Analysis on the First Flush Effect of Stormwater Discharge from Shanghai Drainage System

Study was made on five typical drainage systems along the Suzhou Creek. The dimensionless accumulative mass loading vs. volume curve [M(V) curve] and parameter b were used to discuss the first flush effect of storm water discharge from Shanghai drainage systems. The result shows that there is no first flush effect in the five systems according to the standard of 30/80; while according to 50/50, little first flush effect is observed in the combined system; and in the separate system, the discharged stormwater quality is varied greatly with the storm events and no first flush effect exists in general. COD and BOD have stronger first flush effect than SS. The strength of first flush effect is increased with the increased proportion of impervious area and is decreased with the increased catchment area. The above findings provide the basis for the planning and design for the non-point pollution control facilities including stormwater storage tank and so on.