Extraction, processing, production and display of geographic data
Hamid Ganjaeian; Fatemeh Menbari; Afshan Ghasemi; Mozhgan Nosrati
Abstract
Extended AbstractIntroductionSubsidence risk, unlike many risks such as floods and earthquakes, is insignificant and in the long run causes a lot of damage such as cracking of buildings, sloping of high facilities, destruction of agricultural lands, subsidence, etc. So the areas at risk are facing a ...
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Extended AbstractIntroductionSubsidence risk, unlike many risks such as floods and earthquakes, is insignificant and in the long run causes a lot of damage such as cracking of buildings, sloping of high facilities, destruction of agricultural lands, subsidence, etc. So the areas at risk are facing a lot of challenges. Among the areas that are at risk of subsidence are the plains of arid and semi-arid regions, including the plains of Iran. In fact, the location of a large part of Iran in the arid and semi-arid region has caused these areas to face a shortage of surface water resources, and this has led to overuse of groundwater resources in recent years and the occurrence of the risk has subsided. One of the areas that is at risk of subsidence is Kaboudar Ahang-Famenin plain in Hamadan province. Due to the lack of limiting geomorphological barriers, this plain has been associated with the development of many agricultural lands and due to the lack of sufficient surface water resources, the utilization of groundwater resources in this plain has been more than allowed and this has caused a decline. Extreme groundwater resources in this area and eventually the risk of subsidence. Due to the importance of the issue, in this study, the subsidence of Kaboudar Ahang-Famenin plain has been evaluated and the effective factors in its occurrence have been analyzed. Materials and methodsIn this study, in accordance with the subject and objectives, statistical information (information about 13 piezometric wells in the study area), library and video (radar images related to Sentinel 1 satellite, Landsat satellite images and also 30 m high digital model SRTM) has been used as research data. The tools used in the research include GMT software (to prepare subsidence mapping using radar interference and Russian SBAS time series method), Google Earth (to monitor area and identify subsidence) and ArcGIS (to prepare final maps). According to the objectives, this research has been done in three stages. In the first stage, using the digital model of 30 m altitude SRTM and Landsat satellite images, the geomorphological status and land use of the region have been studied. In the second stage, in the second stage, using information related to 13 piezometric wells, the groundwater depletion situation of the region was investigated and in the third stage, using Sentinel 1 radar images and SBAS time series method, the amount was evaluated. Subsidence of Kaboudar Ahang-Famenin plain has been studied. Discussion and resultsThe study of the altitude situation of the region shows that there is a very small difference in height between the cities of Kaboudar Ahang and Famenin and also there are no significant obstacles and landforms in this distance. Also, the study of the slope classes of the region shows that the area of Kaboudar Ahang-Famenin plain is less than 10% in the slope class and the region does not have steep and restrictive areas. According to the prepared maps, Kaboudar Ahang-Famenin plain, in terms of geomorphology, has no limiting obstacles for the development of agricultural lands as well as residential areas. In fact, the lack of restrictive barriers has led to the development of agricultural lands in this region, especially irrigated agricultural lands in recent years, and this has led to excessive pressure on groundwater resources in recent years. The results of the study of the decline in groundwater resources in the region indicate that the rate of decline in water levels during a period of 24 years has been between 14.7 (Hemehkasi well) to 78.1 (Einabad well) meters. Also, according to the calculations, most of the studied wells have faced an average of more than 2 meters of water level drop annually. Also, the results of the assessment of subsidence in the region indicate that the study area has had a subsidence of 29 to 216 mm during a period of 5 years (from 16/01/2015 to 14/01/2020). ConclusionThe results of studying the natural state of Kaboudar Ahang-Famenin plain have shown that this plain has a high subsidence potential due to its geomorphological and hydro-climatic conditions. In fact, in terms of geomorphological status, this plain is without limiting obstacles for the development of agricultural lands, and this issue has led to the development of irrigated agricultural lands regardless of environmental capabilities, including the hydro-climatic situation of the region. According to the above cases, the development of agricultural lands, regardless of the capacity of water resources in the region, has led to over-harvesting of groundwater resources and as a result, a sharp drop in groundwater levels Based on the results of the evaluation of 13 wells studied, most of the studied wells, with an average annual water level drop of more than 2 meters and this issue has caused the Kaboudar Ahang-Famenin plain during The 5-year period (from 16/01/2015 to 14/01/2020) should have a subsidence of 29 to 216 mm. Also, the results of the study of the spatial distribution of subsidence have shown that the highest amount of subsidence is related to the middle areas of the region and the distance between Kaboudar Ahang and Famenin cities, and considering that in these areas there was the highest level of groundwater loss, Therefore, it can be said that the main cause of subsidence in the region has been a sharp decline in groundwater resources. The sum of the results of this study has shown that Kaboudar Ahang-Famenin plain is in danger of subsidence and this issue has led to the emergence of numerous depressions in this plain which is a serious threat to human facilities and habitat.
Manijeh Ghahroudi Tali; Khadijeh Alinoori; Homa Rivandi
Abstract
1. Introduction Sabzevar plain is one of the areas facing subsidence phenomenon in Iran due to a sharp decline of groundwater table, development of residential areas over aqueducts or tectonics processes. The present study investigates the impact of these cases. Sabzevar County is located in a northwestern ...
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1. Introduction Sabzevar plain is one of the areas facing subsidence phenomenon in Iran due to a sharp decline of groundwater table, development of residential areas over aqueducts or tectonics processes. The present study investigates the impact of these cases. Sabzevar County is located in a northwestern plain in Khorasan on the hillside of Jogatai Mountains. Rapid agricultural development and increased water demand in recent decades have resulted in annual groundwater harvesting of about 400 million cubic meters and an annual deficit of about 30 million cubic meters in water reservoirs. The groundwater table in this plain annually experience an average decline of one meter. Despite increased precipitation in the last two years, only a 10 mm increased precipitation was recorded in Sabzevar station and the area still faces drought according to comparative analysis of rainfall. 2. Methodology Data used in the present study include 6 C-band single-look complex (SLC) images received from the ASAR sensor of Envisat. These images were captured during June, May, October, and December 2004 – 2008. Moreover, data including the groundwater table and the depth of water in local wells of Sabzevar County were collected from Khorasan Razavi Water Management Organization for the statistical period of 2003 – 2008 and 1974 – 2014. Data collected from local water wells and aqueducts were used to investigate subsidence. Following the geometric recording of the images, related interferograms were prepared. In order to calculate ground displacement, other effects were removed from the interferograms, and the effect of topography was corrected using the STRM digital elevation model (DEM) with a spatial resolution of 90 m to further improve the results. An adaptive filter was applied on the images to reduce the level of noise. In the phase correction stage, DEM produced through interferometry was used to correct the images and separate the deformation signal resulting in a differential interferogram. In order to estimate the groundwater decrease and study the resulting subsidence, the depth and groundwater level of 88 piezometers in Sabzevar were interpolated using the IDW method. Overlap methods were also used to investigate the relationship between the spatial distribution of subsidence occurrence and the location of wells, aqueducts, and faults. 3. Results Results indicates that the deformation of the area is the consequence of the high rate of subsidence in this short period of time. The maximum level of subsidence has occurred in the northeastern parts of the study area with a southwest-northeast direction starting from the hillside of Mish Mountain and moving with an increasing trend towards the hillside of Joghatay Mountain. Sabzevar and other cities of the county face an average subsidence rate of 10 cm per year. Images of displacement in the study area were obtained through interferometry and based on their overlap with subsidence. These images were then used for spatial analysis of aqueducts, wells, faults to study their impacts on subsidence. Results indicates that the subsidence rate has changed from 1 cm/year in 2007 to 14.6 cm/year in 2008. Active faults were also located in the western part of the study area across formations such as conglomerate, sandstone, red marl, and gypsum-bearing marls. Faults were generally developed perpendicular to the direction of subsidence indicating their role in downward displacement. Interpolation was performed for the 1974 – 2014 period to study long term consequences of this finding. Findings indicates that the decline in groundwater level has deteriorated moving from Sabzevar plain toward the surrounding areas. 4. Discussion and conclusion The study area was located on the hillside of Joghatay Mountain. Agricultural activities have developed in the area resulting in increased annual demand for water. Despite recent precipitations, the area still suffers from drought, decline in groundwater level, and subsidence. Results of a three-year interferometry selected from the period for which appropriate images were available have proved the occurrence of subsidence in the study area. A comparison between this image and the piezometric level in similar statistical years indicated the significant impact of groundwater level decline on subsidence. A comparison between the distribution pattern of faults, wells, and aqueducts and the subsidence area showed that a large number of wells were associated with subsidence, and the dominant faults were perpendicular to the surface of subsidence areas (Figure 1). Therefore, groundwater decline was the most important factor contributing to subsidence in this region, and long term piezometric level also have confirmed this effect. Faults perpendicular to the surface of subsidence areas might also intensify this phenomenon. In other words, further decline of groundwater table in the region will result in a higher rate of subsidence.
Shirin Mohammahkhan; Hamid Ganjaeian; Laila Garosi; Zahra Zanganetabar
Abstract
Extended Abstract
Introduction
The land subsidence is the descending or collapse of the land under the influence of natural and human factors. The land subsidence is one of the issues that are being exacerbated by human factors, including excessive exploitation of groundwater. Subsidence can affect ...
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Extended Abstract
Introduction
The land subsidence is the descending or collapse of the land under the influence of natural and human factors. The land subsidence is one of the issues that are being exacerbated by human factors, including excessive exploitation of groundwater. Subsidence can affect many constructions and facilities, causing problems for the industry, the environment, etc. This phenomenon is one of the most important environmental hazards that have been less considered than other natural phenomena due to the low human losses. The Qorveh plain is considered as one of the plains which have been introduced as a forbidden plain in the province of Kurdistan in recent years due to the over-exploitation of groundwater. Considering the amount of groundwater level drop and its direct impact on the subsidence level of the region, the present study evaluates the subsidence rate of the Qorveh plain during the period of 2017.12.19 to 2016.01.11. In this research, in order to evaluate the status of the groundwater drop, the statistical data from the Regional Water Organization of Kurdistan province has been used, and the Sentinel-1 images and the SBAS method were used (due to the unique capabilities of this method in terms of dimension, cost, time and accuracy compared to other remote sensing techniques) to estimate the subsidence rate of the region.
Material and Methods
In this research, first, the status of the groundwater of the Qorveh plain and the drop rate of its level has been investigated. Then, the subsidence rate of the area and its relation with the groundwater drop has been investigated. Radar interferometry and SBAS were used to evaluate the subsidence of the study area. Radar interferometry method is one of the most powerful tools for monitoring the subsidence phenomenon. By comparing the phases of two radar images taken from a region at two different times, this method can determine the land surface changes at that time interval. The phase taken from a feature on the land surface is proportional to its distance to the radar sensor. Therefore, making any changes in this distance affects the measured phase. In this research, the Sentinel-1 images (2017.12.19 and 2016.01.11) have been used to perform the radar interferometry.
Discussion and results
The hydrograph of the alluvial aquifer of the Qorveh plain has been provided for the water years of 1966-1676 to 2010-2011. During the 24 yeas, the groundwater level fluctuations in this plain are -13.29 meters, with an annual average of -0.55 meters. The least rate of dropping in the wells is in the wells located south of the Qorveh plain, and the rate increases toward the eastern and northeastern parts. In this research, the subsidence rate of the Qorveh Plain was estimated from 2017.12.19 to 2016.01.11 using the SBAS method. The final map indicates that during this period, the study area subsided between +61 and 216 cm, with the lowest subsidence occurring in the southern areas of the Qorveh plain, which corresponding to the sedimentary heights and slopes of Badr and Parishan and the rate has increased toward the east and west of the Qorveh plain.
Conclusion
The results of this study indicate that Qorveh Plain has witnessed a sharp drop in groundwater level over the recent years. Considering that the southern parts of the Qorveh plain corresponds to the heights and slopes of Badr and Parishan, and the rate of exploiting groundwater in these parts is lower, the rate of subsidence is less. The plain has also subsided further towards theeastern, western and northern parts and the outlet of the Shoor River, due to the growing increase of exploitation. The results indicate that the rate of subsidence is consistent with the rate of groundwater drop so that in the southern part which corresponds to the Badr and Parishan slopes, the rate was less than 10 millimeters during the period of 2017.12.19 to 2016.01.11. The results of the SBAS method indicate that the study area had subsidence of 216 mm during the 2 years and also a 61 mm uplift. Based on the final result, the highest rate of subsidence was related to the eastern and western parts of Qorveh plain and on the outskirts of the city of Dezaj and the villages of Ghasem-Abad, Shokuh-Abad, Avangan, Ganji, and others. A series of the aforementioned factors suggests that the Qorveh plain subsides about 20 centimeters per year. This is due to the over-exploitation of the groundwater. Unlike some areas where the displacement (subsidence and uplift) is due to the tectonic conditions, the results of this study have shown that in the Qorveh plain, the subsidence has a direct relationship to the drop of the groundwater. Therefore, it is necessary to monitor the use of groundwater, especially in the agricultural sector, and the rate of the exploitation should be proportional to the amount of recharge because in addition to the water shortage problems, the continuous use of the groundwater can lead to the irreversible risks of subsidence.
Zohreh Fanni; Seyyed MohammadReza Ghashami
Abstract
Extended Abstract
Introduction
The natural behaviors of the human life environment where the settlements are constructed without recognizing and studying these behaviors are called hazards. The distinctive features of natural hazards are the changes in the hazard severity in different locations, as ...
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Extended Abstract
Introduction
The natural behaviors of the human life environment where the settlements are constructed without recognizing and studying these behaviors are called hazards. The distinctive features of natural hazards are the changes in the hazard severity in different locations, as in the urban environments, human activities along with greater vulnerability in the environment, aggravate the hazard and the extent of its occurrence. The city and its infrastructure development in providing security and various needs of human are of the most substantial areas for the development of social life. In general, identifying areas prone to hazards is a key tool for decision makers to reduce the damages caused by natural hazards. On the other hand, abstract study of the nature’s behaviors in the form of flood, earthquake, land slide and subsidence has always made managerial decision-makings difficult, so that avoiding the aggravating factors of a hazard has caused to get close to another hazard.
Objectives
The main objective of this study is to evaluate areas affected by these four natural hazards in all 22 Districts of Tehran City. In other words, this research with the aim of comprehensive and integrated zoning of hazards such as flood, earthquake, landslide and subsidence has proceeded to identify, evaluate and adjust the findings in the form of a comprehensive map of the susceptibility of these behaviors under the title of four environmental hazards within the 22 districts of Tehran city.
Discussion
Multiple-risk analysis, including a range of data, provides a more realistic model of the natural environment management. In this regard, studies have been conducted on the various approaches to analyze spatial data, how to create a combination of environmental hazards and how to determine their risk and vulnerability levels. To generate a probabilistic model, the basic assumption is that the risk level is determined by risk factors and possible hazards in the future, and with an emphasis on the past events. In this study, the creating and effective factors in environmental crises are related and calculated with each other with respect to several risks.
Research Methodology
One of the usual algebraic methods is the Analytic Hierarchy Process (AHP), which, as a weighted evaluation method, evaluates different scenarios and selects the best option by combining the qualitative and quantitative factors. The Analytic Hierarchy process as one of the multi-criteria decision-making methods provides the ground for performing applied spatial analyses by examining the effects of different factors in contradiction with each other. The research method is quantitative-analytical, and all the factors affecting the occurrence of each hazard have been identified and digitized in ArcGIS environment and modeled using Frequency Ratio (FR) model. Then, each of the four susceptibility maps was combined in fuzzy method and the final susceptibility map was classified into 5 classes of very high, high, moderate, low and very low susceptibility, and was extracted and presented as a map and a table.
Results
This research resulted in the production of the susceptibility zone map for more probable hazards including flood, earthquake, landslide, and subsidence of Tehran City in the separation of 22 Districts. This map includes several factors such as slope degree, slope direction, slope shape, elevation layers, distance from the river, distance from the road, distance from the fault, geology, land use, and the rain The result show that the effective factors in flood are the distance from the river, and the slope; the most effective factors in the destruction are the wasting of groundwater and eliminating the geotechnical properties of the soil; the most effective factors in the occurrence of earthquake are the distance from the major and minor faults which determine the length of major and minor faults. Based on the results of this research and their analyses in Tehran’s districts, areas with very high, high, moderate, low and very low susceptibility were observed. Then, considering this study, their percentages were calculated in each class and reported in the form of a table. Among the 22 districts of Tehran city, districts 1, 3, 18, 5, and 4 are more susceptible than the rest of districts and districts 9, 10, 11, 12, and 17 are less susceptible in terms of the four aforementioned hazards.
Therefore, it is recommended that the process of reinforcement and standardization of existing facilities and infrastructure to be implemented by prioritizing hazardous zones. Concerning the construction and development of new infrastructure and facilities, the occurrence and exacerbation of these natural hazards within the hazardous areas may be prevented by imposing restriction or not issuing construction permits.
