圖書典藏及影音數位平台

考量水利署依據水利法修正條文之授權，刻正推動「逕流分擔與出流管制執行機制之規劃」，擬定逕流分擔與?流管制之相關子法，鑒於國內尚無擬訂逕流分擔計畫之經驗，且考量相關子法同步擬定，為落實推行須有適當案例執行，故本案就基隆河流域辦理逕流分擔規劃及計畫(草案)，作為後續被公告為特定河川流域或區域排水集水區域辦理逕流分擔計畫之基礎。

The Keelung River flows through the most essence district in the country with high density development. The increased rainfall in recent years has caused the peak discharge of 200-year return period at estuary increased to 5,350cms (after Yuanshanze Diversion) from 3,690cms (after Yuanshanze Diversion) published originally. The increased peak discharge has caused river bank overtopping along some reaches and increased risk of urban area flooding. The occurrence of flooding will cause a huge damages, therefore, it is really necessary to implement runoff allocation policy and further enforce flood management measures for the Keelung River Basin. The goal of runoff allocation plan for Keelung River has been established as follows: the allowable river channel discharge is set at the flood peak discharge (4,840cms at estuary) of the Nari Typhoon event and 25-year return period hydrological conditions is recommended for regional flood control standard. Based on the relevant regulations of the “Runoff Allocation Technical Manual (Draft)”, this project used the two dimensional hydraulic model SOBEK to analyze the flood flow drained into Keelung River and volume of flood inundation under the design basis of main stream facilities considering drainage of tributaries and operation of pumping stations. The result of SOBEK modeling indicated that the flood discharge of a 200-year return period at estuary was 5,030cms which was 190cms higher than the peak discharge of 4,840cms during the Nari Typhoon event. The excessive runoff of 190cms would be handled by the Water Resources Agency. In order to maintain the allowable flood discharge within Keelung River channel, the local government agency should control the total flood discharge draining into the main stream by regulating runoff control facilities. The allowable discharges of a 50-year return period and a 25-year return period were used for tributaries and drainages respectively. There were no excessive runoff problems in tributaries and drainages because all peak discharges from tributaries and drainages are all less than discharges estimated for the Nari Typhoon event. The inundated areas and the estimated excessive flood volume of 3,180,000 cubic meters are provided as a reference for promoting the runoff allocation plan by local governments. The goals established in this project should be discussed with all relevant agencies prior to a final decision is made. Once the allowable discharge is set for the Keelung River, any additional discharge drains into Keelung River channel should be controlled so as not to exceed the allowable discharge. Local governments should reduce pumping discharges by promoting runoff allocation facilities and sharing runoff by increasing storage capacity of land to meet the allowable discharge requirement of each reach of Keelung River. For example, the total pumping capacity in the Zhongshan Bridge reach is 1,312cms, the allowed pumping inflow is 720cms. The analysis results indicated that the uncontrolled pumping capacity of 1,312cms draining into Keeling River during the design flood event would cause flood stages increasing 0.6-1.0m at cross-sections 43, 55 and 73 with a flood overtopping risk for a length of 3,445m. The preliminary runoff allocation measures for the excessive runoff in Keelung River include diversion scheme:Sijiaoting diversion to reduce discharge by 530cms at estuary; detention scheme: to provide temporary detention storages for reducing runoff discharge; total pumping discharge control: to control pumping discharges along Keelung River according to the allowable discharges at each river reach. This project has completed “ Runoff Allocation Evaluation Report(Draft)”. The runoff allocation review committee will discuss with local governments to determine the runoff allocation implementation limits. After the approval of the “Runoff Allocation Evaluation Report”, it is recommended that a runoff allocation report should be completed within 2-3 years including the the excessive discharge in the main stream responded by the Water Resources Agency and the control pumping discharges along Keelung River responded by local governments. The promotional schedule should also be included in the runoff allocation report.