# Hydraulic Diameter of a Channel of Water

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D_H =
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AndrewS.Hydraulic Diameter of a Channel of Water
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The Hydraulic Diameter of a Channel of Water calculator computes the hydraulic diameter of a channel of water based on the width of the channel and the depth of the water.

INSTRUCTIONS: Choose units and enter the following:

• (a) This is the depth of the water.
• (b) This is the width of the channel.

Hydraulic Diameter (DH): The calculator returns the diameter in meters.  However, this can be automatically converted to compatible units via the pull-down menu.

#### The Math / Science

D_H = (4*a*b)/(2*a+b)

where:

Can also be used to find the Hydraulic Diameter of a partially filled rectangular duct.

For the limiting case of a very wide duct (i.e. a slot of width b where > a), DH = 4a.
A hydraulic diameter is useful for dimensionless quantities (e.g.  Reynolds number) which employ a single variable for flow analysis.

Hydraulic diameter is mainly used for calculations involving turbulent flow. Secondary flows can be observed in non-circular ducts as a result of turbulent shear stress in the turbulent flow. Hydraulic diameter is also used in calculation of heat transfer in internal-flow problems.