Determination Topographical Threshold Condition for Initiation of Gully Erosion with Using GIS (Case Study: Reyhanlou- West Azerbaijan)

Predicting vulnerable areas to gullying, focus on conservation tasks and prevent loss of resources is very important. The study area is located in the Reyhanlou region of Chaldoran city in the northern of West Azerbaijan province. In this research 20 active gullies were selected in Reihanlu area in 2011. Boundaries of the gullies and gullies head drainage-basins were delimited with using aerial photographs (1:40000), topographic maps (1:25000) and global positioning system (GPS). Some gully properties include mean slope of gullies head drainage-basins (S, %) and gullies head drainage-basins areas (A, m2) at the point of gullies initiation were determined by Arc-GIS software with using topographic maps. The statistical analysis such as clustering classification based on gullies topographic characteristics were done by SPSS 16 software. The cluster analyses were classified gullies into three groups. The classified gullies are very similar terms of topographical characteristics including altitude, area, slope percent, slope aspect and processes involved in the development of the gully heads. The investigation of the morphological properties of gullies in the study area showed that the areas of gullies head drainage-basins are variable (2300 m2 - 109300 m2). The mean slope of gullies head drainage-basins was %25.6 (slope was between %6.5 to %43.1). The relationship between the slope (S, %) and area (A, m2) was evaluated and the exponential equation (S=3.81A0.18) to was obtained (R2=0.16). The positive sign of exponent (b) in the (S=aAb) equation also indicate that sub surface runoff is dominant on gully development. Application of S-A relation showed that it is possible to predict the location of gullies. Due to the correlation coefficient was low (R2=0.16), so can be concluded that the topographical threshold condition is not the only factor to develop the gully erosion and to determination of topographical threshold conditions for gully erosion, other factors, such as soil properties, vegetative cover should also be considered.