Storm Sewer Systems

Storm drainage system is put in place to convey surface runoff to the designated point of storage, or disposal. Storm drainage system is allowed to periodically surcharge and overflow causing local flooding, with a predictable recurrence interval. It is the result of having selected a storm return period for estimating the magnitude of corresponding peak flow, and then basing the size of the pipeline on this data. Sanitary sewers, on other hand, are designed to carry a peak flow for a given projected population; and, thus, without overflowing. However, it may be mentioned that a sanitary sewer may overflow sometimes due to excessive inflow of ground or surface water because of poor construction or maintenance. Storm sewers are usually having a much larger diameter than the separate sanitary sewers for the same area that they serve - it is so because storm sewers have to be sized to carry larger peak flows, though these carry no flow during dry weather season. Further, storm sewers are placed at shallow depths to minimize excavation: whereas, sanitary sewers are placed in relatively deeper trenches to accommodate service connection.