The intensity of mechanical water erosion in Veternica Basin

Abstract

According to the interpretation of the erosion map of Serbia, is the specific erosion in the Veternica basin 323 m3/km2/year, or about 646 t/km2/year. By using the hydrotechnical method, it was calculated that the specific silt flow in the Veternica basin for 32 years is 95,7 t/km2/year. The big difference between the information's, which Lazarevic calculated by using (he empirical method and the information's explained in this work comes partly from not measuring the bed load. However, there is the question: is it possible, that the bed load is 5-6 times higher than the silt flow. It was not noted in literature so far, that such a relation exists ill gently inclined riverbeds of bigger rivers: it is eventually possible in smaller gulches. By the so far analysed chosen basins, the same appearance could be seen: the results given by the hydro-technical method are manifoldly smaller than the information's given by the empirical method. For example, is in the catechment from Pek to Kucevo the specific silt flow 17,5 m3/km2/year, and according to the empirical form 65 m3/km2/year, that is 3,7 times more. In the Dragovištica basin (Mustafić S., 1998) is the specific silt flow 17,9 m3/km2/year, and the specific mechanical water erosion according to Lazarević's map is 777 m3/km2/year. In the Jablanica basin to the profile of Lebane (Dragicevic S., 1997) is the specific silt flow 9,2 m3/km2/year and according to the erosion map 300 m3/km2/year. According to Manojiovic P. and Gavrilovic Lj. (1992), the specific silt flow in the basin Crni Timoka is 1,7 m3/k2/year and in the interbasin of Beli Timok (between Knjaževac and Zaječar) 93 m3/km2/year; according to the erosion map are the corespondent values 88,4 m3/k2/year or 238 m3/km2/year. So, at some basins the difference is relative small, at other very high. The reason for this can be found in the exactness of the empirical formula especially the coefficient sight of erosion ((p), further in the neglecting of the fact that part of the produced and denuded material is accumulated on the lower ground. A big problem is the way of taking water examples, and the not existing permanent measuring of bed load. The combination of the hydrotechnical method with the information's given by the method of the erosive parts gathered in the empirical formula, will probably give corrected information's about the intensity of erosion and accumulation in the basin. The intensity of the specific chemical erosion in the Veternica flow is 45 t/km2/year (Manojiović P., 1995) with an average yearly total mineralisation of 212-422 mg/1 (Manojiović P., 1998). That means, that the chemical erosion in this basin is about 2 times fewer than the silt flow. That is surely the result of a smaller afforestment of the basin or, the domination of the metamorphic rocks. In other basins a reverse relation was established: the chemical erosion is several times more intensive than the mechanical (Manojiović P., 1990, 1993). The big production of drifts and a relatively higher amount of specific mechanical water erosion in the Veternica basin in relation to the chemical erosion, is the result of the combination of physical-geographical factors, and also of the big allotment of agriculture areas.

Primenom hidrotehnočkog metoda izračunato je da specifični pronos silta u slivu Veternice za 32 godine (1959-1990) iznosi 95,7 t/km2/god. Prema tumaču Karte erozije SR Srbije (Lazarević R.,1983). u slivu Veternice specifična erozija iznosi 323 m3/km2/god, tj. oko 646 t/km2/god. Razlog te pojave sigurno se nalazi kako u tačnosti empirijske formule, naročito koeficijenta vida erozije (psi), zatim zapostavljanja činjenice da se deo produkovanog i erodovanog nanosa na nižem terenu akumulira. Kombinacija hidrotehničkog metoda sa podacima dobijenih metodom erozivnih parcela pretočenih u empirijsku formulu. verovatno će dati tačnije podatke o intenzitetu erozije i akumulacije u slivu.