Design flow factors for sewerage systems in small arid communities communities

Reliable estimation of sewage flow rates is essential for the proper design of sewers, pumping stations, and treatment plants. The design of the various components of the sewerage system should be based on themost critical flowrates with a focus on extremely lowand peak flowrates thatwould be sustained for a duration related to the acceptable limits of behavior of the components under consideration. The extreme flow conditions and towhat extent they differ from the average values are closely related to the size of the community or network, and the socioeconomic conditions.Asingle pumping station is usually sufficient to pump flowfromsmall community in either flat or non-undulating topography. Therefore, the hydraulic loading on the wastewater treatment plant (WWTP) results fromthe pumped flow from the pumping station rather than the trunk sewer flow. The intermittent operation of the pumping units further accentuates the sewage hydrograph in the final trunk sewer. Accordingly, the design flow for the various components of the WWTP should be determined based on their relevant flow factors. In this study, analysis of one representative small community out of fivemonitored small communities inEgypt and theKingdom of SaudiArabia is presented.Pumped sewage flowrates were measured and the sewer incoming flows were hydraulically derived. The hourly and daily sewer and pumped flow records were analyzed to derive the relationship between the flow factors that would be sustained for various durations (instantaneously, 1 h, 2 h, etc.) and their probability of non-exceedance. The resulting peaking factors with a consideration for their sustained flow duration and specified probability would permit the design of the various components of the treatment plant using more accurate critical flows.