Sediments in Sewers

A recent survey has suggested that up to 25 OOO km of UK sewerage networks may be affected by inpipe sediment deposits. Field evidence indicates that, typically, up to 90% of the pollution load discharged from storm sewage overflows may be derived from the erosion of accumulated in-system sediment, commonly referred to as silt. A sewer flow quality simulation model is being developed under the aegis of the WRcIWater Industry Collaborative River Basin Management research programme. Such a model will enable sewerage engineers and water quality planners to produce more effective designs for sewerage rehabilitation schemes to control river pollution. In order to produce this model it is necessary to understand the nature, characteristics and controlling mechanisms of in-pipe sediment deposits. Field observations, coupled with sampling and analysis of combined sewer sediment deposits, have produced a five category classification for such sediments. Each category has distinctive characteristics in terms of appearance, composition and polluting potential.