Manning’s roughness coefficient of vegetated channels

Abstract

The conventional Manning's formula is not applicable to the flow in vegetated channel,since the flow resistance is composed of wall friction and vegetation resistance.In this paper,a series of equivalent hydraulic parameters based on flow resistance equivalence principle are suggested.The formulas of equivalent comprehensive Manning's roughness and the additional vegetation roughness coefficient are proposed.Besides,the condition of adopting the water depth as the hydraulic radius for hydraulic calculation is discussed.Laboratory experiments are also carried out with stiff cylinders used as vegetations to study the law of flow resistance both for emersed and submerged situations.The experimental result proves the theoretical analysis and shows that the Manning's coefficient calculated by using water depth as hydraulic radius can be used to express the additional resistance coefficient due to vegetation for emersed cases.The formula of equivalent comprehensive roughness coefficient can be applied to engineering practice.