圖書典藏及影音數位平台

秀姑巒溪流域位於台灣東部，地跨花蓮、台東兩縣。其北接花蓮溪流域，南與卑南溪流域相鄰，主流秀姑巒溪發源於中央山脈崙天山南麓，東流入台東縱谷後，受海岸山脈阻擋，乃沿縱谷平原向北流，在匯納兩岸諸水後，於瑞穗鄉舞鶴山前再折轉向東流，並以其巨大侵蝕力橫切海岸山脈，而在豐濱鄉大港口附近流入太平洋。流域行政區域包括台東縣之海端、池上與花蓮縣之富里、卓溪、玉里、瑞穗、萬榮及豐濱等八鄉鎮。本溪流域為台東縱谷平原三大水系之一，流域面積1,790.46平方公里，其在花蓮縣部份，占全縣面積三分之一強，居住人口約十萬人，占縣人口三分之一弱，主流全長81.15公里，為全台21條中央管河川之一。主要支流有五條由南至北依序為：樂樂溪、卓溪、豐坪溪、紅葉溪及富源溪。 秀姑巒溪現況防洪構造物多屬老舊堤防，為能尋求有效維修與補強方案，擬藉由堤防結構安全檢測計畫來全面檢視秀姑巒溪堤防之安全，以利後續維護管理。 本計畫主要目的為暸解秀姑巒溪堤防結構現況，先以人員目視進行檢查並提出期初報告，後續採用非破壞檢測方式如透地雷達探測等，檢查堤防構造物之使用狀況與內部損壞狀態，包含結構體內部裂縫及淘空狀況等情形，以便未來做為堤防管理、維護之參考依據，以及尋求有效維修與補強方案，擬委外辦理堤防結構安全檢測分析及研擬改善方案。

1. Project Cause and Work Items The majority of current flood-control structures for Xiouguluan River consists of old levees. In consideration of the recent climate change, extreme rainfall incidents and the potential risks caused by change of channels, it is deemed necessary to inspect the hydraulic structures in order to understand the current condition of the levee structures at Xiouguluan River. The personnel first visually inspects the surface of levees, followed by conducting non-destructive testing methods such as ground penetrating radar tests to check the condition of usage and the status of internal damage in levee structures. The inspection will be adopted as reference for future levee management and maintenance, as well as seeking for the effective maintenance and reinforcement solutions. Hence, a safety assessment analysis and drafting of improvement solutions will apply. The content of the project work includes 3 visual inspections on levees, namely one scheduled and two unscheduled inspections. Non-destructive tests include 26,000 meters of ground penetrating radar length and 18 sites for levee structure strength investigation, based on drilling core test. In sum of the various testing results, the levee undergoes the current condition safety assessment and improvement actions will be drafted based on the assessment results. The main project effect include: (1) Assess and classify the on-site survey for the level of external structure damage on the levee and list the sections of dangerous levees on the river course in addition to propose suggestions for improvement with priority. (2) Non-constructive testing is adopted to understand the condition of the internal structure in levees and the overall damage; propose levee safety assessment analysis and draft repair measures. (3) Propose fittest solutions for maintenance and management and suggestions for improving existing flood-control structures. 2. Basic Data Investigation for Scope of Project The regulation plan for Xiouguluan River started in 1931, which underwent multiple planning and project maintenance during this period. Recently the “Xiouguluan River System Regulation Project Review” was readopted in 2016. Currently the regulation project review has been ratified and audited. Additionally, the investigation on the scope of potential flood scope includes 8 county-owned regional sewage and 6 sites of farmland sewage. The project analyzes the average height for the channel plains of sewage effluent within the flooding scope. The results show that some sewage effluent height is lower or slightly higher than the average height for the external channel plains, which is inferred that some river sections have partial shallow and sand island that are coincidentally situated on the sewage effluent, causing obstructed sewage and backwater flooding. 3. Levee Structure Inspection Results The project undergoes 1 scheduled and unscheduled levee visual inspection work. A total of 7 damaged sites were discovered and the 9Th River Management Office lists the 7 damaged sites into the annual open contract project for improvement in addition to complete the aforementioned improvement by November. Additionally there are 36 sections of channel approaching levee sections, including exposures of the levee basic structure in Ayexi River, Qingshui River, Luantian River, Xiouguluan River, Lingya River, Shigong River, and Luozi River, while some river sections are coincidentally situated in indentation. 4. Inspection Result of Non-destructive Inspection The ground penetrating radar for this project executes in vertical direction of 25,950 meters in total length and in horizontal encrypted direction of 618 meters. The hole-signal consists of minor holes with cumulative total length of 954 meters, accounting for 3.68% of lines inspected, without the detection of signals for medium-size hole. In particular, the Right Bank No. 5 Levee on Fuxing River is detected with 124 meters of minor hole-signal and account for the longest in the project. Moreover the comparison of encrypted test results can be inferred that some holes could exist deep under the levees and can be ruled out the cause of water porosities formed by external water seepage. Hence, the hole-signal detected from the aforementioned levee will not affect the levee structure safety yet and will still require continuous monitoring of changes in the holes. 5. Investigation for Levee Strength With regards to the strength of levee materials, the compression strength of drilling core sample falls between 96 kgf/cm2~418 kgf/cm2, with the exception of the concrete material strength of Mingli No. 1 Levee at Luntian River being only 96kgf/cm2. The rest compression strength of drilling core sample retains the standard of 168 kgf/cm2 or higher. The rebound value for site hammer test falls between 12 and 53.1. Except for the values of some points smaller than the detectable scope, the other points are estimated to have strength between 104 kgf/cm2~389 kgf/cm2. The regression equation for the aforementioned results has a determinant coefficient of 0.1194, which indicates lower correlation between the two. The reason could be related to the partial aging and deterioration on the surface of levee concrete. Additionally, the inspection of the scouring situation of the levee materials under the drilling hole and the results of ground penetrating radar test are compared with excellent conformance discovered. The comparison suggests that the ground penetrating radar test is currently a test method of non-destructive testing technology with higher accuracy and efficiency. 6. Assessment Results of Levee Inspection The project establishes a set of assessment system for current levee condition, which assessment results indicate that the majority of the project levees are in excellent condition. The scores for each levee falls between 1~33 points with a total of 4 sets of assessment sections under project improvement section and 107 sets of assessment under normal sections. No levee is under the level for attention required for improvement. In sum of the risks associated with the existence of insecure levee sections, the risks in general include inadequate slope strength, inadequate levee protection, channel deep-groove approaching the levees as well as other anomalies. This project proposes a budget of NTD 3,160,000 for levee related improvement construction. 7. Suggestions for Levee Maintenance and Management The update on the safety maintenance manual for Xiougular River System flood-control and sluice structures mainly focuses on the review on the activation time for unscheduled inspection. The review results suggest precipitation of 330, 350 and 400 mm as the activation value for prairie area, low hill area and the mountain area; the water level will still adopt the level-2 alert water level announced every year. The levee journal is recorded with 179 levees and revetments, which content includes the name and length of levees, the start/end coordinates, the styles, site photos, and the drawing for relevant project outcome. The project resume is divided into records of historic disasters and project records from previous years. Additionally, the large water map and channel approaching map are drawn as reference for subsequent maintenance and management.