عوامل مؤثر در شكل گيري و گسترش فرسايش خندقي در لس ها

Factors effecting initiation and advancement of gully erosion in loesses

Gully erosion in one of the different types of soil erosion by water that initiation and advancement of it can tend to the great changes on landscape, degrades the lands and deteriorates the environment. Considering the variety and rate of different factors effecting initiation and progress of gully erosion which varies from place to place, recognition of the most important factors contributing in gulling that can lead to identify alternative solution for its prevention and control ,Arab Gareh Haji watershed locating in Golestan province-Iran,where vast part of it is covered by loess depositions were selected as study area. In order to conduct the study remote sensing data (i.e. aerial photos data 1956 and 1967 together, with land sat ETM+ images dated 2002) using geographic information techniques were applied for Mapping and determining sequential changes of gullied area size. Characteristic of environmental factors were than analyzed to find out probable relations between them and rate of gully initiation and progress on loess depositions using correlation analysis method. Finally based on the results of the study, Alternative solutions were presented that seem to be effective in preventing and / or controlling gully erosion in loess covered areas. Results of the study were shown that initiation and advancement of gully erosion are function of mean annual precipitation, weather temperature, land slope class and aspect, lithology, source of land, soil type and its physical and chemical characteristics, vegetation type,land use and mean annual runoff depth of given area. Accordingly,it was fund out that land slope,and soil characteristics including soil depth, SAR, Ec, Na and TDS of soil are highly correlate to the rate of gully initiation as well as its progress (i.e. morphometeric characteristics of the gullies) thus based on the gained results, the best strategic solution for prevention and control of gully erosion in the studied area and the areas with similar environmental conditions can be prevention of surface runoff concentration and land rehabilitation together with vegetal cover management particularly controlling over grazing by livestocks, improper road construction and cutting tress and shrubs through out the watershed.