Sewer sediment management: some historical aspects of egg-shaped sewers and flushing tanks

This paper presents a historical review of some concepts and techniques used to manage sewer sediments and to cleanse sewers. Two aspects are illustrated: i) the use of egg-shaped and similar types of sewers in order to ensure self-cleansing velocities even during low low periods, and ii) the use of flushing tanks to scour deposited sediments and keep sewers free of deposits. After a brief survey of antecedent periods, the paper focuses on the evolution since the middle of the 19th century. Mainly based on French and English complementary examples, because both countries were leaders in the development of urban drainage in the period 1840-1880, the paper also provides information from Germany and the USA and shows that some aspects remained rather unchanged during 150 years while other have been completely revised during the same period.