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The discharge formula, Q = A V, can be used to rewrite Gauckler–Manning's equation by substitution for V. Solving for Q then allows an estimate of the volumetric flow rate (discharge) without knowing the limiting or actual flow velocity. The formula can be obtained by use of dimensional analysis.
The variations of Q/Q (full) and V/V (full) with H/D ratio is shown in figure(b).From the equation 5, maximum value of Q/Q (full) is found to be equal to 1.08 at H/D =0.94 which implies that maximum rate of discharge through a conduit is observed for a conduit partly full.
Most charts or tables indicate the type of friction factor, or at least provide the formula for the friction factor with laminar flow. If the formula for laminar flow is f = 16 / Re , it is the Fanning factor f, and if the formula for laminar flow is f D = 64 / Re , it is the Darcy–Weisbach factor f D.
The momentum equation for open-channel flow may be found by starting from the incompressible Navier-Stokes equations : ⏟ + ⏟ ⏞ = ⏟ + ⏟ ⏟ + ⏟ where is the pressure, is the kinematic viscosity, is the Laplace operator, and = is the gravitational potential.
A general rule is that the shear velocity is between 5% and 10% of the mean flow velocity. For river base case, the shear velocity can be calculated by Manning's equation. = (/) n is the Gauckler–Manning coefficient.
The Chézy Formula is a semi-empirical resistance equation [1] [2] which estimates mean flow velocity in open channel conduits. [3] The relationship was conceptualized and developed in 1768 by French physicist and engineer Antoine de Chézy (1718–1798) while designing Paris's water canal system.
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The following table gives Reynolds number Re, Darcy friction factor f D, flow rate Q, and velocity V such that hydraulic slope S = h f / L = 0.01, for a variety of nominal pipe (NPS) sizes. Volumetric Flow Q where Hydraulic Slope S is 0.01, for selected Nominal Pipe Sizes (NPS) in PVC [ 14 ] [ 15 ]