Evaluation of the Effects of Geology and Agricultural Development State on the Quality of Surface Water Resources Affected by Constructing Reservoir Dams (Case Study: Marun - Jarahi Basin)

The statistical tests such as T-test and Kruskall-Wallis test were used to study and analyze the difference between the quantitative parameters before and after constructing dams and the effect of different factors on water quality. The results of statistical tests showed that the values of the investigated water quality parameters (except EC value) before constructing (pre) dams were significantly different from the values after constructing dams in reservoir downstream stations. Sulfate (SO2-4) concentration in downstream stations of Marun Dam (Behbahan and Cham Nezam) reduced by 30 and 23 percent, respectively, and Cl- concentration increased 21 and 12 percent, respectively. Similarly, the difference between the values before and after constructing Jarreh dam at Mashin station was a 106% reduction in the concentration of sulfate ion (SO2-4) and a 78% increase in the concentration of chlorine ion (Cl-). The reason for this increase is probably due to the effect of river flows on the Formation and the relationship between the reservoir and the Formations where water has a long residence time and then reduced due to the exposure to the Geological Formations as well as the existence of agricultural activities downstream and before quality monitoring stations could be another reason for this claim. In addition, in the reservoir system, the concentration of soluble salt may be diluted by runoff from winter snowmelt and spring rains. Therefore, it can be concluded that water quality characteristics of Marun and Roudzard rivers in the studied basin has been affected by the constructed reservoir dams.