Document Type : Research Article
Author
Department of Civil Engineering, Faculty of Engineering, Urmia University, Urmia, Iran
Abstract
Water quality indices serve as a tool to simplify complex data and quantify the quality of different water resources. Gathering a variety of data in a single index is associated with relative sensitivity and uncertainties which remain unquantified. In this study, we compared two indices: IRWQIsc and NSFWQI. The assessment was based on water quality data from the Shaharchay River—six stations, seven sampling periods from July 2022 to March 2024. Beyond trend tracking, sensitivity tests and Monte Carlo simulations (1,000 iterations, 95% confidence interval) with parameter-specific coefficients of variation were conducted. According to the findings, both indices showed water quality improvement over time. IRWQIsc ranged from 37.9 (relatively poor) to 95.8 (very good); NSFWQI from 42.1 (poor) to 89.4 (good). A major pollution event hit the downstream station in February 2023 (IRWQIsc = 37.9), but by March 2024, the river had recovered (80.9). IRWQIsc was 2.5–4.2 times more sensitive to electrical conductivity and about 2.3 times more sensitive to fecal coliform, while NSFWQI was 1.8–2.4 times more sensitive to dissolved oxygen and BOD, making it better for detecting organic pollution. Uncertainty margins were ±4.2 for IRWQIsc and ±3.8 for NSFWQI, and the February 2023 event and March 2024 recovery were statistically significant. Based on the results, IRWQIsc is recommended for routine monitoring in arid-region rivers, and NSFWQI is advised for detecting acute organic pollution, or both where resources permit. Nevertheless, the proposed framework offers a replicable template for other regions with similar settings.
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