In arid and semi-arid regions of Iran, concurrent and comparative studies of water and wind erosion have been rarely performed. Therefore, comparative study and survey of these erosions by using MPSIAC and IRIFRE.A models were the main goal of this research.In this research, some difficulties with evaluation of effective factors in wind and water erosion in MPSIAC and IRIFRE.A models have been defined which should be modified based on climatic and edaphic conditions of Iran.In this research, the maps of land credibility to water and wind erosion by MPSIAC and IRIFR.EA models were designed and the sedimentation potentials of both erosions have been compared.The results show that Lalehzar basin with 41 percent of total area, has 49 percent and Negar basin with 59 percent of total area, has 51 percent of sedimentation caused by water erosion.Wind erosion sedimentations in the mentioned basins are 14.5 and 85.5 percent respectively. In Lalehzar basin the total sedimentation potentials by water and wind erosion showed 36.2 percent and 63.8 percent difference respectively. These figures in Negar basin are 76.4 percent for water erosion and 23.6 percent for wind erosion.Therefore, it is clear that wind erosion in some parts of desert regions is more important than water erosion. Although it is better to study both wind and water erosion and estimate the total sedimentation potential.

In this study the erosion and sediment rates of Aglagan-chia basin was estimated on the basis os FAO and MPSIAC methods. In FAO method the yearly erosion rate is 3.87 tons and the sediment yield rate is 167 ton in hector. Six environmental factors were studied; namely, surface geology, soil, topography, landcover and landuse. In MPSIAC method, however, the yearly erosion rate is 3.1 ton and sediment yield rate is 133 ton in hectar. Nine enviromental factors were studied in this method, including, geology, soil, climate, runoff, topography, landcover, landuse, surface erosion and river erosion. The estimated rates of sediment by FAO and MPSIAC were contrasted with those of Hydrometry station. The'results achieved indicate that using MPS lAC method is acceptable in estimating erosion and sediment.

Soil erosin is a complex process and pervasive geomorphologic hazard (earth cancer) and its rate is counted as a comprehensive index for assessing degree of development and sustainability of land management programs of the countries. Due to the strong dependence of pedogenesis on geomorphic systems, there is a close relationship between geomorphic units and erosion at different spatial level. In this research the potential erosion rate of watershed was estimated by MPSIAC model within geomorphologic facies (as work unit) that differentiated on the homogeneity of topography. Litho logy and erosion reaction at semi-detailed level and 1:50000 scale. Based on obtained results, this watershed contains three from II to IV sediment yield and five from II to VI erosion intensity classes. Their mean specific sediment and erosion rates are 322 and 1105 m3/km2/y respectively. A regression equation with R=0.981 was established between specific erosion rate and effective factors of model in each geomorphic facies that significant at 5% level. Also, in multiple regression analysis (backward) all of the nine effective factors remained in the equation with R2=0.95478 at significant level. Differences of erosion rate inter geomorphologic unit (unit., type, sub-type and facies (76 polygons with repeat) and also differences in number and area of polygons of unit maps and sediment and erosion intensity map was compared by Chi-square test. In 17 tests, beside differences in polygon number of unit, sub-type, erosion and sediment maps, the other differences are significant at 0.01 to 0.05 (0.01<P<0.05) body ><level. different at watersheds in management hazard erosion and sediment of estimation for units work suitable as used be can other each to relation genetic close hierarchy spatial with geomorphologic Therefore watershed. Kashidar rate type diversity indicate relationships These>

Many of the small and mid-size watersheds in Alborz south ranges are un-gagged for estimation of the sediment yield, and therefore, having a suitable empirical model to estimate the sediment yield is essential for any soil conservation and watershed management in this part of the country. However these types of models should be calibrated through some gagged watersheds in the similar environmental setting to validate the empirical models to be able to use them in the un-gagged watersheds. In this study, MPSIAC (Modified Pacific South-West Inter-Agency Committee) model is used for estimation of six gagged sub-watersheds in the Alborz south ranges to validate the model. Six gagged small to mid- size watersheds of Emameh, Roodak, Afgeh, Siara, Bilagan and Gozledareh with the range of 1800-6000 hectares are used for this validation study. The comparison of the observed sediment yield in the gagged station at 1 present level in the Emameh, Roodak, Afgeh and Gozledareh watersheds with the estimation made by the model have no significance differences. However in the. other two watersheds, Siara and Bilegan, the difference were significant at the same significant level, therefore, this model is not recommended to be used to estimate the sediment yield of the similar watersheds in this area. The poor estimation of the topography and land use factors and the low number of the sediment data collection years in these two watersheds were the main reason for the failure test. The difference between the observed sediment yield and the estimation by the model were 27.8, 43.2, 46.46, 80.9, 64.4 and 13.5 in Emameh, Roodak, Afgeh, Siara, Bilegan and Gozledareh, respectively.