Use Colebrook White to find ...
Published by Ken Sutherland, Hydraulic Engineering/Building Services/calculators
Use Colebrook White to find your pipe size. For example say C-W gives a pipe size of 110mm, but that pipe size does not exist, and the next available pipe size is 150mm. Then you know that this pipe is oversized and won't be flowing full.
Use the chart below to find the actual velocity when flowing part full.
You know the proportional discharge, (your required flow compared to the 150 pipe full flow,) the chart will show you the proportional velocity compared to the 150 pipe full velocity, and the proportional depth.
Saves a lot of mucking around working backwards from the hydraulic radius.
If you haven't used this chart before, its interesting to note that both the maximum flow and the maximum velocity do not occur when the pipe is flowing full.
That is because for a circular pipe the maximum hydraulic radius does not occur when the pipe is full.
Hydraulic radius = Xsect Area / wetted perimeter.
