天然壩破壞型式中以滲流引發之驟然破壞最具威脅性，潰壩流量對下游保全對象所造成之災害衝擊遠遠超過其他破壞型式，若能於天然壩形成初期有效且快速評估天然壩可能破壞型式，將有助於天然壩防救災應變能力之提升。影響天然壩破壞型式主要與：（1）壩後入流量與壩體滲流量；（2）壩體組成材料；（3）壩體幾何形狀；（4）滲流臨界安定坡度等４項參數有關。本研究透過46組天然壩室內實驗，分析各參數對破壞型式之影響性並予以量化，建立溢流與滲流破壞之區別函數，其正確率為95.5%，並進一步將滲流破壞以滲流臨界安定坡度理論區分為漸進式與驟然破壞，以8處天然壩案例予以驗証，評估結果與實際結果十分符合。本研究建立之天然壩破壞型式判別方法，於天然壩形成初期配合天然壩所在之地形、壩體形狀與河川水理等資料，可有效且快速研判天然壩可能之破壞型式，供天然壩防救災相關單位之參考。

Suddenly failure of landslide dam caused by seepage is the highest risk in landslide dam failure type and itcaused damage is larger than other failure types. To determine failure types of landslide dam, a rapid and efficientassessment method is needed, because different counter measures of landslide dam failure should be considered in disaster prevention. The four factorsare relevant to landslide dam failure types: (1)inflowdischarge and seepage discharge for dam; (2)material properties of landslide dam; (3)geometry of landslide dam;(4)the critical stable seepage Slope. This study based on 46 laboratory experiments to analyze and quantify the relation of each impact factor of landslide dam failure type. The discriminant function of overtopping and seepage failurewas established by result of laboratory experiments. The correct rate of discriminant function is 95.5%. Then seepage failure is progressive failure or suddenly failure can be evaluated by The Critical Stable Seepage Slope. To prove the rapid assessment method by collecting 8 cases of landslide dam, prediction result and actually result match very well. The stability and failure type of dam can be evaluated by geometry and hydrology parameters, thenit could provide a plausible results immediately after formation of landslide dam.