Wetting Perimeter of a Rectangular Channel Formula |
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\( P_w \;=\; b + 2 \cdot h \) (Wetted Perimeter of a Rectangular Channel) \( b \;=\; P_w - 2 \cdot h \) \( h \;=\; \dfrac{ P_w - b }{ 2 }\) |
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| Symbol | English | Metric |
| \( P_w \) = Wetting Perimeter | \( ft \) | \( m \) |
| \( b \) = Bottom Width | \( ft \) | \( m \) |
| \( h \) = Fluid Depth | \( ft \) | \( m \) |
For a rectangular open channel, the wetted perimeter is the total length of the channel's boundary that is in contact with the flowing liquid. Unlike a full pipe, an open channel has a free surface (the top of the water that is exposed to the atmosphere). Therefore, the wetted perimeter does not include the top width of the water surface. This is important in hydraulics, particularly for determining the hydraulic radius, which is the ratio of the cross-sectional area of the flow to the wetted perimeter. The hydraulic radius is a key factor in equations like Manning's equation, used to estimate flow velocity and discharge in open channels, as it accounts for the frictional resistance between the water and the channel's boundaries.
