Design Aid for Grass-Lined Channels

The Manning roughness factor varies with the hydraulic radius in grass-lined channels. The functional relationship between the roughness factor and the hydraulic radius is highly nonlinear. This necessitates a lengthy and tedious trial-and-error method to solve the Manning formula in the different stages of the traditional design procedures for grass-lined channels. Various charts are presented in this technical note that can be used in designing grass-lined channels without a need for trial-and-error. The charts were developed using predetermined solutions to the Manning formula. They are presented in terms of dimensionless parameters and can be employed with any consistent unit system. The use of the charts is demonstrated through an example.