SUSPENDED-SOLIDS IN COMBINED SEWER FLOWS

Many studies have identified the first flush phenomenon as being the r elatively high concentration of pollutants in the initial phases of co mbined sewer flow following a storm. One way of controlling the first flush is by the provision of a storage tank such that the effluent can be discharged in a controlled manner. To optimise the storage volume, both the total pollutant load discharged and the temporal variation i n pollutant concentration within an event need to be predicted. Sophis ticated models to predict the pollutant concentrations in urban sewer flows, for example QSIM and MOUSETRAP are already available. However, the data requirements for these models are extensive, which usually li mit their application to major or environmentally sensitive schemes. T his paper describes attempts to relate the peak concentration of suspe nded solids in combined sewer flows to observed storm characteristics. In this study, it was hypothesised that the peak concentrations of su spended solids could be related to the hydrological parameters of maxi mum rainfall intensity, storm duration, and antecedent dry weather per iod prior to the storm which are commonly used as the basic parameters for urban sewer design. Data from two sites at Great Harwood and Clay ton-le-Moors in the North-west of England has been used in the study a nd an attempt has been made to define an upper limit of the first flus h concentration of suspended solids corresponding to storms which have been categorised into bands defined by their peak rainfall intensity. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd.