Lithological and Geological Impacts on Gully Erosion (Case Study: Seif Abad Watershed, Lorestan)

Soil erodibility and gully erosion and their expansion occur under geological formation and soil characteristics. This study aims to find the rate of soil and formation effects on gully erosion in Seifabad watershed. To that end, aerial and field work were used together to determine the rate & expansion of 17 gullies in 12 year's period from 1997 to 2009. The soils were sampled for each gully in 50% interval distance with 0-30 cm horizontal surfaces and >30 cm depth. Some factors were estimated from the soil such as EC, PH, Silt, Clay, Sand & limeston percentages. Statistical analysis was done using SPSS 14 through non-parametric tests such as Kruskal-Wallis & Mann-Whitney. Spearman coefficient was used to investigate the relation between volume of gully & litological factors. The results showed a positive correlation at 1% level for the PH with the gully erodibility in surface soil, but for the depth of soil this relation belonged to the silt percentage, and sand showed a negative relation at 5%level with the volume of the gully sediments. Finally, there was no statistical relationship between geological formation and the sediment yield in gullies.