Effect of incipient gullying mechanisms on topographic threshold conditions for gully initiation in southwestern Iran (Boushehr-Samal watershed).

Gully erosion is widespread process of land degradation in dryland regions and has attracted the interest of a large number of researches. although much research has carried out on soil erosion in arid and semi arid regions of iran, few studies have been conducted to understand the threshold conditions of gully incipient. this study was conducted on gullying mechanism and topographic threshold conditions of gullies in an arid region of iran. since the dynamics of gully development channel initiation and extension are controlled by a variety of processes and factors, the data collection and analysis consist of field studies to the determine predominance process responsible for incipient gullying and digital model elevation (dem) analysis to examine slope-area relationship. soil attributes (ec and sar) and landuse practices were known as major factors to initiate piping and the potential of this process to initiate gully is very significant for bank gullies. it seems that topography and soil attributes are the major factors determining the effective process for incipient gullying in our study area. in the other hand all of gullies occurred in the main drainage streams and consequently are the main processes for landscape evolution. correlation analysis showed an inverse linear relationship in log-log plot of upslope area and local slope dataset related to permanent gully heads. however for dataset associated with landsliding the s-a relation was not significant. results of s-a relation can be used to determine vulnerable areas to gullying.