The Dynamics of Mining Subsidence in Knurow Area in Poland Derived from SAR Interferometry and Topographic Data
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The Dynamics of Mining Subsidence in Knurow Area in Poland Derived from SAR Interferometry and Topographic Data Tomasz Wojciechowski(1) (1) Faculty of Earth Sciences, University of Silesia , ul. Bedzinska 60, 41-200 Sosnowiec, Poland E-mail: [email protected] ABSTRACT The paper presents the results of GIS analysis concerned in Knurow town in Upper Silesian Coal Basin in Poland. The strong terrain surface changes are caused here by underground exploitation of hard coal which continued since 100 years. Based on Digital Terrain Models (DEM) constructed from archival and present topographic maps, the 18 meters of lowering due to subsidence and 25 m of relative uplift have been archived. The relative uplift was observed at recent mine-waste storages and was identified as the effect of waste dumping. The map of surface changes was then compared with geological maps and maps of underground mining to explain the spatial distribution of subsidence. Thanks to SAR interferometry the information about surface displacements of short time range have been received and the areas of recent subsidence of 10cm/35 days have been identified. The interferometric data have been compared with leveling data and maps of underground exploitation to explain the dynamics of subsidence. This analysis show exact agreement among parameters of subsidence troughs and the geological conditions of exploited strata. The presented analysis have been completed with the maps of changes in hydrological conditions of the area and other surface damages. Presented analysis shows the effectiveness of applied GIS approach to evaluate the anthropogenic impact on the terrain surface. SAR interferometry plays very important role as the independent tool which allows to effectively map the recent subsidence and study its dynamics. INTRODUCTION Knurow town is located in southern Poland in western part of Upper Silesian Coal Basin (Fig. 1), it occupies 34,2 km2. Two stone coal mines be placed on area of town - ªSzczygøowiceº Coal Mine and ªKnurówº Coal Mine. Intensive underground exploitation the system of single long-walls was applied for mining with caving, she caused the rise of considerable deformations of surface terrain in figure of troughs the lowering thresholds and hollows over formed thickness abandoned workings. These changes have caused hydrological transformations, in result of that become many drops fulfilled performed water, flooding also housing estates [1]. Thanks to computer methods, modern measuring methods InSAR, possible it stood examining the size of alternatively the surface of terrain in hundred-year mining activity, as well as examining dynamics of these changes. Fig. 1. Location Knurów town of the Polish part of Upper Silesian Coal Basin and ERS-SAR coverage. GEOLOGICAL CONDITIONS AND MINIG The size of alternatively of surface terrain, influencing on hydrology, they be dependent from geological conditions and mining. Exploitation of hard coal on area of investigations she has be led on depths since 250 to 850 m in rocks of carboniferous period, which they make up already overburden over abandoned workings. The oldest exploited rocks belonging to ªsaddleº beds they be built from sandstones, packstones and mudstones among which hard coal steps out [2]. Peaceably on them step out carboniferous sandstones from settlings packstones - mudstones of ªrudaº beds and then the packstones and mudstones of ªzaøężeº beds [3]. Over obtained layers step out the concise sandstones of trias about thickness only just dozen or so metres, being in southern part of area. The whole covers miocene clays from limestones and marl, thickness their it was estimated on 250 m [4],[5]. Quaternary cover about thickness achieving 30 m build sandy settlings as well as boulder clay. Described formations be connected from asymmetric syncline into longitudinal of the Knurów Fold, located to the east of the Orlova overthrust [1]. Formation of Carboniferous in which hard coal exploits incline from 5° to 65° and be cup out numerous fault about amplitude reload achieving 50 m. Litology and tectonics it favours area formation deformation. Moreover hundred-year exploitation be led in 29 layers of hard coal, it what influenced considerably on weakness of resistance on deformations overburden of rocks. Despite intensive work land reclamation led through mines on area of investigations, the surface of terrain stays in considerable way deforms. Changes relief are so many large, that every works having on aim minimalizing the results of exploitation of hard coal can only to reduce deformations. QUANTITATIVE CHANGES OF SURFACE TERRAIN So far general view of these alternatively area, it wasn't introduce. They would get him one compared data come from with the archival topographical maps of type Messtischblatter in scale 1:25 000 given in 1936 year, with data from Topographic Map of Poland in scale 1:10 000 given in 1997 year. In 1936 year mining work were insignificant and they had not yet larger influence on relief, it therefore it was accepted, that introduced on maps from this year the surface of terrain it is reflecting surface initial condition. All sheets were registered in coordinate system 1942 according to tens characteristic points well-known co- ordinates which part was got thanks to field measurements GPS. The digitalisation of topographical data was conducted in programme MapInfo 5,5 Professional getting the gatherings of data including rectangular co-ordinates a few hundred thousand points. On their basis models DEM (Fig. 2a,b) were generated in programme Surfer 8, it as well as height differences were counted among surfaces of terrain getting the colourful painting of changes (Fig. 2c) what dropped in among 1936 and 1997 year. On representing the changes of surface terrain painting to be visible the interior depressions, which water be full not infrequently. By occurrence hydrographic system, primitive regime of waters became unsettled creating threat for habitable housing estates. It was in 1997 year, when during great it fares it was flooded housing estate ªKorfantyº, which it was in trough lowering [1]. Water keeps to today there creating reservoir. He presents areas where the surface of terrain was lowered as a result of underground exploitation of hard coal, as well as terrains where surface became overheap mining wastes. Results what were got it was introduced in table 1. Counted volume, about what the surface of terrain lowered it carries out 0,162 km3. For positive values calculation gave result 0,043 km3. Adding up, the surface of terrain underwent the change in time lately 100 years about 0,205 km3 and changes have included area 66,24 km2. Results these be approximate and often across fact, that the mine waste dump be situated in depressions, they make up final stage alternatively not taking into account their course. Fig. 2. Topography of terrain with 1936 year (A), with 1997 year (B) Up-painting condensed countour lines, down-DEM C - Quantitative painting of changes surface of terrain what dropped in between 1936 year and 1997 year. at the bottom ± photograph changes of surfaces Changes (m) Changes area on map (km2) Changes area in borders of town (km2) -1 ≥ 40,31 19,35 -5 ≥ 10,41 5,49 -10 ≥ 2,37 1,54 -15 ≥ 0,09 0,06 +1 ≤ 8,69 4,79 +5 ≤ 1,96 2,01 +10 ≤ 1,3 1,09 +15 ≤ 0,94 0,8 +20 ≤ 0,19 0,11 +25 ≤ 0,07 0 Table. 1. Size of surface terrain subjected superficial changes. Visible changes on surface are conditioned geological building overburden exploited rocks, as well as mining conditions, therefore studying these dependences comparative analysis was conducted for 6 chosen of points (Table 2). For every point was counted sum thickness abandoned workings from regard inclination layers and thickness individual emissions in overburden. Point 1 Point 2 Point 3 Point 4 Point 5 Point 6 Subsidence (m) 12 10 18 6 4 6 Summarised thickness layers to exploit (m) 16,69 14,7 25,6 7,59 01.06.13 14,55 The thickness of overburden (m): Trias 0 0 0 0 0 ~25 Neogen 160 180 120 110 130 110 Quaternary 14 10 22 30 40 18 Relation of exploitation to settlement 0,72 0,68 0,7 0,79 0,65 0,41 Table 2. Punctual comparative analysis subsidence with mining conditions and geological. Comparative analysis leading was affirmed, that the differences in thickness formation of neogen, which they achieve 70 m, they have not the visible influence on deforming the surface of terrain. Also variety in formation Quaternary she did not show no meaning to discuss problem. It was affirmed however significant influence occurrence on sizes the trias of subsidence. Stepping out in point 6 the shoal of hard sandstone about thickness 25 m, caused redution deformation, it eats enfeebling enough strongly. On subsidence it has the largest influence however thickness of abandoned workings. In majority of cases relation thickness of emptinesses to settlement it hesitates in borders 0,68 - 0,79 meters. It results from this, that discuss area the size of subsidence the state average 75% the thickness of exploited layers. MEASUREMENT InSAR Interferometric analysis delivered many very valuable information of area investigations. SAR interferogram on needed of investigations was generated in programme the DORIS, the profile of used steam SAR interferograms was introduced is was in table 3. Number MASTER SLAVE Base distance Temporary base of path (m) (days) Satelita Orbita Date Satelita Orbita Date 494 ERS-2 14376 19.01.98 ERS-2 14877 23.02.98 91,9 35 Table 3. Composition of steam SAR The analysis of painting shew that among 19.01.98, and 23.02.98 superficial movements be hugged 8,49 km2, what state 10,4 % the area of investigations. Comparison interferogram (Fig. 3)from mining maps of exploitation it was conducted only for southern part of area of investigations where was located area "Szczygøowiceº Coal Mine.