圖書典藏及影音數位平台

鑒於以往水利建造物檢查僅單點式針對構造物本身是否受損，預防因建造物損壞所造成的災害，無法全面性的檢視潛在危險，加以防範避免災害的發生。因此導入風險管理之觀念，猶如全流域健檢，藉由流域水系之風險評估，以了解高風險河段之致災原因，並考量環境可用資源，擬定可行的對策及計畫，依計畫分年分期執行，並隨時檢討執行的成果作為後續精進的參考，以達減低災害發生的目標。

In response to extreme weather events and trends, it is imperative to assess the potential hazards of the water system under the jurisdiction of the River Management Office. to this end, the River Management Office conducted the risk assessment of Beigang River System to identify high-risk courses, and drew up countermeasures and response plans accordingly to reduce the occurrence of disasters. The scope of the risk assessment is the entire water system of Beigang River, including Beigang River, Huwei River, Sandie River, Shigui River, Yeziliao River, Jiuxiongkeng River, Dahukou River, Shiniu River, Lunzi River, Gan River, Dapu River, Niupu River, Shiliuban River, Meilin River, Shizikeng River, Haifenglun River, Yunlin River and Bajiao River.Beigang River originated from Qixingling in Linnei Township, the western foot of the Alishan Range, and finally entered the sea at Hukou Village and Taizi Village, Kouhu Township, Yunlin County. The basin spans 19 towns and villages, including Yunlin County and Chiayi County. The total length of Beigang River is about 82 kilometers, with an average gradient of 1/159. The geology of the basin is Quaternary alluvium, alluvial deposits of gravel, sand and clay. There are three active faults in the basin, namely, Dajianshan Fault, Chiuchiunkeng Fault and Meishan Fault. Since 1998, there have been 36 seismic activities, the highest intensity of which was the 1999 Jiji Earthquake, which measured 7 on the magnitude scale at Gukeng Station in Yunlin County.In reference to the Assessment Report published by the Intergovernmental Panel on Climate Change in 2013 (IPCC AR5), this program designed storm rainfall and the methodology and process of analysis based on the latest river management planning report. To avoid underestimating the flood risk control of embankments, this program proposed to use a 10% increase in rainfall or a 10% increase in the approved flow rate, whichever is larger, as the basis for analysis in the risk assessment. Then, this program analyzed the flood risk control of the entire water system using HEC-RAS to identify the course of each river lacking for flood risk control.Three visual inspections of 151 embankments and revetments along Beigang River was conducted, with the total length of inspections reaching 220 kilometers. A total of 56 embankments and revetments were damaged. As to the type of damage, about 37% of such damage was caused by emptying, followed by 32% by subsidence; damage caused on the top of the embankments accounted for about 32%, followed by 25% on the front and foundation of the embankments. The range of the ground-penetrating radar covers 18 embankments, including Huwei River and Beigang River. Among the test results, holes extended all over Jungong Embankment and Xiqiancuo Embankment.According to the risk assessment framework under the UN Plan of Action on Disaster Reduction for Resilience, this program conducted the risk assessment using the following four steps: risk identification, risk analysis, risk assessment and risk management.Risk identification: In addition to the Risk Assessment Factor Database created by the Water Resources Agency, Ministry of Economic Affairs, this program looked into the characteristics of Beigang River and the causes of embankments prone to disasters to select factors with high correlations. After conducting interviews and questionnaires with experts and scholars and the engineers from the 5th River Management Office, Water Resources Agency, this program determined relevant risk factors and weights through the analytic hierarchy process (AHP).Risk analysis: Taking the section as the unit, this program scored the risk factor for each section; the factor score was then multiplied by the absolute weight to arrive at the weighted score. Based on the total weighted score of each factor, the hazard and vulnerability levels of each section corresponding to the range of the score were obtained. There were 2 high-hazard sections, 313 medium-hazard sections and 1,185 low-hazard sections; there were 120 high-vulnerability sections, 1,236 medium-vulnerability sections and 144 low- vulnerability sections.Risk assessment: A 3×3 risk matrix was adopted for the risk assessment. The risk level was divided into five water consumption warning signals designed by the Water Resources Department (extremely high, high, medium, low and extremely low) and corresponding colors (red, orange, yellow, green and blue). This program found that there were 244 extremely low-risk sections, 1,950 low-risk sections, 782 medium-risk sections, 24 high-risk sections, and no extremely high-risk section.Risk management: Before risk treatment, the sites should be investigated for severe damage (action: take heed and make improvement or make immediate improvement); after repair, 56 damaged sites were identified through visual inspections. This program floated a repair plan for each damaged site. The total repair cost was approximately NT$4.009 million.No extremely-high-risk section was identified in this program. There were 11 high-risk embankments, which were intolerable and required countermeasures and immediate management. Priority was given according to the hazard and vulnerability of each section. As the hazard indicates a higher probability of disasters, relevant risks were managed successively according to the hazard scores. After risks were managed, their hazard and vulnerability decreased accordingly; subsequent results were used for the residual risk assessment. For some sections, it was difficult to reduce the risk factor score due to the on-site environment or different jurisdiction. Hazards such as flood level, flood discharge from upstream reservoirs, current height of embankments and revetments, and constructions to be built were reduced through the improvement in engineering measures. Vulnerabilities such as evacuation sites, disaster prevention capabilities and flood risk control were reduced by non-engineering measures, including designing more evacuation measures and improving resilience. The results showed that taking proper risk management measures could effectively reduce the probability of disasters or damage.There were more objects to be protected along Beigang River and Huwei River, so vulnerability was higher. The entire course of Beigang River has been treated. Except for some sections where embankments are yet to be built, Huwei River was mainly at a low risk; except for one high-risk section at Yidepi Weir of Lunzi River, Lunzi River, Sandie River, Shigui River, Yeziliao River and Jiuxiongkeng River were mainly at a low risk; except for Shiniu River, which flows through Dounan Town and was at a risk of flooding in the flooding simulation and thus required the construction of embankments at flood control gaps, Shiniu River, Lunzi River and Dahukou River were mainly at a low risk; except for some sections of Gan River that were high vulnerability and had no embankments built and Wensheng Community, which was frequently flooded by Yunlin River and was therefore at a high risk, Gan River, Dapu River, Shiliuban River, Meilin River, Shizikeng River, Niupu River, Haifenglun River, Yunlin River and Bajiao River were at a low risk. Overall, additional attention and treatment were required for the sections lacking embankments and the sections where high-capacity industry parks were located, while daily inspections and maintenance were conducted for the low-risk sections of Beigang River.Jiuxiongkeng River was previously managed by the Chiayi County Government, whose management priorities were different from those of the River Management Office. It is now under the jurisdiction of the River Management Office, but no management plan has been made so far. It was proposed that a planning report be made as a subsequent management policy. As high-capacity units (industry parks) were protected by some sections, these sections were at a high risk. The review of the management plans for these sections indicated that embankments are yet to be built. It was proposed that they be included in the subsequent embankment construction plan to mitigate disputes over damage caused by flooding. For high-risk sections, this program proposed to coordinate efforts with other units to improve disaster prevention capabilities. As climate change is accelerating, rivers are vulnerable to flooding and deviation due to features on high-level beaches that blocked their flows. It was proposed that regular surveys of large sections be conducted for subsequent observation and analysis of rivers.