Abstr act. The paper contains data about the destructive effects of gully erosion on the environment. It provides general information about the gully erosion in several countries around the world including Romania and is considered a case study for a river basin located in the Semenic Mountains (Bârzava drainage area). The case study is based on the following assumptions: the presence of different types of soil, the constant rain intensity over the entire river subbasins, the land use is the same over all the sub-basins; there are no soil erosion control works. The model was applied to the each area of the bed (gully), by calculating the quantity of the soil lost, depending on the soil type. The data entered in the program are: the use of the land - forests, climate - the average monthly temperature and precipitation, the soil characteristics, the subbasins areas, the characteristics of the river beds: the average width of the river bed and the river bed type (channel river bed in the forest area). Keywor ds: gully erosion, exogenous factors, water erosion, anthropogenic factors, river basin, the calculation model 1 Intr oduction In its evolution, the Earth has suffered and continues to suffer major changes due to the action and interaction between endogenous and exogenous factors. Crust movements, caused by endogenous factors, lead to the activation of exogenous factors such as gully erosion. In 1983, according to the estimates made by FAO in the world, an area of 5-7 million hectares of land were removed from the agricultural lands, due to the degradation processes (erosion, toxic chemicals, soil salinization, urbanization, etc.) the estimated losses at the end of year 2000, being of 100-140 million ha. In Europe, an area of about 115 million hectares (about 12% of the Europe's surface) is affected by water erosion. The most affected areas are the Mediterranean region and large areas in the central and eastern parts of the continent due to natural contributing factors (relief, climate, In: M. Salampasis, A. Matopoulos (eds.): Proceedings of the International Conference on Information and Communication Technologies
Copyright ©by the paper’s authors. Copying permitted only for private and academic purposes. soil, etc.) and to anthropogenic factors (massive deforestation, improper practice of agriculture, overgrazing on the same area).
In Romania, taking into account the specific indicator of the erosion intensity (t/ha/year), counties in the bend area of the Carpathians Mountains (Buzau, Vrancea, with values of approximately 40 and respectively, 35 t/ha/year) are clearly different from the maximum allowable erosion of 4-6 t/ha/year. According to Motoc (1982), Romania weighted average was of 16.28 t/ha/year. Gully erosion in the world has various effects on the environment, namely:
- In Russia, land area is degraded by approximately 500 thousand ha/year.
Through water erosion, approximately 400 thousand gully erosion formations were
formed, covering over 500 thousand hectares
- In Pakistan, 75% of the country is affected by water and wind erosion and gully
erosion affects 36% of the agricultural area of the country
- Greece has about 40% of the total area of cultivated land affected by erosion, and over 800 active torrents transport over 30 million m3 of solid material (Vousaros A. quoted by 123(+4$V., 1986).
- China is affected by erosion - approximately 3.7 million km2 (about one third of
the country
- In India, gully erosion affects 3.67 million hectares
- In Romania, a network totaling over 25,000 km of gully erosion in formations
assets has been inventoried
From an economic and environmental point of view, the development works of the gully erosion formations are of particular importance. The development of these formations causes damage primarily to agriculture, to socio-economic objectives, to silting of storage lakes and to water courses. If a storage lake has a calculated dead volume, which should be filled with silt in 80-100 years, there are cases when the storage lakes were no longer usable due to sealing, in only a few years or decades.
The annual volume of sediments transported by rivers in Romania is over 44 million tons (C. Diaconu, 1971), to which gully erosion contributes by 31% (5(6('$ M. 1984). 2
In order to estimate the losses of soil erosion on slopes, various computational
models have been developed
In what follows, we treated soil losses through erosion and their impact on the environment in the Bârzava river basin (Romania) by two methods.
The estimation of the soil erosion in the Bârzava river basin by the physical modeling.
Universal soil loss equation developed by Wischmeier and Smith (1960) is based on the experimental technique applied by the two researchers. Subsequently, soil erosion assessment and prediction were improved by modeling techniques and by the elaboration of computer programs that allow separate treatment of the deployment processes of soil particles and fluid flow.
Thus, Trott and Singer (1983), using research with the rain simulator and measuring leakage, developed an equation of sediment production based on granulometric composition, for the forest soils in California:
SY= -9,391+25,298(P+A) – 0,2297(P+A)2 – 12,551(Kaolinite) + 31,420 (Smectite)
Where: SY = sediment produced in g/m2; P+A = dust percentage + clay percentage; Kaolinite = kaolinite percentage present in the soil; Smectit = smectite percentage present in the soil.
This equation was developed by Covaci, D. (2002) using the erosion tester and by Rogobete Gh. and Grozav, A. (2006) using the plot with the rain simulator, which gave the following equation:
SY= -9,391+ 25,298(P+A) – 0,2297(P+A)2 – 12,551(Kaolinite) + 31,420 (Smectite)-6,18(Humus).
Where: Humus = percentage of humus on the soil surface
The estimation of the solid leakage by applying the WEPP model
The perimeter studied in her doctoral thesis by Grozav, A. (2011), is located in the Semenic Mountains, near Gozna Peak (1444m), being the catchment basin of the Eagles’ Bathroom’s source.
The studied area has a mountainous terrain with altimetry values between 600 and 1400m.
The case study is based on the following assumptions:
- the presence of different soil types (aluviosol, podzol, prepodzol, histosol, districambosol) - constant rain intensity over the entire river sub-basins; - the land use is the same in all the sub-basins; - there are no works to combat the soil erosion.
The model was applied to each area of the river bed sector (gully), by calculating the quantity of the lost soil depending on the soil type.
The sub-basin was divided into sub-basins corresponding to the river bed sectors taking into account the direction of the water flow. The sub-basins are noted with H and the river beds with C (river beds sectors). (Figure 2)
The data entered in the program are: - land use - forest; - climate - the average monthly temperature and precipitation; - soil characteristics; - sub-basins areas; - characteristics of the river beds: the average width of the river bed and the river bed type (river bed channel in the forest area).
The scheme of the river sub-basin, resulting from the application of the WEPP program is shown in Figure 1 and the river network diagram in Figure 2. In addition to the quantities of soil loss, several graphs of variation of erosion and deposition processes on each slope and the maximum rate of entrainment of soil particles on each slope were also presented (Figures 3-7). Graphs of variation of erosion and deposition processes
Fig. 3. The evolution of the erosion process on slope H2 (Aluviosol, maximum involvement of soil particles at 484m - 57.1 kg/m2, the maximum deposit at 556m - 6.72 kg/m2) Fig. 4. The evolution of the erosion process on slope H8 (Histosol, maximum involvement of soil particles at 509m - 767kg/m2, without deposit) Fig. 5 The evolution of the erosion process on slope H26 (Prepodzol, maximum involvement of the soil particles at 264m - 7.79 kg/m2, without deposit) Fig. 6. The evolution of the erosion process on slope H29 (Podzol, maximum involvement of the soil particles at 648m - 74.2 kg/m2, the maximum deposit at 842m - 11.5 kg/m2)
H4 H5 H6 H7 H8 H9 H10
ha 10,663 20,796 44,586 15,716 10,295 24,991 6,587 26,551 12,277 10,909
Fig. 7. The evolution of the erosion process on slope H6 (Districambosol, maximum involvement of the soil particles at 615m – 342kg/m2, the maximum deposit at 741m – 10,5 kg/m2)
Hill H13 Hill H14 Hill H12 Hill H16 Hill H15 Hill H18 Hill H19 Hill H17 Hill H20 Hill H21 Hill H22 Hill H23 Hill H24 Hill H25 Hill H27 Hill H28 Hill H26 Hill H34 Hill H35 Hill H36 Hill H37 Hill H38 Hill H39 Hill H32 Hill H33 Hill H30 Hill H31 Hill 29 TOTAL 7,331 2,725 2,810 0,516 8,466 12,837 2,341 5,306 0,231 12,922 14,017 8,302 19,382 5,929 8,193 14,721 4,340 4,578 17,575 8,356 23,086 2,269 4,683 4,050 43,287 23,277 25,003 14,270 58,027 542,203 700,1 253,7 94,9 28,4 783,5 261,2 287,3 176,7 13,2 251,0 602,4 229,2 469,0 202,5 743,1 0,0 0,0 0,0 0,0 262,9 645,3 36,2 284,5 117,9 1017,1 455,8 782,0 335,7 0,0 4944,1 2371,9 1180,5 187,1 10908,9 5080,5 2698,3 3282,3 27,1 4444,0 12516,5 3803,5 9368,2 1942,6 11672,9 0,0 0,0 0,0 0,0 2734,7 10983,9 563,1 3656,5 1060,0 15284,1 5305,6 5840,6 1706,7 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 1,5 0,0 24,2 0,0 0,0 0,0 0,0 0,0 0,0 0,0 6,9 0,0 0,0 0,0 4,2 0,0 0,0 0,0 0,0
The emergence and development of the torrential gullies in the studied river basin evolved over time; The erosion values in this basin exceed the maximum allowable erosion; The muddy leakage produced on this river basin area also affects the downstream lake; The massive deforestation in the area, without reforestation in that area and without other works to combat the erosion of this river basin, leads to the environmental degradation with serious long-term consequences. Because are not allocated money (in present) for erosion control works cannot be a reason for the serious effects from the future.