Effects of Rainfall on Microbial Water Quality on Haeundae and Gwangan Swimming Beach

ABSTRACT

The associations between storm events, urban runoff and costal water quality have not been well investigated in Korea. A temporal and spatial analysis during summer, 2015 was conducted to determine associates between urban runoff and fecal indicator bacteria (Escherichia coli, Enterococcus) levels at two popular coastal beaches (Gwanganri beach and Haundae beach) in Busan. In this study, a clear relationship between rainfall and elevated number of indicators was observed. Two beaches met the costal beach water health standards after less than 3.0 mm of rain. Only for storms less than 2.5 mm was no observable rainfall effect. Our results revealed that exceedances were greatest in 5 hours following 41.0~45.5 rainfall, then declined the bacterial concentrations in 8 hours after the storm and they generally returned to levels below water health standards within 10~14 hours. But it took 2.7 days to get the level of water quality of dry days. The time required for water quality recovery depends on the intensity and duration of rainfall. In the event of intense rainfall issuance of beach closure by public authorities is warranted to protect public health.