Investigations and Analysis on Sedimention Cause of Floodgate

台灣位處熱帶與亞熱帶交界區，全年降雨量豐富，惟降雨大多集中於夏秋雨季，常造成雨季洪患旱季缺水現象，且近年來由於社會變遷與經濟發展快速，居民對於河川邊際土地需求激增，原屬洪氾區之土地相繼開發，造成築堤、設置閘門、抽水站等成為不得不然之措施。閘門主要功能為平時讓內水順利排出，洪水時期阻絕外水倒灌，然受自然環境影響，閘門佈設處易形成土砂淤積，影響閘門正常運作，因此本研究針對水利署各河川局轄管閘門進行調查工作，探討防潮閘門出口附近之淤積原因，並根據調查結果提出可行之防砂或減砂措施。研究結果顯示，閘門主要淤積原因多為因漲潮造成之漂砂淤積、因地形及床砂特性造成之淤積、閘門內水淤積、風砂堆積、植物蔓生、漂流物或雜物淤積等原因；研擬之因應措施為建議研判當地優勢輸砂方向，以減少沿岸區域漂砂落淤於閘門口影響閘門運作、閘門出口處建議設置導流堤以攔截沿岸漂砂，減少漂砂淤積、建議側牆與閘門具交角之形式，利於泥砂運移與河道穩定、以及建議以機械或人工撈除及噴灑除草劑方式搭配生物防治法防治水生植物之蔓生。Taiwan is located at the junction between subtropical and tropical regions. The rainfall is abundant and concentrates in summer and autumn which causes flooding in the rainy season. The social change and economic development results in demand of marginal land in recent years. Due to the development of land around the flooded areas, it is necessary to build embankments, floodgate, and pumping station to reduce the flood potential. The floodgate is frequently used to avoid the outland water flowing backward during flooding periods. Recently, the sediment deposition around the floodgate due to the natural environment becomes a serious problem in floodgate operation. This study intends to investigate the present conditions of floodgates in Taiwan. The field investigations on the floodgates, under management by the Water Resources Agency, were performed. The analysis of the reasons for sediment deposition around the floodgate is expected to provide feasible advices and designs for preventing sediment deposition in future planning. As a result, the general causes of floodgate deposition are, for example, the deposition caused by rising tide, topography and sediment characteristics, aeolian sand, and the sprawling plants. In accordance with the survey results, this study proposes varied preventive strategies for preventing sediment deposit, wind-sand deposit, vegetable overgrowth, and drift deposit around floodgates