Gully erosion hazard zonation in Torood watershed

Subject Areas : Geopolitic

Zahra Arab ghashghaie ¹ , Davood Nikkami ² , Samad Shadfar ³ , Abolfazl Moeini ⁴

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Received: 2011-11-06 Accepted : 2012-03-12 Published : 2011-10-23

Keywords: gully erosion, zonation, Torood watershed, GIS,

Abstract :

Gully eroaion is one of the developed forms of water erosion which redolent ofsurface soil destruction in the lands. Recognize of the effective factors in happence ofgully erosion and it’s zonation is a basic implement to manage and control thisphenomenon. this study has been performed with aim of recognizing the effectivefactors on the gully erosion making and it’s zonation in the watershed of Torood. Themost important effective factor in happending gully erosion such as slope, aspect,litology, land use, distance of communications network, land and canopy cover wereselected as the most important factors on gully development and their layers wereprovided in GIS environment. All three gullies in the area were selected for the study.For each gully, three soil samples were collected from 25, 50 and 75 percent of gullylength and three from outside of gully for comparison. This Samples have examinedfrom the view of Gypsum, Organic Carbon, Salinity, Saturation Percentage, Lime,Sodiun Absorption Ratio and PH. Gully erosion zonation map of Torood watershedwas prepared using 1:40,000 areal photos of 2001 and field measurements using GPS.The area covered by gully erosion in each class of effective factors, were computed byoverlaying gully erosion zonation map with effective factor layers. Effective factorsand their classes in related layers were weighted using Multi Class Mapsmethod.Results demonstrated that 88 percent of gullies are located at high to very highclasses of vulnerability zones. Soil analysis also indicated that salinity, gypsum andsodium absorption ratio in the gullies are higher and the amount of organic carbon isless than that of surrounded areas. But, there were no significant difference betweensaturation percentage, lime and pH in the gullies and surrounded areas.