圖書典藏及影音數位平台

本計畫分配年度執行，其主要目的乃是利用水工試驗方法探討於河口外側興建離岸潛沒式構造物來攔蓄河川輸砂，使其成為沿岸漂砂來源可行性以達成穩定海岸之成效。試驗部份共分定床試驗及動床試驗兩種，第一年定床試驗中找出幾種較佳攔砂效果之離岸潛堤的提高及設置位置後，在由動床試驗之探討，找出最佳之攔砂潛堤佈設條件。而執行之試驗範圍則為八掌溪河口至北岸1公里及南岸1.5公里，總計3公里，另外本計畫亦就研究範圍內之各項海、氣象、地形漂砂進行資料蒐集與分析之工作。 　　於第一年計畫中蒐集與分析各項八掌溪河口段之水文、氣象、漂砂及海象資料等，規劃並進行定床水工試驗。藉由19次試驗結果得知，較佳攔砂效益之潛堤條件為堤高2.0公尺~2.5公尺，設置於水深3.5公尺~4.0公尺之間，其最大攔砂效益介於14.9%~29%間。加入造波條件後，其下游區之沿岸漂砂來源最遠之沿岸距離可傳輸至距河口800公尺以上，該處之淤砂率約尚有0.1%以上，河口中心200公尺處之總淤砂率最大可增加約20%，離河口中心400公尺處之總淤砂率最大則可增加約15%，河口中心600公尺之下游段，其總淤砂率約有5%左右之增加率，至800公尺外，約尚可獲得3%，距河口中心1公里內之下游段其總淤砂率平均約增加7%左右，最後由造波試驗分析結果得知潛堤高度2.0公尺及2.5公尺，設置於3.5公尺及4.0公尺水深處之佈置條件，可將攔蓄於堤內之淤砂堆往下游，對下游側之效益相當良好，故將此幾種佈置條件作為第二年度動床試驗規劃之參考。 　　第二年計畫之動床水工試驗主要探討八掌溪河川外側設置攔砂潛堤用以保護海岸之可行性，計畫中亦就研究範圍進行海岸進退距離與面積變遷進行分析，河口灘面面積在2002年前南、北岸灘面面積變化甚大，且有大幅縮減情形，而在2002~2007年間河口南、北灘面面積之變化已大幅減緩，尤其北岸已漸減穩定，海岸線變遷分析結果則顯示八掌溪河口至布袋間之海岸線自1976~2007年間接皆呈現侵蝕大於堆積之情形，至2002~2007年間海岸線每年仍後退約有3.2公尺。而八掌溪口南岸至雙春間之地形於1992年前海岸線之前進量尚大於侵蝕量，但1992年後海岸線已轉為侵蝕狀況，至2002~2007年間，其整段海岸線每年平均後退約有4~5公尺左右。且藉由試驗分析結果找出最佳攔砂效益之設計方案。由各試驗結果發現佈設潛沒式欄砂潛堤於河口外側後，皆能有效攔阻河口外流之河川輸砂，且這些堆蓄於潛堤外側之土砂在波浪之作用下皆可被沿岸水流帶往下游側成為額外之沿岸漂砂量，由零米線之分析中可之攔砂潛堤設置後，河口下游側海岸線與未設置攔砂堤比較分析可發現設置後，海岸線皆有前淤之效果，最大可有近40公尺之前淤長度，最小仍有約5公尺之前淤量。在淤砂損失率之分析中可發現設置攔砂潛堤後確實可有效將外流損失之輸砂堆蓄在潛堤內，由無因次分析結果可發現潛堤設置後最少亦可攔下約7%左右之放流砂量，另由河道至河口外側水位分析結果顯示，攔砂潛堤設置後，雖然部分試次有河口抬升之現象，但抬升量甚小，最大抬升量不超過15公分，故各試次之潛堤佈置方式，應不致對八掌溪口之排洪能力造成影響，在綜合海岸線變化量、堤趾淘刷量、淤砂損失率及河道水位抬升等現象之評估後，各項分析結果皆以潛堤高度2.0公尺、設置於離岸水深4.0公尺處會有最佳之防護效果，其結果可供未來施政、規劃及決策者進行參考。

This scheme allocates Executive. The main purpose of this plan is the use of Hydraulics model test to the estuary outside of Longshore sediment transporting and storing estuary’s sand. making it a source of coastal drift sand in order to reach a stable coast feasibility of effectiveness. Test part are divided into fixed bed test and movable bed test. First year fixed bed test in finding out some kinds of better Submerged breakwater effects of offshore breakwater improve and set location after the test of movable bed, find out the best in protecting the sand breakwater layout criteria. The test performed within Ba-jhang estuary north shore of 1 km and the South Bank of the 1.5 km, total 3 km. In addition to this scheme had also examined the various sea, weather, terrain and bleaching sand for data collection and analysis of the work. 　　In the first year of the plan. We collection and analysis of various Ba-jhang River of hydrology, meteorology, drifting sand and walrus data, planning, and fixed bed model test. By 19 times test that. Better protecting the sand benefit of breakwater conditions are dike height 2.0 m and 2.5 m, set in the depths of 3.5 m and 4.0 m, its maximum blocked the sand efficiency between 14.9~29%. Join the artificial waves conditions, its downstream areas of coastal drift sand source farthest distance that can be transferred to the coast from the estuary of the 800 meters, upon sedimentation rate around there 0.1 %, 200 meters the estuary of the center of the total sediment yield maximum can be increased by about 20%, 400 meters away from the center of the estuary of the total sediment yield maximum can be increased by about 15%, 600 meters from the estuary of the center of the downstream segment, its total sedimentation rate of about 5% of the increase in the rate, to 800 meters, is about to get 3%, 1 km from the Centre of the estuary of the river section of its total sedimentation rate increase on average of around 7%. by artificial waves and analysis. The dike height of 2.0 m and 2.5 m and set in the 3.5 m and 4.0 m down the layout conditions, can be impounded for inside of sediment heap to downstream. On the downstream side of the benefit is quite good, so will this several layout conditions as the second year movable test planning. 　　The second year of the plan of movable test of Ba-jhang estuary lateral settings Submerged breakwater protects coast feasibility. Plan also research scope and retreat to the coast range and analyze changes in the area, the estuary of the beach area in (A.D.) 2002 in the southern and North Beach area of over, and substantially reduced circumstances, and in (A.D.) 2002 ~ 2007 estuary in the South, North Beach area of change have been substantially slow, especially on the North Shore has been decreasing steadily, coastline change analysis results show the Pachang estuary to bag between the coastline since (A.D.) 1976 ~ 2007 indirect rendering erosion is greater than all of the circumstances, to accumulate (A.D.) 2002 ~ 2007 coast still back about 3.2 meters. The South Bank of the estuary and Ba-jhang River to Bu-dai terrain between spring 1992 years ago before the amount still coastline is greater than the amount, provided the coastline erosion, has turned to (A.D.) 2002 ~ 2007, its entire coastline annual average back about 4~5 meters to the left. And to analysis the data to find the best benefits of Submerged breakwater. The test results found that the arrangement of the submerged bar sand breakwater at the estuary of the lateral are effective in arresting the outflow of the river estuaries lose these heaps of sand. On breakwater outside of sand in the wave of action can be taken to a coastal water flow downstream side become extra Coastal drift sand content. From zero-metre coastline of analysis of silt and sand breakwater settings, the estuary side of the coastline and is not set to stop grit comparative analysis can be found settings, coastline has the effect of the former silting, up to almost 40 m in length, before you check minimum there are still about 5 m before the sediment. In the analysis of the sediment yield loss can be found in the set of Submerged breakwater after does effective loss of exports will drain sand storage in the breakwater. The dimensionless analysis results can be found the breakwater at least after the setting is also stopped by about 7% of the amount of releasing and sand, the other rivers to the estuary lateral water level analysis revealed, Submerged breakwater setting. Although some Case have the uplifting of the estuary of the phenomenon, but the lifting of very small, maximum lifting capacity of not more than 15 cm, so each Case of breakwater arrangement, not on Ba-jhang River’s drainage capacity, the impact. Change in the composite coastline, embankment toe brushing the quantity, the loss rate of sediment and water lifting and other phenomena of this assessment. The results were breakwater height 2.0 m, set to the shore to the depth of the 4.0 m will have the best protective effect, its results will be available for future planning, and decision makers.