圖書典藏及影音數位平台

本案計畫為加強重要河川流域之維護管理，提高水利建造物之安全，藉由專業技術顧問團隊或專業學術團隊，執行全面性檢查，並適時輔以專業透地雷達技術或鑽探分析，辦理高屏溪流域水系風險評估及堤防、護岸等水利建造物檢查工作，並提出高屏溪流域水系風險評估及水利建造物安全性檢測規劃報告，俾利作為未來高屏溪流域水系河堤維護管理之參考依據。

Gaoping River often encounters circumstance of extreme rainfalls due to climate change. In spite of the invasion by Typhoon Morakot in 2009, the damaged areas have been restored eventually but some old levees still have some hidden risks. Moreover, the hydraulic structure within the water area are still subject to the threats from unforeseeable disasters such as typhoon, torrential rain or earthquakes and hence risk assessment and hydraulic structure safety test are adopted to effectively lower the risks in waters while valid maintenance and reinforcement solutions on levees with high risks are sought for subsequent maintenance and management. Visual inspection on damaged sites shows that 33 sites of levee structure were damaged. The 7th River Management Office has completed improvement on 28 damaged sites and the quantity of damage has been reduced to 5 sites. The 7th River Management Office still prepares budget for improvement funding in addition to reporting for repair. UAV aerial shots of roads of river sections adjacent to the levee position reveal 38 branches of Gaoping River. Ground penetrating radar measured the test length reaching 55,707 meters and 1,234.5 meters of which were detected with minor cavity signals, 55.5 meters of which detected with intermediate cavity signals, and 4 meters detected with severe cavity signals. About 46% of branches with intermediate cavity signals are located on Yuemei No. 2 revetment and levee, 34% are located on Tuku Levee while severe cavity signals all fall into Cailiao Levee. With regards to the material strength of levee structure, the rebound hammer test results fell between 100~560kgf/cm2 with a total of 30 sites having test results lower than 175kgf/cm2. In particular, the right-bank revetment upstream of Goping Bridge showed the lowest test value of 0K+062 while concrete drilling core test fell between 235~531kgf/cm2. The project compiled the climate change data of Meinong River from the IPCC AR5 provided by TCCIP and analyzed the maximum precipitation in the waters of Gaoping River per month under the influence of climate change between 2021 and 2040. In particular, RCP2.6 scenario showed maximum increase of volume by 10.00% in August. Moreover, Gaoping River elevation is located in downstream of the river and currently the levee height meets project flow without level overflow. Nonetheless under hydraulic volume increase, some cross-sections are still subject to inadequate level free-board. In consideration of the greater change in the influence of flood elevation due to the average riverbed scoruing in Gaoping River, unscheduled dredging method can be adopted to control the rate of riverbed siltation. The cross-sections of Laonon River and Qishan River are all located on the upstream of the scope of basic management for this project due to the inadequate level free-board, which flood prevention facilities belong to low-level protection design while the post-levee security object mostly consist of forest lands or miscellaneous lands, which had greater level of overburden in flooding. In the future, close attention may be need to be drawn to if the riverbed scouring situation aggregates under the increase of hydraulic volume that leads to the loss of facility foundation due to inadequacy of depth. Since some cross-section of downstream levee of the river has not met the level height in the project, for example most cross-sections can meet the hydraulic volume increase by 20% after the levee height increases to 1 to 1.5 meters when the plan reports recommends for the inadequate levee height. Nonetheless the upstream section within the basic management scope of the project requires close attention to if the riverbed scouring situation aggregates under the increase of hydraulic volume that leads to the loss of facility foundation due to inadequate depth. Currently Kouai River has not been announced with the basic management project and most of the flood prevention facilities consist of gabion revetment designed for stabilizing the riverbanks. The analysis shows slightly severe condition with inadequate level free-board which can be currently maintained for existing conditions or improved depending on the conditions of existing sites. After the subsequent basic management project has been completed, the management will take place according to the content of project. Only the upstream cross-section of Wuluo River – 09 Right Bank showed overburden in flooding by 20% of increase in hydraulic volume. In the future, dredging project can be adopted to control the rate of riverbed siltation and lower the likelihood of overburden in flooding. The frequency of economic activities and population concentration area are recognized as high vulnerability according to the level of levee significance for flooding potential and levee security object evaluation. Additionally the upstream area is included in community or tribe adjacent to the levee or revetment to increase the significance. The sections susceptible to damage evaluation consisting of the levee sections in Meinong River, followed by the levee section in Kouai River, mostly because the elevation of some levee and top of levee in Meinong River and Kouai River could not satisfy the flooding level of project flow, and hence the scores for the overburden of flooding were the highest. The site conditions of 3 industrial zones in the downstream of Gaoping River underwent feasibility evaluation according to the common flood prevention and disaster reduction strategies. It is suggested to set up flood-prevention wall outside the industrial zone and adopt post-level roads as temporary drainage canal to induce the flood flow into downstream. The rainfall station evaluates based on the precipitation data analysis provided by TCCIP while the rainfalls stations of the river increased by the 7th time to 16 stations. The discretion between the Thiessen Method for average rain and the primary data have minimized to about 1% while the water level station and warning water level have increased/decreased with water level stations and the warning water level for Gaoping River according to the 2018 Executive Yuan Gazette – “Central Control River Warning Water Level List.” Risk analysis adopts semi-fixed volume analysis, adopting the loss of hydraulic structure damage leading to levee flooding as the risk factor and other consideration of analysis. The evaluation of level significance and susceptibility to destruction evaluation results are adopted as vulnerability and hazard evaluation as well as defining the relation between risk of flood prevention facilities, Risk = Hazard × Vulnerability to evaluate the risk level after multiplying the vulnerability and hazard through risk matrix for hydraulic structure in Gaoping River. The risk evaluation for Gaoping River includes 650 levee sections, including 15 high-risk levee sections, 11 intermediate-risk levee sections, and 141 low-risk levee and 483 extremely low-risk levee sections. There are 11 sites cross the bans of the mainstreams of Gaoping River that are evaluated as high-risk river sections mostly because the urban plan zone and industrial zone of Kaohsiung City and Pingtung County are located here. Consequently the vulnerability is higher, driving the risk level to high risk. Some sections of Laonong River are evaluated as low and intermediate level of levee vulnerability since the urban plan zones of watershed are away from the riverbanks. Hence the highest risk level ends at intermediate risk level. With regards to Qishan River, flood invasion occurred due to damaged flood prevention structure while the flood restoration design has taken consideration of flood threats and lowered the risk level. Hence the maximum risk level also ends at intermediate risk level. The waters of Kouai River are adjacent to the levee of Shuimen Village while levees also face with approaching flow canal and hence the risk level is evaluated as high-risk levee section. Since the Meinong urban plan zone is located on the two sides of the river canal, the vulnerability of Meining River waters is increased in vulnerability. Moreover the right bank faces with excessively close distance for offshore trough and hence is evaluated as high-risk levee section. The Gaoping Village community of Kouai River is situated in the back of the revetment while the flood-prevention height of revetment could not satisfy the project flow and is subject to overburden, thereby is evaluated as high risk section. Wuluo River in contrast has lower risk and it is inferred that the water level is located in non-flooding potential area while the post-levee security objects consist of areas without population concentration or frequent economic activities, which drives to the evaluation result as extremely low risk areas. The response strategies for the high-risk sections in Gaoping River are divided into short-term and long-term strategies, which are also included in non-engineering action strategies except for the relevant engineering actions. Moreover, the levee detection relies on the recommended restoration solutions for each damaged site. Visual inspection shows the restoration fund for 5 sites of damaged sections is summed to NTD 3,090,000. With regards to risk response measures, the engineering actions adopt river canal management or spur dike improvement of approaching flow canal or direct scouring while the upstream river sections with unstable flow canal adopt canal management and building of beach or in-depth or strengthened foundation as well as other response strategies. The river sections with inadequate levee height are recommended to install flood-prevention wall or adopt runoff distribution and outflow control at upstream river sections to lower the flooding level height. Additionally, areas with high vulnerability shall adopt secondary prevention line to prevent flooding and incorporates with hydraulic structure for regular maintenance to assure the normal operation of facility functions during flooding period. Non-engineering actions adopt safety evaluation mechanism, establishment of warning and water prevention system, rescue and evacuation site plan and canal, hillside and flood-prevention structure with regular monitoring and control to lower the likelihood of risk occurrence. Additionally, the project collection of the 3 temporary flood-prevention wall designs used in Europe and U.S. can be referred, including the FreeView Flood Barriers produced by FloodBreak in Kansas State, U.S., SCFB developed by Neverland, and the Removable FloodWall produced by Prairie Supply in North Dakota, U.S, for adoption in the subsequent disaster prevention plan. The project is based on the content of relevant regulations from Japan and EU. It is recommended to adopt sites with river risk evaluation rated intermediate risk level as reference to certain scale. Moreover, sites with high potential for flooding should include key security objects such as the key urban area, infrastructure, high economic activity zone, and specific conservation zone as high vulnerability. It is recommended to incorporate the scope of certain scale for the aforementioned areas. The items and content of safety evaluation are suggested for division into pre (or initial evaluation) and post regular evaluation items with notations of the update schedule or update conditions per item. With regards to flood prevention and drainage structure safety evaluation system and regulations, it is suggested to refer to the EU practice by establishing cross-section work teams and develop common regulations or manual for the management units within the river to process or take into consideration accordingly.