Study of Morphometric Characteristics of Gullies and Factors Affecting Gully Development in Dryland Farming Area in South of East-Azarbaijan Province

Gully erosion is one of the most important types of water erosion, due to sediment production and severe soil degradation. There is a few information on development of gully erosion in agricultural rainfed areas. This study was carried out to investigate the relationship among gully morphometric characteristics and to find out the effect of land factors (gully length, slope, surface drainage area, land use and plough direction) on gully formation. Also, some conservation strategies for reducing soil losses were studied in a 900 km2 agricultural area in south of Eastern Azarbijan province. For this purpose, 223 gullies were identified in the study area and some characteristics including length, width, depth, elevation difference between the two sides of gully, cross section area and volume, along with land factors consist of slope gradient of land and upland, slope length, surface drainage area, and management factors (land use and plough direction) were determined. Based on the results, gullies have developed in the areas with a drainage surface ranged from 1.5 to 45.1 ha and their length varies from 52 to 2088 m and the volume is between 150 and 35088 m3. Significant correlations are found between gully volume and length, width, depth, shape factor and cross section area. The length is the most important morphometric characteristics to explain gully volume in the lands. Gully development is directly affected by land’s factors including the elevation difference between the two sides of gully (r= 0.51), surface drainage area (r= 0.71), and length (r= 0.78), while it inversely affected by land and upland slope. The gully length is the major factor controlling gully erosion in the area. So that in long slopes, the longitudinal development of the gully and consequently the volumetric expansion of the gully is more. In such areas it is necessary to carry out soil conservation practices.