COMPUTER ASSISTED MAPPING OF SOIL EROSION DANGER LANDS OF RECLAMATION FUND OF GEORGIA

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1 COMPUTER ASSISTED MAPPING OF SOIL EROSION DANGER LANDS OF RECLAMATION FUND OF GEORGIA V. SHELIA, G. GOGICHAISHVILI, I. NATROSHVILI Georgian Agroecological Research Institute. Tbilisi, Georgia. I. KRUASHVILI Georgian Agrarian State University. Tbilisi, Georgia. ABSTRACT Selection of erosion control systems and their distribution by the separate arable lands is very important for optimal development of the agricultural lands. For that case it is important forecasting of erosion in different scales. Basically soil conservationists are using two methods: the Universal Soil Loss Equation (USLE) and the hydromechanical model of soil erosion. On the first stage synthesized algorithm of USLE for each factors of soil erosion was created and respective program- written. Finally a map of estimation erosion danger lands of reclamation fund of Georgia was composed, which is based on the quantitative forecast of soil erosion. Optimal use of land is the important problem in agriculture. Intensity of development of agriculture, production of plants and finally financial success of farming depends on it. In most countries this problem comes from the occurrence of erosion on the agricultural lands. Because of this production of agricultural plants is decreased about 25-30%. Selection of erosion control systems and their distribution by the separate arable lands is very important for optimal development of the agricultural lands. In different countries arable lands occupy vast areas and occurrence of erosion processes are very important ecological problem. Proceed from this it is necessary to provide optimal developing of lands under background of erosion control system. For that case it is important forecasting of soil erosion in different scales. Basically, soil conservationists use two methods: 1) the Universal Soil Loss Equation (USLE) (Wishmeier and Smith, 1978); 2) the hydromechanical model of soil erosion (Mirtskhoulava,1978). The universal soil loss equation (USLE) is A = R K L S C P (1) Where A is soil loss, t/ha.year; R- the rainfall factor, MJ.mm/ha.h; K- the soil erodibility factor, t.ha.h/ha.mj.mm; L and S are dimensionless slope length and steepness factors; C is the dimensionless cover and management factor and P is the dimensionless support practice factor. 325

2 METHOD R-Factor is kinetic energy multiply to 30 min. maximum intensity of rain (Wishmeier, Smith, 1978): R = E / 100 (2) I 30 Where R is erosion index of rain, t/ha.h/ha.mj.mm; E kinetic energy of rain, MJ.t/ha. Mm; I min. maximum intensity of rain, mm/min; Relationship (Eq.2) was developed by Gogichaishvili (1998) from 65 recorded data varying from 10 to 60 year in the lands of the reclamation fund of Georgia. For estimation of geomorphological Factor research territory was divided by geomorphological districts in 1: scale. For each geomorphological district was selected topographic map in 1: scale. For lowlands we have to take no less then 10 sheets of topographical maps, for mountainous (hilly) region - no less then 20 sheets. Measuring length and inclination of slopes on the selected sheet made by poin-statistical method (Litvin, Mirgorodskaia,1976; Litvin, 1984). In the geomorphological region on each arable land would be taken measurements. Factor of slope length and inclination (LS) determine by equation (Wishmeier, Smith, 1978): 2 LS = X / ( S S ) (3) K Factor. The erodibility factor K is the average soil loss per unit of R, measured on a 72.6 foot(22.13 m), 9 percent slope in tilled continuous fallow. Soil erodibility factor is based on six factors: % clay, % silt, plus very fine sand, % organic matter, coarse fragment content, permability and structure (Wischmeier, Smith, 1978). This factor (K) is determined by nomograph (Wischmeier, Johnson, Cross, 1971) for each mapped soil and thus can be readily assessed based on existing surveys. C Factor identified by type of land use, agricultural system and content of plant, annual percentage distribution of erosion index of precipitation. Vegetation period is divided by six period: 1) plough, 2) spring up, 3) striking root, 4) vegetation, 5) ripen, 6) stubble. All agricultural plants were divided by following groups: 1) winter crop, 2) spring crop, 3) highstalk plough plant (maize, sunflower); 3) low-stalk plough (sugar beet, fodder root-crops, melons, potatoes); 4) perennial grasses. These groups were divided by soil cultivated method and agrotechnics: a) over turn layer, b) plane cut till, c) industrial technology (Larionov, 1984). P Factor. For the determination of the erosion danger lands of the reclamation fund of Georgia soil erosion factor (P) was not used (P=1.0). 326

3 RESULTS The Universal Soil Loss Equation as applied on computer assisted soil erosion potential map for the lands of reclamation fund of Georgia, predicts potential long term average annual soil loss (tonnes.ha 1.year -1 ) on the basis of soil erodibility, rainfall, slope steepness and assumed slope length, vegetative cover and management conditions. The map assigns each delineation to one of five soil erosion classes as explained in table 1(FIG.1). TABLE 1 Surface erosion potential classes 1.Negligible (<2.5 tonnes.ha -1.yr -1 ) 2.Slight ( tonnes.ha -1.yr -1 ) 3.Moderately severe(5-10 tonnes ha -1.yr -1 ) 4.Severe (>10.0 tonnes ha -1.yr -1 ) No special practices required to reduce soil erosion losses No special practices normally required except for shallow soil and where soils are adjacent to water bodies Either crop management (C) and/or erosion control(p) practices are normally required to reduce soil losses Combined C and P practices are normally required to reduce soil losses From ha erosion lands of reclamation fund of Georgia, ha is slightly eroded, ha moderate severe and severe eroded. Area of eroded lands are three times more in East Georgia then in West Georgia. From the ha lands of reclamation fund of East Georgia in the condition of erosion danger are ha. From these area ha are in the condition of slightly erosion danger, ha moderately severe and ha severe erosion danger. Among them on the erosion danger condition are ha of the areas requiring irrigation. Elementary area selected on the map were divided by 6 categories: among them 5% of first category of land required erosion control practices; On the 2nd category of land erosion control practices required 6-20% of the lands; On the 3 rd category %, 4th category %, 5th category %, and 6th category more then 80% ha or 19 % of erosion danger lands of the reclamation fund of Georgia are slightly danger of erosion; ha are moderately severe and ha (76%) severe erosion danger. 327

4 LEGEND Erosion danger of the lands Conditional designation % of lands required erosion control I - < 5% II 6-20% III % IV 41-60% V 61-80% VI - >80% 328

5 Morphological districts I 1 -Hollow of Racha-Lechkhumi I 2 -Hollow of Tianeti II 1 1 -Folded foothills of Kolckheti plane II 1 2 -Plateau of Odishi II 2 -Plane of Kolckheti II 3 1 -Plateau of Chiatura-Sachkere II 3 2 -LOW MOUNTAIN AREA OF OKRIBA II 4 1 -PLAIN TIRIPHONI-MUKHRANI II 4 2 -FOOTHILLS BORDER OF PLAIN OF WITHIN KARTLI II 5 -Hollow of Ertso II 6 1 -Plain of Gardabani-Marneuli II 6 2 -FOOTHILLS BORDER OF PLAIN OF QVEMO KARTLI II 7 1 -Denudation plain of river Iori II 7 2 -Accumulation plain of Iori II 8 1 -Plain of riv. Alazani II 8 2 -Foothills of Gombori III 1 -Hollow of Akhaltsikhe III 2 -Clinker plateau of volcanic upland of Javakheti III 3 -Foothill plain of volcanic upland of Javakheti CONCLUSIONS AND PERSPECTIVES Most of the land of the reclamation fund of Georgia is situated on the slopes with high erosion danger (average annual soil losses is more than 10 tone). More than 80% of them required erosion control systems. Using our methodology it is possible to map potential erosion processes of vast territories in middle and small scales of agricultural lands. It also gives us possibility for calculate average annual soil losses from the slopes in farms and make projects for erosion control systems. 329

6 REFERENCES Gogichaishvili, G.P., (1998) Estimation of climatic factor of potential erosion danger of the lands in Georgia. Bull. Of the Georgian Academy of Sciences, 1, pp Larionov, G.A., (1984) Methodika sredne- i melkomasshtabnogo khartirovania erozionnopasnikh zemel. In coll. Aktivnie voprosi eroziovedenia., M. Kolos, pp Litvin, I.F., Mirgorodskaia, N.N., (1976) Khartographo-Statisticheski metod otsenki krutizni sklonov. In coll. Zakonomernosti proiavlenia erozionnikh I ruslovikh protsessov v raznikh prirodnikh usloviakh. M. MSU, pp Litvin, I.F.,(1984) Otsenka reliefa pri sredne i melkomasshtabnom kartoggraforovanii erozionnopasnikh zemel. In call aktivnie voprosi erziovedenia. M.Kolos, p.p Methodical recommendation for prognosis of rainfall erosion. (Workde up by Ts. Mirtskulava 1978), M. VASKHNIL, 60 pp. Wishmeier, W.H., Smith, D.D., (1978), Predicting rainfall erosion losses. U.S. Dept. Agricultural Handbook, No Washington D.C. 58 p.p. Wishmeier, W.H., Johnson, C.B., Cross B.V.,( 1971) A soil erodibility nomograph for farmland and construction sites. Journal of Water and Soil Conservation, 26, 5, p.p