Investigation of effective factors and proposed model for definepotential gully head advancement (study area: Hableh Roud drainagebasin)

Gully erosion is one of the most complicated and destructive kinds of watererosion. In order to prevent this erosion, the important factors of gully headadvancement must be recognized. For this case, this research has been done in one ofthe sub basins of Hable Rood drainage basin with name’s of Dehnamak in arid andsemiarid weather. Then, effective factors of gully head advancement of four models:Thompson, SCS(І), SCS(ІІ) and FAO, that are: gully head cut watershed area, claypercentage amounts, gully bottom slope percentage and other factors such as solublesalts percentage, silt percentage amounts and sand percentage amounts have beenminded. Meaning amount of each effective factor with gully head advancementamounts in stage of 95% in period of time 1956 to 2005 studied.Result of statistical studies shows, factors such as gully head cut watershed areawith correlation coefficient of 0.98, soluble salts percentage with correlationcoefficient of 0.97 and clay percentage amounts with correlation coefficient of 0.96,intermittently have a most meaning in stage of 0.95. After this, model with usingeffective factors, above mentioned, and SPSS software and two methods, Enter andBackward formed. Then, potential of gully head advancement in following years in theway of comparison estimated amounts by models and measure amounts by aerialphotos studied. Finally with regards to minute difference of 0.001% between twomethods Enter and Backward, Backward method proposed.