Normal‐Depth Equations for Irrigation Canals

Abstract

Normal depth is an important parameter occurring in the design of irrigation canals. Direct analytic solution of normal‐depth problems is not possible, as the governing equations for the practical canal sections are implicit. The solution requires tedious methods of trial and error. Tabular and graphical methods also available for solution are subject to errors of double interpolation and errors of judgment in reading the graphs. Furthermore, the methods are based on Manning's equation, which is valid for a hydraulically rough boundary having a narrow range of relative roughness and involves a roughness coefficient having awkward dimensions. Reported herein are explicit equations for normal depth in various irrigation‐canal sections.