Abstract
Ecosystem conservation has become one of the purposes in river management as well as flood mitigation and water resources management, and understanding of river flow and morphology in a stream with vegetation becomes important. Recently 2D depth averaged analysis is familiar even in a stream with vegetation by taking account of form drag due to vegetation. However, the shear stress in vegetated area is not properly described because the resistance law due to bed roughness is not reasonably modified in vegetated area. In this study, we discussed the bed roughness boundary layer in flow with non-submerged vegetation to deduce a reasonable relation between U and u* in vegetated area toward improving the analysis of sediment transport. The results show that the modification of resistance law using by thickness, velocity distribution in that layer was found to bring significant improvement of accurate estimation of shear velocity and subsequently the sediment transport. The proposed modification is improved by 2D depth averaged analysis based on this concept, and its application is certificated through flume experiment.
Highlights
Flood mitigation and ecosystem conservation are simultaneously required in recent river management, and understanding and analysis of flow and river morphology in a stream with vegetation have become important topics in river hydraulics
The depth-averaged 2-dimensional model has become familiar with the analysis of river morphology, and the key in this line is how to model riparian vegetation, where vegetation is dealt with as a group of dispersive obstacles to be represented by spatially averaged form drag
In the conventional depth-averaged analysis for flow with vegetation, the form drag for vegetation is introduced in addition to the bed friction in the vegetated area, but the resistance law due to bed roughness is treated by employing the same equation with that in non-vegetated area (Equation (1))
Summary
Flood mitigation and ecosystem conservation are simultaneously required in recent river management, and understanding and analysis of flow and river morphology in a stream with vegetation have become important topics in river hydraulics. In the conventional depth-averaged analysis for flow with vegetation, the form drag for vegetation is introduced in addition to the bed friction in the vegetated area, but the resistance law due to bed roughness is treated by employing the same equation with that in non-vegetated area (Equation (1)). Though the resistance law is not necessarily sensitive for calculation of depth and depth-averaged flow, it brings underestimation of the shear velocity and subsequently sediment transport rate, and it may not bring a reasonable analysis of sediment transport and subsequent fluvial process. We discuss the bed roughness boundary layer in flow with non-submerged vegetation and deduce a reasonable relation between U and u* in vegetated area to proceed the analysis of sediment transport
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