Abstract:The aim of this research was to analyse the changes in the soil erosion intensity caused by erosion control works (ECW) in Grdelica Gorge (The South Morava River) in the period between 1953 and 2016. For the purpose of quantifying the erosion intensity changes, the erosion potential model (EPM) was used to calculate the annual gross erosion (W), sediment transport (G), and erosion coefficient (Z) in the study area. As a result of the performed technical and biotechnical erosion control works, there was a general decreasing trend in the intensity of soil erosion processes in the last 63 years. The specific annual gross erosion in Grdelica Gorge was 1920.34 m 3 /km −2 /year −1 in 1953, while in 2016 it was 492.42 m 3 /km −2 /year −1 . The specific sediment transport was 1421.05 m 3 /km −2 /year −1 in 1953 and 364.39 m 3 /km −2 /year −1 in 2016. Due to the changes in the intensity of erosion processes, the specific annual gross erosion in the study area decreased by 1427.92 m 3 /km −2 /year −1 and the specific sediment transport by 1056.66 m 3 /km −2 /year −1 . The value of the erosion coefficient was reduced from Z = 0.84 in 1953 to Z = 0.32 in 2016. The results show that there is a significant correlation between the soil erosion intensity (erosion coefficient) and ECW (biotechnical works) performed in Grdelica Gorge. The permanent control of erosion processes in Grdelica Gorge is very important for torrential flood prevention and protection of two very important traffic routes (Belgrade-Skopje-Athens railway and motorway-Corridor X), as well as settlements, local roads, and other facilities in this area. Furthermore, these results are the basis for future water management projects, soil and environmental protection, spatial planning, agriculture, and other human activities.

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Aiming at the protection of the future storage »Selova« against erosion and sediment, and also to protect the settlements and roads in the drainage basin against torrential floods, erosion control works in the upper part of the river Toplica basin, upstream of the storage »Selova«, started in 1947. The works included buildingtechnical works (check dams) and biological works (afforestation and grassing of bare lands and other erosion risk areas). During the period 1947 -2006, the following erosion control works were performed: afforestation of bare lands on the slopes 2,257.00 ha, grassing of bare lands 1,520.00 ha, and altogether 54 dams were constructed in the river Toplica tributaries. This caused the decrease of sediment transport in the main flow of the river Toplica. This paper, based on the field research in two time periods: 1988 and in the period 2004-2007, presents the state of erosion in the basin before erosion control works; type and scope of erosion control works and their effect on the intensity of erosion in the river Toplica basin upstream of the future storage »Selova«.

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