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標題: Application of Grid Rational Algorithm for Predicting Hydrograph (GRAPH) Model for Runoff Simulation of Ba-zhang Creek Watershed
作者: 鍾亦婷
Chung, Yi-Ting
關鍵字: Runoff coefficient
Rainfall-runoff model
Ba-Zhang river
出版社: 水土保持學系
摘要: 八掌溪流域上游坡度陡峻,下游則屬平地沖積平原,常因洪水漫溢兩岸釀成災害;且921震災後集水區上游土石鬆動,每逢暴雨易引發山崩、地滑及土石流等土石災害,危害居民安全。為避免災害之發生,建置集水區分析系統,即時推估集水區流量歷線,供水利防洪演算、河道輸砂量推估以及災害應變措施之擬定極為重要。 本研究選取八掌溪軍輝橋及義竹橋上游之集水區為研究範圍,應用網格式合理化法(GRAPH),以等集流時間之概念,利用常態化差異植生指標(Normalized Difference Vegetation Index, NDVI)計算集水區內每一網格之初始逕流係數,建立八掌溪集水區逕流係數變動模式,配合降雨資料建立合理化公式-流量歷線修正式,再透過監測站之實測流量資料,推求合理化公式-流量歷線修正式之、校正係數,建置八掌溪集水區降雨-逕流模式,為調整洪峰到達時間之係數,為調整洪峰流量之係數。 模式推估結果,以單峰型暴雨較佳;低流量或多峰型暴雨時,模式所推估之流量歷線常因上升段或退水段過度靈敏而影響推估結果。α校正係數可代表集水區對各場暴雨水源涵養能力,且集水區面積愈大其α值愈小,乃因下游集水區受人為開發破壞影響較大,導致集流時間加速,加快洪峰到達時間;β校正係數可作為水流含砂濃度之指標,本試區由於上游坡陡下游坡緩,使下游入滲效果佳,量測到之實測流量較低,β值須往下調整,故上游站之β值有大於下游站之趨勢。
Flood hazards frequently attack riverine areas and cause casualties on the Ba-Zhang River watershed both in steep headwaters and downstream alluvial floodplains. After the 921 Earthquake, the loosened soils and rocks are easy to collapse. Massive landslides and debris flows are regularly induced by storm events. The human lives and properties are under threatened. In order to prevent watershed hazards, a systematic watershed control and management is an appropriate suggested method. The watershed analysis system simulates real-time data to predict hydrograph. The calculate results can provide critical information for hydraulic routing, sediment transport estimation, and emergency rescue measures. The Junhui Bridge and the Yizhu Bridge as the outlets for the Ba-Zhang River sub-watersheds were used in this study. Combining the concepts of isochrones for time of concentration and raster runoff coefficients derived form Normalized Difference Vegetation Index (NDVI), the dynamic simulation model for the Ba-Zhang River watershed was established. Using precipitation data, the revised rational formula method for predicting runoff hydrograph was employed to simulate real-time flow discharge. The  and  correction coefficients were proposed to modify the predicted hydrograph. The rainfall-runoff simulation model for the Ba-Zhang River watershed was established successfully. The proposed  and  values are the correction coefficients of peak arrival time and peak flow. From the simulated results, a better model efficiency was obtained for the single-peak rainfall pattern. The model acquired lower accuracy for excessive sensitivity in raising limb and recession segment reactions during low discharge or multi-peaks rainfall patterns. The proposed α correction coefficient represents water resources conservation capability. Because the disturbed downstream watershed may decrease the time of concentration, the larger area is simulated; the lower α value will be obtained. The β-value can be regarded as the index of sediment concentration.
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