بررسی آستانه‌های توپوگرافیکی وتحلیل نقش نوع سازندهای سطحی در توسعه خندق‌ها در دامنه‌های کوهستان‌های نواحی نیمه خشک مطالعه موردی: حوضه شورچای

  Investigation of topographic thresholds and analysing role of surface materials on gully development in the hillslope of semi arid areas.Case study: Shoorchay     M. Bayati Khatibi. ( * ),   Associate Professor of Geomorphology, university of Tabriz, Tabriz, Iran.   e mail: m_bayati@tabrizu.ac.ir     M. Rajabi.   Associate Professor of Geomorphology, university of Tabriz, Tabriz, Iran.     F. Karami.  Assistant Professor of Geomorphology, university of Tabriz, Tabriz, Iran.   Received: 21 Desember 2009 / Accepted: 17 August 2010, 5-8 P     Extended abstract   1- Introduction   In the surface of semiarid regions, erotion accures severe and rapidly. Liner erosion, specially gully erosion –as a hazardous erosion type ,is important factor for delivery materials into runoff and flood plains. This erosion type is formed in semi arid mountains that is not covered by plants. In intensive erosion, many factors are interference, but magnetude of erosion on suitable materials or erosible materials is very high. In shoorchay catchement on Eastern slope of Sahand (located from 36˚ 05́ to37˚ 20́ N and from 46˚ 42́ to 47˚ 15́ E)     Big gully is developed on the hillslope of silt and clay. In this article have been effects of factors on studied gully formation and development many indices, such as V and TCI. The results of this study show that in many parts of Shorchay Basin, slope and surface materials have important role on development of gullies.     2- Metodology   In this article, was investigated linear erosion factors by V and TCI indices. River gradient, flow velocity, time concentration and power erosion of rivers, have been studied and computed as creation and development factors. TC (time concentration) was related to physiographic characteristics, eg., surface property, shape of basin, lengh and slope of reaches, relief, type of plant covers, soil texture. Therefore these factors were presented erosion potential of basin. TC was estemited using Willimas methods. Rn, C, T, FN indices have been used in this study, as morphometery indices.   3- Discussion   In the shoorchy as a sub basin of Garangoo Basin, rate of sediment is very high. Unstable materials, unstable slope on course of river,unprotect slope and salt dom which don’t have suitable plant covers, are main causes of intensive erosion in Shoorchay basin. In the gentle parts of basin, erosion is higher than slope. Mentioned site of basin, in spite of presence sustainble materials on surfaces, rate of erosion is low. These land are farmlands.     4- Conclusion   The rate of TCI is high in Northern and Western part of Shoorchay Catchement. these results also were sugessted that these sites have very high potential for gulling processes. In most site of Shoorchay catchement, when lengh of slope is increasing, the rate of TCI also is increasing. This result show affect of gathering water on erosion. The rate of V at up parts of catchement was high and was decreasing in the midle and down parts of catchement. Most of gullies were made and developed on the sites with marn and silt. Results showed that V and TCI were not conformed in many parts of catchement. The analysis of used indices in many parts of study area showed that numurical data were higher than limit of thresholds .These results show that potential of slope for liner erosion is high   Key words : liner erosion, gully erosion, topographical factors, surface materials eastern slope of Sahand muntain.       References   Amsler, L. M., C, G. 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