Research and Application of Composite Roughness in Sewer Flow

摘要

Deposits in sewer system can cause serious problems such as reduction in hydraulic capacity, flooding etc. Bed roughness is very different from sewer walls due to the solids deposits. A formula for computing composite roughness in sewer system is deduced according to continuity and momentum equation in this paper. This formula includes bed roughness and walls roughness and hydraulic factors. It can reflect flow resistance in sewer system well. With this formula we also can analysis the effects of bed roughness and wall roughness to flow resistance respectively in sewer system. Verification of ULB hydrodynamic model ( developed by Free University of Brussels ) which introduced the composite formula with the measured sewer flow data shows that the predicted discharges follow the measured ones very closely in last 3.3 km channel of Brussels North Sewer System. Measured data in this system show that bed roughness changes are agreed well with the deposits layer. So the tuned bed roughness by this modified ULB model can be used to present the deposits layer developed tendency. Base on the tuned bed roughness and the deposits cleaning time records we can find out the best cleaning time of sewer system.