جستجوی مقالات مرتبط با کلیدواژه "سازند گچساران" در نشریات گروه "جغرافیا"

Determining the type of relationship between different components of soil erosion can provide more complete information about the performance of these components in different watersheds and land uses. In this study, in order to determine the type of relationship between different components of soil erosion in different land uses of Gachsaran Formation deposits, a part of Kuhe Gach watershed with an area of 1202 hectares was selected. In this study, using univariate regression, the type of relationships between sediment - runoff, sediment - infiltration, sediment - runoff and erosion threshold, runoff - infiltration, runoff - runoff and erosion threshold, infiltration - runoff and erosion threshold were determined and also, the relationship between them was also examined. Sampling of erosion different components at 6 points with 3 replicates and at different rainfall intensities of 0.75, 1 and 1.25 mm/min in three land uses of the range, residential area and agricultural lands using a rain simulator was performed. SPSS and EXCEL software were used for statistical analysis. The results showed that in general in the intensity of 0.75 mm/min in all three land uses, range, agricultural and residential and in the relationship between all the different components of soil erosion in seven cases, there is a positive relationship and in eleven cases, there is a negative relationship. And at an intensity of 1 mm/min in all three rang, agricultural and residential land uses and in the relationship between all the different components of soil erosion in seven cases, there is a positive relationship and in eleven cases, there is a negative relationship. And at an intensity of 1.25 mm/min in all three uses of the range, agricultural and residential land uses and in the relationship between all the different components of soil erosion in eight cases, there is a positive relationship and in ten cases, a negative relationship.

Mainly containing thin gypsum units, evaporite formations cover 8% of the Earth's surface and 25% of the Earth's continental surface (Ford and Williams, 2007). The term karst refers to a set of geological processes and the phenomena resulting from the dissolution of carbonate rocks. Decomposing the structure of the rocks forms a unique hydrological regime, leading to the development of special landforms (Ministry of Power, TAMAB, 1994). In general, the eight elements needed to develop a karst are: precipitation, relief, lithology, thickness of carbonate layers, carbon, low temperature, pressure, and tectonic rocks (White, 1988). Sinkholes are the enclosed depressions that are known as the characteristic of carbonate and evaporite karst landscapes. In recent years, several genetic classifications have been published for sinkholes (Gutierrez et al., 2008).

To conduct this research, a 160,000-m2 area of the Gachsaran formation in Maroon plain with a high density of sinkhole was examined and visited. The exact geographical location and specifications of 51 sinkholes were surveyed, and it was found that the sinkholes totally account for 25% of the surveyed area. Table 1 lists the specifications of the sinkholes. Also, in another field visit conducted in this study area, a sub-basin with an area of 6.2 hectares, average slope of 28%, and length of 2301.7 m was selected for the surface runoff sampling during the precipitation, which also included a number of previously surveyed sinkholes. The surface runoff samples taken included the first moment of runoff onset, which began 3 hours and 27 minutes after the start of precipitation. Then, 5:19, 5:45, 8:10, 9, and 9:20 after the start of precipitation, other samples of surface runoff were taken again to monitor the changes in the ions dissolved in the runoff in the spatial and temporal intervals. The minimum height of this sub-basin is 520 m, and its maximum height is 888 m above sea level. Also, in this regard, to estimate the average long-term rainfall of the region from the 20-year rainfall data of the meteorological stations in the study area, the daily rainfall data of the Maroon meteorological station in the vicinity of the study area, 1:100,000 geological map of Behbahan sheet, 1:50,000 topography, and 10-m DEM of the study area were used as the research data.

The obtained results showed that a total of 25% of the surveyed area is covered with the surface and visible sinkholes. It should also be noted that the dissolution in the Gachsaran formation is not the only erosion process that is taking place. In addition to the dissolution of gypsum, the marls of this formation are eroded by the surface runoff due to the precipitation and leave the basin as a suspended load, which accelerates the formation of sinkholes. Therefore, it can be stated that the time interval estimated in this study can be shorter, because the effect of the accelerating factor of the suspended load was not calculated, which requires the investigation and study to calculate the suspended load. Directing the runoff by sinkholes to downstream areas is likely to lead to the same expansion of the underground karst and tunnel, which is not visible. Also, it is not clear how many cavities and tunnels formed in the subsurface of this area, but this is not expected to be low based on the obtained results. There are roads, agricultural lands and, more importantly, residential areas on the gypsum zones, at least 25% of which are visible sinkholes, and the subsurface tunnels that are expanding every year at this dissolution rate. In addition to the effective rainfall, the presence of agricultural lands requiring continuous irrigation and intensifying the dissolution rate can lead to surface collapses and expansion of sinkholes, which ultimately threatens the life and financial security of the inhabitants in these areas.

Based on the field observations and the conducted studies, the sinkholes in the stream course have a generally elongated form and often have several ponors. Given that the sinkholes do not retain the aggregated runoff inside the sinkhole and the runoff exits through the same ponors, such diversity in the number of ponors results in a number of sinkholes in the stream course, which are connected together through a subsurface path. Unlike calcareous sinkholes that can direct the runoff current to karst aquifers, water is rapidly saturated due to the high solubility of gypsum. The dissolution is mainly limited to the opening area of the sinkhole, and less runoff finds the opportunity to expand the sinkhole in depth. It should be noted that based on the results, to increase the safety factor and reduce the risk of gypsum dissolution, it is necessary to monitor and study the subsurface area and to examine the subsurface cavities and tunnels that have formed so far. Finally, to reduce the risks of the dissolution rate, some arrangements such as sinkhole risk zoning should be made. This is because the cavities in the gypsum layers with the high dissolution rate can easily expand and prepare the conditions for the sudden collapse so that the whole plain suffers the collapse, incurring human and financial losses.

The presence of formations containing gypsum layers will enhance the formation of gypsum karst forms. The thickness of the gypsum layers and the quality of the mentioned beds influence the formation of such landforms. The Maroon plain is located in the folded zone of the Zagros Mountains in Kohgiluyeh and Boyer-Ahmad Province. The existence of the Gachsaran Formation and occurrence the karst phenomena (among which sinkholes are the most significant) in this plain have a very destructive impact on the roads, facilities, farmlands, residential units, and the reservoir of the Maroon Dam located in the plain; but unfortunately, this phenomenon is not well-known and well-studied. In this research, karst evolution zoning map was prepared using the fuzzy model; to produce this map, ten environmental factors including the slope, slope direction, geology, distance from Knick line, distance from flow line, distance from the river, elevation, land use, climate, and the NDVI Index were used. The results of this study demonstrated that 55.2% of the study area is situated in the zero-risk zone because it is situated out of the Gachsaran Formation realm and lacks the gypsum layers; as well, 11.2% of the area is in the high-risk zone, 18.5% in the medium-risk zone, and 15.1% in the low-risk zone. Field observations and studying the zoning map indicate that the main factors influencing on the karst evolution of this area are slope and streamlines which superimposed on the gypsum layers.

The erodibility of watershed area is a function of several factor, one of these factors is topography. Including main topography features is slope aspect of which directly or with the effect on other environmental factors is caused changes in soil hydrological processes particularly the potential for runoff and sediment production. Soil erosion is the most important environmental factor in the world that adversely affects all-natural ecosystems as well as those under human management. Although soil erosion has existed throughout history, it has been intensified in recent years due to improper land use. Environmental factors, such as climate situation, topography, soil, and land use affect sediment formation in watershed areas. Aghajari formation is among the most erodible in Iran. Aghajari formation, covered with Bakhtiari conglomerate, is located on Mishan marl formation. This marl formation was formed between Pliocene and Miocene. Aghajari formation consists of gray and brown calcareous sandstone, gypsum red marl, and siltstone. Its main section spreads from Omidiyeh to the Aghajari oil field and it has a thickness of 2965 meters. The presence of gypsum marls has made Aghajari formation apt to erosions of different kinds, especially surface erosion, rill erosion, badland, and mass movement. One of the most eridibility of Iran is the Gahsaran formation. Gahsaran formation has oil industries that yearly thousands of tons of sulfur and carbon dioxide interpolate into the air. And it can be caused by acidic rainfall. Thus investigating the role of acidic rainfall on soil erosion and sediment production in these areas is necessary. Gahsaran formation has a thickness of about 1600 meters. A viewpoint of lithology is consisting of salt, anhydrite, colorful lime, and some shale. Gahsaran formation age is lower Miocene.

In this investigation in order to investigate sensitivity to the erosion and sediment yield the main aspect of slope of Aghajari and Gachsaran formation deposits, part of margha and kuhe gach watershed areas in Izeh Township respectively with the area of 1202 and 1609 hectares was elected. In this investigation in order to determine productivity runoff and sediment in 8 points and with 3 replicates in Gachsaran formation and in 8 points and with 3 replicates in Aghajari replicates in rainfall intensities 1 and 1/25 mm in min in 4 slope aspect; northern, southern, eastern and western with using of kamphorst rain simulator was done. In order to analyze statistical from SPSS and EXCELL was used. The study utilized the Kamphorst rainfall simulator. This fully standardized, easily portable rainfall simulator was designed to cover a plot area of 625 cm2. The rainfall simulator is used to determine the characteristics of soil, erosion, water infiltration, and is also suitable for soil research. It is a standard method to use it to determine the erodibility of surface deposits. The experimental plot area of 625 cm2 with a smooth gradient was selected, which was the representative of the main slope aspects. Meanwhile, the Kamphorst rainfall simulator was installed at the height of 200 cm to reach to raindrop boundary velocity.

The highest of sediment rate in both Gachsaran and aghajari formations in rainfall intensities 1, 1/25 mm in min is belonged to eastern slope aspects. The highest of runoff rate in aghajari formation is belonged to northern slope aspect and in Gachsaran formation is belonged to southern slope aspect. There was a significant difference in the south-east, south-west slopes in comparison of the amount of sediment produced in different aspects of the slope in the Aghajari Formation at the intensity of 1 mm/min. But, there was a significant difference in the amount of runoff produced and permeability of north-west slopes. And at 1.25 mm/min intensity, sediment production in south-east and south-west slopes showed a significant difference. But runoff was significantly different in north-south, north-east and north-west slopes. In terms of sediment production in Gachsaran and Aghajari formations, the total rate was highest at two intensities of 1 and 1.25 mm/min in the eastern slope. But, in terms of runoff in Aghajari Formation, the northern slopes have the highest runoff and in Gachsaran Formation, the southern slopes have the highest runoff. And, in terms of permeability in Aghajari Formation, the southern slopes and in the Gachsaran Formation, the western slopes have the highest penetration rate in the two intensities.

The rate of productivity sediment also in Aghajari formation in both mentioned intensities is more than Gachsaran formation. But the rate of productivity runoff in mentioned intensities in Gachsaran formation is more than Aghajari formation. The rate of changes in productivity sediment and runoff in various slope aspects in both formations also significance difference showed.Key words: Soil erosion, Sediment production, Aghajari formation, Rain simulator, Gachsaran formation

Satellite imagery is considered as one of the most important tools of land resource management, due to the wide vision that emerges from one area and its regular repeated coverage. Using remote sensing technology, in particular radar interferometry (InSAR), it is possible to study the movements and changes caused by phenomena such as earthquakes, volcanoes, glaciers, landslides, salt diopters, and other irregular phenomena. In this research, differential radar interferometry was used to illustrate the displacement of the Earth's surface within the Gotvand Dam area and to investigate the short-term and long-term changes in the incident. There have been several studies conducted to investigate the effects of water reservoirs of lakes and dams, as well as the processing of satellite images of landslides and subsidence. For example, Haghighat-Mehr et al. (2010), using Radar interferometry technique to determine the subsidence rate and Landsat slides of the Hashtgerd plain, used 4 images of the ENVISAT radar during the 4-month period (July 11, 2008 to October 24, 2008), and estimated that the maximum rate of downslope in the plain was 35 mm per month. In addition, Jennat et al. (2009) used the radar interferometry method to determine the surface deformation in the Golpayegan Plain. In the current research, differential radar interferometry was used to illustrate the displacement of the Earth's surface within the Gotvand Dam area and to investigate the short-term and long-term changes in the incident. The term interferometry is derived from the combination of two words including interference and measurement meaning that two waves interact on the surface of the earth. Radar interferometry technique is the combination of two electromagnetic waves on the surface of the earth and the synthetic valve radar technique (Dehghan, 1391). This technique is based on the difference in the ground-back signal phases in two SAR images taken with a time delay or with parallax from an area to extract altitude or information on land surface changes. In order to do this research, 4 images of the SLC Band C, the ASAR satellite ENVISAT for the period of 2007 to 2011, were taken as a research project from the European Space Center with an area of 100 × 100 km2. Through processing of the images with a time interval of one year and more than one year, 4 independent interferograms were obtained. The SRTM DEM region with a resolution of 90 m was used to remove the topographic effects of interferograms. Interfragm processing was performed using Sarscape software. The DOR-VOR file containing the DORIS satellite image capturing information from the European Space Agency was used to correct image distortion caused by the gravitational force of the moon on images. In the first phase of the analysis chain, the data was designed with the aim of constructing the interferometer. Due to the different resolution of this sensor along the radial mile radius (7/80 m) and azimuth (4/5 m), the power dissipation information in line with the range can be converted to the resolution of the earth according to equation (7). A differential interferometer derived from the removal of the topographic effects in the previous stage contains noises that result from the time difference or the time interval received by two radar images. It can also be due to the difference in the basis of the spatial base as well as the resulting spots that have no signal and may result in lower interference imaging; therefore, it is necessary to remove the effects of noise from interference by implementing adaptive filters. Subsequently, the final results of this phase, with the help of Digital Ground Modeling (DTM), were transmitted to Arc GIS for thematic maps. Finally, the results of the landslide detection at the region level, by using field survey and its adaptation to existing information, was controlled and evaluated in the Google Earth environment.
Result, Discussion and The results of this study indicated that the maximum displacement rate in the region reaches about 3.5 cm per year (from 2007 to 2011). To obtain the final landslide map in the area, after processing the pair of radar images, the existing displacements were identified and in the software environment, these changes were derived from each interferometer, combined, and their common areas were deleted. Also, landslides that occur parallel to the flight of the satellite cannot be removed because the landslides in the direction of vision (LOS) of the PALSAR sensor can be picked up. Based on the results of the radar interferometry, the maximum subsidence level in the study area is estimated to be about 3.5 cm per year. In addition, the maximum subsidence rate in Gachsaran and Anabal salt mine is 3.5 cm.

The Soil erosion mapping is the priority basement of soil conservation program in the watershed management. This study aimed to apply the FAO model and assessing factors affecting erodibility of soil using GIS and producing soil erosion map in Maroon watershed. For this purpose, the basin maps were digitized in a scale of 1:50,000 and they were integrated with each other by using ArcGIS10.3 software. Homogeneous units map was produced. Then, according to the scoring table used in the model of FAO and surveying using GPS in the field and apply the factor scores for each homogeneous units was estimated the final score for each factor and the severity of erosion in homogenous units by GIS. Finally, the produced weight map was reclassified according to the FAO model and the minimum and maximum score of the erosion for the evaluated factors. It was categorized in four classes by including low, medium, high and very high classes. The results revealed that 95 percent of the study area located in the moderate erosion (49.06%) to high (45.98%) and only 5% of the area in the relatively moderate erosion (3.66%) and very high (1.30%) were occurred.