A Traditional Analysis of the First Flush Effect for Nutrients in Stormwater Runoff from Two Small Urban Catchments
Nonpoint stormwater runoff remains a major threat to surface water quality in the USA. More effective stormwater control measures can be designed by understanding patterns in pollutant export with respect to the runoff hydrograph. In particular, nutrient concentrations in urban stormwater can cause deleterious effects in sensitive watersheds in the Southeast and Mid-Atlantic USA. A year-long study captured stormwater samples from 36 storm events at two catchments (one primarily impermeable and the other substantially wooded) and analyzed for total suspended solids and various nutrient species. Using these data, the first flush effect (the assumption that the initial portion of a rainfall-runoff event is more polluted than the later portions) was evaluated based on several published methods and definitions. Based on an analysis of multiple methodologies, the ranking of first flush strength among the pollutants was total suspended solids (TSS) > ammonia (NH3) > total Kjeldahl nitrogen > NO2-NO3 > total phosphorus > orthophosphate (O-PO4). Nitrogen species generally displayed a stronger first flush than phosphorus species, with O-PO4 showing the weakest first flush effect. Various relationships ° climate, land use, and the first flush strength were also explored. Of the rainfall characteristics analyzed, total rainfall and runoff volume each inversely affected the first flush strength of TSS on the more impervious catchment. Although orthophosphate did not have a strong first flush effect, the relative first flush strength for O-PO4 increased with increasing rainfall or runoff. Land use did not influence the first flush strength of the pollutants. On average, most pollutants exhibited a slight first flush effect, but substantial pollutant loading still occurred in the latter portion of the storm’s total runoff volume. Thus, treating the majority of a storm’s total pollutant load requires capturing a commensurate fraction of runoff volume.
KeywordsStormwater Runoff First flush Watershed Catchment TSS Nutrients Nitrogen Phosphorus
- APHA, AWWA, WPCF. (1995). Standard methods for the examination of water and wastewater (20th ed.). Washington, D.C.: Am. Public Health Assoc.Google Scholar
- Geiger, W. F. (1984). Characteristics of combined sewer runoff. In Proc. 3rd International Conference on Urban Storm Drainage (pp. 851-860).Google Scholar
- Geiger, W. F. (1987). Flushing effects in combined sewer systems. In Proc. 4th International Conference on Urban Storm Drainage (pp. 40-46).Google Scholar
- Hathaway, J. M., Moore, T. L. C., Burkholder, J. M., Hunt, W. F. (2012). Temporal analysis of stormwater SCM effluent based on harmful algal bloom (HAB) sensitivity in surface waters: are annual nutrient EMCs appropriate during HAB-sensitive seasons? Ecological Engineering. (in press).Google Scholar
- Helsel, D. R., Kim, J. I., & Randall, C. W. (1979). Land use influences on metals in storm drainage. Journal of the Water Pollution Control Federation, 51(4), 709–717.Google Scholar
- Natural Resources Conservation Service (NRCS). (2010). “Soil data mart.” http://soildatamart.nrcs.usda.gov/. 15 Dec 2010.
- Stahre, P., & Urbonas, B. (1990). Stormwater detention for drainage, water quality and CSO management. Hydrological Sciences Journal, 37(3), 298.Google Scholar
- Vorreiter, L. & Hickey, C. (1994). Incidence of the first flush phenomenon in catchments of the Sydney region. In Proceedings of the Water Down Under 1994 Conference. Part 3 (of 3), Nov 21-25 1994, 359-364. Adelaide, Australia: IE Aust, Crows Nest, NSW, Australia.Google Scholar
- Wanielista, M. P., & Yousef, Y. A. (1993). Stormwater management. New York: Wiley.Google Scholar