Contributions of Dry and Wet Weather Runoffs to Annual Pollutant Loading in Tropical Urban Catchments

Abstract

This study compares the relative contributions of potential contaminants discharged in dry weather flow (DWF) and wet weather flow (WWF) from typical type of catchments in Malaysia. A total of 52 storm events were monitored for WWF quality evaluation. Hourly DWF samples were also collected manually during selected weekday (Wednesday) and weekend (Saturday and Sunday). All water samples were analyzed for TSS, COD, BOD, oil and grease (O&G), NO2–N, NO3–N, NH3–N, soluble P, total P and Zinc. The results indicate that TSS, BOD, COD and O&G were mostly transported in WWF than in DWF. More than 70% of the total annual load of TSS and O&G were transported in storm water runoff. Conversely, annual loadings of NH3–N and soluble P were mainly evacuated by DWF at the commercial and industrial catchments. Storm water runoff contributes greater loadings of N and P in the residential catchment. In general, each pollutant and land use would give different relative contributions to the annual pollutant loadings. In conclusion, this study have recognized the relative pollutant loading contributions by dry and wet weather flows in typical urban catchments in Malaysia. This findings will help the decision makers to develop better target specific pollutant treatment strategies to reduce the urban water pollution.