Wetted Perimeter

Published: October 31, 2018 | Last updated: July 5, 2023

What Does Wetted Perimeter Mean?

Wetted perimeter of a pipe is the area of the pipe in contact with the fluid that it carries. Sewer systems are designed to perform in a uniform and steady manner to prevent blockage due to deposition of solids due to low velocity of flow or scouring due to high velocity of flow.

Flow parameters such as wetted perimeter and hydraulic radius are important factors in designing an effective sewerage system. Damaged or blocked pipes can be rehabilitated using trenchless rehabilitation techniques such as cured-in-place pipe (CIPP), sliplining and pipe bursting. These new liners or pipes are inserted into the old pipes through manholes, eliminating the need for excavation.


Trenchlesspedia Explains Wetted Perimeter

Sewer systems normally use pipes having circular cross-section and are designed based on the Manning model, with a partially filled flow section. There are two flow situations in a pipe namely, the less than half full and more than half full flow. The area of flow is calculated as the difference between the total cross-sectional area of a pipe and the cross-sectional area of the space above the fluid.

The wetted perimeter is likewise calculated as the difference between the total perimeter of the pipe and perimeter of the dry portion above the fluid.

Wetted Perimeter of a circular channel, P = αD

where α = cos-1 (1-h/r)

h – height of flow

r- radius of pipe


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