Assessing dissolved oxygen dynamics in Pasig River, Philippines: A HEC-RAS modeling approach during the COVID-19 pandemic

Abstract

The water quality in Pasig River has been impacted by urbanization, industrialization, and the pandemic conditions. This study involved comparative analysis of dissolved oxygen (DO) levels before and during the pandemic. Field measurements, including water temperature, salinity, and DO, were conducted during neap and spring tides. To further understand and simulate DO distribution, a one-dimensional mathematical model, specifically Hydrologic Engineering Center-River Analysis System, was employed. Results showed that DO increased during the pandemic, ranging from 3.26 to 7.25 and 1.08 to 5.69 mg/L during neap and spring tide. From the minimum standard DO level, out of eight stations, seven passed during neap tide, while one station passed during spring tide. Salinity levels were higher during spring tide, which may have affected the DO. Salt intrusion was evident until 4 km from the confluence. The hydraulic model yielded average water level differences of 5.1 and 8.3 cm during calibration and validation, respectively. The DO calibration and simulation exhibited very good statistical evaluation outcomes, with values of 0.9 for Nash-Sutcliffe Efficiency and 0.3 for Root Mean Standard Deviation Ratio. These findings hold significant potential for formulation of water quality enhancement plans and implementation of solid waste management and pollution policies. HIGHLIGHTS Dissolved oxygen (DO) increased during the pandemic in upstream and downstream areas.; The hydraulic model showed very good statistical evaluation results of 0.94 for Nash–Sutcliffe efficiency (NSE) and 0.24 for root mean standard deviation ratio (RSR) for calibration and 0.91 for NSE and 0.29 for RSR for validation.; The hydraulic model validation generated average water level difference of 8.3 cm during spring tide.; The DO simulation showed very good statistical evaluation results of 0.9 for NSE and 0.3 for RSR during the neap and spring tide, respectively.;

Keywords

• covid-19
• dissolved oxygen modeling
• hec-ras
• pasig river
• water quality