Kinetic energy and momentum correction coefficients in straight compound channels with vegetated floodplain

• Published in: Journal of hydrology (Amsterdam) 2016-06, Vol.537, p.10-17
• Main Authors: Hamidifar, H., Omid, M.H., Keshavarzi, A.
• Format: Article
• Language: English
• Subjects: Asymmetry; Channel flow; Compound channel flow; Compound channels; Density; Doppler effect; Floodplain vegetation; Kinetic energy; Kinetic energy coefficient; Mathematical analysis; Momentum correction; Vegetation; Velocity distribution
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2016.03.024

•Velocity distribution coefficients (α and β) in compound channels are investigated.•The effect of flow relative depth and vegetation density are analyzed.•Some new empirical equations were developed for calculation of α and β.•Vegetation can increase the average values of coefficients α and β by 52.8% and 21.6%, respectively. In this paper, the effect of flow relative depth (ratio of the floodplain to the main channel flow depths) and vegetation density on the kinetic energy and momentum correction coefficients (termed as α and β, respectively) was described based on an experimental study. A series of experiments was run using rigid dowels with seven flow relative depths and four vegetation densities in an asymmetric compound channel. The local flow velocities were measured using an acoustic Doppler velocimeter (ADV). Using regression analysis, velocity data were considered and equations were developed for calculating the kinetic energy and momentum correction coefficients as a function of the flow relative depth and vegetation density. The results show that the values of α and β decrease as the relative depth increases. Also, as the vegetation density increases, the effects of the vegetation on α and β increase too. Finally, by comparing with the findings of the previous researchers, it was found that the average values of the α for asymmetric compound channels with vegetation are 26.5% and 43.3% greater than those for asymmetric and symmetric compound channels without vegetation respectively while these values for β are 12.7% and 18.1%, respectively. Furthermore, the floodplain vegetation can increase the average values of coefficients α and β by 52.8% and 21.6%, respectively, in comparison with single channels.