The variability analysis of overland roughness coefficient in different topographical watersheds

• Main Authors: Mao-Tsun Ywh, 葉茂圳
• Other Authors: Kwan-Tun Lee
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/69834646931636194457

碩士 === 國立臺灣海洋大學 === 河海工程學系 === 96 === 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.