Introducing a water quality index for assessing water for irrigation purposes: A case study of the Ghezel Ozan River.

Rivers are one of the main water resources for agricultural, drinking, environmental and industrial use. Water quality indices can and have been used to identify threats to water quality along a stream and contribute to better water resources management. There are many water quality indices for the assessment and use of surface water for drinking purposes. However, there is no well-established index for the assessment and direct use of river water for irrigation purposes. The aim of this study was to adopt the framework of the National Sanitation Foundation Water Quality Index (NSFWQI) and, with adjustments, apply it in a way which will conform to irrigation water quality requirements. To accomplish this, the NSFWQI parameters for drinking water use were amended to include water quality parameters suitable for irrigation. For each selected parameter, an individual weighting chart was generated according to the FAO 29 guideline. The NSFWQI formula was then used to calculate a final index value, and for each parameter an acceptable range in this value was determined. The new index was then applied to the Ghezel Ozan River in Iran as a case study. A forty five year record of water quality data (1966 to 2010) was collected from four hydrometery stations along the river. Water quality parameters including Na+, Cl-, pH, HCO-3, EC, SAR and TDS were employed for water quality analysis using the adjusted NSFWQI formula. The results of this case study showed variation in water quality from the upstream to downstream ends of the river. Consistent monitoring of the river water quality and the establishment of a long term management plan were recommended for the protection of this valuable water resource.