تعیین میزان فرونشست زمین در محدوده مخروط افکنه جاجرود با استفاده از تکنیک تداخل‌سنجی تفاضلی راداری

دشت ورامین یکی از مناطق متاثر از فرونشست در ایران است که در مخروط افکنه رودخانه جاجرود قرار دارد. این پژوهش به بررسی فرونشست مخروط افکنه جاجرود با تاکید بر جوادآباد ورامین از سال 1395 تا 1398 با استفاده از روش تداخل سنجی تفاضلی راداری می‌پردازد. در این مطالعه، 41 تصویر از سنتینل (2016 2019) برای تعیین میزان و دامنه فرونشست زمین با استفاده از روش پراکنده‌کننده‌های دائمی استفاده شد. نرم‌افزار snap برای پردازش تداخل سنجی راداری انتخاب شد. . ه‌منظور یافتن علت فرونشست، اطلاعات چاه‌های پیزومتریک (1395 1375) منطقه موردمطالعه و تغییرات زمانی آن بررسی شد. منطقه جوادآباد واقع در ورامین یکی از مناطق دارای فرونشست قابل‌توجه که فرونشست به میزان 20 سانتی‌متر در سال رخ می‌دهد. یکی از عوامل اصلی فرونشست زمین در منطقه جوادآباد به دلیل افزایش عمق چاه‌های پیزومتریک در دوره موردمطالعه را می‌توان به پمپاژ بالای منابع آب زیرزمینی نسبت داد .وو وقوعونشست زمین باعث تغییر درشیب سطح محلی شده و این امر باعث اختلال در شبکه زهکشی و مسیر جریان آب‌های سطحی شده است که درنهایت منجر به بروز انواع فرسایش شده است.

determining the amount of land subsidence in jajrood alluvial fan using differential radar interferometry technique

introductionthe phenomenon of land subsidence involves the collapse or sinking of the earth's surface,which can also have a slight horizontal displacement vector. this movement is not limited interms of intensity, extent, and measure of the involved areas. subsidence in cities leads to costlyand serious damage to urban infrastructures such as buildings, roads, and railway tracks. landsubsidence can occur for various reasons: groundwater abstraction, subsidence due to oilextraction in oil fields, displacement due to landslides, and collapse of internal walls of mines.interferometric synthetic aperture radar (insar) is a powerful technique for measuring thetopography of a surface and its changes over time. varamin plain is one of the areas affected bysubsidence in iran, which is located in the alluvial fan of jajrood river, and its development andprosperity is due to the quality and fertility of the soil in this region. irregular and over pumpinggroundwater has caused many subsidence cases in the study area. this study investigates thesubsidence of jajrood alluvial fans with emphasis on javadabad varamin from 2016 to 2019,using the permanent scatter radar interferometry method.materials and methodsin this study, 41 images of sentinel (2016 2019) were used to determine the rate and amplitudeof land subsidence using the method of permanent dispersants. permanent scattering points (ps)were selected based on the domain scattering index.according to the threshold limit, the amplitude scattering index is usually considered to be 0.4or 0.42 in various studies, which means that all selected points are not located in the set of pspoints, and only those points to be selected that the amplitude scattering index value isexceeding the threshold. then, a points network (ps) was prepared at this stage to evaluate theprocessing performed. the prepared spatial network in this section is derived from the delaunaymodel. since the amount of displacement is relative in this method, one of the points in the areais selected where the amount of displacement is relatively zero compared to other points, andother ps points are applied to it. because of seasonal temperature changes and their effect on buildings that cause elevation changes (the effect of temperature on the structure of buildings),the selected point must be located on the ground. snap software was selected for radarinterferometry processing. in order to find the cause of subsidence, the information of piezometric wells (1996 2016) in the study area and their temporal changes were investigated.results and discussionin general, land subsidence has occurred in two significant areas. the northern region is locatedin the jajrood alluvial fan. the length of this zone is 44 km, and its width is 7 km, which coversan area of more than 300 square kilometers.the highest subsidence in this area is related to the golabbas area, which is about 120 mm peryear. the presence of jajrood alluvial fan and agricultural lands in this area is considerable.the second region is related to the southern zone. the northern part of this zone is bounded bythe city of pishva, qala e sin, and the east of varamin city. in these areas, the annualsubsidence rate reaches to maximum six cm. the southern part of this zone is surrounded byhesargol and jahanabad areas.in these areas, the land subsidence rate is lower compared to the central areas and is about 20 to40 millimeters per year. in the northern part of the jahanabad region, the maximum landsubsidence is 60 mm per year. the southern zone in which the study area is located has acircular shape, and the amount of land subsidence increases from the periphery to the center ofthe region. the highest rate of land subsidence in the study area occurred in salman abad,khaveh, javadabad, hesar e sorkh, and zavarehvar areas, with the amount of between 160 to200 mm per year. areas such as tajreh, rostamabad, and hesar kouchak also show significantland subsidence, about 120 to 160 mm per year.conclusionthe result of radar interferometry studies has demonstrated that subsidence has occurred in themain parts of the jajrood alluvial fan's surface. javadabad region, which is located in varamin isone of the areas with significant subsidence that subsidence occurs at rate of 20 cm per yearstudies conducted in the study area depicted that the decreases in groundwater level in the studyarea is linear and this is acceptable in justifying land subsidence. so that the patterns obtainedusing the radar interferometry method in order to find the pattern of land subsidence andgroundwater were consistent and somewhat uniform. in this regard, one of the main causes ofland subsidence in the region in javadabad due to the increasing depth of piezo metric wells inthe study period can be attributed to the high pumping of groundwater resources.according to the physiographic shape of the region and the pattern of land subsidence, thehighest rate of land subsidence was observed in areas consisting of low slopes, includingjavadabad and varamin. in terms of risk, population, roads and buildings, railroads are involvedin the phenomenon of land subsidence in this region. the railroads of tehran, mashhad,garmsar and qom are the connecting roads in this region.