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 200,000 m3 yearly since the renovation project 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 May 14th to December 31th. The main work include 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 by Typhoon Soudelor and Typhoon Dujuan, water level station of Agondian Stream and sedimentation survey have been collected. Besides, satellite image of the watershed area was also collected. An aerial photography was carried out in May. 2.in-situ observation and data analysis Water samples were taken at hydrological observation points in the watershed area by 0520 heavy rain, 0705 Typhoon Linfa, 0721 heavy rain, 0807 Typhoon Soudelor and 0928 Typhoon Dujuan for sediment concentration analysis. Water samples were also taken at the downstream of the spill shaft by Typhoon Soudelor while reservoir flood control operation was in progress. 613 samples were taken totally. The highest inflow sediment concentration is 64,461mg/L at Bailing drainage culvert by Typhoon Soudelor. And the highest outflow sediment concentration at the downstream of spill shaft is 59,622mg/L. At this time point, the water storage elevation is about 29.45m. The data of sediment concentration and the related flow 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 174,000m3 by using flow data and abovementioned rating curve. The released sediment is 8,000 m3 acoording to the observed result. The increased reservoir sediment amount is then estimated to be 166,000m3. The actually increased reservoir sediment is 176,400m3 by evaluating the result of sedimentation survey. Sediment is deposited between alluvial fan and spill shaft mostly. There is no apparent change in the main channel. In general, the deposit zone （EL. 29 m extent）has expanded over the spill shaft. Besides, reservoir flood control operation by Typhoon Soudelor（max. discharge 35 cms） did not cause a direct flood-prevention impact in the downstream area. 4.evaluation of desiltation efficiency Flood control operation was carried out by Typhoon Soudelor. Inflow sediment could be released by flood sluicing at the same time. The inflow sediment by Typhoon Soudelor is estimated to be 23,000m3 and the released sediment is about 8,000m3. It calculates that the desiltation efficiency is 35%. 5.suggestion of increasing 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 with high sediment concentration could pass through the reservoir. It is suggested that the water storage level should be lowered to 30m because the desiltation efficiency will decline if the water storage level is higher than 30m. The variation of inflow sediment concentration should be taken into consideration by flood control operation for sediment releasing. The gate of spill shaft should be lifted in 2 hours after high sediment concentration has been detected by the turbidimeter at Bailing Culvert. And the gate could closed for water storage if the outflow sediment concentration reduced to 2,000mg/L.