a study on the topographic threshold and effective factors on sediment production and gully development in neyriz,fars province

gully erosion has an important role in fars province due to sediment production and enormous damages to land, roads and infrastructures. in this research, 15 gullies were selected to measure their morphometric characteristics. the length, depth, top and bottom width and volume of gully erosion were then measured. influential factors on the sediment production and gully development were analyzed and determined by using stepwise method in spss software. the results indicate that sediment production due to gully development is related to three variables including drainage area, silt and the sand percent of the watershed above the gully heads. these results imply that surface runoff is acting as dominant hydrologic process on gully development. investigation on the topographic threshold reveals that drainage area exponent (b) is negative and these results are in the same line with the results of some recent relevant studies. the results also indicate the watershed characteristics and geological formation impact on the gully sediment production. gully development could be reduced by decreasing the area of bare land as the main source of surface runoff by vegetation planting and terracing. constructing of small earth dams at the end of gullies collect surface runoff and provides better situations for vegetation establishment around gullies.