First flush

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It is well known in urban hydrology, that the constituents are normally more concentrated in the first part of runoff. This phenomenon was already described in the beginning of the 20th century (METCALF AND EDDY, 1916) as “first flush” or “first foul flush”. The term is often also used to address the first flood after a dry period, which is supposed to contain higher concentrations than a subsequent one. This should be referred to as “first flush flood”. There are various definitions of the first flush phenomenon, e.g. in DEH (2005), GUPTA AND SAUL (1996) or GEIGER (1987).

The term “first flush effect” refers to rapid changes in water quality (concentration or load) that occur after early season rains. Soil and vegetation particles wash into the streams, sediments and other accumulated organic particles on the river bed are resuspended and dissolved substances from soil and shallow groundwater can be flushed into the streams.

Because the reference of the first flush is not always clear, SANSALONE AND CHRISTINA (2004) introduced the terms “concentration-based first flush” (CBFF) and “mass-based first flush” (MBFF). Apart from this definition, there are a number of rating parameters in literature to determine the occurrence of a first flush (e.g. in SANSALONE AND CHRISTINA, 2004).

[edit] References

DEH (2005) Glossary of Terms; http://www.deh.gov.au/ssd/glossary/; Australian Government, Department of the Environment and Heritage
GUPTA AND SAUL (1996) Specific Relationships for the First Flush Load in Combined Sewer Flows; K. Gupta, A.J. Saul; Water Resources, Volume 30 No. 5, pp. 1244-1252; 1996
METCALF AND EDDY (1916) American sewerage practice, Disposal of sewage; L. Metcalf, H. Eddy; Vol. III, McGraw-Hill; New York, 1916
SANSALONE AND CHRISTINA (2004) First flush concepts for dissolved solids in small impervious watersheds; J.J. Sansalone, C.M. Christina; Journal of Environmental Engineering, Vol. 130, No. 11, pp. 1301-1314; November 2004