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The flow structure over vegetation in ecological channel is rather complex and the resistance caused by vegetation is affected by many factors, such as discharge, flow depth, vegetation density and patch arrangement types, etc. In order to simplify vegetation characteristics, the rigid cylindrical sticks arranged in the open channel were used to simulate the stems of non-submerged vegetation. The volume of the vortex structure near the vegetation patch can be determined through velocity distribution in vegetated channel and the velocity distribution is measured by Acoustic Doppler Velocity meter. A new formula of equivalent roughness based on the vortex volume near the vegetation patch has been proposed and the form drag can be further determined by the new equivalent roughness. Based on theoretical analysis and experimental results, it shows the vortex volume plays an important role on flow resistance caused by vegetation. The theoretical and experimental results on form drag achieve a good agreement on various experimental conditions. The relation between the relative roughness and relative vortex length was also derived and verified by different experimental conductions. For the dependence of relative roughness on vegetation density, the empirical formula between relative roughness and vegetation density was further proposed and analyzed. INDEX TERMS Form drag, equivalent roughness, vortex structure, rigid vegetation, open channel.

Based on the flow partition theory, we derive a mathematical expression by using the log-law for the characteristic point location (CPL) of depth average velocity in channels with flat or concave boundaries. It can manifest the position of the characteristic points in the vertical direction relative to the channel side wall or bed. Taking rectangular and semi-circular channels as research objects, we put forward a method to calculate the discharge of channels with CPL. Additionally, we carried out some experiments on rectangular and semi-circular channel sections. CPL’s analytic expression is validated against experimental results through comparison of velocity and discharge. The proposed formulation of characteristic point location could be extensively employed in flow measurements of flat and concave boundary channels, which has practical application value in simplifying the flow measurement steps of open channels.

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Ecological management of river channels is a hot topic for current sustainable development and flow measurement of ecological river is an important part. In this article, a flow velocity distribution model of the channel containing flexible vegetation is constructed from the vegetation riverbed theory and the bursting phenomenon to reveal the microscopic mechanism of the flow velocity distribution in the upper layer of vegetation. In the vegetation riverbed law, the effect of flexible vegetation is evaluated by the mixed length formula. The bursting phenomenon law considers the influence of the channel sidewalls on the flow and a two-dimensional velocity model is established by introducing the concept of average turbulence structure. The mechanism of the downward shift of the maximum flow velocity point on the channel sidewall is explained. The verification of the calculated velocity profiles is carried out based on data obtained in laboratory experiments. The results show that the combination of the two models can well describe the velocity distribution of the whole channel. At the end, the phenomenon of flow velocity zoning in open channel is discussed, which provides a solution for flow measurement in ecological channel.