Non-deposition design criteria for sewers with part-full flow

Abstract

In this study, the existing self-cleansing design criteria for sewers based on minimum velocity and minimum bed shear stress have been reviewed. Based on several laboratory experiments, the study then develops non-deposition criteria for non-cohesive sediment in uniform flow. The developed criteria take into account geometry of flow sections, hydraulic and sediment properties based upon three dimensionless parameters, namely, the densimetric Froude number, the volumetric sediment concentration and the relative grain size. The proposed criteria provide improved estimates of self-cleansing minimum velocities compared to the traditional one-parameter design criteria and agree well with the well-known existing design criteria, namely, Macke's formula for suspended load and May's formula for bed load. The present study therefore contributes new non-deposition design criteria for sewers with part-full flow in the range of the experiment conducted and yet which are simple for practical applications. Further research work is required to substantiate the preliminary character of the results presented for wider application of the proposed self-cleansing design criteria.

Keywords:

• non-deposition design criteria
• scour of bed deposit
• bed load
• suspended load
• part-full flow
• sewers

Acknowledgements

The authors wish to express their grateful acknowledgements to the Danish International Development Assistance (DANIDA) and the Asian Institute of Technology (AIT) for providing financial support for this study. Sincere thanks and acknowledgements are also due to Dr. Pichai Nimityongskul and Dr. Sutat Weesakul of AIT for their valuable comments and suggestions during the study.