ارزیابی روند تغییرات دوره‌ای سطح آب زیرزمینی حوزه آبخیز بهادران استان یزد

آب‌های زیرزمینی بزرگ‌ترین منبع آب موجود برای تامین آب در مناطق نیمه‌خشک است. به‌همین‌منظور توسعه و بهره‌برداری از منابع آب زیرزمینی برای برآوردن این نیازها از اهمیت زیادی برخوردار است. ازاین‌رو تغییرات سطح آب زیرزمینی حوزه آبخیز بهادران واقع در استان یزد مدنظر قرارگرفته است. اطلاعات کمی منابع آب زیرزمینی در یک بازه زمانی 17 ساله تهیه شد. سپس نقشه‌های هم‌تراز و هم عمق آب زیرزمینی برای بازه پنج‌ساله و کل دوره برای بررسی تغییرات سطح تراز آب زیرزمینی بر اساس اطلاعات چاه‌های مشاهداتی در محیط نرم‌افزار arc gis تهیه شد. علاوه بر آن در نقشه‌های تهیه‌شده، مناطق تغذیه و تخلیه‌ی آب زیرزمینی مشخص شد. مطابق نتایج، بیش‌ترین عمق آب زیرزمینی در آبخوان‌های بهادران و شمس در سال 1397 به ترتیب برابر با 68 و 47.7 متر است که در نواحی شمالی آبخوان بهادران و جنوبی آبخوان شمس به حداکثر مقدار رسیده و به سمت نواحی جنوبی آبخوان بهادران و بخش‌های شرقی- غربی آبخوان شمس از عمق آب کاسته شده است؛ به‌طوری‌که کم‌ترین عمق آب زیرزمینی در هر دو آبخوان به حدود 11.8 متر می‌رسد. هم‌چنین بیش‌ترین سطح تراز آب زیرزمینی در آبخوان‌های محدوده‌ی بهادران در سال 1397 مربوط به نواحی جنوب غربی و غرب آبخوان‌ها و حدود 1538.91 متر است؛ به‌طوری‌که در بخش شرقی آبخوان بهادران به 1447.3 متر و در بخش جنوبی آبخوان شمس به 1190 متر در این سال می‌رسد. تراز آب زیرزمینی در سال‌های 92 و 87 نسبت به سال 1397 بالاتر می‌باشد که تغییر چندانی نداشته است. میزان افت تراز آب زیرزمینی در بازه‌ی زمانی 1387 تا 1392 و 1392 تا 1397 به ترتیب حدود 13.14 و 6.68 متر بوده است. نتایج این پژوهش اطلاعاتی از روند تغییرات منابع آب زیرزمینی در آبخوان‌ها را در اختیار سیاست‌مدارن و مدیران قرار می‌دهد که می‌تواند در راستای مدیریت بهینه به‌کار برده شود.

evaluation of periodic changes in groundwater level in bahadoran watershed, yazd province

groundwater is the largest source of water in semi-arid regions. it is, therefore, essential to develop and exploit underground water resources to meet these needs. precipitation is the main source of recharge for many aquifers. changes in precipitation and groundwater level depth are closely related. it is more difficult to quantify groundwater availability and the long-term effects of climate change on groundwater than surface water. although groundwater resources are more resilient than surface water, they are increasingly vulnerable to overexploitation, drought, pollution, and the lack of permanentconsistent precipitation, reducing quality and availability. the decrease in aquifer quality and storage capacity as a result of extraction exceeding the available surplus is due to the development of urban areas, the use of water-based industries, and an increased cultivation area, which jeopardizes underground water sources. although human factors have a strong influence on groundwater, the natural hydrological cycle plays a key role in regulating the condition of the aquifer. in arid and semi-arid countries and regions of the world where surface water resources are relatively scarce, groundwater is often the most important or even the only source of water for regional food security, drinking water, economic development, and environmental conservation.materials and methods quantitative information about groundwater resources related to wells, springs, and qanats was provided by relevant organizations, including the iranian water resources research organization (tamab) and the yazd regional water organization, as well as previous research. for a more detailed investigation, the level and depth maps of underground water were drawn for five years based on the available information. the zoning map of five-year underground water changes was prepared using arcgis software to analyze the amount of water level drop in the observation wells. this research considered the distribution of wells, springs, and qanats and the trend of changes in their number, discharge, and annual consumption in different parts. there are 25, 122, 0, and 11 semi-deep wells, deep wells, springs, and qanats. it is worth mentioning that the statistics of the selected wells in each plain were used in the calculations and for the underground water maps, which have the most complete statistics during the selected period, so the number of wells mentioned in each plain is not necessarily the same as the number of wells in the piezometric network, and the length of the statistical period used did not necessarily cover the entire statistical period.results and discussion the maximum depth of underground water in the bahadoran and shams aquifers in 2018 was 68 m and 47.7 m, respectively, with the deepest points in the northern areas of the bahadoran aquifer and southern shams aquifers, toward the southern areas of the bahadoran aquifer and the eastern parts. the water depth in the west of the shams aquifer has decreased; therefore, the minimum depth of underground water in both aquifers is approximately 11.8 m. the highest groundwater level in the aquifers of the bahadoran area in 2018 was approximately 1538.91 m in the southwestern and western areas of the aquifers. in the eastern part of the bahadoran aquifer, it reached 1447.3 m, and in the southern part of the shams aquifer, it reached 1190 m in 2018. the groundwater level in 2013 and 2008 was higher than in 2018, but it did not change significantly. the decline in groundwater level from 2008 to 2013 and from 2013 to 2018 was approximately 13.14 m and 6.68 m, respectively. examining the changes in the groundwater level during the statistical period shows that the overall trend has been downward.conclusion this study investigated the level and depth of underground water sources in the bahadoran watershed in yazd province. the results indicate an alarming drop in the groundwater table. the spatial distribution of groundwater extraction differed throughout the watershed, so some areas experienced a severe decrease in the water level. in addition, due to the use of these resources, the seasonal variation in water level reduction differs. in the absence of surface water sources due to a decrease in precipitation and prolonged droughts, the majority of groundwater extractıon is done for various purposes, such as increasing the area of agricultural cultivation. this excessive extraction occurs through additional water wells. therefore, it is necessary to carry out comprehensive studies to investigate the relationship between the extent of vegetation in the area and the amount of groundwater extractıon from aquifers using satellite images. in addition, it is suggested to evaluate the balance between groundwater extractıon and recharge in all watersheds of the country. the results of this study provide policy makers and managers with information on changes in groundwater resources in aquifers, which can be used for optimal management.