Document Type : Research Article
Authors
1 Islamic Azad University, Shiraz
2 Ferdowsi University of Mashhad
Abstract
Introduction: Water resources quality assessment of the dam sites is one of the primary studies in the designing of these structures. The main challenges in Iran are the reduction of water resources and the limitation of groundwater exploitation. Much of these resources are formed in karst water resources in the karstic susceptible formations such as the Asmari carbonate formation in Zagros Mountain, Iran. In this study using laboratory and field studies, various parameters and indices were assessed to investigate the water resources quality of Bazoft dam site for different purposes. Bazoft dam is a double-curvature arch dam with a height of 211 meters which is located in Chaharmahal and Bakhtiari Province of Iran. The bedrock of the dam site consists of limestone and dolomite rocks of the Asmari and the Jahrom formations. The Jahrum formation formed the right abutment, the riverbed and the lower parts of the left abutment. The Asmari formation formed the rocks in the middle and upper part of the left abutment.
Materials and Methods: After field studies, chemical analyses have been performed on the collected water samples from the water resources such as springs, river and the exploratory boreholes in the dam site. PH and electrical conductivity (EC) were measured by pH meter and electrical conductivity apparatus was measured at 25 ° C. Concentration of ions such as calcium, magnesium, bicarbonate was measured by titration method. The concentration of ions such as sodium and potassium, sulfate and nitrate were measured using the Flame-Photometry, and Spectrophotometry methods, respectively.. The test error in all cases was low and the results were confirmed. The indices such as Langelier saturation index and Ryznar stability index, sodium adsorption ratio (SAR), soluble sodium percentage, residual sodium carbonate, permeability index, Kelly ratio, were calculated based on related equations. Principal factor analysis (PCA) is used to determine the most influential variables when the number of variables is investigated and the relationship between them is unknown. In this method the variables are set on the elements so that the first factor is reduced to the next factor of the variance, hence the variables that are based on the first factors are the most influential. PCA reduces the dimensions of the initial data by turning the main components around the vertical and horizontal axes of coordinates. This rotation actually increases the variance between the main components and therefore it is called Variance Maximize Varimax or orthogonal rotation. The Varimax command is one of the most common methods of orthogonal rotation that preserves the independence between the extracted agents. This method reduces the number of the larger factor loadings to the lowest number. In this method, the scree plot chart determined the number of factors extracted. Parameters of R2 and RMSE in order to investigate the performance of relations have been used. As R2 is closer to the one and the RMSE is closer to the zero, the proposed relationship will yield better performance.
Results and Discussion: Anions such as HCO3, Cl, SO4, CO3 and NO3 and cations such as Ca, Na, Mg, and K are the most, respectively. From the viewpoint of hardness, all waters are placed in the hard category. According to the percentage of Na, the spring’s water is excellent, the water of the borehole is good and the river is acceptable. The results of factor analysis showed that 87.13 percent of the water quality variations are controlled by four factors. The most important factors affecting the water quality of the dam site include EC, TDS, Na %, SAR, Cl, SO4, alkalinity, Na, and CO3 with 50.91 %. The second factor include calcium, magnesium, potassium ions with 15.82 %, the third factor include nitrate, bicarbonate, and hardness with 11.61 % and pH and carbonate with 7.17 % are fall into the fourth factor. The correlation matrix of the parameters was investigated and the accuracy of some relationships was examined on the basis of different statistical criteria. The relationships of LSI with RSI and EC with TDS in the dam site and their comparison with previously suggested equations indicated that there is a high correlation and each relationship is applicable for a particular area. Also, the trend of points obtained from each equation has the appropriate consistency but the RMSE of the assessed equations is high. EC plot against TDS to determine the relationship between the two parameters in the Bazoft dam site is TDS=0.70Ec-31.24.
Conclusion: The concentration of all assessed cations and anions is lower than the WHO permissible limit. The water resources are corrosive and all indices indicated the appropriate quality of water resources for farming and drinking.
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