Quantifying the first-flush phenomenon: effects of first-flush on water yield and quality

Brett Martinson, T. Thomas

Research output: Contribution to conferencePaperpeer-review

467 Downloads (Pure)


First-flush diversion is increasingly recognised as a useful intervention to reduce both suspended and dissolved contaminate loads in rainwater systems. Such first flush systems rely on the early rain to wash the roof before water is allowed in the store. While there is almost universal acceptance that this is beneficial, there is no agreement on just how much water is to be diverted and the reset of the device rarely considered. In a paper delivered at the 12th IRCSA conference the authors presented a number of field measurements and derived an exponential decay constant for the first-flush phenomenon based on rainfall depth. This paper builds on these results by applying this decay constant, and a time constant for debris accumulation derived from the same data, to a waterbalance model. The results show that most current first-flush devices used in the field have a poor performance; however it is possible to remove up to 85% of incoming material while retaining 85% of the water if the device is designed carefully. Better material removal performance is possible but only at the expense of lower water yield; similarly water yield can be improved by reducing overall material removal. The key to good performance is found to be to use a slow device reset combined with a large water diversion, though not as large as had been initially feared. A design procedure is discussed along with practical technical constraints, possibilities and currently available techniques.
Original languageEnglish
Publication statusPublished - 2009
Event14th International Rainwater Catchment Systems Conference - Kuala Lumpur
Duration: 1 Aug 2009 → …


Conference14th International Rainwater Catchment Systems Conference
CityKuala Lumpur
Period1/08/09 → …


Dive into the research topics of 'Quantifying the first-flush phenomenon: effects of first-flush on water yield and quality'. Together they form a unique fingerprint.

Cite this