Document Type : Research Paper
Authors
1 Research Assistant Professor, Desert Research Department, Research Institute of Forests and Rangelands, AREEO, Tehran, Iran
2 Research Professor, Botany Research, Department, Research Institute of Forests and Rangelands, AREEO, Tehran, Iran
Abstract
Background and objectives
Groundwater resources can be collected through wells, tunnels, and drainage paths; or inherently percolate to the surface through seepage or springs. It is consumed for drinking, agriculture, industry, environment, and ecosystems (Asadi et al., 2023). Management of underground water resources is particularly important in arid and semi-arid regions, due to surface water is scarce. Hence, the dependence upon groundwater is quite remarkable. Evidence shows that factors including population growth and climate change play a crucial role in the intensification of groundwater levels (Hall et al., 2008).
Lack of proper knowledge and excessive exploitation of underground water resources, irreparable damages such as a sharp and irreversible drop in the underground water level, reduction of the flow rate of wells and canals, changes in the pattern of underground water flow such as the advance of waterfronts. It has followed the saltiness and interference of salty waters. Therefore, in this research, the quantitative characteristics of underground water in the central desert watershed during the statistical period of 2001-2002 to 2017-2018 have been evaluated.
Research Methodology
The drainage basin of the central desert is a part of the great section of central Iran, which includes important cities such as Garmsar, Semnan, Damghan, Shahrood, Neishabor, Mashhad, Sabzevar, and Kashmer, creates an area of 226,523 Km2 between the south of Alborz and the northeast of Zagros. Considering the necessity of studies on the factors affecting the decline of the water level of groundwater resources, including hydrogeological droughts and human interventions, along with behavioral assessment; it is essential to provide appropriate protection and management solutions for groundwater resources.
Hence, in the present study, various time lapse-year aligned maps, representative hydrographs of the study area, the average annual changes in precipitation and groundwater drought index (GRI), and the level of exploitation of groundwater resources for the target plain were calculated. To evaluate the quantitative status of underground water, the water level and the observation wells data in the aquifers of the study areas of the Central Desert watershed were used in the mentioned statistical period. In the following zoning maps, variations of underground water level fluctuations, aquifer storage volume, and drought conditions were analyzed. It is necessary to note that all the maps were drawn using Arc GIS and kriging tools.
Results
The results at the level of the central desert watershed, based on the updated statistics up to the water year 2019-2020, indicate the number of 29,360 underground water sources (wells, springs, and aqueducts) with the volume of discharge and withdrawal of 3659 million cubic meters per year. The number of springs, aqueducts, and deep and semi-deep wells is about 19, 21, 39, and 21% respectively in terms of number and terms of discharge about 9, 16, 72, and 3% of the total number and discharge of underground water sources.
An annual survey of the number of groundwater resources in the study areas shows that the trend of deep wells increased until 2011 and then decreased. Increasing the number of wells can increase the exploitation of groundwater levels, and unprincipled management in the exploitation of groundwater resources for agricultural development causes a drop in water levels and a decrease in the qualitative value of groundwater resources, and subsequently turns dry areas into critical centers of wind erosion (Nasirian et al., 2018).
In general, in most of the study areas, the rate of discharge from wells is much higher than that of springs and qanat. Therefore, the dominant system of groundwater exploitation is deep wells. Groundwater extraction by deep wells has increased significantly in different years, while its consequences could be seen as a direct impact on the existence of qanats, springs, and their average water supply. On the other hand, a decreasing trend in deep wells could be due to excessive extraction in previous years and well-greening events in the study area. Previously, excessive extraction of groundwater resources in the plains of the central desert such as Neyshabur (Rokni et al., 2016) and its consequences such as a water level depletion (4.8 meters in the ten years 1996- 2006), land subsidence, and a decline in water quality have been mentioned.
Also, the most water level changes have occurred in the Rashtkhar, Ivanki, and Kashmar areas, which have a deficit of -29.30, -25.50, and -18.40 meters, respectively. The annual and cumulative changes in the storage volume of the reservoir in the Central Desert watershed area during the statistical period of 1998 to 2018 show that the volume of the reservoir has decreased by 25317 MCM. The continuation of the changes in the GRI shows that the first drought occurred in 2019, while the general trend of the GRI value was decreasing.
Conclusions
Generally, in most of the study areas of the central desert integration area, the amount of discharge from wells is far more than from springs and qanats. Therefore, the dominant system of using underground water is in the form of deep and semi-deep wells. Additionally, the results indicate the unsustainable use of water to maintain and expand human activities in the largest area of Iran, located in the arid/semi-arid sector. If not controlled, such excessive use of underground water can cause environmental problems and serious socio-economic consequences. Finally, due to the unpredictability of climatic droughts and the impossibility of preventing them, it is necessary to reduce their negative effects by planning and applying proper management of underground water resources.
Keywords
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