جستجوی مقالات مرتبط با کلیدواژه « فرونشست زمین » در نشریات گروه « محیط زیست »

Mamloo dam in Tehran province has been built to meet the needs of agricultural water in Varamin plain, but due to the drinking water supply in Tehran, a limited amount of stored water is supplied to the plain. One of the most important effects of the insufficient supply of surface water in Varamin plain is the reduction of groundwater aquifers and land subsidence. In this study, the effect of the Mamloo dam on land subsidence in the Varamin plain was investigated.

The changes in groundwater level and the unit hydrograph of the plain and quantitative changes of groundwater in the study area of Varamin plain located downstream of the dam were studied and analyzed in two periods before and after the operation of the Mamloo dam.

Based on the results obtained from the selected piezometric network and according to the division of the study area into northern and southern regions, the greatest amount of decline was in the northern part. After the construction of the Mamloo Dam, new evacuation points were created based on the potential maps in the northern and central parts, where the population and agriculture centers were located. In the south, due to the type of geological structure and less alluvial thickness, the emptying of the pores of the aqueous layer has led to subsidence in some areas. Finally, the adaptation of the areas with the greatest decrease in groundwater discharge to the areas with the highest vertical displacement in the southern and central regions in the radar maps was quite clear.

By investigating the results obtained from the analysis of the drop of piezometers in the study area of ​​Varamin plain and the expansion of the number and depth of deep wells in the mentioned plain, the change in the underground water flow regime and the reduction of the aquifer volume are clear. After the construction of the Mamloo dam, the amount of this drop has increased, especially in the lands of the northern part. In addition, the lack of proper planning in meeting the needs of the agricultural sector of the plain, which has a major share in the consumption of water obtained from underground sources, has caused major challenges in the climatic and social conditions downstream of the dam. Due to the construction of the Mamloo dam at the entrance of the Jajrood River to Varamin plain, the level of the water table has decreased over time due to the significant reduction of surface flow to the region. This decrease had higher values ​​in the northern half of the plain and in the areas where the thickness of alluvium is greater. Based on the output of satellite and subsidence maps, the areas that experienced more discharge and drop during the statistical period correspond to the areas with more subsidence in the subsidence maps.

One of the major challenges of groundwater is its over-consumption in agriculture. Therefore, it is necessary to pay attention to water resources management to prevent the drop in groundwater levels. Chahardoli Plain in Hamadan Province has faced an increase in groundwater abstraction in recent years due to the lack of surface water resources. In this study, due to limited water resources and irregular use of groundwater, the drop in water level and its management in the aquifer of Chahardoli Plain of Asadabad was considered.

This is an applied study in which both documentary and survey methods were used for data collection. In the documentary method, the statistics of annual rainfall in a 27-year period of the General Meteorological Department of the province, and the amount of groundwater level drop (43 wells) were used. In the survey method, interviews with farmers that used groundwater resources of Chahardoli Plain (56 subjects), experts of the regional water company (40 subjects), and the necessary tools were designed to investigate the decrease in groundwater level and its side effects. Cronbach's alpha of the instrument was 0.86, which showed that it had good reliability.

The results showed that the groundwater level has dropped by an average of 67.1 cm per year over 27 years. In contrast, the rainfall chart showed an average of 303.3 mm of precipitation per year. The overall slope of the equation for the drop in groundwater level data was -0.77 m and the overall slope of the equation for the rainfall data was 0.083 mm. This means that the slope of the groundwater was higher than the slope of the increase in rainfall. Meanwhile, the SPI index was negative in the first 21 years. The correlation coefficient between the drop in water level and precipitation was equal to r = 0.14 and p = 0.08. This showed that the relationship between groundwater level drop and precipitation was not significant. In order to interview farmers and experts on water management problems, according to the results, nine factors were examined and prioritized from the perspective of participants. Participating in farm water management courses from the experts' point of view and the existence of educational programs on radio and television for the farmers were the two main priorities. The priorities of farmers and experts regarding the factors of responsibility, risk-taking, and understanding the severity of water resource degradation were quite similar. In the case of water resources protection, non-leveling of lands was the first priority of both groups of experts and farmers. In the planning section, the first priority of farmers and experts was to develop optimal water distribution laws for the optimal use of water resources. In the case of water productivity management, the first priority of both was to replace rain-fed crops with products with high water requirements. In financial problems, according to experts, the lack of a proper and timely budget was the first priority, while farmers considered it to be reducing the price of manufactured products at the time of sale.

The results showed that management problems were related to the drop in groundwater levels in the region. Considering the consensus of experts and farmers on taking responsibility for the destruction of water resources and the effectiveness of educational programs, it seems that the preparation of educational programs on radio and television, and improving educational programs of regional water departments and agricultural institutions will increase the desire to maintain groundwater. According to the results, the decrease of groundwater level is not related to the amount of precipitation and human factors have a more important role in this regard. Therefore, all users of the plain, i.e. farmers, experts, officials in charge of water resources, agricultural jihad, and the environmental organizations have a role in reducing this problem. Therefore, these organizations should prioritize their goals in codified and integrated plans for short-term and long-term plans to conserve groundwater resources. Also, according to the results of the research, the downward trend of the aquifer level will continue in the next few years, which necessitates a serious review of water abstraction laws in the plain.

Land subsidence occurs more slowly and gradually in comparison with other natural hazards, such as floods and earthquakes; therefore, it has received much less attention from human communities. However, the subsidence over time causes irreparable damage to the structure of underground aquifers, vital infrastructure such as roads, power lines, and urban structures. In this study, in order to monitor land subsidence in Chahardoli and Qorveh plains located in Hamadan and Kurdistan Provinces, the method of Permanent Scatterer (PS) was used using 59 images of Sentinel satellite in ascending passage and 58 images in descending passage. According to the average displacement of PSs in the region between Hassan Abad Emam and Ahutapeh villages of Asadabad city located in Chahardoli plain of Hamadan Province, displacement in the form of subsidence for Ahutapeh and Hassan Abad Emam villages respectively about -170 and -166 mm was happened in the time period of 2017-2018. Moreover, the research found that the subsidence in the northern part of Chahardoli plain in Hamadan Province is much more than the subsidence in the southern part of Chahardoli plain in Kurdistan Province. In order to find the cause of subsidence, the approach of examining the information of piezometric wells in the region and their changes over time was used. In this regard, it can be concluded that the land subsidence in Qorveh plain and Chahardoli plain of Hamadan and Kurdistan provinces can be attributed to the uncontrolled extraction of groundwater resources.