下水道系統都市集水區劃分對於出流推估之影響探討

Abstract

都市集水區劃分通常是由建模者根據研究區域資料，決定子集水區數量、大小以及匯流位置，此種劃分方式會因不同建模者而有不同劃分結果，進而對下水道出流產生影響。所以本研究欲探討都市集水區劃分對於下水道出流之影響，首先利用SWMM(Storm Water Management Model)建置數值試驗模式，分別模擬在不同降雨條件下，改變單一子集水區匯流方向以及將所有子集水區往前一段管長之人孔點匯流兩部分情境。透過比較出流歷線、洪峰時間誤差以及洪峰流量誤差，以了解兩部分情境對下水道出流之影響。模擬結果洪峰時間誤差大於5%的降雨條件有降雨延時為10分鐘，最大降雨強度為60mm/hr、120mm/hr、240mm/hr以及降雨延時為30分鐘，最大降雨強度為60mm/hr，洪峰流量誤差大於5%的降雨條件有降雨延時為10分鐘，最大降雨強度為60mm/hr、120mm/hr、240mm/hr。說明在短延時的降雨條件下，集水區的劃分方式對系統的影響較大。 最後以撫遠抽水站集水區為例，用三種劃分方式建置依街道輪廓劃分、子集水區匯流點為角落之人孔點、依流向劃分之三種情境，分別模擬6小時延時定量降水350毫米、24小時延時定量降水650毫米、歷史延時7小時之豪雨事件、歷史延時11小時之大雨事件以及歷史延時1小時之降雨事件，比較不同情境間之出流，洪峰時間誤差和洪峰流量誤差皆小於5%，符合數值試驗模式之結果，說明在降雨延時較長的情況下，都市集水區劃分對於下水道出流之影響可被接受。 關鍵字：下水道系統都市集水區、劃分方式、洪峰時間誤差、洪峰流量誤差、流量歷線、SWMM

The sewershed delineation is usually done by the modeler based on the study area data to determine the number, area size, and flow direction of subcatchments. The delineation method will have distinct results due to different modelers, which will have an influence on the sewershed runoff estimation. The purpose of this study was to examine the influence of sewershed delineation on runoff. Firstly, use SWMM to construct two scenario numerical test models to simulate changing the flow direction of a single subcatchment, and all subcatchments outlet junctions move forward a pipe length under different rainfall conditions. By comparing the discharge hydrograph,the error of peak discharge, and the error of time to peak, it can help to understand the influence of the two scenarios on outflow. The results show that the error of time to peak or the error of peak discharge is more than 5%, mainly arise in the rainfall duration is 10 minutes, the maximum rainfall intensity is 60mm/hr, 120mm/hr, and 240mm/hr. The results demonstrate that the delineation of sewershed has a greater impact on the outflow under short-duration rainfall condition. Finally, constructing three scenarios with three methods of delineation in a case study on the watershed of FUYUAN: the subcatchments are delineated according to the outline of the street, the outlet junction of the subcatchment is the corner manhole, and the subcatchments are delineated according to the flow direction. For the three scenarios, simulate 6-hour duration quantitative precipitation of 350 mm, 24-hour duration quantitative precipitation of 650 mm, 0908 extremely heavy rain, 0525 heavy rain, and 0627 rain event. Comparing the outflow between different scenarios, the error of time to peak and the error of peak discharge are both less than 5%, which fit the results of the numerical test model. It shows that the influence of sewershed delineation on the outflow can be accepted under the long-duration rainfall condition. Key words: sewershed, methods of delineation, the error of peak discharge, the error of time to peak, discharge hydrograph, SWMM