Manning Equation 
Open channel flow calculator using Manning equation 

Units in Manning calculator: ft=foot, m=meter, s=second. Manning Equation: k is a unit conversion factor: k=1.49 for English units (feet and seconds). k=1.0 for SI units (meters and
seconds). Manning n varies with the roughness of the pipe, culvert, or channel. The higher the n, the rougher the material. Table of Manning n values. The Manning Equation is the most commonly used equation to analyze open channel flows. It is a semiempirical equation for simulating water flows in channels and culverts where the water is open to the atmosphere, i.e. not flowing under pressure, and was first presented in 1889 by Robert Manning. The channel can be any shape  circular, rectangular, triangular, etc. The units in the Manning equation appear to be inconsistent; however, the value k has hidden units in it to make the equation consistent. The Manning Equation was developed for uniform steady state flow (see Discussion and References for Open Channel Flow). S is the slope of the energy grade line and S=h_{f}/L where h_{f} is energy (head) loss and L is the length of the channel or reach. For uniform steady flows, the energy grade line = the slope of the water surface = the slope of the bottom of the channel. The product A/P is also known as the hydraulic radius, R_{h}.
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To: LMNO Engineering home page (more calculations) Related calculations: Design of Rectangular Channels Design of Trapezoidal Channels Circular Culverts using Manning Equation Culvert Design using Inlet and Outlet Control Q=VA simple flowrate calculator
