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The magnitude and frequency of extreme rainfall due to climate change is increasing. Increasing rainfall causes serious hydrological problems in cities. Rainfall does not infiltrate the soil, but mostly flows through the sewer pipes into the stream. Most old urban watersheds have combined sewer pipes. When rainfall exceeds the capacity of the combined sewer pipes, sewage mixed with stormwater overflows the sewer pipes and flows directly into the stream. This is called Combined Sewer Overflows (CSOs). CSOs enter the stream with non-point source pollutants accumulated on the surface and pollute the stream. CSOs are one of the major water quality problems in older urban watersheds. This can be solved by replacing the combined sewer pipes with separated sewer pipes, but in reality it requires astronomical costs. As an alternative, the Low Impact Development (LID) technique has recently been introduced. In this study, we analyzed the effects of climate change on CSOs in urban watersheds and applied LID techniques to offset the effects. The LID facility was applied with the most commonly used Bio-Retention cells. HIGHLIGHTS Applicability of bio-retention to offset the negative effects of climate change on urban streams are investigated using EPA SWMM.; Run-off, TP load, and CSOs in urban watershed show high potential for increases by climate change.; The bio-retention cell is useful for offsetting the negative effects of climate change.;

Personal Computer Stormwater Management Model (PCSWMM) was applied to investigate: (1) hydrological responses in the Myponga catchment as a result of land use changes; and (2) the possibility of adopting Water Sensitive Urban Design (WSUD) technologies (bio-retention cells) to manage resulting floods. Calibrated and validated models predicted the measured data with satisfactory accuracy and reliability. Different urbanization scenarios were tested. When the level of urbanization increased from 10% to 70%, mean discharge increased from 45% to 322%. Frequency of flood at 2-year Average Recurrence Interval (ARI) increased from 1 to 44 and frequency of floods at 100-year ARI increased from none to 8. At 70% urbanisation, trialled bio-retention facilities used as WSUD measures almost completely ameliorated 2-year ARI floods by reducing the frequency of such events from 44 to 2. Floods at smaller ARIs (2, 5, 10 and 20 years) were effectively managed by WSUD measures while floods at 50- and 100-year ARIs remained unchanged. The overall results improve understanding of the severity of the impacts of land use changes on the hydrology of a catchment and the ability of bio-retention cells to alleviate the risk of small to medium floods in the Myponga catchment. [ABSTRACT FROM AUTHOR]

Personal Computer Stormwater Management Model (PCSWMM) was applied to investigate: (1) hydrological responses in the Myponga catchment as a result of land use changes; and (2) the possibility of adopting Water Sensitive Urban Design (WSUD) technologies (bio-retention cells) to manage resulting floods. Calibrated and validated models predicted the measured data with satisfactory accuracy and reliability. Different urbanization scenarios were tested. When the level of urbanization increased from 10% to 70%, mean discharge increased from 45% to 322%. Frequency of flood at 2-year Average Recurrence Interval (ARI) increased from 1 to 44 and frequency of floods at 100-year ARI increased from none to 8. At 70% urbanisation, trialled bio-retention facilities used as WSUD measures almost completely ameliorated 2-year ARI floods by reducing the frequency of such events from 44 to 2. Floods at smaller ARIs (2, 5, 10 and 20 years) were effectively managed by WSUD measures while floods at 50- and 100-year ARIs remained unchanged. The overall results improve understanding of the severity of the impacts of land use changes on the hydrology of a catchment and the ability of bio-retention cells to alleviate the risk of small to medium floods in the Myponga catchment.