Abstract
It has been known that in-sewer sediments significantly contribute to combined sewer overflow (CSO) loads. However, knowledge is limited on the behavior of in-sewer sediment. In this study, characteristics of the accumulation and entrainment of in-sewer sediment were analyzed in a drainage area of 42.2 km2 using a distributed sewer model based on Ackers & White's theory on the sediment transport. It was found that there is a large spatial variation in the amount of sediment deposited during dry weather and entrained during wet weather. It indicated that spatial characteristics of sediment accumulation and entrainment should be considered in a sewer network in order to identify the significant sources of the CSO loads. Then the reduction of CSO loads was evaluated by removal of in-sewer sediment by flushing with water. The reduction of CSO loads by water injection for sediment flushing at 3 points was estimated and compared. The results showed that CSO loads were reduced by 18.3 % in the case of 32400 m3 of cleaning water. This study demonstrates that model analysis is useful to evaluate the effectiveness of the CSO reduction measure by the removal of in-sewer sediment by flushing with water.
