為改善防砂壩設置於七家灣溪與高山溪河道所造成櫻花鉤吻鮭的族群隔離以及近親交配等現象，相關研究已完成防砂壩進行改善之室內水工模型試驗，而雪霸國家公園管理處亦完成高山溪三、四號防砂壩之改善工程。為瞭解防砂壩改善工程之功效，本研究針對防砂壩改善前後河床狀況進行追蹤觀測調查。根據調查結果，本研究發現四號壩上游滯洪坑已完整出現，因受左岸陡壁及壩體之影響而 向右岸擴大但未加深；梯形沖刷槽因第17至19月的颱風暴雨而使其深度與寬度增加近一倍；原先四號壩下游河道中間之深?，在開口完成後9個月消失，隨後的九個月又因進入雨季而增強之流量而恢復；原四號壩的22.84%淤砂在完工後的9個月內被運往下游，但因河床護甲作用而僅約12.86%淤砂於隨後的9個月被運移；河道坡度則由改善前之3.86%變陡至完工9個月之6.73%，隨後九個月坡度略有變動但皆在6.6%至6.94%之間。針對四號壩上游沖刷槽所出現之巨石階梯，本研究套用Abrahams & Atkinson (1995)的巨石階梯穩定狀態公式而發現這些這些階梯狀河床目前屬於穩定狀態。在棲地型態變化調查方面，由於八十九年九月之雨量充沛、改善後之砂石運移以及工程機械的人為破壞等因素之影響，促使改善之溪流深度、流域面積、深潭和深流面積皆比改善前略為減少；此外，三號壩改善後，壩體上游形成50公尺長之深槽，而使原有之深潭消失。然而，由四號壩改善後一年所形成的壩前深潭和壩後的流速減緩，可知改善工程對於鮭魚棲地之正面助益。

　　　　　To lessen the threats of blockading migration pathway, population isolation, and close-blood mating by check dams, previous studies suggested that removing partial dam body appropriately is one of the approaches for habitat restoration of Formosan Landlocked Salmon. After the implementation of dam remodeling for Dam #4 and Dam #3, this paper focused on the follow-up investigations on the morphological changes of observed channel. Based on the conclusions of investigation, various major findings were categorized. Based on the surveys applied at Dam No.4, the upstream detention pool of the remodeled dam has developed completely and it is expanding toward the right bank without increasing its depth for the constraints of left bank cliff and remaining dam body. The flushing chute did not change apparently between the 9th and 16th months while it expanded double in size during the following three months' heavy storm season. The original scouring pool at downstream side of dam was filled with sediment at the 9th month of remodeling and appears again by the increasing stream discharge during the next 9 months. Longitude cross section investigations indicate that 22.84% of trapped sediment beyond Dam No.4 was delivered downstream within the first 9 months and the sedimentation was slowed down to 35.7% at the 18th month for the protection of armor-layer channel boulders. Channel slope changed from its original 3.86% to 6.73% at the 9th months and stayed between 6.6% and 6.94% in the following 9 months. Affected by the factors including heavy rain in September, sediment transportation around dam site, and channel interruption by mobile equipment, the result of habitat investigation indicated that flow depth, flow area, and areas of ponds and deep flow were declined after the remodeling of No.3 Dam. Besides, the new-developed 50-meter long flush chute behind Dam No.3 destroyed several ponds. However, positive effects on channel habitat are found around dam site of Dam No.4 by its ponds and slow flow. Based on the equation developed by Abrahams & Atkinson (1995) for boulder step-pools, the steps found in the flusing chute are in the stable condition for their H/L/S values being between 1 and 2.