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Orhan Doğan 1 , Nurgül Küçükçakar 1 , Mehmet Emin Özel 2 , Hülya Yıldırım 2 1 Ankara Research Institute of Rural Services, 2 Turkish Scientific and Technical Research Organization (TÜBİTAK) Marmara Research Center Space Technologies Department (MAM) ABSTRACT CORINE METHODOLOGY is a standart method used by the countries of the European Community to determine the erosion risks and qualities of the lands. Using the methodology, countries of the European Community sharing the coasts of Mediterranean Sea have completed their erosion risk maps and classification of their lands. However, land classification studies using CORINE Methodology in Turkey are very limited. On the other hand, having erosion risk map of Turkey using Corine Methodology will be helpful for the integration of future scientific studies between European Community and Turkey which will be a full member in the near future. This study can be accepted as a pilot project in this concept. A pilot erosion mapping study has been conducted in Dalaman River Basin with the financial support from TEMA (The Turkish Foundation for Combatting Soil Erosion Reforestation and the Protection of Natural Habitats) foundation and cooperation of TÜBİTAK-MAM (Turkish Scientific and Technical Research Organization-Marmara Research Center Space Technologies Department) and KHAAE (Ankara Research Institute of Rural Services). The pilot study aimed at use of Remote Sensing (RS) and Geographic Information System (GIS) which have recently shown rapid progress. Erosion mapping and determination of state of erosion using GIS have been realized by applying three different methods (CORINE, ICONA and USLE). In this paper, the studies conducted based on CORINE method will be explained. According to the method, more than 1/3rd of the basin soils (36 %) has highly erodible texture, the soil depth of more than half of the basin (57 %) is less than 75 cm and half of the basin soils has stoniness problem. When potential erosion risk was considered, only 16 % of the basin soils has low, 45 % has moderate and 35 % has high erosion risk. On the other hand, according to the Actual Erosion Risk, which is determined by considering vegetation cover, 27 % of the basin soils has low, 40 % has moderate and 29 % has high level of actual erosion. INTRODUCTION Erosion in Turkey as in the whole world, is one of the most important ecological problems threatening the natural resources of the country. Turkey is located at the Southwest / Central Asian-North African belt which a big portion of it is under most eroded and deserted lands. According to the sediment measurements made on 26 large basins, the amount of sediment transported to seas and lakes is about 500 million tons per year (EIE-General Directorate of Electric Power Resources Survey and Development Administration, 1993). Conservation of ecological balance, land use planning and a good management of natural resources may be possible by having a good knowledge of the present status and problems of soil and plant cover. Soil erosion is of vital importance in the Mediterranean basin, especially at the coastal parts due to some physical and socio-economical conditions. Some of the characteristics of Mediterranean basin like; rough and disordered lands, climate characterized by arid and heavy thunderstorm periods following each other very often (specifically heavy rainfalls occuring during the periods of poor vegetation cover) poor soil structure, low organic matter content of the soil and shallow soils are among the physical factors increasing the severity of erosion. Socio-economical factors, on the other hand, comprise the damaging of rangelands and forestlands to gain areas for cultivation, forest fires ending up with the disappearance of natural vegetation cover and misuse of agricultural lands. The determination of soil erosion with its all aspects is very difficult and studies related with this subject are very limited and insufficient. MATERIAL AND METHOD Material Description of the Study Area Dalaman river basin, where the project was conducted, is located in the Mediterranean region of Turkey.The basin has so many diverse characteristics as of climate, topography, land slope, soil structure, vegetation cover, vegetation density, settlement areas and other social and economical properties that are important factors in the analysis of erosion. Climatic Characteristics of the Basin The altitute of Dalaman basin starts from the sea-level and reaches to 2420 m as gone to the northern parts. The width of the basin is 45 km and it is 113 km long. The coastal part of Dalaman basin has a typical Mediterranean climate with warm and rainy winters, and dry and hot summers and the climate gradually becomes harsher as approached to the northern parts of the basin (TOPRAKSU 1972, 1973). Annual average rainfall in Dalaman county is 1035 mm and as approached to the northern parts of the basin, this amount decreases gradually and becomes as low as 547.7 mm in Acıpayam and 527.3 mm in Tefenni counties. High altitudes and northern parts of the basin are mostly snowy during winter months. Nearly 82 % (845.1 mm) of the average total rainfall (1035 mm) in Dalaman county is recorded during November-March period. For that reason, winter and fall rainfalls at this part of the basin mostly have very high erosive power. Although the erosive power of the rainfall in Dalaman county is very high (162.9) according to Fournier Index, it is very low in Acıpayam. In addition, "rainfall erosivity index" which is a function of rainfall and temperature has a high value (3) in Dalaman county and a moderate value (2) in Acıpayam county. At the same time, although "rainfall erosivity index R" calculated using USLE model was found as 350 t.m/ha for Dalaman county, it was found as low as 26.3 t.m/ha for Acıpayam county. Mapping Method CORINE Method in erosion mapping analyses the following some factors for the determination of actual erosion risk (Doğan and Küçükçakar, 1994). These factors are; 1- Vegetation cover 2- Land Slope 3- Meteorological conditions 4- Soil Properties In compliance with the method, first the vegetation cover density of the study areas was determined with the help of data from satellite images followed by the ground truth analysis at the basin. Because land slope plays an important role in soil movements resulting in erosion, Digital Elevation Model (DEM) of the basin was constructed with the help of GIS. Using the Digital Elevation Model of the basin, slope values were calculated at each pixel. Basic soil properties like soil structure, soil depth and stoniness, which are important as of erosion were analysed in the laboratory. As a result of these analysis, an average soil erodibility parameter was determined for each soil polygon and the soils of the basin were classified in three categories as low, moderate and high erodible soils. Among the parameters having impact on erosion, temperature and precipitation were analysed together and precipitation Index and Bagnouls Gaussen aridity index were calculated as described in the methodology. Basic soil properties like soil structure, soil depth and stoniness, which are important as of erosion were analysed in the laboratory. As a result of these analysis, an average soil erodibility parameter was determined for each soil polygon and the soils of the basin were classified in three categories as low, moderate and high erodible soils. Among the parameters having impact on erosion, temperature and precipitation were analysed together and Fournier precipitation index and Bagnouls Gaussen aridity index were calculated as described in the methodology. Both indices were analysed together and "erosivity" parameter was determined for the basin. "Soil erodibility" parameter which reflects the soil characteristics, "erosivity" which determines the impact of precipitation and temperature and " land slope" which is an important factor affecting erosion were considered all together to reach to "Potential Erosion Risk" map of the basin. At the last step of the method, by incorporating the vegetation cover larger, the "Actual Erosion Risk" values were determined for the basin. RESULTS AND DISCUSSION Erosion risk of Dalaman basin according to CORINE method has 4 different classes. The characteristics of the basin, as determined by the method, can be listed as follows: (a) Soil samples taken from 702 sampling points were analysed in the laboratory of Ankara Research Institute of Rural Services . According to the results; ( i ) Soils of more than 1/3rd of the basin (36 %) have highly erodible texture. (ii ) The depth of soils of more than half of the basin (57 %) is less than 75 cm. (iii) Soils of the half of the basin (50 %) have a serious stoniness problem. (iv) If all three (texture, depth and stoniness of the soils) were evaluated together, the area covered by highly erodible soils reaches to 56 % of the basin. (b) According to the climatological data, 90 % of the rainfalls recorded in the basin is moderately and 8 % is highly erosive. Dalaman basin, which is located between 36° 38¢ 55² and 37° 40¢ 55² North Lattitudes and 28° 39¢ 20² and 29° 49¢ 55² East Longitutes of West Mediterranean Region, has a drainage area of 4481 sq.km. Long years average discharge of Dalaman basin is about 43.8 m3/s. According to data (30-year) from E.I.E's Akköprü measurement station (closest station to the sea), about 1 106 450 ton/year of sediment is transported to the sea from 87 % of the total area of the basin. Sediment yield of the basin is about 247 t.y-1.sq.km-1 (E.I.E, 1994). Soils of Dalaman Basin According to the soil surveys made by TOPRAKSU, Non-calcerous Brown Forest Soil Group has the largest portion (29 %) in the basin. These soils have A (B) C profile. The depth of these soils range between 40-70 cm. Natural plant cover generally consists of deciduous forest trees. This group is followed by Red Brown Mediterranean Soil Group with a portion of 25 %. The soils of this group have ABC profile. Brown Forest Soil Group is the third largest group (17 %) in the basin. The soils of this group have A (B) C profile and the depth of the soils ranges between 50-90 cm. The profile of brown forest soils under Mediterranean climate is completely calcerous. The other Great Soil Groups cover less than 10 % of the basin area and consist of a wide variety of soil groups from Kolluvial to Rendzina with descending ratios of area coverage. Topographic and Drainage Characteristics of Dalaman Basin The topographic and drainage characteristics of the basin can be summarized as in the following table.  (c) Nearly 3/4rd of the basin (72 %) has high slope steepness (15 % or more), which is subject to high erosion rate. About 1/5th of the basin (20 %) has low slope steepness (5 % or less) on which erosion can be controlled through some vegetative studies. The rest 8 % has moderate slope steepness (8 % - 15 %). Erosion rate on this type of land can be reduced by agricultural practices like contour tillage, strip-cropping and rational crop rotation methods. (d) When Potential Erosion Risk of the basin was examined (according to CORINE method); (without taking plant cover into account) only 16 % of the soils has low erosion risk. About 45 % of the soils has moderate and 35 % has high potential erosion risks. Vegetation cover density is one the most important factor preventing erosion. When this factor is taken into account, about 27 % of Dalaman basin has low, 40 % has moderate and 29 % has high erosion risks. As can be seen, the existence of plant cover has highly reduced the potential erosion risk at the basin. REFERENCES COMMISSION OF THE EUROPEAN COMMUNITIES, 1992, " CORINE Soil Erosion Risk And Important Land Resources." Luxembourg. DMI, 1989 Türkiye Klima Atlası, DMI Yayınları. Ankara. DOĞAN, O., KÜÇÜKÇAKAR, N. 1994 "Erozyon Haritalamasında Bazı Metodolojiler", Köy Hizmetleri Ankara Araştırma Enstitüsü Yayınları, Ankara. E.I.E. (1994) Sediment Yıllığı TOPRAKSU GENEL MÜDÜRLÜĞÜ. 1972. Muğla İli Toprak Kaynağı Envanter Raporu. Yayın No: 243, Rapor Serisi: 31, Bakanlık Yayınları:159, Toprak Etüdleri ve Haritalama Dairesi Arazi Tasnifi Şubesi, Ankara. TOPRAKSU GENEL MÜDÜRLÜĞÜ, 1972. Burdur İli Toprak Kaynağı Envanter Raporu. Yayın No: 265, Rapor Serisi: 52, Bakanlık Yayınları: 180, Toprak Etüdleri ve Haritalama Dairesi Arazi Tasnifi Şubesi. Ankara. TOPRAKSU GENEL MÜDÜRLÜĞÜ, 1973. Denizli İli Toprak Kaynağı Envanter Raporu. Yayın No: 244, Rapor Serisi: 32, Bakanlık Yayınları: 160, Toprak Etüdleri ve Haritalama Dairesi arazi Tasnifi Şubesi, Ankara. |