The combined use of GIS and water quality indices for environmental assessment of Ouislane River watershed, Morocco

The Ouislane River, located in the R’Dom watershed, is significantly polluted owing to urbanization, industry, and agriculture. Given its importance to the region and its evident degradation, understanding the extent and nature of this pollution is crucial. The reasons for the assessment of water quality in the selected river are strongly related to industrial and domestic wastewater discharges and agricultural activities, which are considered to be the main causes of the deterioration in its quality. The novelty of this work is to integrate a geographical information system (GIS) technique with water quality models and to provide a good picture of the surface water adequacy. The present study aims to assess the water quality of the Ouislane River on the basis of measured water variable data for irrigation uses, utilizing a combination of GIS and water quality indices. The specific objectives of this research project are: (i) to assess its water quality status by using the water quality index (WQI), synthetic pollution index (SPI), and water quality parameters such as the sodium adsorption ratio (SAR), sodium percent (%Na), and residual sodium carbonate (RSC); and (ii) to classify and determine the suitability of the natural river waters for irrigation purposes. Fifteen samples from the river were collected to determine their suitability for irrigation use. The results showed that the WQI values range from 38 to 198, while the SPI values range from 0.99 to 5.5. This result was confirmed and validated by a satisfactory correlation between the WQI and the SPI (R² = 0.99). On the basis of the GIS interpolated map, the WQI and SPI models show that the river water was suitable for irrigation purposes. According to the SAR, % Na⁺, and RSC values, irrigation use of the water was acceptable and permissible. The results of this research will help water managers develop strategies to mitigate the potential adverse effects of surface water pollution on environment. They will also improve water quality assessment in the region and could provide an essential reference for quality studies and valuable guidance for watershed management strategies.