This article deals with doline degradation due to uncontrolled waste dumping in the past in the Logatec Polje in Slovenia. It introduces a concept for determining 3D geometric characteristics (shape, depth, radius, area, and volume) of formerly concave landforms (i.e., recently filled dolines) by using a combination of two methods: (1) photogrammetric stereo processing of archival aerial photographs and (2) electrical resistivity imaging (ERI). To represent, visualize, and study the characteristics of the former surface morphology (i.e., the dolines before they were filled), a digital terrain model (DTM) for 1972 (DTM1972) was made using digital photogrammetry processing of five sequential archival aerial photographs (1972, © GURS). DTM1972 was visually and quantitatively compared with the DTM5 of the recent surface morfology (DTM5, © GURS, 2006) in order to define areas of manmade terrain differences. In general, a circular area with a higher terrain difference is an indicator of a filled doline. The calculated terrain differences also indicate the thickness of buried waste material. Three case-study dolines were selected for 3D geometric analysis and tested in the field using ERI. ERI was used to determine the genetic type of the original doline, to confirm that the buried material in the doline is actually waste, and to ascertain opportunities for further study of water pollution due to waste leakage. Based on a comparison among the ERI sections obtained using various electrode arrays, it was concluded that the basins are actually past concave landforms (i.e., dolines) filled with mixed waste material having the lowest resistivity value (bellow 100 ohm-m), which differs measurably from the surrounding natural materials. The resistivity of hard stacked limestone is higher (above 1,000 ohm-m) than resistivity of cracked carbonate rocks with cracks filled with loamy clay sediments while in loamy alluvial sediment resistivity falls below 150 ohm-m. Nevertheless, the contrast is sufficient to confirm the landfilled waste in all studied dolines. Based on the resistivity values of buried waste and the proximity of furniture and paper factories in the Logatec Polje, it is assumed that the dolines are filled with organic waste, mostly wood material mixed with other waste (municipal, construction, and demolition waste), which causes the variability of electrical resistivity.
Breg Valjavec, Mateja.
Study of filled dolines by using 3D stereo image processing and electrical resistivity imaging.
International Journal of Speleology,
Available at: https://digitalcommons.usf.edu/ijs/vol43/iss1/6