Numerical Modeling of COD Transportation in Liaodong Bay: Impact of COD Loads from Rivers Flowing into the Sea

Pollution loads pose a major threat to the health of the marine environment and the long-term viability of the coastal economy. The present study developed a coupling model to simulate the chemical oxygen demand (COD) transport in upper rivers (1D) and subsequent diffusion in the coastal zone (2D) in Liaodong Bay, based on the HydroInfo system. Three main seagoing rivers, including Daliao, Liao, and Daling Rivers, were selected and investigated for hydrodynamic and hydrochemical analyses. The mathematical model was evaluated by monitoring data from state-controlled cross-sections scattered along the three rivers, and the observation data showed good agreement with simulated values, confirming the model’s accuracy in terms of spatial and temporal distribution. The transport and propagation process of COD in inlet rivers, such as Daliao, Liao, and Daling, including the sea area of Liaodong Bay, were simulated and analyzed. Simulated results revealed that the pollution range of COD in Liaodong Bay was 258–391 km2 in different seasons. The pollutant leakage scenarios for the three rivers entering the sea were simulated utilizing the developed mathematical model. The study simulated and predicted that, in the event of a sudden water pollution accident (e.g., sneak discharge and leakage at various sections of sea-entering rivers, such as Daliao, Liao, and Daling), pollutants might take 2–11 days to reach the sea-entering mouth, and the sea area would take 8–32 days to reach the maximum pollution range. Our numerical modeling may be used to analyze and make decisions on pollution control in Liaodong Bay and major sea-entry rivers, and be useful to water environment management in sea-entry rivers and Liaodong Bay, and water pollution emergency responses