Empirical equations for solids transport in combined sewers

An investigation of the transport of solids in combined sewers during both dry weather flow (DWF) periods and storms is described. The study was based on data obtained from a number of sites in the combined sewer system of Dundee, Scotland. The relationship between hydraulic conditions in a combined sewer and the transport of solids in suspension was examined. The aim was to arrive at a methodology by which an appropriate model could be selected or developed which would predict solids transport rates given information on hydraulic conditions. It was found that for individual sites, site-specific regression equations could be developed separately for dry weather and storm conditions. A non-site-specific regression equation was also developed, which was found to be preferable to the site specific equations, in terms of accuracy and ease of use. More important, however, were the fundamental procedures (ie the methodology) developed by which the model type was in each case selected and subsequently developed.