Evaluating effects of extreme rainfall on stormwater flows and water quality

• Main Author: Koh, Lin Yang
• Other Authors: Qin Xiaosheng
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Extreme rainfall
• Online Access: https://hdl.handle.net/10356/177528
• Institution: Nanyang Technological University

Extreme rainfall can have profound effects on urban drainage infrastructure and water quality. Hence, it is important to evaluate these effects, especially in a high population density and large urban environment. By understanding these effects, proper mitigation strategies, such as low-impact developments can be implemented. This study investigated the effects of extreme rainfall events on stormwater flow and quality using the Storm Water Management Model (SWMM). In total, 120 rainfall scenarios with varying return periods, durations, and temporal distributions (Huff distribution) were simulated. The results demonstrate a complex relationship between rainfall characteristics and the corresponding hydrological response. Results also shows that peak and average flow rates are shown to increase with higher return periods, but this rate of increase diminishes with an increasing return period. Shorter rainfall events with a similar return period tend to exhibit higher peak flows. Temporal distribution influences peak flows, with Type IV exhibiting the highest peaks. The time taken to reach peak flow remains unaffected by the return period. Analysis conducted on stormwater quality revealed that peak concentration of total suspended solids (TSS) decreases with increasing return period, potentially due to initial wash-off and effects of dilution. Additionally, rainfall durations significantly influence peak concentration, with shorter events exhibiting a higher peak. Temporal distribution also influences peak concentration, with specific distributions potentially favouring pollutant transport. Total TSS load as expected, increased with increasing return period while time to peak concentration remained unaffected and preceded earlier than peak to flow rate, likely attributed to the “first flush” phenomenon.