Subsidence of Mahyar plain of Isfahan using D-insar interferometric technique

Dissertation for Master's degree (M.A)

Treatment: remote sensing and urban and rural geographic information system

Abstract:

The phenomenon of subsidence is one of the natural disasters that causes the reduction of underground resources such as underground water, oil, etc. due to the occurrence of such a phenomenon.

One of the most important causes of land subsidence is the drop in the static level and the increase in the effective stress in the sediments. It is an aquifer.

The Mahyar plain is one of the important plains in Isfahan, which has been faced with the phenomenon of subsidence due to the indiscriminate withdrawal of underground water, which has been associated with the growth rate of subsidence in recent years. Using the DINSAR technique and using radar images in the years 2008-2010, the maximum amount of subsidence in the Mahyar plain is 22.4 cm and the maximum uplift in the Mahyar plain of Isfahan is calculated to be approximately 9.3 cm.

By examining the graph of the decrease in the groundwater level in the Mahyar plain of Isfahan, which was prepared using the regional water data of Isfahan province, the reason for the subsidence in the Mahyar plain can be determined. Management of underground water resources in Mehyar Dasht, Isfahan.

Using radar interferometry and obtaining an interferogram map and color fringes, the DN value of the output images of the SUBCIDANCE and UPLIFT of the region is calculated and considering geoduality theory in this research will be effective for better conclusions. ground, radar interferometry, interferogram)

Introduction:

Earth subsidence includes the collapse or downward settlement of the earth surface, which can have a small horizontal displacement vector (Bates and Jackson, 1980). will result in severe environmental and economic risks (Waltham, 1989)

The risk of subsidence due to the drop in the underground water level is a global risk and subsidence occurs mostly in dry and low-rain areas.

Regional subsidence due to the drop in the underground water level mainly occurs in unconsolidated or semi-consolidated sediments that are adjacent to sand layers (Tahoni). 1386)

In other words, when the pore water pressure decreases due to drainage, the applied stress is gradually transferred from the pore water to the grain structure of the sediments, and at the same time as the pore water pressure decreases, the effective weight of the sediments in the semi-saturated region gradually increases (Adrian et al, 1999). The new arrangement reduces the volume and vertical thickness of the layer and eventually settles. (Bell, 1999) It is widely used for measurements of displacement of the Earth's crust or movement of surface objects on local scales in the landscapes observed from related satellites.

Using the radar interferometry technique and images received from the European Space Agency ESA and using the C band with a wavelength of 5.6 cm, the amount of subsidence and uplift of Isfahan's Mahyar plain is examined and calculated.

Mahirar plain of Isfahan with an area of ??about 850 km The square is located between longitudes 45.51 to 52.20 east and latitudes 32 degrees to 32.25 north and is located in a narrow valley with a width of about 20 kilometers and a northeast-southwest trend in the southern slope of Kolah Ghazi National Park. This plain is surrounded from three directions, north, south, and west, by the heights that all have a northwest-southeast trend, and from the east side, it is limited by the hills of Varzaneh village and the blood cow swamp.

The amount of land subsidence and the regional water data of Isfahan and the calculation of the graph obtained and the study of the land use of the studied area, which includes the agricultural sector of the Mahyar Plain, indicate the excessive consumption of underground water in the region and the creation of unauthorized wells in the Mahyar Plain of Isfahan, which requires more optimal management of groundwater resources as the only agricultural resources that can be harvested during drought.

The crisis plains of Isfahan province include Ardestan, Kashan, North and South Mahyar, Degh Sorkh, Barkhar, Bad Khalid Abad, Abiazan Roads, in all these areas the effects of the subsidence or advance of the salt water table towards the fresh water table can be seen.

- Uneven changes in the slope and slope of rivers and waterways and water transfer structures 2- Failure and protrusion of the well wall pipe and as a result compression stresses caused by the compression of aquifers and disruption in the exploitation of underground resources. and the sanding of wells 3- Advancement of waves in coastal lowlands 4- Irreversible reduction of all or part of underground water reservoirs as a result of the loss or reduction of useful porosity of deposits 5- Reduction of productivity or destruction of vital arteries and important structures Among the effective factors in causing subsidence, it seems that over-harvesting of underground water resources, thickness of sedimentary layers and engineering features of sediments are the main factors causing subsidence in most plains of Iran.

Areas that are currently in a critical condition of creating sinkholes and subsidence include Hamadan, Varamin, Nazarabad, Tehran, Mashhad and Neishabur plains, Kerman, Isfahan and Qazvin plains. By using a pair of radar images and determining the amount of subsidence and determining its exact location and the factors that cause such an environmental hazard in Isfahan's Mehyar plain, it is possible to use water resources in management systems. And by comparing it with the water wells and the amount of underground water harvested, he determined a model that can be predicted by not preventing the decrease of underground water in the Mahyar plain of Isfahan in the coming years. The movement is not limited in terms of intensity, extent and extent of the involved areas, and subsidence can be caused by natural geological phenomena such as dissolution, melting of ice and density of deposits, slow movements of the crust and the exit of lava from the solid crust of the earth, or human activities such as mining, extraction of underground water or oil. According to UNESCO, this phenomenon is the collapse or subsidence of the earth's surface that occurs for different reasons on a large scale. Normally, this term refers to the downward vertical movements of the earth's surface that can be associated with a small horizontal vector. The mentioned phenomenon does not include landslides whose movement has a significant horizontal vector, as well as settlement in manual soils. To determine the amount of land subsidence, it can be determined by using radar interferometry and using the D-insar technique and using software. sarscap investigated the amount of subsidence of the area. The principles of this technique were first expressed by Graham in 1974.

Differential radar interferometry calculates the phase changes from two pairs of radar images that were taken at different times and based on them, it clearly expresses the changes in the earth's crust quantitatively and qualitatively. Since the early 1990s, with the operationalization of radar satellites, radar interferometry has also been widely used by earth science experts. Earthquakes, volcanoes, mass movements, displacement of glaciers, and subsidence and landslide phenomena have been used. The damages caused by subsidence are:

Statement of the problem (explanation of the dimensions, limits of the problem, detailed introduction of the problem, statement of unknown and ambiguous aspects and variables related to the research questions, purpose of the research)

B.  The method of collecting information (field, library and

- if there is a practical purpose, stating the names of the beneficiaries (both educational and executive institutions, etc.):

Municipalities, Ministry of Roads and municipalities, knowing about subsidence areas and the dangers that threaten these areas, do not dig and create tunnels for subway lines or urban passages, as well as build bridges and overpass facilities in subsidence areas. do