Study the relationship between rainfall characteristics and urban-runoff quality in an arid area (A case study: Maghsud Beyk watershed, Tehran)

With decreasing of fresh water availability via population growth, collection and re-use of urban runoff as a non-drinking water source was suggested for the development of the cities located in dry area. But, non-point polluting sources in urban areas should affect the quality of urban runoff . A direct relationship was observed between rainfall characteristics and the amount of contaminants in urban runoff. Primary runoff contain the greatest amount of the pollution. Disposal of primary runoff (first flash) according to rainfall condition can significantly mitigate urban runoff pollutions problems. In this study, the relationship between rainfall characteristics and discharge with urban runoff quality was investigated in an urban area. For this propose, 9 factors of water quality was investigate annually, seasonally and also for 25 individual rainfalls event. Statistical relationship between rainfall characteristics and urban runoff quality parameters was analyzed via Pearson analysis method. According to results, total dissolved solid (TDS) of runoff deceased with increasing of rainfall. A significant relationship was observed between rainfall intensity, EC and TDS of runoff (R2 = 0.56, and 0.68 respectively), while an inverse relationship was observed between rainfall duration and runoff quality (R2 = -0.543). The most seasonally change in groundwater was happened in the spring and winter.