Sensitivity assessment of two water quality models NSFWQI and IRWQISC in Haraz River

Water quality indicators are a standard for classifying surface water based on the use of standard parameters and is a mathematical tool that converts a large amount of data used to describe water properties into a number and obtains a water quality level. The aim of this study was to assess and compare the sensitivity of NSFWQI and IRWQISC water quality indicators to quality parameters using variance-based methods on Haraz River with monthly sampling in 2022 in 7 selected stations in the range of Panjab to Haraz reservoir Dam in the province Mazandaran. The results of the present study have shown that the water quality in S1 (upstream) and S2-1 stations are relatively good at best, and bad at worst. Water quality in stations of S2, S3, S4, S5-1 and S5 (downstream), in the best case is moderate and in the worst case in September have poor quality. SRC method was used to analyze the uncertainty and sensitivity of the NSFWQI index and FAST and SOBOL methodologies were used for the IRWQISC index. The results of sensitivity analysis based on Factor Prioritization approach showed that in NSFWQI index, DO, BOD, CF, T and P parameters respectively and in IRWQISC index after DO parameter, BOD, P and N parameters had the most impact on output. In the uncertainty analysis, the results of applying SOBOL methodology for different stations of Haraz River were consistent with FAST method, but the results of sensitivity analysis obtained from these two methods were different from each other. Considering the obtained results and despite the similarity of the results of the two methods, it can be said that SOBOL methodology has been more successful than FAST methodology in this study due to unconditional convergence.