Determination of best management timing of nonpoint source pollutants using particle bins and dimensionless time in a single stormwater runoff event

Efforts to alleviate nonpoint source (NPS) pollution contributing to the degradation of water quality in aquatic environments have increased over the last several decades. In this research, dimensionless time (τDL) and particle size bins were applied as indicators to optimize the management timing for NPS pollutants. Field experiments that included four single storm events and two multiple storm events were conducted in order to measure the flow and to collect water samples for the analysis of particle size bins at each monitoring site. Particle bins for all samples were measured using an LS230 laser diffraction particle size analyzer. An analysis of variance (ANOVA) test was carried out to statistically identify the importance of τDL. By considering the particle size bins of NPS pollutants during a single stormwater runoff event, these results showed that τDL3 which is triple time of τDL1 after τDL0 optimized the flow management timing. ANOVA and post hoc tests further confirmed that τDL3 can be viewed as an equivalent time for the end of particle discharge during a single storm event. In practical terms, this study thus suggests that the volume of first-flushed stormwater captured prior to τDL3 is an important criterion for best management practices. It is also expected that the methodology proposed in this research using particle bins and τDL3 can be further extended to different drainage areas and land uses.