Dispersion due to surcharged manholes

The modelling of urban drainage systems has, in the past, focused on the systems ability to convey a maximum discharge. More recently, the design of drainage systems has adopted a more environmentally aware outlook. With increasing numbers of sewer overflows discharging into natural water courses, there is an ever present need to quantify the magnitude of the pollutants entering the environment. To enable accurate predictions of pollutant discharges from sewer systems into the environment, the transport of a pollutant within the sewer system must first be elucidated. As a pollutant travels through a sewer system it will be diluted in the surrounding flow, thus causing a general spread in both the temporal and spatial domains. Studies measuring the spread of a pollutant as it passes through a pipeline have already been conducted. However, no such study has yet been undertaken to quantify the effects of the ancillary structures within the sewer system. This thesis examines the effects on a pollutant as it passes through the most commonly occurring of these ancillary structures, the manhole. Through the construction of a scale laboratory model, data has been acquired from a variety of manhole chambers that are subjected to a range of surcharges and discharges. By utilising, and expanding upon, two existing numerical modelling techniques, the changes that occur in the distribution of pollutant as it passes through these structures has been quantified within a temporal field of reference. From these results, a set of general equations that represent the passage of a pollutant have been derived. Through the comparison of predictions made using the derived equations, the most effective predictive tool has been identified.