جستجوی مقالات مرتبط با کلیدواژه « فرونشست زمین » در نشریات گروه « علوم پایه »

Natural hazards are one of the factors that cause financial loss every year, and they occur in most regions of the world, including Iran. One of the hazards that mankind has been dealing with in recent decades, especially in alluvial plains is the phenomenon of land subsidence and sinkhole. Land subsidence and sinkhole due to natural and human causes have been reported in many places. Subsidence or sinkhole will damage human structures that are supported by the earth. Land subsidence is the most important environmental problem in Iran. A major cause of this phenomenon is overexploitation of underground water resources has led to land subsidence, and underground water extraction plays an important role in causing land subsidence. The study area is Abarkooh plain with an area of about 250 square kilometers is a part of the Eqlid-Abarkooh watershed. The lowlands are covered by Quaternary alluvial and some older sediments such as unconsolidated conglomerate, clayey, sandy, and saline areas. Based on geographical location, the study area is located in the geographical range of 53 degrees to 53 degrees and 32 minutes east longitude and 30 degrees and 50 minutes to 31 degrees and 12 minutes north latitude. This area contains medium to fine alluvial fan sediments that end in the salt playa or Abarkooh desert. To determine the high-risk and low-risk areas and routes in the study area, to discover subsurface holes and stratigraphic fractures underground up to a depth of 5 meters and the safe route for contracting works, etc., was used the ground penetrating radar (GPR) method. The results showed that in the areas where there are sinkhole traces in the determined distances around in current research, the attenuation signal of the ground penetrating radar, including the effects of subsurface cavities and stratigraphic fractures was discovered and revealed by GPR. On the side of the mountain slopes and high altitudes in the upstream region, no signal attenuation was observed, and sediments and soil were observed uniformly underground. The ultimate goal of the GPR section is to obtain a cross-section that is most consistent with the geological realities of the region and finally, at the final stage, we can talk about the characteristics, effects, and objectives of the research. The GPR method is an easy and low-cost method that is widely used in the field of natural resources and it is also used in other scientific fields. Regarding the common phenomenon of subsidence and sinkhole, these effects can be found underground, so that humans can prevent the development and expansion of this phenomenon. Also, this method can determine the route and safe area for contracting works, urban development, etc.

Subsidence is affectedby several factors, the most important and most common of which is excessive groundwater extraction from alluvial aquifers and, conversely, reduced aquifer recharging.Subsidence of the Damaneh-Daran plain, like many of the country's plains has recently expanded.The alluvial aquifer of the plain is unconfined, but part of it operates confined due to lithological diversity and has the potential for subsidence.In this regard, in this paper,first the subsidence rate inthe aquifer was determined by radar interferometer method and the results showed that the subsidence is almost spread in most of the southeastern part of the plain and its maximum is about 6.38 cm.In order to correlate the drop in water level in the aquifer with land subsidence, the aquifer model was prepared by finite difference method, which indicates an alluvial aquifer tank deficit of 33.8 million cubic meters. Prediction of groundwater level due to50% reduction of pumpingfrom the aquifer compared to current pumps showed thatthe predicted water level shows a correlation of more than70% in thesoutheastern part of the aquiferwhere similar conditions of the aquifer are confined with subsidence and indicates its significant effect on reducing subsidence in the aquifer.The results of this study show that oneof the most important proposed solutions to control the current state is to reduce the exploitation of groundwaterresources at least 50%, which can be important bymodifying the licenses of wellsand then closely monitoring the allowable abstraction. It can be done through the installation of smart meters and the optimaluse of water inthe agricultural sector.

The phenomenon of land subsidence, which is affected by human activities and various geological and hydrogeological parameters, is occurring in different parts of Iran. Land subsidence susceptibility mapping is a necessary prerequisite for land subsidence management. Proper assessment of land subsidence requires the determination of parameters affecting land subsidence to discover the spatial relationships between them and land subsidence. For this purpose, first, according to the land site subsidence, eight parameters affecting the subsidence in the Damaneh-Daran plain, two models were prepared. In the first model, eight parameters including annual groundwater level drawdown, aquifer medium, land use, pumping volume, aquifer thickness, net charge, distance from fault and topography called WALPSRFT based on weighting parameters and the second model based on optimization and compatibility of eight effective layers in subsidence, Was prepared by AHP-Fuzzy2 method and the final map of land subsidence vulnerability was obtained by combining layers in ArcGIS. Radar images and a Radar Interferometer (InSAR) were used to validate the models. The results show that both maps show a good correlation with radar data, and the map prepared by the hierarchical-fuzzy method shows the highest correlation with real radar data and subsidence in the plain. It separates in more detail on the whole surface of the plain. According to this model, most areas of the plain, especially the eastern part, are subject to subsidence, and management programs should be considered to control subsidence.

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.

Due to the consequences of falling groundwater levels in this study, land subsidence in Shahriar and Mallard plains due to groundwater abstraction has been investigated and its impact on infrastructure is investigated and determined. For this purpose, after collecting the statistics of water wells in the region and determining the characteristics of the aquifer and items such as depth of groundwater level, annual harvest and distribution of wells, the initial data were obtained, then by specifying the thickness of alluvium and layers Sediment taro of the bedrock of the area was identified from exploratory boreholes and well logs, diversity of stratification and sediment type in the area. Determining the immediate and consolidation meeting, the annual subsidence rate is calculated and the amount of subsidence in the study area is determined through satellite data from 2014 to 2020. During these years, the results showed that the highest subsidence rate in the region is 8 cm.

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 is a nonlinear and complex process that data-driven computational intelligence models can model it. In this study, the accuracy and efficiency of hybrid fuzzy logic gene expression planning hybrid model in estimating land subsidence risk and its factors in Varamin aquifer standardized. For this purpose, after selecting and gathering information from 15 factors affecting the subsidence event based on research records in the GIS environment, they were first standardized by fuzzy membership functions and then gene expression programming method was used to integrate the layers. Finally, using seven important statistical benchmarks based on radar image data, the model was validated in 4 different scenarios in input data and operators. The results showed scenario 1 with input parameters of bedrock level, Debi of pumping wells, groundwater drawdown, geology and operators, +, - ×, ÷, sqr, exp, Ln, ^ 2, ^ 3,3Rt, sin, cos, Atan, is the best model in training and testing. Accordingly, the groundwater drawdown parameter had the highest effect on land subsidence in the study area.

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.

Land subsidence is one of natural hazards which is involved with most of plains in Iran and leads to damages of urban area, roads, bridges, power transmission lines, agriculture lands, wells and piezometers. Generally, regional subsidence is depended to human activities such as overexploitation of groundwater and geological conditions which can induce considerable damages to economical basis of the area if it be occurred. In the last few decades, the rapid development of agriculture and the increase in the need for water has led to overexploitation of groundwater in the Semnan plain. In this paper, the occurrences pattern of regional subsidence phenomenon in the south and south-east of the Semnan plain and also the zoning of this region in terms of the susceptibly of land subsidence have been discussed. In this research at the first step data of 18 piezometers for 24 years period (May 1993-2017) were used to provide iso-potential lines of drawdown groundwater level and unite hydrograph of the plain. Furthermore, for the determination of type and thickness of the subsurface layers some data including piezoelectric log, geoelectric studies and geological map with a scale of 1: 250,000 were used. Then, using the drawdown groundwater level map and the subsurface layers conditions map, a subsidence susceptibility map of the Semnan plain was prepared. The results showed that during the period of 1993-2018 continuous overexploitation of groundwater caused a drop of 18.9 meters of groundwater level and provided conditions for consolidation of clayey layers and land subsidence. The subsidence hazard zonation map indicates that the region with a high potential of subsidence in this plain is located in the northeastern part of the plain and in the south-southwest of the Semnan industrial park.

Mashhad city, the second largest metropolis of Iran, is located in an arid and semi-arid region. Overexploitation of groundwater in Mashhad plain has caused up to 22.5-meter drop in the groundwater level from 1984 to 2013. The groundwater depletion in the unconsolidated aquifer has resulted in subsidence and cracks on the land surface. To determine the land subsidence rate map and the reasons for hot spot subsidence, the latest Envisat images of the ESA Space Agency's Archive for Mashhad plain were used. leveling and GPS data were combined with the radar interferometry results and the annual subsidence rate maps with high precision were obtained. Finally, the geology and soil texture maps of study area are compared to the land subsidence map.
Methods and

To assess the land subsidence in Mashhad plain three methods of leveling, GPS and Insar are used. Leveling data are available in three profile of of Mashhad-Quchan (BCBD), Mashhad-Kalat (BDBE) and Mashhad-Sarakhs (BEBN) in two time interval of 1994-2003. The highest rates of subsidence in the BCBD, BDBE and BEBN lines are 7, 3.5 and 8.1 cm/year, respectively. Six permanent GPS stations have been installed in Mashhad plain, among them, NFRD, GOLM and TOUS have recorded the land subsidence, with the highest annual rate of 21.2 cm/year at TOUS Station. The third method applied to assess the history of land subsidence was InSAR radar interferometry which provided the extent and pattern of subsidence in all of the study area. For this, 23 images of the Envisat ASAR are processed during the 05/24/2010 to 06/30/2003 time period. The highest subsidence rate estimated by this method was 32 cm/year in the northwest of Mashhad. In general, two subsidence bowls, in the northwest and south east of Mashhad city are identified. Fig. 1 shows the annual subsidence rate map in Mashhad plain. Using the root-mean-square error (RMSE), the accuracy of the InSAR method was verified with GPS and leveling data.

The rate and distribution of land subsidence in Mashhad plain are affected by geological factors such as soil texture, deposit thickness, geological structures and groundwater drawdown. The geological and geophysical studies and exploratory drilling results in the Mashhad Plain indicate that the bedrock morphology is very rough. The bedrock outcrops in some places while in some other places covered by more than 300 meters alluvial deposits. Generally, by distance from the mountain, alluvium thickness and as a result the likelihood of subsidence would be increased. Mashhad plain is surrounded by the active and quaternary faults in the north and south edges. In the north of Mashhad plain Marly bedrock is uplifted by Tous fault and outcropped in the north of fault. In the south of Mashhad two normal faults have resulted to the increase of alluvium thickness in south and central of Mashhad plain. The change of river pathway also let to deposition of a sequence of the fine-grained and coarse-grained soils in central of plain between Toos and southern branch of South Mashhad fault (F2).used to draw the cross sectionIn order to evaluate the subsurface conditions and its effect on the land subsidence, the soil texture are studied using the deep water wells and piezometers log (Figure 2). Fig. 3 shows the longitudinal section (northwest to southeast) of the area. As it can be observed, the soil texture includes of alternation of fine and coarse grains layers (Figs. 4). In this condition, sandy soils help to shortening the drain path of clayey layers and leads to acceleration of the consolidation. The average rate of annual subsidence in the area is 14 cm for one meter of drop in the groundwater level.Nowadays, in the urban area, due to the urban sewage waters, there is a rising of groundwater level.  Therefore, no land subsidence has occurred in the central parts of the city. It is expected by completion of urban sewage network about 62 million cubic meters of sewage water will be eliminated from the aquifer recharge, which will cause a notable drop in the groundwater level and prominent land subsidence in specific area of the city. Considering the geological conditions and the operation of the existing faults, it is expected that in the case of groundwater drop, no significant subsidence will occur in south of the F2 fault, due to the decrease in the alluvium thickness and to the coarse texture of the soil. But in the northern and northeastern parts of the city, which are located between F2 and the Tous faults, high rate of land subsidence is expected.
Figure 4: The cross section of soil texture and the annual average rate of land subsidence and groundwater level drop

Using the radar interferometry processing, the highest annual rate of subsidence in Mashhad plain is about 32 cm/year. Land subsidence in Mashhad plain has an increasing trend and the geological conditions have a critical role in the subsidence rate and its pattern. Generally, soil texture near the mountain area in South is coarse and grain size decreases toward the center of the plain. But because the outcrop of Marly formation in the north slopes, soil texture is mainly fine grains. In the center of Mashhad plain soil texture constituted of fine and coarse grains which are converted together as inter fingering facieses, which have a critical role in decreasing of the consolidation time and increasing the land subsidence rate. It is predicted by complimenting of the urban wastewater network, the groundwater level will be dropped in the city area and the northwest and southeast subsidence ellipsoids which already can be seen will be connected together. Therefore, the area between F2 and Toos faults, will be shown the highest rate of subsidence, due to high thickness and fine-grained soil texture.

Semnan plain is located on the northern edge of Iran's central desert and has a semi-arid climate. In recent decades, rapid population growth, increasing Industrial areas and water demand has led to excessive extraction of groundwater resources. As a result, the crisis of the severity of the decline in groundwater levels and ground subsidence in Semnan plain was reported. Satellite imagery interferometry (InSAR) monitoring in the specific period of 2003 to 2004 shows that maximum of 133 mm of ground subsidence in Semnan city has been occurred. The factors affecting the ground subsidence of Semnan plain were investigated by drawing hydrographic charts of groundwater level using the results of 15 observational wells. Continuous drawdown of groundwater levels can be seen during the water period of 2003 to 2009. Minimum rate of decline in groundwater level equal to 22 centimeters per year was reported. Merging the results of ground subsidence and decline of groundwater level illuminated the exploitation of groundwater resources over the aquifer recharge rate which increases the effective stress in soil layers and thus sediments high consolidation. This was the key factor for subsidence in Semnan plain with respect to the geotechnical properties of the aquifer. Therefore, water resources management was recommended for sustainable development of agriculture and industry.

Land subsidence is an environmental phenomenon that involves gradual or sudden settlement of the land surface because of compaction of underground material. Groundwater withdrawal، which occurs due to excessive use of water resources، is among the most important reasons for this phenomenon. Therefore، land subsidence can lead to destructive results in residential، industrial and agricultural areas. As a result، subsidence caused by excessive use of groundwater resources has occurred in many countries in the world. Tehran metropolitan plain in Iran is one of the most obvious examples، where land subsidence is happening. Although the relationship between land subsidence، groundwater level decline and changes in the physical properties of subsurface material is broadly understood، a comprehensive and precise model to predict land subsidence remains unconstrained. Land subsidence modeling is a complicated matter in geological engineering but can help to better understand subsidence and possibly prevent damages. The commonly used numerical methods for modeling land subsidence are generally based on simple assumptions، which make the model results to be associated with some errors. In this study، artificial intelligent methods such as Artificial Neural Networks (ANN) were used to propose a new method to predict land subsidence. The efficiency of this method was then tested in the South Tehran plain as a case study. We have used hydrological، geotechnical، remote sensing and ambient vibrations for site effect investigations. First، the collected data was studied statistically. Then، the delay between groundwater withdrawal and subsidence was computed by genetic algorithms using available hydrographs and GPS data in a period of 27 months. Model input parameters include changes in groundwater level، natural frequency of soil، alluvial thickness، defined geographic coordinates and time. The model output was an estimated subsidence measured by radar interferometry method. The model was built in 15 time steps using a set of data having 4 months of time difference with the data used to create the model. The comparison between the predicted (modeled) and real (measured by remote sensing) subsidence shows a good correlation، which makes the proposed model reliable.

Generally, alluvial basins of arid and semiarid zones are the places with excessive groundwater withdrawal, and also they have a high potential for land subsidence. Excessive groundwater withdrawals have caused severe land subsidence in Tehran, Iran. At present, the maximum land subsidence rate is 36 cm/year, covering an area of nearly 530 km2. In the 2000s, as a result of economic and population growth, the area of groundwater withdrawals expanded to both the west and the east. Over the past 28 years, groundwater level has decreased 11.65 m. As a result, the impacts of land subsidence, such as major drop in groundwater level, damage and tilting of buildings and civil structures, and rupture of well casings, have increased in the southwest of Tehran. In accordance with the field and laboratory data, we have constructed a new conceptual model for alluvial basin recognition of the study area. This model describes various hydro-geological units according to their physical properties. Based on this model, a multi-layered aquifer system in southwest plain of Tehran includes three aquifer units and three aquitard units.

Based on recent research by geological survey of Iran (GSI), an extensive subsidence area was observed in Hashtgerd plain (Tehran province). The geographical position of this area is 35° 47' 45" to 35° 03' 05" N and 50° 29' 05" to 50° 54' 28" E. The maximum and mean rates of this subsidence are 16 and 8.4 cm per year. In general, the main aquifer of plain is composed of Kahrizak and Tehran formations. These formations are alluvium type. The Kahrizak formation consists of gravel, sand and silt. This formation scatters in north of plain. Tehran formation is composed of pebble, gravel, sand and clay in fluvial cone form. Toward the center and south of plain the amount of fine material increases. The subsidence is shown in Tehran formation only. Based on geoelectrical and well-logs data, the confined to semi confined aquifer area is recognized in south and west of Hashtgerd plain. This area is in accordance with subsidence area. In the upper part of confined aquifer we can find an unconfined aquifer. The whole of penetrated water from surface of plain recharges the unconfined aquifer. The extortion of water from confined aquifer and unconfined aquifer in north of plain has caused subsidence phenomena. The unique recharge resources of confined aquifer is unconfined aquifer in north of plain. To take notice of the position and properties of confined and unconfined aquifers in this place is very important in suitable planning and management to prevent and mitigate subsidence occurrence in future.