A LABORATORY STUDY OF THE EROSION AND TRANSPORT OF COHESIVE-LIKE SEDIMENT MIXTURES IN SEWERS

Surveys of sewers in the UK have indicated that many sewer systems hav e significant in-sewer deposits. Many of these existing combined sewer s have been constructed at such a gradient and experience such a range of hydraulic conditions that over a period of time they experience re peated phases of sediment deposition, erosion and transport. Depositio n of sediment in sewers with its consequent loss of discharge capacity can lead to the surcharging of sewerage systems and the premature ope ration of combined sewer overflows. The sudden erosion and transport o f large quantities of deposited in-sewer sediments during periods of i ncreased flow can significantly contribute to the pollution load impos ed on receiving water courses and sewerage treatment plants. It is the refore important not only to be able to estimate the hydraulic perform ance of sewers but also the conditions under which significant erosion of deposited sediments occur. This paper reports on the rationale beh ind and the initial results from a laboratory study which aims to inve stigate the erosion and transport of ''cohesive-like'' sediment mixtur es in controlled laboratory conditions. The choice of the sediments us ed was aimed at representing the characteristics of sewer sediment mix tures found in the field. These deposits have been found to exhibit a significant degree of cohesion not found in previously studied granula r sediment beds. (C) 1998 IAWQ. Published by Elsevier Science Ltd.