Water Distribution System Asset Deterioration and Impact on Water Quality – a case study

摘要

This paper reports on the results of a repeated uni-directional flushing programmeover a 4 year period as part of an asset maintenance study to prevent water qualityfailures through discolouration. By monitoring the resultant turbidity as accumulatedmaterial layers are eroded due to changes in system hydraulics it is shown thatmaterial regeneration/asset deterioration is a continuous, repeatable and thereforepotentially viable modelling process. The monitored site had originally been selectedfollowing rehabilitation in 2001 which for the most part involved the scraping andlining of larger diameter cast iron pipes. The first monitored field study was 1 yearafter rehabilitation, the next a year later, then 2 years on and the final exercise afurther year again. Flushing was conducted using a planned stepped increase in flowto assess the shear strength characteristics of the developing pipe wall particulatecohesive layers, primarily of iron and manganese composition in the UK, responsiblefor discolouration if mobilised. Once cleaned from the pipe walls it is hypothesisedthat the layers regenerate and are conditioned by the hydraulics found within thesystem.The results from the monitored pipe sections all show a similar and repeatableresponse to increasing system pipe wall shear stress, with each step mobilisingadditional material, corroborating the particulate cohesive layer approach todescribing discolouration. Results also suggest that flushing was as effective asrehabilitation for controlling deterioration in this network and that the magnitude of apotential discolouration event is determined by the conditioning system hydraulics.These results can be used to inform operation and maintenance strategies to reducethe likelihood of a discolouration incident.