Sahereh Kaykhosravi

Daily flow variation through waste water collection systems (WWCS) should be considered in the proper design of the network. Traditionally, design procedures are carried out by estimation of maximum hourly flow, whereby sewers diameters are calculated. Empirical formulas such as Babbitt, Gifft, and Harmon are used to calculate maximum hourly flow. Based on these formulas, Kmax, which is proportional to population, is used to calculate maximum hourly sewage flow rate, by multiplying Kmax by mean daily sewage flow value. Then, diameters of sewers are estimated using this flow estimation. Recently, flow measurement is carried out in a greater extent compared to the past. This has been possible by vast development of sewer network construction and advances in flow measurement devices technology. Therefore, more information is available to detect flow variation through sewers in WWCS. Nevertheless, use of these data helps designers to obtain real flow estimation, traditional procedures are immensely in use by engineers due to lack of such data. Recent studies have unveiled some disparities between real flow data and common empirical formulas. In this paper, empirical procedures have been compared to each other by reviewing relevant key literature. Then, results of using empirical formulas were compared with the real measured flow data from residential, commercial, but industrial zones in greater Tehran and Isfahan WWCS. Consequently, significant differences between real data and empirical formulas, especially in zones with lower populations, were revealed, which demonstrated that Kmax derived from empirical formulas is not applicable for both Tehran and Isfahan cities. A design, which is based on real-measured data, was recommended and carried out for these two WWCSs.