ABSTRACT
This chapter derives the Chezy equation from a force balance and the Manning equation related to the Chezy equation. Most one-dimensional hydraulic models and many three-dimensional hydrodynamic models use Equation to quantify friction losses. The equation is commonly used to estimate the effects of friction in the momentum equation, assuming that the effects of frictional resistance are the same for either steady or unsteady flows. Unlike the theoretically derived Chezy equation, the Manning equation was originally based on some data sets. For some water quality applications, estimates are required to compute the variations in flows or velocities across a channel cross-section where the total flow and water surface elevation are known. Differences in roughness frequently occur over the wetted perimeter, introducing nonuniformities into the velocity distribution. The Froude number provides an approximate method of determining the flow regime and the rate of flow by observing the propagation of small surface waves.
