Sediment transport in sewers - a step towards the design of sewers to control sediment problems

It is the purpose of combined sewerage systems to convey a variety of solid s, and associated liquid wastes, for treatment and return to the environmen t. The movement of the solids in sewers has come under increased scrutiny i n recent years, due to the pollution and maintenance concerns associated wi th this material, The real or perceived physical, biochemical, ecological a nd aesthetic impacts of sewage spills into the environment, via separate st orm sewers, combined sewer overflow (CSO) structures and treatment plants, have recently entered more prominently into public awareness and perception . Worldwide, engineers have become increasingly aware that the methodologie s currently in use to design sewers to prevent solids deposition and minimi ze the hydraulic and other effects, are inadequate. A modified design appro ach, recently proposed by the Construction Industry Research and Informatio n Association (CIRIA), aims to address these problems by providing a standa rdized procedure to minimize sedimentation in sewers. This approach relies substantially on laboratory-based work for calibrating the sediment transpo rt, and to a lesser extent, hydraulic resistance relationships. This paper examines the basis of the CIRIA design methodology, and compares the labora tory work with real sewer conditions (based on real sewer sediment data col lected in the UK, and other European sewers). The aim is to provide sewerag e designers, managers and planners with information about the general appli cability of current methodologies regarding the design of sewers, to manage sediment problems. This information is presented in the context of the cur rent understanding of the physical processes which control the movement and deposition of real sewer sediments, rather than those studied in laborator ies.