Retardance coefficient of vegetated channels estimated by the Froude number

The Manning Equation is widely adopted to estimate open channel flows, and selecting retardance coefficient is always one of the most difficult tasks for estimating velocity and discharge. In cases of estimating accurate retardance coefficient values of vegetated channels, countless trials and errors are to be made before reaching conclusive results due to conditions created by various aquatic plants. The majority of past studies on this subject, however, are established based on terrestrial plants and plastic moulds as laboratorial factors, and only few are done with natural aquatic vegetations. Hence, in this study, two different types of natural aquatic plants are applied to estimate retardance coefficients; and the result indicates that each type of plant affects differently in terms of flow resistance. Analysis of hydraulic parameters indicates there are strong correlations between the retardance coefficient and the Froude number. The Froude number is most important and commonly used parameter of open channel hydraulics. The retardance coefficient and Froude number are exponentially related. Therefore, the Froude number can replace the product of velocity and hydraulic radius (VR) to estimate the retardance coefficient, in which VR (product of velocity (V) and hydraulic radius (R)). Additionally, it can be used accurately to estimate velocity and discharge during river and wetland restoration.