10.2478/sggw-2018-0016 Annals of Warsaw University of Life Sciences – SGGW Land Reclamation No 50 (2), 2018: 195–211 (Ann. Warsaw Univ. of Life Sci. – SGGW, Land Reclam. 50 (2), 2018) Analysis of the causes and effects of landslides in the Carpathian flysch in the area of Milówka and evaluation of their prevention methods MAŁGORZATA JASTRZĘBSKA, MARIAN ŁUPIEŻOWIEC Faculty of Civil Engineering, Silesian University of Technology, Gliwice, Poland Abstract: Analysis of the causes and effects of Geological Institute shows that 95% landslides in the Carpathian flysch in the area of the landslides in Poland occur in the of Milówka and evaluation of their prevention Carpathian area, some occupy from 30 methods. The paper presents a comprehensive stu- to 40% of the gmina’s area. The first at- dy on the causes and effects of landslides occur- ring in the gmina Milówka (gmina is the admini- tempt to list the landslides in Poland was strative district in Poland, similar to a commune or undertaken in the years 1968–1970. municipality) from 1947 until today. The analysis At that time, they were estimated at includes the identification of probable causes of 8,500, and 2,970 of which posed a threat landslides and a discussion of possible remedial to residential buildings. Since then, methods, including preventive ones. The following landslide phenomena have intensified to were considered: results of laboratory, geophysical the alarming level (www.pgi.gov.pl). In and seismic tests; meteorological data; vegetative and transpirational properties of plants and agricul- 2010 a special landslides counteracting tural crops; intensity of farming; forest clearance. program was introduced called system Attention was also paid to the tree-ring eccentricity osłony przeciwosuwiskowej (abbrevia- among spruces. Additionally, a numerical analysis tion SOPO). The primary objective of of the current landslide stability was carried out in SOPO is an ongoing monitoring of the Z_Soil program. Finally, it was found that de- threatened areas (Fig. 1). The basis of termining the exact value of the stability coefficient activities is an underground observation is not possible due to the numerous assumptions necessary for the numerical analysis. However, it (piezometers, inclinometers) and over- is possible to predict with high probability which ground (GNSS satellite scan, laser scan- of the slopes are threatened with landslides. ning, interferometric synthetic aperture radar – InSAR, rain gauges). Key words: landslides, stability analysis of the The authors seek to determine the cor- slopes and escarpments, gmina Milówka relation between this phenomenon and atmospheric precipitation and anthropo- INTRODUCTION genic factors, such as the forest clearance or shrinkage of agricultural fields on the The landslide problem concerns moun- slopes. tainous areas (but not only) around the Transpiration properties of plants play world. Data collected by the Polish a significant part in maintaining water 196 M. Jastrzębska, M. Łupieżowiec FIGURE 1. A map of landslides with SOPO monitoring (www.pgi.gov.pl) balance in the substrate. For example, computational model, assessment of the the alfalfa needs 859 l and a larch needs accuracy of geological and geotechnical 1,165 l of water in order to produce 1 kg research on rock mass and appropriate of dry mass. This is the reason why in interpretation of the obtained param- the case of large areas threatened by eters, determination of the impact of landslides, solutions developed by bio- vegetation on soil and water conditions, technical engineering (including the determination of filtration coefficients, construction of terraces, regulation of and analysis of possible solutions, e.g. soil–water relations, afforestation, etc.) by draining water out of the colluvium are introduced (Begemann and Schiechtl of landslide. 1999). In the 1980s a new direction in deter- Each proposed solution (engineering mining the landslide phenomena called or biotechnical) is preceded by a thor- dendrogeomorphology appeared (Shro- ough analysis of a specific case, which der 1980, Butler 1987). It is based on the is extremely complex in relation to the conviction that the external disturbances Carpathian flysch. correspond to changes in the anatomy of Flysch is a heterogeneous, discon- wood e.g. the deconcentricity of the tree- tinuous and anisotropic medium. The -growth radial. This idea was developed landslide phenomena occurring in it by, among others, Wistuba and Malik most often arise as a result of shifting of (2011), followed by Wistuba et al. (2012, weak weathered top layer following the 2013, 2014) by introducing the substrate underlying strong layer (usually rock), sliding activity index (deconcentricity caused by a change in water relations index method). When comparing decon- and a decrease in the strength parameters centricity of the tree-growth data with of the weak layer (Instruction 2009). For rainfall data, it is possible to reconstruct this reason, each analysis concerns many previous mass movements of the ground threads and contains elements such as: and determine the threshold conditions reconstruction of the adverse phenom- triggering such phenomena (dendro- ena history in a given area, creation of chronology). The effectiveness of the Analysis of the causes and effects of landslides in the Carpathian flysch... 197 method was confirmed in the studies Municipal Office of Milówka (Cempura conducted on the Keprnícký landslide et al. 2009, Documentation 2010a, b, (Hrubý Jeseník, Eastern Sudetes, the 2011a, b, 2016). Czech Republic; Wistuba et al. 2012) A described landslide is located in and on the Milówka landslide (foots Milówka in the lower and middle part of of Prusów Mt 1,020 m a.s.l., southern the southern slope of the Prusów Moun- Poland, flysch Western Carpathians; tain. At the foot of the slope is located Wistuba et al. 2013, 2014). The above the stream called Salomonka flows. The mentioned studies have shown that area of landslides was mostly dominated dendrochronological analysis of growth by meadows with single trees, orchards, disturbances in trees is a promising arable lands, and only the lower part of approach to determine landslide hazards the slope was covered by mixed forest. in the extensive mountain ranges. It can The access road to the hamlets above the serve in early warning of the risk related stream Salomonka was located on the side to catastrophic landsliding. of the stream where the landslide forehead In the context of the presented infor- is now situated. The landslide is an old mation, a comprehensive analysis of the landslide, and although it was considered causes and effects of landslides occur- to be inactive. Studies of deconcentricity ring in the gmina Milówka from 1947 of tree-rings conducted by the team of until today has been conducted. Wistuba et al. (2014) in fact showed its alternating activity in 1947, 1950, 1962, MATERIAL AND METHODS 1968, 1977, 1993, 1997, 2004, 2007 and 2008. On 3 September 2010 there was Inventory of landslides and substrate another full activation, which resulted in exploratory study catastrophic consequences (Fig. 2). The Inventory of the existing state was con- cause of the landslide was the infiltration ducted on the basis of the site inspection of rainwater into the soil mass. The land- of landslide in Nieledwia, in Siedloki slide covered the area of almost 12 ha, and and on Prusów mountain and on the basis the average ground movement speed was of materials received from the Polish 2 cm/h. It is worth noting that on 5 Sep- Geological Institute (PIG) and from the tember 2015, the whole landslide area was a b FIGURE 2. General view of the damage on the Milówka Siedloki landslide in September 2010 (www. onet.pl): a – a part of a landslide; b – destroyed regional road 198 M. Jastrzębska, M. Łupieżowiec still subject to massive movements on its amounted to over 6 m (Fig. 3). Within entire surface, resulting in the destruction the colluvium of the landslide there were of the county road and tightening the Salo- numerous secondary niches, crevices and monka riverbed (Fig. 2). In the upper part cracks (Fig. 4) filled with water during of the landslide, surface displacements rainy periods. The strong hydration of the a b FIGURE 3. General view of horizontal displacements on the Milówka Siedloki landslide in June 2015 (Dziedzic and Golan 2016): a – upper edge of a landslide; b – main landslide threshold a b FIGURE 4. General view of the colluvium of the landslide in Milówka Siedloki (Dziedzic and Golan 2016): a – “a drunk forest”, niche filled with water; b – visible cracks – winter 2014/2015 Analysis of the causes and effects of landslides in the Carpathian flysch... 199 colluvium is also confirmed by presence strength characteristic based on CD+u of the typical plants for wetlands. Finally, tests (φ' = 27.8°; c' = 5.3 kPa; φ' = 25.6°, the following were destroyed: four resi- c' = 7.9 kPa). Samples for testing were dential buildings, four outbuildings, one taken from six different depth levels up summer house, one building under con- to 9.0 m, on which the movement of soil struction, low and medium voltage line, masses was observed. The ground water telephone line, access roads and regional was drilled at a depth of 2.75 m. The road (including 2 bridges). Area protec- borehole was deepened to 30 m and used tion – related works after the disaster cost for inclinometer observations. During the PLN 3.2 mln (Gardas 2011). observations three potential slip surfaces At the same time, a research program were found, respectively at the depths of: was initiated. A set of geotechnical tests 12.9, 20.9 and 21.8 m. was carried out at the request of the PIG Laboratory tests were supplemented at the Institute of Geotechnics of the with geophysical tests carried out by Cracow University of Technology (Doc- Przedsiębiorstwo Badań Geoficznych umentation 2011b). The tests included Sp. z o.o from Warsaw (Documentation the basic recognition of the physical 2011a).