921大地震草嶺堰塞湖下遊社區洪災緊急應變措施之規劃

Flood Emergency Response Measures for Tsao-Ling Landslide Lake Formed by 921 Earthquakes

921大地震造成中部各縣市慘重之災情，除了房屋傾毀及人員傷亡外，水利設施亦嚴重受創。在另一方面，由大規模山崩土石堆積於河道中，阻塞了清水溪而形成草嶺堰塞湖。而由於崩落土石阻塞河道之面積廣且體積大，一時清除不易，阻塞之溪水無處宣洩，當時造成堰塞湖水位節節上升，已達溢壩之危險，經相關單位緊急開挖溢洪道，疏導湖內積水，已暫時減少發生大規模潰壩發生之風險。然而，近年來汛期暴雨所產生之山區徑流仍大量流入堰塞湖中，一旦天然壩體有安全上之顧慮，將能對堰塞湖下游社區居民造成嚴重災害。因此本文應用對堰塞湖下游淹水潛勢資料，規劃下游社區防救災緊急應變措施策略，南投縣政府可依據本文研究成果，提供量化之洪災影響範圍圖，並結合清水溪沿岸社區防災體系，協助堰塞湖下游社區研擬洪災境況緊急應變措施。

Followed after large surface displacements caused by the 921 Earthquake, the largest earthquake of the last century in Taiwan, the Tsao-Ling Landslide Lake was formed by massive landslides blocking Ching-Shui Creek. The inflows from upstream watersheds were accumulating and caused the water level of the lakes rising. Although emergency spillways have been constructed to prevent the water from overtopping, dam failures may still occur due to large inflows to the impoundment during raining season. As a result, the downstream communities will have serious inundation and the safety of people and properties will be in immediate danger. The purpose of this paper is to simulate the inundation potentials of downstream valleys of Tsao-Ling Landslide Lake and establish a flood emergency response measures. The results can provide Nanto County Government and local authority quantifiable information to establish flood hazard map and demonstrate the flood hazards scenarios for the residents of downstream communities.