本文探討於河川出海口外設置潛堤，是否能有效攔阻河川輸砂，進而減緩海岸侵蝕。本試驗模擬嘉義縣的八掌溪河口形狀，並簡化其地形，採用換算為現地水文站資料統計之兩年頻率年的固定流量，放流試驗砂條件、放流時間及試驗水位皆相同，只變化潛堤高度及設置位置，並在試驗場地鋪設磁磚做為捕砂網格。經放流加砂試驗結束後，量測每塊磁磚上之淤砂重量，得出不同條件下其淤砂趨勢與變化，再與無設置潛堤之對照組比較後，探討各種設置方式之攔阻效益。試驗結果發現，設置攔砂潛堤後確實可發揮不等程度之攔砂功效，即可將本來會往外海漂流之泥砂蓄存於潛堤內。以無潛堤之對照組淤砂總重為分母之重量分析結果，當潛堤高度為0～2公尺時，攔砂重效益與潛堤高度成正比，堤高超過2公尺後，攔砂重效益與潛堤高度成反比。攔砂重效益與潛堤設置水深成反比，當潛堤設置水深加大(離岸距離增加)則攔砂重效益減少。而使用相對淤砂率做分析之攔砂率效益隨堤高增加而增加，隨潛堤設置水深加大(離岸距離增加)而減少。

The main purpose of this paper is discussing whether the submerged breakwaters set on the estuary can effectively block the sand transported by the river, and then slow down costal erosions. The experiment is simulating the shape of the estuary of Bajhang River in Chiayi County, simplifying the topography, and using the hydrological data which converted to the frequency statistics of the two-year fixed flow rate. The condition of releasing sand, releasing time and the water level is remaining the same. The heights and the setting positions of the submerged breakwaters are the conditions which only changed in the experiment. The tiles are laid on the testing ground as a sand catching mesh. After releasing sand in the experiment under different conditions, we can obtain the trends and changes of the sediment by measuring the weight of sediment which is on the each tile. Then we discuss the blocking efficiency under different setting conditions of the submerged breakwaters which compared with the experiment of non-setting submerged breakwaters. The results show that the submerged breakwaters really perform the varying effects of blocking sand, in other words, the sediment which is originally drifting out to sea can be remained inside the submerged breakwaters. Useing non-submerged total weight of sediment derived from experiments as denominator to analyze. When the submerged height between 2 meters and 0 meters, the weight of sediment blocking efficiency is proportional to the height of submerged breakwater . When the submerged height of more than 2 meters, the weight of sediment blocking efficiency is inversely to the height of Submerged breakwater. And the weight of sediment blocking efficiency is inversely to the location of the water depth of submerged breakwater (increasing distance offshore). Useing non-submerged relative percentage of sediment derived from experiments to analyze. The percentage of sediment blocking efficiency is proportional to the height of submerged breakwater. And the percentage of sediment blocking efficiency is inversely to the location of the water depth of submerged breakwater (increasing distance offshore).

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