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SOIL EROSION PROCESSES AND MODELLING IN THE UPPERBREGALNICA CATCHMENT

Ivica Milevski, Ivan Blinkov, Aleksandar TrendafilovUniversity St. Cyril and Methodius

Skopje, Republic of Macedoniaivica@iunona.pmf.ukim.edu.mk

Abstract

Bregalnica is one of the largest rivers (225 km long, 4307 km2 catchment area) in theRepublic of Macedonia, which drainage surface waters from most of the eastern part ofthe country. Because of suitable, sensitive natural factors (geology, soils, topography,

climate, hidrography, vegetation) and human-related excess deforestation, huge area ofBregalnica catchment is characterized by strong erosion potential. This is especially evi-dent upstream from Kalimanci dam, where most of the tributaries are torrential, andlandscape represent real system of gullies, earth pyramids, badlands and landslidesformed in soft Pliocene lacustrine sediment rocks. Aside of that are numerous depositionfans in the torrents bottom, as well as large flats of sedimentation. For that reason, inthis upper part of Bregalnica catchment (1124.7 km

2), are recorded sites with high an-

nual erosion rates, among the highest in the Republic of Macedonia. In respond of sucherosion risk, from the 1960-ties detailed studies with erosion modeling and mapping forthe area are performed, dominantly based on traditional empiric model of prof. S. Gavri-lovic. Having in mind fast transformation in the landscape, previous traditional approach

is updated by implementation of suitable GIS tools.

Keywords: Soil Erosion, Deposition, DTM (DEM), Satellite Imagery, GIS.

1 INTRODUCTION

Because of favourable natural factors and strong human impact over environment dur-ing centuries, area of the Republic of Macedonia is characterised with high soil erosionrate. According to Erosion map of the Republic of Macedonia (Djordjevic et al., 1993),average soil loss per year is near 700 m

3/km

2, which is among highest values in Europe.

In last decades, faster economic growth of the country and lack of soil resources, freshwater, forests etc., reinforce the need for soil protection and soil conservation. That in-creases the interest for erosion research, especially in the areas highly affected by soilerosion. One of those areas is catchment of river Bregalnica - largest left tributary (225km long) of Vardar, which is in turn a major river in the Republic of Macedonia. As a re-sult of very suitable characteristics (soft rocks, sandy soils, steep slopes, climate, sparsevegetation, anthropogenic influence) upper part of its catchment has very high soil ero-sion rate. For that reason, in 1960-ties begins more detailed researches in this area,with primary goal to protect newly constructed Kalimanci reservoir from excess sedimen-tation. Later were published other studies in which fully or partly were treated soil ero-sion landforms in the area (Manakovic and Andonovski, 1979; Manakovic, 1980; An-

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donovski, 1982; Milevski, 2004), soil erosion factors (Blinkov 2003), and soil erosion in-tensity (Rakicevic, 1975; Djordjevic et al., 1993; Blinkov, 1998). For soil erosion risk as-sessment in the upper part of Bregalnica catchment, previously mentioned Erosion map

of the Republic of Macedonia, has great significance. This map is created according tothe Erosion Potential Model by prof. S. Gavrilovic, widely used and confirmed in formerYugoslavia. Recently, Gavrilovic model is updated by newly accessible DEMs and re-mote sensing tools, offering even more valuable results.

2 STUDY AREA OVERWIEW

Bregalnica catchment is located in the east of the Republic of Macedonia, drainagingsurface waters from area of 4307 sq. km or 16.7 % of the country. Upper part of theBregalnica catchment, which is the subject of our interest, extending upstream of Kali-

manci Dam (in the easternmost part of the Republic of Macedonia), from 222744 to230203 East longitude, and from 413509 to 420916 North latitude.

Figure 1: Geographic location of the upper Bregalnica catchment.

The catchment cover Malesh and Pijanec tectonic depressions, and it is bounded by:Vlaina Mountain (1932 m) from the East, Maleshevo Mountain (1745 m) from the South,Plackovica Mountain (1754 m) and Golak with Obozna Mountain (1536 m) from theWest and Osogovo Mountain from the North. In that extent, upper part of Bregalnica

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catchment has area of 1124.7 sq. km which is 26.1% of total area, or 4.4% of countryarea. It has southeast-northwest direction in length of 55 km, with altitude from 2203 m(Mal Ruen peak on the Osogovo Mountain) to 510 m (Kalimanci Lake) which means alti-

tude difference of 1693 m. There are tree mid-to small size towns in the area: Delcevo,Berovo and Makedonska Kamenica, as well as numerous villages.

3 FACTORS OF SOIL EROSION

There are many natural and anthropogenic factors influencing soil erosion in upper partof Bregalnica catchment: lithology and soil structure, topography, climate, hydrography,vegetation (land cover), and human impact in the environment. However, aside that al-most all natural factors forcing soil erosion process, human impact has leading signific-ance trough the influence to most of other factors, especially of land cover.

Lithology of the research area is represented by various metamorphic (gneiss, mica-schists, schists), magmatic (granitites, gabro) and clastic sediment rocks, with variableerodibility. It is important that huge areas in the central part of the catchment (up to 1200m of altitude), are composed by easily erodible Pliocene sands and sandstones - depo-sits from the Neogene lacoustrine phase in the Malesh and Pijanec basins. Exactly inthat areas are sites with highest erosion rate and greatest production of deposits. Greenschists and other schists, who cover significant area, are also highly erodible, exposedto intensive weathering and decomposition. Except this direct effect on soil erosion, li-thology influencing soil structure as well. So most of the area is cover by eroded sandysoils and clay soils, excluding lowest parts of the basins and valleys, and dense forests.In latest, soils have better structure which is more resistant to soil erosion.

Topography is another significant factor of soil erosion expressed by hypsometry,slopes, slope inclination (aspects), terrain relief etc. Hypsometry of upper Bregalnicacatchment has generally indirect influence on soil erosion processes, thru the climaticand biogenic (vegetation) zonality, as well as intensity of human impact. The catchmentlay between 510 m (Kalimanci Lake), and 2203 m (Mal Ruen peak on Osogovo Moun-tain), with mean altitude of 1000.5 m. Lower parts of the catchment, from 510 m to 1000m, cover greatest area (56.6%, from which nearly 40% is between 750-1000 m). Exactlyon these lower altitudes, there are low precipitations but with frequent stormy rain occur-rences, with high daily and seasonal temperature amplitudes, sparse (human changed)vegetation, and significant human activity. Thus here it can be expecting elevated ero-sion potential, which is shown in further analysis. Higher elevations (1000-1500 m cover

38.4%, 1500-2000 m cover 5.3%, and above 2000 m is only 0.05% of the total area),are better protected from raindrop impact because of the better vegetation cover.Slopes like first hypsometry derivatives, has strong effect on soil erosion processes, es-pecially by slope angle. Moreover, some earlier soil erosion models and equations werebased only on slope parameters (Zingg, 1940). Thus, slopes in upper Bregalnica catch-ment are generally moderate with average value of 12. Largest areas have slopes of 5-10 (31.7%), and 10-15 (28.3%), or both of them have 60%. Those are moderateslopes, here usually characterized with surface sheet to rill erosion. Higher slopes of 15-20 and 20-25 cover 15.9% and 7.2% respectively, typically related with gully erosion,badlands (mel), landslides and rock falls. Lower slopes of 0-5 cover 12.4%, and insome cases are related to deposition areas (on the bottom of wider river valleys).

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Inclination or terrain aspect is another valuable parameter related to soil erosion poten-tial. In study area (according to latitude), south aspects are dryer, hotter, barer, andmore eroded from north aspects. Analyses show that in general, south side terrains has

greater fraction (53.7%) than north sided (46.3%). According to 4 main inclinations, west(30.5%) and south (24.8%) aspects prevails, then east (24.0%), and last north aspects(20.7%). It is clear that greater domination of south slopes trigger higher erosion risk,especially evident on south-east Osogovo and Vlaina Mountain slopes.Climate is very important factor of soil erosion in the region, especially in regard to tem-peratures and rains. Because of the geographic position, closeness of the region andhigh altitude, local climate has continental characteristics with high annual, seasonal anddaily amplitude of the temperature. From meteorological station records in Berovo andDelcevo it is evident that minimal winter temperatures may drop bellow -30C, whilemaximal summer temperatures can reach 38C (Lazarevski, 1993). Daily temperaturescan have high amplitude of more than 20C. It is clear that such differences provoke

strong weathering and decomposition of the rocks and deterioration of soil structure,making them more vulnerable to erosion. High summer temperatures for prolonged pe-riod, lead to faster drying of the soil which is then very susceptible to stormy rains, be-cause then vegetation is weak as well. Because of dominance of water erosion in thearea, most important climate factor are precipitations, especially the rains. According tolocal meteorological station records, mean annual sum of precipitation is from 562 mm(gs.Delcevo - 630 masl), 595 mm (gs Berovo - 824 masl) up to 802 mm (gs Sasa - 920masl). Seasonality is not so much expressed like in other parts of the Republic of Mace-donia, so the maximum of precipitations are in months of May and November (70-80mm), and minimum is in August or September (40 mm). Stormy rains affect this areafrom May to November sometime with intensity of more than 50 mm/day causing very

high erosion rate.As already mentioned, main hydrographic object is river Bregalnica, which has overalllength of 225 km, while upstream of Kalimanci Dam (in the analyzed part) its length is93.3 km. Altitudinal difference from the river spring on the Malesevska Mountain (1670masl) to the Kalimanci reservoir (519 masl) is 1170 m, which is in average 79,7 %o. Al-most all tributaries of Bregalnica, has torrential character with high amplitude in waterdischarge. The most significant tributaries are: Kamenicka (21.5 km), Zelevica (19.2km), Ribnicka (10.3 km), Lukovicka River (10.5 km) etc.Vegetation is another significant factor of soil erosion in the area, which is highly influ-enced in past by excess human impact. According to historical sources, in last few cen-turies, natural vegetation represented generally by forests is almost totally destroyed or

degraded in lower part of the cathcment, especially up to 1200 masl. For defining of thepresent vegetation cover, Landsat ETM+ imagery (acquired in 2000) was used in thestudy. Vegetation indices are derived from the spectral bands 4 (near infrared) and 3(red) in widely used NDVI-Normalized Difference Vegetation Index, where: NDVI=(b4-b3)/(b4+b3). NDVI for upper Bregalnica catchment is in range of -0.96 to 0.82, and forbetter calculation (without negative numbers), these values are transformed according toequation: tNDVI =(NDVI+1)*100. Resulting tNDVI generally range from 60 (water sur-faces) to 160 (dense forests). Areas with vegetation index from 70-100, cover significant34.4% (387.2 sq. km), representing bare soils, sparse grasslands and croplands (loweraltitudes of Malesh and Pijanets depression). On the other side, values of tNDVI inrange 140-180 represent dense or medium forest, and these areas occupy about 24.9%

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(higher altitude on mountain areas on: Osogovo, Vlaina, Malesevska). Average vegeta-tion index for the catchment is 121.5, and it significantly rise with altitude. These datastell about weak overall vegetation, with slight protection effect against raindrop impacts.

If other elements are appropriate (slopes, aspects, precipitation), which is case alongthe rim of depression-mountain areas (altitude of 600-1000 m), frequently sites with se-vere erosion occur.

4 SOIL EROSION LANDFORMS IN UPPER BREGALNICA CATCHMENT

Strong erosion processes in the upper Bregalnica catchment, resulted in waste varietyof erosion and deposition landforms. There are several types of erosion landforms:pluvial forms (rill, gully erosion, badlands, earth pyramids (earth pillars), landslides, land-falls, rockfalls etc.

Rills frequently occur on cultivated land areas with processes of irrigation, or on erodiblehilly terrain with overland flow. They are narrow and shallow ephemeral V-form incisionsin the soil, and usually produce significant amount of deposits. Depending of soil erodi-bility and slope, rills often develop in more permanent gullies. Because of suitable envi-ronment, large areas in the upper Bregalnica catchment, as well as in their tributaries(Kamenicka River, Zelevica and others) have extremely developed gully erosion. Thegullies are in variable shape (V, U, W-shaped) and evolution stage, characterized withexcess sediment production. Larger gullies, like those in Kamenicka River watershed,formed alluvial fans in the bottoms with continual deposition of sediments.Landslides are also very common in this area, especially in the lower parts of the cat-chment, below 1200 m altitude. Their formation is enabled with characteristic lithology

resembled by soft sediment rocks (sands, sandstones) on top which lie above inclinedPliocene clay layer. Another reason is high human impact on the environment. One ofgreatest landslide is recorded in the valley of Crnicka River near Crnik village. Thelandslide is located on the left (south) valley side, and it is 300 m long, 60-100 m wide,and 15-20 m deep. According to estimations, Pliocene sands of 650.000-700.000 m

3vo-

lume are under sliding. This stratigenic type of landslide, slowly moving toward CrnickaRiver, which in turn permanently detaches material from their frontal part, especially dur-ing the torrential event (Milevski, 2004). Numerous landslides are recorded in the valleyof Kamenicka River downstream from the village Sasa. This part of the valley is com-posed by soft erodible schists and Pliocene sediments, mostly uncover, eroded and un-der steep slope. Because of that, soft weathered rocks on the valley sides almost entire-

ly slide-down toward the valley bottom, making and enormous system of landslides withtotal estimated volume of 5 millions m3. That is particularly evident near the village Ko-sevica where the village itself has in danger. Aside of that, several landslides are regis-tered on the coastal region around the Kalimanci Lake, then in the catchments of Luko-vicka and Ribnicka River etc. All of them highly influence the soil loss rate and depositsintake in the Bregalnica River.Interesting forms of soil erosion in this region are so called mels. Mels are particularform of badlands with amphitheatric, semi-rounded shape, deeply incised in soft clasticsands and sandstones. Usually they have huge dimensions: 150-300 m width and 30-100 m height, representing forms of excessive deep erosion with extreme deposit pro-

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duction. Most remarkable mels in the area appear near villages Crnik, Smojmirovo andIstevnik.

Figure 2: Large mel near Crnik village

In the upper Bregalnica catchment, there are several occurrences of earth pyramids (pil-lars), especially near v. Trabotiviste. Here, on the side of one large mel, numerous in-dividual pillars are shaped in forms of animals, human being etc. Local people call themKukulje. Similar but in smaller extent are earth pyramids near v. Kosevica which are ininitial phase. Both occurrences are result of pluvial erosion in soft clastic sediment rockswhich are partly protected on top with more resistant patches of rocks and soils.Landforms of rock weathering are present where terrain is composed by rocks with hete-rogeneous erodibility. Weathering processes in mica-schist, gneiss, granite, result inmany stone pillars, rock falls, talus-cones etc. located mostly in the Kamenicka Riverwatershed, then on Golak, Bejaz Tepe and Vlaina Mountain.Deposition landforms appear in the areas where erosion and transport capacity of the

waters decrease, usually with decreasing of slope. These landforms strictly correlatewith erosion intensity, so largest deposition landforms was created in the regions of se-vere erosion, and most of them are along the valley bottom of Kamenicka River. Down-stream from Sasa village, valley bottom represent large alluvial plain with huge amountof fresh deposits from the near torrents. Along the left side of the bottom, these torrentsformed 6 large alluvial fans (200x250 m). Most of the upper Bregalnica torrential tributa-ries have smaller alluvial fans and alluvial plains.

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5 ESTIMATION OF EROSION RATES

There are numerous GIS-based methods of soil erosion rate estimation, depending of

the purpose of that estimation, available tools and expected results. Usually those areempiric equations, frequently adapted to GIS-aided computations. Worldwide there aremany such methods: USLE, WEPP, EUROSEM etc., providing better or fever outputs. Inthe Republic of Macedonia, estimation of average soil erosion potential and soil erosionrisk is generally achieved with equation of prof. S. Gavrilovic (1972). The equation is inform: G=T*H*3.14*sqrtZ3*f, where: G is average annual soil erosion in m3, T is tempera-ture coefficient (0.1*t+0.1), H is annual precipitation in mm, Z is erosion factor and f iscatchment area in km

2. Among these factors, Z has special importance combining: soil

erodibility (Y), land cover index (Xa), index of visual erosion processes (), and meanslope (J) in relation: Z=Y*Xa*(+sqrtJ). Values of Z usually ranged between 0 (no ero-sion) and 1.5 (excess erosion). Because of proven accuracy, there are several recent

GIS adaptation of this equation (Milevski, 2001; Milevski, 2005; Petras et al., 2007). In-stead of traditional cartographic tools, in our approach most of the equation parametersare derived from 3SRTM DEM and thematic layers of Landsat ETM+ satellite imagery.Thus, from preprocessed DEM (60m), with evaluated vertical gradient interpolation, cli-mate indices T and H were obtained, as well as slope value J (in %) for every cell on thegrid. Land cover index Xa is prepared from CORINE Land cover map or from trans-formed NDVI with values from 0.1 (dense forests) to 1 (bare soils). Index is preparedfrom Landsat ETM+ band 3, according to relation: =sqrt(b3/255). In GIS procedure fac-tor Y (soil and rock erodibility) is taking to be optional, unless sufficient parameters areavailable. Finally with successive calculations of all grid layers, average erosion rate Gis produced. In such way finished, GIS-based soil erosion map (Fig. 3A) is pretty close

with the traditional Gavrilovic-based, catchment oriented soil erosion map (Fig. 3B) pre-pared by Djordjevic et al., (1993). Traditional map show average soil erosion potential ofthe upper Bregalnica catchment of 977 m

3/km

2/y, and our GIS-based map show in aver-

age 925 m3/km

2/y, which is in line with Kalimanci basin sedimentation measurement

(Blinkov, 1998).

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Figure 3:A. Map of GIS-based (according to Gavrilovic model) estimation;B. Map of soil erosion potential (according to Djordjevic et al., 1993).

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0-200 200-400 400-600 600-800 800-1000 1000-1200 1200-1400 1400-1600 1600-1800 1800-2000 2000-3000

m3/km2/y

%Traditional

GIS-based

Figure 4: Chart of specific deposits production according to traditional and GIS basedmethod in the upper Bregalnica catchment.

Coefficient of erosion Z itself, is almost the same on both maps, or about 0.55. However,there are big differences in the area of the sites with weak erosion (less than 500m3/km2/y), which in GIS model account about 307.5 km2 (27.2%) and on traditional maponly 31 km2 (2.8%). It is interesting that sites with high erosion risk (specific erosion ratemore than 1500 m

3/km

2/y) on classical map cover 129.6 km

2(11.5%), on GIS-based

map cover slightly more or 190.0 km2

(16.8%). Previous show that unlike traditional mapwhich has smaller value amplitude, GIS-based map has large differences in coefficient Zand overall erosion production. Further research will confirm which model has to be cor-

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rected. Never less, in regard to both maps as well as to several sedimentation mea-surement of Kalimanci reservoir, average annual sedimentation is pretty high; almost420.000 m3/y. That is significant erosion rate, permanently occurring last decades.

6 CONCLUSION

Because of favorable natural factors and significant human impact on the environmentduring long time, upper Bregalnica catchment is one of the most erosive areas in theRepublic of Macedonia. Strong arguments for that are numerous soil erosion landforms(especially gully erosion, landslides, badlands) as well as estimated soil erosion. Soilloss assessment of the area is performed thru the traditional empiric model of Gavrilovic,and newly available GIS-based adaptation of this model. Both show high erosion rate(near 1000 m3/km2/y, or 1 mm topsoil/y), especially for some areas. Comparison of the

models with sedimentation measurement, confirm close fitting, but further analysis andresearch must be done especially on the GIS-based model, which will allow better accu-racy. Aside of that, because of high erosion rate, complex measures must be taken forsoil conservation and environmental protection in the upper Bregalnica catchment (Mi-levski, 2006). That is key requirement for better socio-economic growth in the future.

References

Andonovski T. (1982): Erosion sites in SR Macedonia. XI Congress of geographers in SFRY, BudvaBlinkov I. (1998): Influence of the rains on the intensity of soil erosion in the Bregalnica catchment up to

the profile Kalimanci Dam, doctoral dissertation-manuscript, Faculty of Forestry, SkopjeBlinkov I., (2003): Water and sediment discharge as a result of the forests and forest activities, scientificproject, MES of RM, Skopje 2003, final report.Blinkov I., Trendafilov A. (2006): Effects of erosion control works in some torrents in the RM, Conferenceon Water Observation and Information System for Decision Support, BALWOIS, Ohrid, 2004Djordjevic M., Trendafilov A., Jelic D., Georgievski S., Popovski A. (1993): Erosion map of the Republic ofMacedonia, Skopje-textual partGavrilovic S. (1972): Engineering of torrents flows and erosion. Special edition, BelgradeJarvis A., Reuter H.I., Nelson A., Guevara E. (2006): Hole-filled SRTM for the globe, Version 3, availablefrom the CGIAR-CSI SRTM 90m Database: http://srtm.csi.cgiar.orgLazarevski A. (1993): Climate of Macedonia. SkopjeLiberti M., Simoniello T., Carone M.T., Coppola R., DEmilio M., Lanfredi M., Macciato M. (2006): Bad-lands area mapping from Landsat-ETM data. Proceedings of the 2

ndWorkshop of the EARSeL SIG on

Land Use and Land Cover, 434-440Manakovic D., Andonovski T. (1979): Relief characteristics of East Macedonia. Geographical reviewNo.17, Skopje 5-32Manakovic D. (1980): Geomorphology of Males and Pijanets. Natural and socio-geographic characteris-tics of malesh and Pijanets - scientific project, SkopjeMarkoski B., Milevski I. (2005): Digital elevation model (DEM) of the Republic of Macedonia. Proceedings:Global automatization and energy optimization of technical processes. SkopjeMilevski I. (2001): Modeling of soil erosion intensity with software tools, in the example of Kumanovo Ba-sin. Proceedings of II Congress of Macedonia Geographic Society, Ohrid, 49-57Milevski I. (2002): Recent soil erosion in Kumanovo Basin. Proceedings of scientific conference in thehonor of D. Jaranoff. Varna, Bulgaria, 344-352Milevski I. (2004): Forms of soil erosion in the Vinichka (Crnichka) valley. Geographic Review No. 39,Skopje, 5-20

7/27/2019 052_Milevski

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Milevski I. (2004): Soil erosion in the Zelevica catchment. Bulletin for Physical geography, Skopje, 59-75Milevski I. (2005): Possibilities for analysis of soil erosion in Republic of Macedonia by using of satelliteimagery. III Congress of Macedonia Geographic Society, Skopje pp. 74-80

Milevski I. (2006): Erosion processes and development of rural areas in the Republic of Macedonia. Ruralareas in the modern conditions of development. Ohrid, 539-556Milevski I. (2007): Morphometric elements of terrain morphology in the Republic of Macedonia and theirinfluence on soil erosion. International Conference Erosion and Torrent Control as a Factor in SustainableRiver Basin Management25-28 September 2007, Belgrade SerbiaMilevski I., Dragicevic S., Kostadinov S. (2007): Digital elevation model and satellite images in assess-ment of soil erosion potential in the Pcinja catchment. Annual of Serbian Geographic Association, BookLXXXVII-No 2, Belgrade, 11-20Moore, I.D., R.B. Grayson, A.R. Ladson. (1991): Digital terrain modeling: A review of hydrological, geo-morphological, and biological applications. Hydrol. Processes, 5 330Zingg A.W. (1940): Degree and length of land slope as it affects soil loss in runoff. Agricultural Engineer-ing, 21, 59-64Olaya V. (2001):A gentle introduction to SAGA GIS. http://www.saga-gis.uni-goettingen.dePetras J., Holjevic D., Kunstek D. (2007): Implementation of GIS-technology in Gavrilovis method for es-

timation soil erosion production and sediment transport. International Conference Erosion and TorrentControl as a Factor in Sustainable River Basin Management25-28 September 2007, Belgrade SerbiaRakicevic T. (1975): Muddy of rivers in the Vardar catchment. Annual of Geographical Institute of FNSM,Belgrade, 21-33