圖書典藏及影音數位平台

阿公店水庫（以下簡稱本水庫）位於高雄市燕巢區境內，係匯集阿公店溪上游支流旺萊溪及濁水溪之水量而成。本水庫自民國42年興建完成迄今已營運50年有餘，為解決本水庫日趨嚴重之淤積、供水及滯洪空間不足等問題，並繼續維持本水庫防洪、灌溉、公共給水等多目標功能，因此本水庫自民國86年起進行更新改善計畫，至民國94年完工，為台灣舊水庫再造的最佳案例。本水庫原為一防洪為主要目標之水庫，為確保水庫蓄水及營運期間壩體之安全及穩定，以提供水庫下游民眾生命財產之安全保證，因此利用大壩埋設之監測儀器，於水庫營運期間持續辦理監測，並對大壩進行定期或不定期安全檢查，以維本水庫營運期間之壩體安全性。

一、Preface The main purpose of Agongdian reservoir is to prevent flood. Main components of the reservoir include the main dam, the left auxiliary dam and the right auxiliary dam. The main dam is a roller compacted dam with a core wall consisted of concrete and the auxiliary dams are without the core walls. Main civil structures include: the main dam, spillway, intake works, and the interbasin transfer spillway. A refurbishment project took place between 1997 and 2006 to resolve issues such as sediment accumulation, water supply and inadequate flood detention, irrigation and public water supply. The project serves as an excellent example upgrading dams. The purpose of the current project is to conduct analyses of existing monitoring data and evaluate the overall safety of Agongdian Dam during its operation to ensure the security and safety of the residents downstream of the dam. Data collected through monitoring devices and through alternative means will be analyzed and assessed to evaluate the behavior and the safety of the dam. The usability of the monitoring devices will also be assessed. 二、Results from Monitoring Devices (一)Out of the 30 sets of piezometers, 16 sets were found faulty (WPE-04,05,07-10,12,14,16,18,20-23,26,30). WPE-01 in particular was producing odd results. The rest of the existing devices remain functioning and reliable. (二)WQR-01 was installed above the ground water level, thus data read through the device is not reliable. After eliminating the effect of rainfall, the flow rate at WQR-03 during dry season coincides with the trend of the reservoir levels. Foundation and ground seepage can be estimated indirectly from WQR-03. (三)The amount of settlements upstream and downstream (max. 9.94mm) are within the threshold limit (10mm/mo) with the rest being stable. (四)Apart from some shallow surface displacements, the largest lateral displacement (max. 9.6cm) experienced at each of the observation well is within the threshold limit. There is no obvious displacement; the remaining wells are otherwise producing normal results. (五)There is a distinct link between the earthquake data collected from both the seismometers and the free-field locations onsite and the dam foundation response to earthquake provided by the Central Weather Bureau. 三、Safety Inspection Results (一)The upstream and downstream slopes are in good conditions. No cracks, slides, protrusions or settlements found due to changes in water level despite some visible sinkholes and erosion paths occurring. However, they generally have little impact of the safety of the dam. The erosion paths on the upstream face are all above normal pool level (EL.37m), and are generally shallow erosions. Plus, the management center has commenced preventative measures by laying out sandbags, therefore continued monitoring of the changes to erosion paths and sinkholes will be a necessary to ensure the safety of the dam. (二)Holes on the downstream face were also repaired in April. Plantations have started growing, however no adverse effects were found. Regular trimming of plantations was found to reduce the number of animal burrows. (三)Cracks found parallel to the centerline of the dam - downstream of the AC road at the crest - have been repaired. Signs of settlement and crack widening are present (cracks re-emerged in September after repair work in June), but since they are minor (within 3mm in length) and that either side of the cracks remain on the same plane, the presence of cracks is not an issue to the dam. (四)Seepage locations found onsite coincides with the distribution of total heads found in the “2013 Safety Inspection and Monitoring Data Analysis of Agongdian Reservoir, Dec 2013”, and the “Safety Evaluation after First Rehabilitation of Agongdian, November 2012” reports. Seepage is no longer an issue in some locations due to changes in topography and land use scenarios. Seepage conditions remain unchanged, and the dam is currently safe. (五)The Kaoshung City Government has recently commenced landscape upgrades 475m downstream from the centerline of Agongdian Reservoir (0k+425m). A new park was constructed which has affected the water level at seepage location 1. The seepage effect should be closely monitored. (六)Structures of the spillway pipes (e.g. diversion piers, gate from at the downstream outlet, channel sidewalls, and floor slabs) and the intake works (e.g. intake tower, diversion structures, connecting bridge) are all in good conditions. No major damages. (七)Weeds emerging from the construction joints of the interbasin spillway weir have been removed, and drainage pipes were installed to provide drainage. Minor surface damages, abrasions, seepage and efflorescence were found at the flood tunnel, but they do not affect the overall function of the structure. (八)Groundwater and dam seepage are two contributing factors affecting WQR-03. WQR-03 is highly influenced by rainfall during wet season and by reservoir level during dry season. This correlation allows for a better prediction of foundation and dam seepage. 四、Behavior & Stability Evaluation (一)Pore pressures and water levels at the dam are stable and all displacement readings are within the threshold. Current deformation and seepage behaviors are normal. Field inspection showed that settlement, sliding, protrusion, and seepage issues are local, and they are currently not concern. (二)The spillway pipes and the intake structures are sound. No anomalies were found. In addition, the function of the downstream channel is fully capable of retaining flood water as accumulated sedimentation has been removed. (三)The concrete structures of the diversion channel, the spillway weir and the stilling pool of the interbasin spillway exhibited no signs of abnormality. In spite of visible spalling, abrasion, cracks, seepage and efflorescence of concrete at the spillway channel, the overall structure is considered sound as damages are minor. 五、Review and Revision of Monitoring Devices (一) Revision showed that some of the piezometers are faulty, and are producing abnormal results. Given that there are risks involved in recalibrating, checking, as well as drilling new boreholes, all of which could lead to the disruption of the embankment fill and subsequently causing hydraulic damages. In addition, given that the dam has been relatively stable since it was completed 60 years ago, it is advised that no alterations to be made to existing monitoring devices in order to minimize damage as well as fulfill basic monitoring requirements. Instead, the piezometers and water gauges near the faulty devices will be used in substitution to predict the behavior of the dam. (二) To prevent readings being affected by the location of the WQR-03 sensor, it is advised that the device is properly braced or anchored. (三)The frequency of collecting data at Agondian Reservoir was found to satisfy the requirements of the “ Structural Management Guidelines of Reservoirs” , which is at 80.6 and the minimum required observation frequency established by USBR 1987, whereby the stated monitoring frequency is between once a week and once every three months. Therefore, the recommendation is to maintain current operating conditions. (四) Warning thresholds for piezometers, water gauges, inclinometers and settlements are based upon “The First Regular Safety Evaluation of Agondian Reservoir after Renewal and Improvement (Dec 2012) ”. Thresholds will be reviewed and revised according to the data collected from reliable monitoring devices.