First Flush Phenomena for Highways: How It Can Be Meaningfully Defined

Abstract
A new terminology and definition is proposed to document mass first flushes of stormwater pollutants. This newly defined terminology is applied to 52 storms over two wet seasons at nine highway sites. Most pollutants showed median mass first flushes where 30 percent of the mass is released in the first 20% of the runoff. Pollutants representing organic contaminants had the highest first flush ratios.