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The variability analysis of overland roughness coefficient in different topographical watersheds
|Authors: ||Mao-Tsun Ywh|
|Contributors: ||NTOU:Department of Harbor and River Engineering|
overland roughness coefficient;watershed topographical property;NV- KW model;HEC-HMS KW model;KW-GIUH model
|Issue Date: ||2011-06-30T07:41:14Z
|Abstract: ||集水區逕流分析時依逕流特性分類，可區分為漫地流與渠流。漫地流由於降雨之時變性、地表面入滲與薄層流匯集效應，具有複雜的逕流過程，因此如何適切決定漫地流糙度係數乃為重要課題。前人研究顯示，坡度會改變糙度係數值之大小；本研究之目地乃在瞭解坡度變異對糙度係數之影響。本研究利用三種運動波模式，分別為(1)考慮河川網路之V形運動波模式，(2) HEC-HMS運動波模式與(3)運動波－地貌瞬時單位歷線模式，藉由不同地形特性集水區之水文資料，以檢定漫地流糙度係數，並對檢定結果進行分析與探討。 研究結果顯示，三種運動波模式在不同地形特性集水區之檢定結果具有相同的趨勢，亦即是漫地流糙度係數與坡度呈現正相關。研究中並以熵理論分析地形起伏與漫地流坡度的關係，結果顯示在陡坡情況下，漫地流流動受到較大的地形起伏變化，因而產生相似於階梯-深潭之形狀阻力。由於陡坡集水區之漫地流流動過程具有較大的水流阻力與能量消散，因而造成運動波模式之漫地流糙度係數大幅提高。|
Runoff is usually classified into overland flow and channel flow in watersheds in performing the rainfall-runoff analysis. The overland-flow process is complicated because of the time-varying rainfall, the infiltration characteristics of surface soil, and the concentration of sheet flow. Consequently, it is an important issue to adequately determine the overland-roughness coefficient. Previous research has shown that slope will affect the value of the overland-roughness coefficient. The objective of this study is to realize the influences of the slope variations on overland-roughness coefficient. In this study, three kinematic-wave models, the Network V-shaped Kinematic-Wave model (NV-KW), HEC-HMS Kinematic-Wave model and Kinematic-wave-based geomorphologic instantaneous unit hydrograph (KW-GIUH), were used to analyze the variability of the overland-roughness coefficients calibrated in different topographic watersheds. The results show that the variability of the overland-roughness coefficient calibrated from three kinematic-wave models in different topographical watersheds has the same tendency. It appeared that the roughness coefficient and the slope were positive related. The relationship between the micro topography and the overland slope was analyzed by using the entropy. The results show that the flow characteristics of the overland runoff were affected by the micro topography in steep hillslopes, which can be linked to the form resistance existing in step-pool mountain channels. Because overland flow receives more flow resistance and results in large energy dissipation in steep watersheds, the overland-roughness coefficient is found highly increase in performing the kinematic-wave models.
|Appears in Collections:||[河海工程學系] 博碩士論文|
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