Author(s): Rahma Yanda, Morihiro Harada, Ichiro Tamagawa
Linked Author(s): Rahma Yanda
Keywords: Double-averaging method (DAM), vertical distribution of streamwise velocity, low relative submergence.
Abstract: The vertical profile of streamwise velocity distribution is necessary information for sediment transport computation and aquatic habitat evaluation. However, predicting velocity distribution for hydraulically rough and low relative submergence is still challenging. In this study, we demonstrate a procedure as an approach for predicting the double-averaging (DA) vertical profile of streamwise velocity distribution for intermediate and low relative submergence condition based on a limited set of known parameters, such as flow discharge Q, bed slope or energy slope S, representative grain size diameter D_84, and channel width B. The procedure consists of two steps. First, the flow resistance prediction with variable-power equation (VPE) is used to calculate the depth-averaged parameters (mean flow depth h, depth-averaged velocity U and shear velocity u_*). Then, these parameters are used in the velocity distribution equation. The results of the measured parameters and predicted velocity profiles are compared using data measured from field and experimental flumes over cobble and gravel beds. On this basis, the mean flow depth, shear velocity, and depth averaged velocity are not found to be significantly different from those of the measurement data. In the bed elevation approach, it is not possible to obtain a good fit between the predicted and measured velocity profiles due to difficulties in representing the roughness height and standard deviation. However, the challenges of DA parameterization can be seen clearly on the relation with flow resistance. In addition, this approach may be a potential approach to describe the flow characteristics over rough beds instead of using turbulence or high cost numerical simulations
Year: 2017