Direct solutions for design of grass-lined channels

Abstract

For grass-lined channels, the Manning roughness coefficient varies with the hydraulic radius and the functional relationship is highly non-linear. For this reason, a trial procedure is required in the traditional design process to solve the Manning formula to determine the bottom width and flow depth of the channel cross-section. To eliminate the trial procedure, direct graphical solutions have been developed for side slope z = 2. This paper presents direct graphical and analytical solutions for bottom width and flow depth for any value of side slope in the practical range of z = 2–8. The solutions are based on new dimensionless forms of the Manning formula. The graphical and analytical solutions for bottom width and flow depth are either exact or nearly exact. Application of the proposed solutions is demonstrated using a practical example. The proposed solutions, which make the design of grass-lined channels easier and more efficient, should be of interest to the hydraulic engineering community.