بررسی وضعیت کمی و کیفی آب¬های زیرزمینی آبخوان دشت کاشان و تأثیر آن بر پیامدهای زیست¬محیطی

Abstract

In this study, the quantitative and qualitative status of groundwater resources in Kashan plain aquifer and its environmental consequences were examined. For this purpose, the groundwater level situation was compared with the past results and using water balance equation, balance components and changes of aquifer storage volume was calculated in the water year of 2017-2018. Then, the chemical analysis results of qualitative parameters of 72 water samples taken from wells belonging to the Kashan Water and Wastewater Company and Kashan Water Resources Management were studied and finally, quantitative and qualitative maps of the aquifer were spatially drawn using ArcGIS. The results showed that the groundwater level has decreased quantitatively in March 2018 compared to March 2006 in more aquifer locations; the highest drops belonging to western border of the aquifer near Khozaq is 25.07 m. The results also showed that the aquifer storage volume has declined more than 35 MCM (million cubic meters) in the water year of 2017-2018. The analysis of the balance components showed that the total exploitation of Kashan plain aquifer in the water year of 2017-2018 is equal to 317.17 MCM. In this year, the total share of agriculture, urban green space, livestock and poultry as well as evaporation from fish ponds is 278.85 MCM, which is equivalent to 88% of the total extractions. The share of water abstracted for exploitation in the drinking, industrial, commercial and public and service sectors is 38.32 MCM, which is about 12% of the total exploitation. The results of the qualitative study on the basis of the samples of Water and Wastewater Company and Water Resources Management showed that the west of the aquifer is better than other parts especially compared to the east and northeast parts of the aquifer and 88.89% of the samples were in acceptable to moderate classes for drinking. In terms of suitability for irrigating farms and gardens, the wells no. 60, 61 and 62 are only in the moderate class and other samples are in high and very high salinity risk classes. Therefore, this would be a limiting factor in the yield of agricultural products. The results show that if the current trend of groundwater exploitation continues, the future horizon of the aquifer in terms of quantity and quality will be worse and the biggest decline will occur in the western regions, where agricultural, drinking and industrial wells are more concentrated. Also, a quantitative decrease of groundwater due to excessive exploitation causes environmental consequences such as subsidence and the decline in groundwater quality due to the increase of anions and cations in the water causes a series of diseases in water users, which will be discussed in detail in this article.