Flow Resistance in Vegetated Waterways

ABSTRACT Anew method to determine the flow capacity of a vegetated channel is presented. The method uses the vegetation's length and stiffness as parameters. Graphs of field data of Manning's n versus the product VR, velocity times hydraulic radius, can be accurately repro-duced. A table of stiffness values for various types of veg-etation for which flow data were available is included. It is shown that the n —VR method of channel design cur-rently in use is based on the correct premise that n is a function of VR regardless of the relative values of V and R. The limitations of the n —VR method are stated. The advantage of the new method is that it is a numerical method which can be easily incorporated in computer programs for other purposes such as backwater or rout-ing models.