Saturday, 21 January 2012

Sewer gradients 2

The Orangi Pilot Project (OPP) in Karachi, Pakistan is a very well known low-cost sewerage project, but what is not so well known perhaps is that the site gradients in Orangi were greater than the minimum required sewer gradient, so hydraulically at least the project was bound to succeed. However, when this low-cost sanitation technology was applied in other cities in Pakistan, problems occurred as the site gradients were lower than the minimum sewer gradients.

I remember, after I gave a talk on simplified sewerage some years ago at a WaterAid meeting in London, a young woman engineer from OPP came up to me and asked if I’d go to Karachi and teach OPP staff how to design sewers! Well, nothing came of that, other than a realisation on my part that sewer hydraulics are incredibly important – a fact that really needs to be more widely appreciated.