Roughness coefficient in operational sections of sewage systems

During the design of sewer systems, laboratory values of flow resistance coefficients are usually used for different pipe materials. This estimation can have important consequences, in particular on the building costs of large sewer systems, and their medium and long term hydraulic performances. Due to the scarce field data available, the present study aims to assess the actual resistance coefficients on sewer systems in use, and identify and classify some of the conditions that influence their variation. In addition, laboratory experiments were conducted to define the experimental design and compare to field results. Results suggest that the material of the studied sections, in addition with management related factors (state and time of service of the sewage sections) have an important effect on the variation of the hydraulic resistance coefficient and on its estimation uncertainty. We confirmed that a prominent difference exists between the average resistance coefficients obtained in the laboratory and in the field for sections of the same material and different diameter.