用HEC-RAS 2D模式以及崩塌前DEM與崩塌後UAV拍攝資料，進行天然壩潰決模型建置及洪水演算。在2017年6月3日，於南投縣小半天瀑布下游發生邊坡崩塌，造成河道堵塞，形成堰塞湖。使用HEC-RAS 2D進行潰決模擬時，避免在壩體穩定性未明情況，衍生之現勘人員傷亡的風險。目前潰壩模式能提供潰壞機制及潰壩參數，可進行參數調整，以此評估潰決影響方案探討。演算結果顯示堰塞湖潰決並未對下游造成明顯的水位變化，但在靠近堰塞湖附近則受到較嚴重的影響，而其洪水波沿著下游逐漸遞減。應用HEC-RAS 2D緊急評估其對下游保全住戶之影響，對政府部門於災情應對與避難決策上有直接助益。
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為能有效執行災害預警，需針對大規模崩塌潛勢區之臨界降雨門檻進行研究。本研究以臺東縣達仁鄉D004潛在大規模崩塌區為研究區域，透過現場調查與細部地質調查，建構潛勢區之水文地質模型，並利用Geo-Studio模式搭配不同降雨條件，探討潛勢區內不同潛在滑動面之災害發生所需之最低雨量。研究結果顯示，在降雨型態部分，尖峰雨量較早發生者對提前崩塌之發生時間，但尖峰雨量較晚者因累積雨量較大，對於邊坡穩定之影響較大。從結果來看，臺東縣達仁鄉D004潛在大規模崩塌區之發生雨量依其發生規模分別為72小時1,667、2,778與3,474公釐。
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近年隨著極端氣候劇烈影響下災害事件逐年增加，豪雨及強颱所帶來的極端雨量更造成山區邊坡崩壞發生頻率劇增。隨著城市不停地發展，不僅改變了當地的環境原貌，快速的開發也破壞了邊坡原本的平衡，以致每當颱風或大量降雨來臨，地下水位上升進而降低邊坡穩定性，故徹底探討降雨引致邊坡崩壞的機制是有其必要的。本研究在探討不同地質條件的邊坡—阿里山公路邊坡（崩積層）、南橫公路邊坡（砂頁岩互層）、藤枝林道邊坡（板頁岩互層）及台174縣道邊坡（泥砂岩互層）之地下水位變動與邊坡穩定性的關係，並制訂各邊坡之臨界地下水位。另外研究降雨與雲層之水氣含量之關係（使用中央氣象局雷達回波標定），建立降雨量與雷達回波之迴歸式，再結合臨界地下水位與雷達回波迴歸式，建構各試驗邊坡以雷達回波為基礎的邊坡崩壞警戒指標。
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A rise of 0.6 m in sea level is a likely figure for 2100, this is mainly consequent to land ice melting and thermal expansion; this latter is expected to continue for centuries even if climate forcing is stabilized. The change in sea level is regionally different as a consequence of several factors, such as currents and gravitational weakening. While, for instance, east of the Philippines the sea is rising three times faster than the average, around Greenland the level is decreasing. Here, the huge ice loss is weakening the local gravity which implies a lower attraction for oceanic water and, despite the factors that increase the sea level, this latter is decreasing. Coastal subsidence can be much quicker and threatening than sea level rise. This happens in particular in mega deltas that undergo, e.g. natural compaction of sediments, deforestation, interruption of sediments inside embanked areas, groundwater and hydrocarbons withdrawal. The vulnerability of the coasts is intensified by the trend of human development in coastal areas that amplifies the challenges for coastal management. The paper and the documents that it presents deal with environmentally friendly techniques aimed at mitigating coastal erosion and subsidence. The loss of mangrove forests and the loss of sediments trapped in the dams may contribute to amplify problems of subsidence and coastal erosion. Extensive mangrove areas, and the important ecosystem services that they provide, have been lost during past decades. In order to help mangroves to grow again in those areas, protection against the waves and restoring the presence of sediment are the necessary steps. Mangrove soil surface has already exhibited the possibility to undergo elevation, thus keeping pace with sea level rise and persisting even over thousands of years. The sediments that typically accumulate in reservoirs, besides reducing the functions of a dam, deprive the environment of materials that prove crucial, e.g. in facing coastal erosion. This is why they are considered ＂resources out of place＂. For these reasons the prevention or the minimization of the sedimentation in a reservoir should be always incorporated in both design and management of a dam. Some of the documents quoted herewith describe methods that can be used to keep or even to restore the original volume of a reservoir. Nowadays the current global rate of net storage loss consequent to sedimentation exceeds the rate of new storage construction.
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日本主要的天災有：氣象災害、地震災害、火山災害、地質災害和海洋災害等五大類；這些災害，彼此之間又會相互影響，進而釀成更慘重的複合型災害；平均每1.6年就會發生一次『巨大天災』（死亡人數超過50人以上）。其中尤以颱風、豪雨、地震及海嘯所引發的災情最為常見且嚴重；此與日本所處的地理位置和自然環境有密切的關係。基於歷次天災的教訓，日本政府乃於1961年頒布「災害對策基本法」，以應各種災害的預警、應變、復原與重建等之需。日本氣象廳針對危害其國人安全的天災之預警發布，原只有「注意報」及「警報」兩種。鑒於2011年311東日本大地震所造成的重大傷亡事件，特自2013年8月起另再加上最高層級的「特別警報」，來提醒全民及早做好防災因應對策。至於預警對策，則有「緊急地震速報」、「海嘯預警」和「緊急警報廣播」等系統，為大眾提供更即時及妥善的災防服務。每當遭遇重大天災之後，日本相關單位均會詳加調查並分析其發生原因和災害特質，進而探討對防救災政策面的衝擊，以及對緊急應變和處置作為的啟發與改進；這種實事求是的態度，值得我們的學習及借鏡。