The problems caused by sediments in sewers are now universally acknowledged. A number of countries have set up comprehensive programmes to study all aspects of sewer sediments; their occurrence, nature and movement. In the UK the Water Research centre and others have funded a comprehensive study of the sediments in the Dundee sewer system. The rate of sedimentation and the yield strength of the sediments have been investigated and considered in terms of the subsequent erosion by increasing flows. The sediments have been found to be cohesive in nature and highly resistant to erosion in the main interceptor sewer, whereas in the trunk sewers the sediments are more granular and less cohesive in nature. A sewer classification system is suggested which is based on physical characteristics, and also relates to the nature of the sediments deposited, and the bed-load material conveyed close to the bed.

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