The silt carrying in Jerma river basin

Abstract

The silt carrying in the upper part of Jerma river basin in amount of 82.3 t/km/year is relatively high, considering the situation in all Serbia. The specific silt carrying in the upper part of Crnica river basin is 23.9 t/km/year (Manojlovic P.), while it is even lower in the basin of Crni Timok river (3.5 t/km/year; Manojlovic P, Gavrilovic Lj. 1991.). In the Kolubara river basin, the specific mechanical water erosion is between 4.6 t/km/year (Gradac) and 73.2 t/km/year in Tamnava basin (Dragicevic S. 2002). Greater erosion in the upper part of Jerma river basin is result of great part of metamorphic stones that intensively disintegrates and significant anthropogenic influence in Znepolje. The great slopes at the left side of the basin, under the Ruj mountain, should be considered, too. That doesn't mean that the erosion is strong, because, for example in the basin of Beli Timok, between Knjazevac and Zajecar, it is 186 t/km/year. Following regression, base on flow and silt concentration values can calculate the silt carrying very precisely: t/day=6251+26875 - C+1058 - Q Based on beta coefficients (0.73 for silt and 0.31 for flow) it could be concluded that concentration of silt has greater influence on erosion, than flow. More interesting is the influence of seasonal factor on the carrying of suspended silt. Months with the highest amount of carried suspended material are March, April and May. During these months 50.5 % of average yearly value is evacuated from a basin. Similar excessivity has been noticed in the other basins (Dragicevic S. 2002), only in other months.