Integrated evaluation model for surface water quality: a case study in Ho Chi Minh City, Vietnam

The assessment of water quality is an important aspect of environmental management. One method commonly applied is the Water Quality Index. The index consists of a group of experimental formulae used for calculating the overall quality of the water environment. In Vietnam, the water quality index is used to calculate water quality based on nine measured parameters, and was officially sanctioned as the standard method for assessing water quality in 2011. In this study another method, adopting the fuzzy logic concept for calculating water quality, is applied. This method has the advantage of dealing with an unlimited number of quality parameters, and can allocate quality classes by calculating quantitative data obtained through monitoring water quality at a number of monitoring sites. However, the method has some limitations such as data loss during the evaluation, and uncertainties due to the method not considering the overall physical environment of the catchments that feed water into the monitoring sites. Fuzzy comprehensive analysis comprises of two main parts: the fuzzy membership and the weights. This study applied the simplest and most used membership function which is triangular and semi-trapezoidal shape, and three different methods of assigning weights: Entropy, Overweight standard and F-statistic for testing the quality of water in the study area, Ho Chi Minh City, Vietnam in South-East Asia, using the monitored quality dataset in 2015. It showed big differences among the results when tested with different weighting methods which is the uncertainty of the Fuzzy method. Therefore, Geographic Information System (GIS) techniques including computer-based sub-watershed delineation modelling using a geographic hydrological model, and geographical regression models, including Ordinary Least Square and Geographically Weighted Regression models, were applied to reduce the uncertainty in the fuzzy process. Results of this study demonstrate the model’s applicability and capability for use in water quality evaluation. From the results, an integrated assessment comprising fuzzy and GIS methods is developed for better assessment of the water quality and therefore contributing to the better management