Critical Rainfall on the Landslide at Shaluntz

豐沛的降雨量常造成邊坡發生崩塌或土石流，嚴重者常危害到人民之生命財產安全。為了配合加強硬體工程設施之有限性，故訂定雨量警戒值疏散避難，然而，過於保守估計時，民眾對其信賴度會較低；而警戒值過高時，則又會置人民生命財產安全於潛勢危險中。 本研究以石門水庫集水區內的砂崙仔集水區為研究對象，根據以往地質調查資料，得知本研究區為老崩積層，平均崩塌厚度約為20公尺，地層構造鬆散，滲透能發達。並且於研究區埋設12個地下水位觀測井，發現地下水易受降雨量而變化，而地下水位反應速率較快的孔位，多分布於武道能敢道路沿線，研判為道路排水不良所致。有4個觀測井仍未測讀到地下水位，其深度最深為50公尺，故研判其地下水位於較深處。 為訂定研究區的雨量警戒值，本研究將地質和土壤資料彙整分析，並考量坡度和土壤含水量之關係，進而推估肇災之臨界含水量。另外，將颱風雨量組體圖和當地滲透曲線比較，發現降雨量僅有小部分被土壤吸收，大部分則形成地表逕流造成土壤沖蝕或發生淺層崩塌。最後，以包絡線指標劃分雨量警戒線，並以降雨強度和平均降雨強度之累積降雨量修正之，縮小其降雨警戒範圍，與艾利颱風和馬莎颱風致災的累積雨量較為符合。因此，將修正後的雨量警戒值則分為低、中、高等潛勢，提供相關單位依照現地避難場所所需時間，訂定合理的雨量警戒值。Abundant rainfall often causes landslides and debris flows on slopes, and even result in serious damage to lives and property of people. In order to strengthen the hardware with the limited facilities, we formulate the rainfall warning threshold value to warn and evacuate. However, if the estimate is conservative, it will lower the risk of people''s lives and property will raise.. In this study, we did the research in Shalunzi watershed in Shihmen Reservoir catchment. Based on past geological survey data, that the study area for the old colluviums, with an average thickness of about 20 meters. The characteristics of geological structure loosely and high permeability. In the study area, placed the 12 groundwater observation wells. Rainfall is likely to influence change in groundwater level. Reaction rate faster groundwater observation wells are distributed in the road. The study judged the road due to poor drainage. There are four observation wells have not read the data, the depth of the deepest underground 50 meters. Therefore, we judged that the ground water in deeper. For the purpose of rainfall warning value, the study compiled information on geology and soil analysis, and considering the relationship between slope and soil moisture, and then estimate the hazard of the critical water content. In addition, comparison of typhoon rainfall and infiltration curve. Analysis results indicated that only a small part of the rainfall infiltration to the soil. Most of the rainfall became runoff causing soil erosion or the occurrence of shallow landslides. Finally, we divide the envelope index warning level of rainfall. This study modified the envelope index, with the cumulative rainfall by maximum and average rainfall intensity. It can narrow the scope of its rainfall warning, with Avery and Martha Typhoons are more consistent with the accumulated rainfall. Therefore, the modified rainfall warning value is divided potential into low, medium and high. Provide information for government to announce the reasonable rainfall warning threshold valueand the needed time for evacuation