The Effect of High Intensities of Rainfall on the Operation of the Combined Sewage System in Populated Areas

Abstract

The present paper deals with the effect of a densely populated area on operating the combined sewage system under higher rainfall intensities using the Storm Water Management Model (SWMM) modelling program. The aim is to simulate a future increase in rainfall intensities for reducing the combined sewage system overflow in the study area, which was the AL-Rashadiya quarter in the city of Najaf, Iraq. The high rainfall intensities have been modelled using the SWMM software to estimate the maximum flooding volumes in the combined sewage system of the study area. To evaluate the models’ performance, a comparison process was used between the values of the pipes flow rates of the combined sewage system models with the design flow rates and the flow rates of only one available event modelling during the study interval. The comparison results showed a good and convergent performance for these models. The results of the flooding volumes using different values of rainfall intensities and different return periods, which were 2,5,10 and 25 years, in the modelling of the combined sewage system are 3817, 6912, 8929, and 13434 m3, respectively. The suggested scenario included increasing diameters of some pipes in the combined sewage system pipelines. The results using this scenario showed a reduction in the total flooding percentage from the integrated sewage system of 53.52%,39.65%,33.3%, and 24.41%. The present study can provide technical support for using software in the planning, controlling, and tests of the sewer systems, which contribute to solving the sewer systems problems.