The quantification of pollutant loading from nonpoint pollution sources is very challenging but crucial. Statistical analyses were performed for identifying differences of stormwater quality among different types of land use and among catchments of same land use in three types of flow (baseflow, snowmelt and stormwater runoff). Results indicate water quality parameters present variations among different types of land use and among catchments of same land use. In addition, Stormwater Management Model (SWMM) was calibrated and verified for industrial and residential land uses. The modeling results clearly demonstrate distinct coefficient values for pollutant build-up and wash-off. Rainfall, as the source of stormwater, in the city was also investigated to characterize the spatial and temporal distribution of rainfall. The identified differences in stormwater quality from statistical analysis and modeling suggest the need of quantifying and modeling pollutant loading from different types of land use.