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Design rainfall for combined sewer system calculations comparison between Flanders and the Netherlands

Abstract:

The high variability of rainfall makes the proper choice of rainfall input the key issue in combined sewer system design. It is understandable that in different countries different criteria (i.e. return periods) are used, but does that also count for the type of design rainfall? When a statistical analysis is made (based on Intensity/Duration/Frequency relationships) of the long-term rainfall series of Uccle (Belgium) and DeBilt (the Netherlands) no significant differences are observed. However, a comparison of the type of design rainfall between the Netherlands and Flanders shows large differences, although both procedures claim to be able to design the system in accordance with similar criteria. This paper looks back to the basic requirements on rainfall input for combined sewer system design and compares it with the Flemish and Dutch approach. To show the influence of the design storm choice on the hydraulic parameters, simulation results obtained with different types of design storms are compared.