Application of 1D-2D coupled modeling in water quality assessment: A case study in Ca Mau Peninsula, Vietnam

A few 1D and 2D models are used to simulate and calculate the water level and water quality regarding four state variable (DO, NH4, NO3, and BOD) observations in the main rivers and coastal estuaries on the Ca Mau peninsula. This study calibrates and validates 1D and 2D models during the dry and flood seasons for 2014 and 2015, as well as assesses water quality in coastal estuaries during the dry and flood season of 2016 by using a 2D model. The calibration and validation results of the hydrodynamic 1D and 2D models show that there is a high degree of conformity regarding the phase and amplitude of water level at observing stations with mean absolute error (MAE) ranges from 0.05 m to 0.37 m. The RMSE-observation standard deviation ratio (RSR) vary from 0.12 to 0.64, and the percent bias (PBIAS) is from - 8.9% to 3.2%. Calibration and validation of water quality parameter (DO, NH4, NO3, and BOD5 concentration) results have a high correlation coefficient during both the dry and flood season of 2014 and 2015. The standards, originating from the National Technical Regulation on Surface Water quality and on Coastal Water Quality, are used to evaluate pollutant concentrations in estuaries in the study area during the dry and flood seasons of 2016. The water quality parameters contain DO (4.6 mg/1-7.9 mg/l) and BOD (4.6 mg/l-10.7 mg/l) concentrations over the National Technical Regulation on Surface and Coastal Water Quality and the Al limit with DO ( > 4 mg/l) and BOD5 (4 mg/l) on surface water quality for domestic water use in the dry and flood seasons. The calculated results will help managers make better plans for aquaculture and aquatic conservation zones in coastal estuaries in the future.