Tuesday, 15 January 2008

‘Small flows flow better in small pipes’

Quite an important hydraulic dictum! So why do many (most?) sewerage design engineers think 100 mm is too small a diameter for sanitary sewers? Simplified sewerage, also known as condominial sewerage, uses a minimum sewer diameter of 100 mm, but whenever I mention this outside Latin America, people just laugh and say ‘Oh no, it just can’t work, it’ll clog very quickly’. Why do engineers (who understand the fundamentals of fluid mechanics) think like this? I’m not sure really, but I suspect it’s just sloppy thinking, or rather non-thinking. They’ll say they’re just following their national sewerage design code − but why does the code say this and why don’t thinking engineers (yes, there are some out there) try to get the code changed? After all, the Brazilians changed their code way back in 1986!

[More on simplified/condominial sewerage soon …]