Alluvium Runoff Study in Gilort Hydrographic Basin

Geographia Napocensis Anul VI, Nr. 1, 2012 ALLUVIUM RUNOFF STUDY IN GILORT HYDROGRAPHIC BASIN 1 GRIGORE CIOCĂZAN ABSTRACT. – Alluvium Runoff Study in Gilort Hydrographic Basin. The study aims the characterization1/2012 of the solid runoff in the Gilort hydrographic basin, analyzing the variations in time (for the period 1982-2007) and in space (for the three major relief units in the basin) of this parameter. The data came from the three hydrometric stations where are performed the measurements for the alluvium runoff:nr. Ciocadia, Târgu-Cărbuneşti (Gilort river) and Turburea. , Key-Words: Gilort hydrographic basin, alluvium runoff VI 1. General characteristics In the river bed, the erosion occurs vertically Defined as the quantity of solid material and horizontally.AN. carried by water, gathered from the surface of a The vertical er osion, more obvious on the hydrographic basin in a given period of time, the superior and middle water course, is determined flowing of the silt is a very complex phenomenon, by the slope, the volume, the geological which has contributed to the origin of the structure, the obstacles in the river bed, as the landscape as we know it, taking into account the tendency is to reach a balance in the lowest geological time (Zăvoianu, 2002). The material point of the river bed. separated and carried by the water is composed of The horizontal or lateral erosion appears on particles of different dimensions, mineralogical the areas with slow slopes, in the middle and and chemical composition. inferior river course. As a result of this, the river The largest amount of silt that comes from bed becomes wider and changes, as the meanders washing the surface of the hydrographic basins appear. is produced by the high rivers during spring The transportation of silt, through the flowing time (due to the disintegrationNAPOCENSIS of the superficial of the river, occurs because of the appearance of layer of earth caused by the sequence of frost silt as a suspension (clay, earth, sand transported and thaw in winter, which is washed away by by the tumultuous movement of the water) and the water resulted from the melted snow or from dragged silt (sand, gravel, rubble). Even if the the spring rains) that carry away the products of suspended silt is better represented in the solid this degradation (Pişotă, 1970). volume measured in a section, the dragged or The flood waves in summer time also have rolled away silt is also important. In time it has a great influence in the flowing of the silt. They formed large debris cones at the line between one are determined by the torrential rains during landscape to the next, and nowadays they which, after a long period of drought, especially determine the river bed to silt up, especially at the on vegetationhttp://geographianapocensis.acad-cluj.ro covered terrains, the impact of the exit of the mountain region towards the rain drops dislocates the soil particles. The subcarpathian region. The silt volume (Da) is flowing of these particles, dislocated by the rain, calculated by adding the volume of silt as GEOGRAPHIAon a slope, appears as a compact layer. The suspension (R) and the volume of dragged silt (G) amount of silt separated from an empty terrain is at least three times larger than the one Da=R+G(kg/s) (1) originating from the vegetation covered terrain. 1 Water Direction Jiu, Water Administration Service Gorj, Bd. Ecaterina Teodoroiu, no. 99, Târgu-Jiu, Romania, e-mail : [email protected] 71 Grigore Ciocăzan 2. Alluvium runoff in Gilort heavily affected by the land slides and crossed hydrographic basin by cloughs; the torrential basins of Bobu, Rea Valley and Tărăţel (together they measure 93 Alluvium runoff, as an expression of the 2 erosion processes, is the final result of all the km ) on the right side of Blahniţa. At the geo-physical factors from a determined basin Târgu-Cărbuneşti hydrometric station, on the (Zăvoianu, 2002). southern limit of the Subcarpathians, the On its entire length of 116 km from North average suspended silt flow is 1,8 t/ha.year. It is to South, Gilort river and its main confluents important to mention the fact that, after 1989 wash the southern side of the Parâng mountains, some agricultural fields from the subcarpathian the Getic subcarpathians and the Getic area have been abandoned by the owners1/2012 who piedmont. Each one of the three types of haven’t worked since then, leaving them to be landscapes has its own characteristic features occupied by the vegetation. Thisnr. is why the composed by the rocks, the vegetation, the soil surface erosion was reduced and, the cloughs are and the degree of human intervention. not very deep. It is estimated that in the future The Parâng mountains, made of dense the contribution of the subcarpathian area to the rocks, with fragmented shapes, valleys and solid silt flowing will beVI less and less important. abrupt slopes, forests composed especially from The Getic Piedmont is crossed by the Gilort foliage trees, which occupy more than 40% of river from Târgu-Cărbuneşti to Filiaşi through a the surface, offer a specific average of large valley, with asymmetrical terraces over suspended silt flow of 0,5-1 t/ha.year. At the three distinctAN. sectors. They have appeared Ciocadia hydrometric station, where the because of the clay, sand and gravel deposits contribution of the of the solid and liquid flow that are not cemented and the depth that favors belongs to the mountain area in proportion of important volumes during heavy rains and snow 95%, the value of the suspended silt flow melting. average (1982 – 2007) is 0,7 t/ha.year. For all The confluents of the Gilort river down the rivers that have the superior river course in stream from Târgu-Cărbuneşti (Socu, Purcaru, the mountain area, an important part is played Vladimir, Sterpoaia, Groşerea, Cocorova, Valea lui Câine, Arpadia) with lengths between 7 and by the quantity of dragged or rolled material 2 (gravel and rocks) accumulated in the 19 km and the surface of the basins of 277 km , depressions situated on the outside of the have a major contribution to the increased mountain chain. Because it is spread on large turbulence of the Gilort river on its inferior areas and it is several meters deep, sometimes course. the rivers flow underneath NAPOCENSISit when the volumes The specific suspended silt flow average at are small. During the important flood waves, Turburea is 3,42 t/ha.year, and the silt volume triggered by the heavy rains, the specific transported in one year is 369216 t/year. maximum of suspended silt flow was 1452 The values shown as characteristic for the silt t/ha.year on June the 7th 1989, at the Ciocadia flow on all three types of landscapes are hydrometric station. highlighted also in the multi-annual monthly The Getic subcarpathians area, by its frail averages or solid volumes that grow from 0,235 rocks (clay, sand, gravel), by the use of the land kg/s at Ciocadia to 11,7 kg/s at Turburea [table 1]. (agriculture), by the contribution of the After analyzing the seasonal solid volume, geomorphologic phenomena on the mountain we notice common aspects and differences: the sides (land http://geographianapocensis.acad-cluj.roslides) contributes heavily to the smallest values of the solid volume appear in increase of the volume of silt carried by the January (0,038 kg/s at Ciocadia, 1,09 kg/s la Gilort river and its confluents. We must Târgu-Cărbuneşti and 2,99 kg/s at Turburea), GEOGRAPHIAconsider in the subcarpath ians two areas with an and the highest monthly average is 0,508 kg in important contribution of suspended silt: Câlnic July at Ciocadia, 8,29 kg/s in April at basin (104 km2) situated on the left side of the Târgu-Cărbuneşti and 30,3 kg/s in July at Gilort river, ranging between the Cârligei Hills Turburea. to the North and Burlani Hills to the South is 72 ALLUVIUM RUNOFF STUDY IN GILORT HYDROGRAPHIC BASIN Table 1. Solid volumes – monthly and multi-annual average values (expressed in kg/s) Hydrometric station Month Ciocadia Tg.Cărbuneşti (Gilort) Turburea I 0,038 1,09 2,99 II 0,094 2,85 9,42 III 0,193 3,70 10,4 IV 0,350 8,29 15,6 V 0,249 6,42 16,2 VI 0,391 6,65 17,6 VII 0,508 2,72 30,3 VIII 0,506 2,25 9,74 1/2012 IX 0,142 1,49 3,67 X 0,144 2,30 8,89 XI 0,119 3,32 9,61 nr. XII 0,088 2,03 6,71, Multi-annual 0,235 3,59 11,7 average VI We notice the contribution of the high spring during the months in which the main flood waves waters in the solid flow at Târgu-Cărbuneşti and occurred. (ex. The year 2005, that shows a the contribution of the high waters of July at deviation towardsAN. left, has the biggest average Turburea. This is the period during which the right annual volume from the analyzed situation, and side confluents of the Blahnita river and the Gilort the main flood waves occurred during July and river down stream from Târgu-Cărbuneşti carry August, when the vegetation is fully developed, during the heavy rains large quantities of silt and the year 2004 that shows a deviation towards because of the propitious geological composition. right, has a maximum volume of 225 m3/s and The graphic representation of the connection th R of 1372 kg/s on November the 15 ).

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