Sewer risk management: reducing pollution using minimum gradient and GIS

Blockages resulting from siltation build-up within the foul-combined sewer network can result in the occurrence of pollution incidences, especially during storm conditions. A common risk factor for such blockage events is pipes that have been laid at an insufficient gradient to achieve self-cleaning velocity. Inspection of such pipes is presently an inefficient and expensive process, requiring manual on-site inspection of sections, with all sewer networks deemed to be at risk even though not all such pipes will block. This paper outlines how the use of a geographical information system can be used to identify better areas of pollution susceptibility compared with the present minimum gradient system alone. Effective targeting of sewer cleansing using this method was found to not only reduce the likelihood of pollution events, but also allow for substantial cost savings by reducing the number of unnecessary site inspections prescribed using the minimum gradient system alone.