The Saul Gupta method allows the engineer to study the water quality performance of the CSO in some detail. The time varying polluto graph of the Saul Gupta technique demonstrated the very large variations in pollution concentration obtained from the different storms. This additional information enables the engineer to maximise the water quality improvement achieved by the storage.The second pollution model (UPM2 EMS method) provides validation of the Saul Gupta method as the results were all of the same order. Both these methods may be calibrated but the default settings provide for a comparative study.Placing the storage downstream of the CSO should produce a better water quality result than having the storage at the CSO. However this is not true in all cases.The assumption is that if the first flush is passed downstream of the CSO into a storage tank then the concentration of pollutant passing over the CSO will be reduced

Reprinted with Permission from Micro Drainage Ltd.