圖書典藏及影音數位平台

阿公店水庫集水區大部分為青灰泥岩地形，質地鬆軟且吸水易化，每遇颱風豪雨即造成庫區大量沉滓運移入庫，自民國42年水庫開始運轉以來，每年約有50萬立方公尺之淤砂量淤積於庫底，至民國80年時，水庫淤積率已達71%。民國86年起辦理「阿公店水庫更新工程計畫」，進行水庫浚渫清淤1,160萬m3，庫區有效容量回復至1,837萬立方公尺，並改建溢洪管及灌溉管，實施空庫防淤操作以大量減少洪水時之沉滓落淤，以永續維持水庫之有效容量，操作至今，每年約有20萬立方公尺之淤積，已較更新前減少許多。由近年來防淤操作之觀察，蓄水高程、溢洪管出流量等因子對排砂效率有明顯的影響；此外，透過機械擾動措施也有助於排砂。因此提出本計畫，藉由現地觀測並整合歷年防淤操作之觀測及淤積測量成果，評估排砂成效，進而提出阿公店水庫之防淤策略，做為水庫後續運轉管理之參考依據。

The sediment amount of Agondian Reservoir increases about 200,000 m3 yearly in average since the renovation project was finished in 2005. The object of this project is to evaluate the desiltation efficiency through in-situ observation and sedimentation survey. The strategy of increasing desiltation efficiency will then be suggested according to the results for operation management. This project is carried out from March 20th to December 31th. The main work includes update of general data, in-situ observation and data analysis, sediment transport analysis, evaluation of desiltation efficiency and suggestion of increasing desiltation efficiency. 1.update of general data Data of annual rainfall, the inflow, outflow and water storage elevation of Agondian Reservoir, water level data of Agondian Stream and sedimentation survey have been updated. Besides, satellite image of the watershed area was also collected. Aerial photography was carried out in March and in October to observe the variation of sediment deposition in the upper watershed and reservoir storage area. 2.in-situ observation and data analysis Water samples for sediment concentration analysis were taken at hydrological observation points in the watershed area by 5 events including 0611 Storm, Typhoon Nepartak, 0711 Storm, Typhoon Meranti and Typhoon Megi. Water samples were also taken at the downstream of the spill shaft while reservoir flood control operation was in progress. 508 samples were taken totally. The highest inflow sediment concentration is 60,675mg/L at Bailing drainage culvert by Typhoon Nepartak. And the highest outflow sediment concentration at the downstream of spill shaft is 32,702mg/L which is also observed by Typhoon Nepartak. At this time point, the water storage elevation is about 29.45m. The data of sediment concentration and the related flow rate are used to evaluate desiltation efficiency and to verify flow-sediment transport rating curve. 3.analysis of sediment transport The total inflow sediment amount is estimated to be 940,000m3 by using observed data and abovementioned rating curve. The released sediment amounts to 310,000 m3 according to the observed result. The deposited sediment amount is then estimated to be 640,000m3. Sediment is deposited between alluvial fan and spill shaft mostly. There is no apparent mophorlogical change in the main channel. In general, the deposition zone (EL. 29 m extent) has expanded over the spill shaft. Besides, reservoir flood control operation by Typhoon Megi (max. discharge 100 cms) did not cause a direct flood-prevention impact in the downstream area. 4.evaluation of desiltation efficiency The desiltation efficiency by Thphoon Nepartak and Typhoon Megi is about 56% and is higher than by other events. According to the observation data, to draw down the water elevation, to open the spill shaft gate as early as possible, to keep the spill shaft gate widly open and to prolong flood control operation are principles of increasing desiltation efficiency. 5.suggestion of strategies to increase desiltation efficiency In order to reduce reservoir sedimentation, it is necessary to try to reduce inflow sediment by channel dredging. On the other side, the main channel in the storage area should be maintained so that the inflow of high sediment concentration could pass through the reservoir. It is suggested to remove sediment layer with a depth of 0.4m in the main channel and 0.6-0.8m in the surrounding area of the intake tower.