Open Channel Flow Quick Reference Guide

Open channel flow forms the foundation of hydraulic engineering for surface water systems. It is distinguished by the presence of a free surface where pressure equals atmospheric pressure, enabling direct interaction with ambient air and making flow depth a dynamic variable. Key governing principles include the continuity equation (conservation of mass), the Bernoulli equation modified for open channels (specific energy concept), and the momentum equation for rapidly varied flow. Flow regimes—classified as uniform, gradually varied, or rapidly varied—are determined by the relationship between actual depth (y), normal depth (y_n), and critical depth (y_c), and further categorized by Froude number (Fr): Fr < 1 (subcritical), Fr = 1 (critical), Fr > 1 (supercritical). Practical analysis relies on empirical resistance laws (e.g., Manning’s and Chezy equations), numerical integration for backwater curves, and hydraulic structures (weirs, jumps, gates) to control or measure flow. Design applications demand careful consideration of sediment transport, erosion control, flood routing, and ecological impacts—especially under unsteady (non-uniform, time-varying) conditions simulated via dynamic wave models.