First flush analysis as an evidence-based method for site-specific design and optimization of low impact development controls for urban stormwater management

• Main Author: Cruz, Gil G., Jr.
• Format: text
• Language: English
• Published: Animo Repository 2023
• Subjects: Urban runoff—Philippoines—Bataan—Management; Civil Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etdd_civ/6; https://animorepository.dlsu.edu.ph/context/etdd_civ/article/1005/viewcontent/First_flush_analysis_as_an_evidence_based_method_for_site_specifi.pdf
• Institution: De La Salle University

Non-point source (NPS) pollution and combined sewer overflow (CSO) pose an environmental threat to the natural receiving water bodies. However, management of stormwater runoff is resource intensive due to the high volumes that may need to be treated. First flush is an important phenomenon commonly used in stormwater treatment system design where only the highly concentrated initial part of the runoff hydrograph is subject to treatment. Understanding the water quality and the duration of the first flush in an urban catchment area that is to be diverted for treatment will be beneficial to apply Low Impact Development (LID) approach in sustainable stormwater management. Despite recent breakthroughs in the modelling and simulation of LID, there is no universal consensus on the standard technical specifications of LID parameters since the majority of the LID application are area-specific. Moreover, due to the complexity of the parameters involved, the estimation of LID efficiency in attenuating the urban surface runoff at the watershed scale is challenging. This study investigates the occurrence of the first flush of urban stormwater runoff from actual rainfall events in Balanga City, Bataan, Philippines as an evidence-based method to design and optimize low impact development controls. It was found that first flush exists through the initial 10%–30% of the runoff for storm events with an average rainfall intensity of 5-10mm/hr. Hence, to effectively treat the stormwater runoff with minimum risk of discharging significant high loads of pollutants to natural receiving water bodies, it is recommended that at least the initial 30% of the runoff should be treated using appropriate LID. Results of the optimization of various LID vertical parameters using response surface methodology and sensitivity analysis showed significant impact on managing runoff flux and pollutant load. This study offers technical and methodological support to area-specific design and spatial allocation of LID for sustainable stormwater management.