Evaluation of periodic changes in groundwater level in Bahadoran watershed yazd Provance

Groundwater is the largest source of water in semi-arid regions. It is therefore very important to develop and exploit underground water resources in order to meet these needs. Rainfall is the main source of nutrients for many aquifers. Changes in rainfall 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 lack of permanent rainfall, leading to reduced quality and availability. The decrease in the quality and storage capacity of aquifers as a result of extractıon more than the available surplus is due to the development of urban areas, the use of water-based industries and an increase in the area under cultivation of agricultural products, which jeopardises underground water sources. Although human factors have a strong influence on groundwater, the natural hydrological cycle plays a key role in regulating the aquifer situation. 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.

Quantitative information about groundwater resources related to wells, springs, and ghanat over 17 years 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 a five-year period based on the available information. The zoning map of five-year underground water changes was prepared in the Arc GIS software environment to check the amount of water level drop in the observation wells. This research considered the distribution of wells, springs, and ghanat in the region and the trend of changes in their number, discharge, and annual consumption in different parts. There are 25, 122, 0, and 11 underground water sources in the region, including semi-deep wells, deep wells, springs, and ghanat. It is worth mentioning that the statistics of the selected wells in each plain were used in the calculations and drawing of 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 was also not necessarily the entire statistical period.

According to the results, the maximum depth of underground water in the Bahadran and Shams aquifers in 2018 was 68 and 47.7 m, respectively, which reached the maximum value in the northern areas of the Bahadran and southern Shams aquifers and toward the southern areas of the Bahadran 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 level of underground water in the aquifers of the Bahadran area in 2018 was approximately 1538.91 m in the southwestern and western areas of the aquifers. Thus, in the eastern part of the Bahadran aquifer, it reached 1447.3 m and in the southern part of the Shams aquifer, it reached 1190 m this year. The level of underground water in 2013 and 2008 was higher than that in 2018, but it did not change significantly. The drop in underground water level from 2008 to 2013 and from 2013 to 2018 was approximately 13.14 and 6.68 m, respectively. Examining the changes in the underground water level during the statistical period shows that the underground water level generally has a downward trend.

In this study, was investigated the level and depth of underground water sources in the Bahadran watershed in Yazd province. The results indicate an alarming drop in the underground water table. The spatial distribution of underground water resource extraction differed throughout the watershed, so some areas experienced severe decrease in the water level. In addition, due to the use of these resources, the time distribution of water level reduction may also be different in the seasons. In the absence of surface water sources due to a decrease in adequate rainfall and resulting droughts, the majority of underground water sources are extractıon for various purposes, such as increasing the area of agricultural cultivation. This amount of underground water extraction is carried out through other 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 water extractıon from underground aquifers using satellite images. In addition, it is suggested to evaluate the amount of underground water resources extractıon and charge in all watersheds of the country. The results of this study provide politicians and managers with information on changes in underground water resources in aquifers, which can be used for optimal management.