Modeling sewer overflow of Karbala city with large floating population

Abstract

The sewer systems of many historical or religious cities are not well associated with present needs. Sudden influx of huge floating population during sacred or festival periods places tremendous pressure on utility services including the sewer system in such cities. Sewer overflow, inundation of roads, environmental degradation, and consequent epidemics are very common during such gatherings. Modeling of sewer quantity and quality with varying population is, therefore, very important for cities with a large floating population in order to mitigate the problem. The major objective of this study is to develop a model to assess the impacts of floating population on sewer systems during pilgrimage, in order to proffer necessary mitigation measures. The Karbala city of Iraq was chosen as a case study in the present research. Statistical and physically based models such as Storm Water Management Model (SWMM), Multiple Linear Regression (MLR), Structural Equation Model (SEM) and Artificial Neural Network (ANN) were used for this purpose. The model outputs were analyzed to assess possible changes in sewer discharge and quality in the context of increasing population. Different adaptation measures were also assessed and suitable adaptation measures were identified for mitigating the impacts. The results showed that sewer flow in Karbala city typically increased in the range of 0.009492-0.0144 m3/s for every population rise of one thousand, measured at 95% confidence interval. On the other hand, the concentrations of total suspended solid (TSS) and Biochemical Oxygen Demand (BOD5) increased by 26-46 mg/L and 9-19 mg/L, respectively at 95% confidence interval, for every 1mm increase in rainfall. BOD5 was also found to increase by 4-17 mg/L for every ten thousand increase in population. The temporal and spatial modeling of sewer overflow shows that it mostly happens during prayer times and in the upstream area, as the sewer system in the region is incapable of carry in a huge inflow of sewer during those periods. The assessment of different technical measures revealed that pipe-jacking system is the most suitable approach in Karbala city for reducing sewer overflow by up to 70%, if properly installed and managed.