圖書典藏及影音數位平台

水利署於民國100年3月7日召開研議「白河水庫更新改善與曾文溪自來水水質水量保護區管制及解編對策」，會議結論指示本局朝阿公店水庫空庫清淤模式辦理更新改善規劃，並就整體供水效益（含農業用水）、防洪（含下游河道治理）、設施更新改善及空庫清淤（含環評）等妥適規劃，本工作計畫書乃依前期規劃檢討成果為基礎，在農委會擬辦理自嘉南大圳北幹線加壓送水供灌白河水庫下游灌區等工程後，進一步評估白河水庫空庫清淤之清淤模式、數量、土方處理方式及地點，設施更新改善（減淤）、供水效益、經費需求及防洪功能等，以增加水庫庫容、減少缺水機率及提昇防洪功能。爰提出「白河水庫更新改善規劃檢討(2)」(以下簡稱本計畫)，以期早日付諸執行，以促進白河水庫之永續利用與經營。

Summarizing results of analyses, trend of reservoir siltation and current water use, it is concluded that the best strategy for rehabilitation of Baihe Reservoir towards a target volume and sustainable use is to combine mechanical dredging and hydraulic sluicing. Considering factors including water supply, flood control and economy, a goal of maintaining the reservoir storage volume at 15×106m3 was selected. Two schemes to reach the reservoir volume have been developed. The preferred scheme is to mechanically dredge 5.64×106m3 in four years plus certain amount of hydraulic sluicing. In case such large amount of mechanical dredging cannot be executed, the alternate scheme is to more on hydraulic sluicing, but the total duration to attend the storage volume of 15×106 will take 16 years. Baihe Reservoir has three silt settling basins, and their effective storage is 195,000m3. They are judged to be sufficient for hydraulic dredging. Therefore, it will not be necessary to construct additional settling basin. To facilitate temporarily storage of excavated earth from the reservoir prior to permanent deposition, two temporary earth storage areas are planned along both sides of the spillway, downstream from the dam. The total area is 4.7 ha and the amount of storage is 235,000m3. It is estimated that annual sediment inflow to Baihe Reservoir is 500,000m3. For sustainable use of the reservoir, a sediment diversion tunnel upstream from the reservoir and a sediment sluice tunnel in the reservoir have been planned. The intake of the sediment diversion tunnel is located on left bank upstream from the existing #3 debris dam. The outlet is located at the left-hand side of the spillway plunge pool. The total length of the tunnel is 2,108m. The intake of the sediment sluice tunnel is located at the right abutment of the dam and its outlet is at the spillway chute. The total length is 369m. Capacities of the diversion and the reservoir sedimentation tunnels are 125cms and 85cms, respectively. The 210cms total capacity is about the peak discharge of 2-year recurrence frequency flood. After rehabilitation, desilting operation of Baihe Reservoir may be classified into empty-reservoir desiliting, diversion desiliting and no-desilting periods. They are: 1. Empty-reservoir desilting period: from mid-May to early June. This is the plum rains season and near the end of first rice-crop plantation. 2. Diversion desilting period: from mid-June to early October. This is the typhoon season and during the second rice-crop plantation. 3. No desilting period: from mid-October to early May the following year. No hydraulic sluicing during this period but mechanical dredging may be conducted. The water right originally approved for Baihe Reservoir is 47.52×106m3. In yr. 2012, the approved water right increased to 63.74×106m3. Both are greater than average annual inflow of 46.06×106m3. Based on existing plantation area, annual agricultural water need is estimated to be about 27.0×106m3. By simulation, it is estimated after restoration of the reservoir to 15×106m3, the water resources may also be capable of providing extra 1.241×106/year for domestic water. This can be used as a reference for re-evaluation of water right after the reservoir rehabilitation. Through various analyses, it is shown that implementation of rule curve will relieve the severity of shortage during drought events. Rehabilitation of Baihe Reservoir include mechanical dredging, construction of reservoir silt sluice tunnel and diversion sluice tunnel, development of temporary earth storage facility, improvement of outlet works and raising of impervious core. The total project cost is 4.132×109 NTD. Results of analysis reveal that the benefit/cost ratio is 1.12. Considering the fact that the rehabilitation will reduce risk of irrigation stoppage, will maintain the function of outlet works, will ensure dam safety, will enhance flood discharge capacity and will help to stabilize water supply in southern Taiwan, etc., it is desirable to go ahead with the rehabilitation of Baihe Reservoir.