ASSESSMENT OF RUNOFF AND SOIL EROSION IN THE RADULICKA

Soil erosion is a natural process that is causing environmental concerns such as land degradation, soil loss, water pollution and ecosystem alteration. The Erosion Potential Method (EPM) is extensively used for identifying watersheds with such problems. One of 57 studied river basins of the Polimlje Region was Radulicka Rijeka Watershed where we studied soil erosion processes using the analytical and computer-graphic method IntErO, based on the EPM method. Calculated peak discharge from the river basin was 185 m 3 s -1 for the incidence of 100 years and the net soil loss was 13157 m3 yr -1 , specific 327 m3 km 2 yr -1 . The use of EPM method and the IntErO model to predict sediment yield, according to our experiences, is recommended for this Region and may also be suitable for making management decisions. At the same time, further research is needed to address model limitations regarding the further development in relation to the GIS adaptations.


INTRODUCTION
Sediments play an important role in elemental cycling in the aquatic environment as they are responsible for transporting a significant fraction of nutrients and contaminants. Large suspended sediment fluxes in river catchments, which result from soil loss due to water erosion, constitute a major environmental issue (Louvat et al., 2008). Soil degradation caused by erosion, together with rapid population increase, are ranked as the most important environmental problems in the world (Stoffel and Huggel, 2012), where the erosion is a key driver of land degradation heavily affecting sustainable land management in various environments worldwide (Ballesteros-Cánovas et al, 2015;Al-Turki et al, 2015;Behzadfar et al, 2015;Stoffel et al, 2013;Khaledi Darvishan et al, 2012).
The South and Southeast regions of Europe are significantly prone to water erosion. In Montenegro water erosion is the most important erosion type (Spalevic, 1999). The main forces of water erosion are precipitations and 1 Dusko Vujacic and Velibor Spalevic (corresponding author: velibor.spalevic@ac.me), University of Montenegro, Faculty of Philosophy, Department of Geography, Niksic, MONTENEGRO. Paper presented at the 6th International Scientific Agricultural Symposium "AGROSYM 2015" Notes: The authors declare that they have no conflicts of interest. Authorship Form signed online. consecutive runoff; but not less important is fluvial erosion in water streams (Kostadinov et al. 2006).
Water erosion has affected 95% of Montenegro. Alluvial accumulation characterises the remaining area, where the deposition of sediments is also affecting agricultural land. Erosion caused by water is dominant in terrain with high slopes due to complex physical and geographical conditions paired with reckless logging (Spalevic et al, 2015a;Gazdic et al, 2015;Spalevic et al, 2014a;Spalevic et al, 2013a;Spalevic et al, 2013b;Fustic and Spalevic, 2000).
According to Blinkov (2015) the most erosive countries in Europe are the Balkan countries Albania and Montenegro, where the mean annual intensity of erosion is more than 10 t ha -1 . This is confirmed by Spalevic et al (2012) for the Mediterranean watersheds of Montenegro: 1900 m³km -²yr -1 for the Zeljeznica river basin of the Adriatic Watershed. On the other hand, for the Polimlje (North of Montenegro, the Black Sea Watershed), the calculated soil losses per km 2 for the 57 river basins were in average 331 m³km -²yr -1 (Spalevic et al, 2015b;Spalevic et al, 2015c;Spalevic et al, 2014b;Spalevic et al, 2014c;Spalevic et al, 2013c;Spalevic et al, 2000).
All stated make clear why erosion risk assessment and its quantification is an important question for this Region.
The idea of this research was the assessment of runoff and soil erosion in the Radulicka Rijeka Watershed, Polimlje, Montenegro, studying spatial characteristics of the various natural phenomena; geological, soil, land use and climate characteristics.

MATERIAL AND METHODS
We studied soil erosion processes in the Radulicka Rijeka Watershed (40 km 2 ), a right-hand tributary of the river Lim, located in the mountainous area of the Polimlje Region, north of Montenegro ( Figure 1).
Morphometric methods were used to determine the slope, the specific lengths, the exposition and form of the slopes, the depth of the erosion base and the density of erosion rills. Google Earth and Google Maps were used for further studying of the morphology of the features.
We used data of geological and pedological research from Zivaljevic (1989), Fustic and Djuretic (2000), who analysed all geological formations and soils of Montenegro including the studied area of the Radulicka Rijeka.
Climatological data were received from the Institute of Hydrometeorology and Seismology of Montenegro (for the period 1948-2015). We analysed torrential rains, annual air temperatures, and average annual precipitations.
Many researchers have attempted to elucidate the interaction between land cover pattern and ecological processes (Fu et al., 2011); and this become the focus of the landscape ecology studies in the field (Casermeiro et al., 2004;Bautista et al., 2007;Fridley et al., 2007;Claessens et al., 2009;Bisigato et al., 2009). Data in relation to the land use and vegetation cover we received from the Institute of Forestry of Montenegro (IoFoM), Statistical Office of Montenegro (MONSTAT), Google Maps and our own research.
Directly observing large-scale hydrological processes is difficult. Modelling has become a key research tool at the basin scale studies (Fu et al., 2011). We applied the IntErO model (Spalevic, 2011) 2 for the assessment of runoff and soil erosion. The analytical equation is the following: where W yr is the annual erosion in m 3 yr -1 ; T, the temperature coefficient; H yr, the average yearly precipitation in mm; Z, the erosion coefficient.
The erosion coefficient, Z, was calculated as follows: where, Y is Soil erodibility coefficient; X is Soil protection coefficient;  is Erosion development coefficient (tables for Y, X and  coefficients available at Gavrilovic, 1972). F is the watershed area in km 2 . The actual sediment yield was calculated as follows: where, G yr is the sediment yield in m 3 yr -1 ; W yr is the total annual erosion in m 3 yr -1 ; R u is sediment delivery ratio. The actual sediment yield was calculated as follows: where, O is perimeter of the watershed in km; D is the average difference of elevation of the watershed in km; L is length of the catchment in km.

RESULTS AND DISCUSSION
Climate. The climate in the studied area of the Radulicka Rijeka is continental, with the absolute maximum air temperature of 35°C and negative of 29.8°C. The location of the studied river basin is classified as Dfb by Köppen and Geiger. The amount of torrential rain, hb, is calculated on 157.6 mm. The average annual air temperature, t0, is 8.9 °C. The average annual precipitation, Hyr, is 983.7 mm. The temperature coefficient of the region, T, is calculated to be 0.99.
Geology and soils. The study area belongs to the Durmitor geotectonic unit of the inner Dinarides of Northern and North -eastern Montenegro. The geological structure of that part consists mainly of Paleozoic clastic, carbonate and silicate volcanic rocks and sediments of the Triassic, Jurassic, Cretaceous -Paleo-gene and Neogene sediments (Frankl et al., 2015).
The coefficient of the region's permeability, S1, according to the analysis of geological substrate is calculated on 0.9. Figure 4: The structure of the river basin, according to bedrock permeability (fp: very permeable; fpp: medium; fo: low permeability).
The structure of the river basin, according to the soil types is presented at the Figure 5. Arable land covers a total surface area of 15%, concentrated in the areas with low slope gradients.
The detailed structure of the river basin, according to the land use is presented at the Figure 6. The assessment of runoff and soil erosion in the Radulicka Rijeka Watershedis presented in the Table 1. Gyr (km²) 327 m³km -2 yr -1 CONCLUSIONS (A)symmetry coefficient indicates that there is a possibility for large flood waves to appear in the river basin. The value of G coefficient of 0.31, indicates there is low density of the hydrographic network. The value of 29.46% indicates that in the river basin prevail steep slopes.
Calculated peak discharge from the river basin was 185 m 3 s -1 for the incidence of 100 years.
The value of Z coefficient of 0.497 indicates that the river basin belongs to III destruction category; according to the erosion type, it is surface erosion.
The net soil loss was 13157 m³km -², specific 327 m³km -² per year, what indicates, according to Gavrilovic, that the river basin belongs to V category; region of very weak erosion.
The use of EPM method and the IntErO model to predict sediment yields, according to our experiences, is recommended for this Region and may also be suitable for making management decisions. At the same time, further research is needed to address model limitations regarding the further development in relation to the GIS adaptations.