جستجوی مقالات مرتبط با کلیدواژه « فرسایش آبی » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

The study of erosion and sedimentation is a crucial aspect and an integral part of watershed studies in a basin. The methods employed to prevent erosion and sedimentation play a significant role in basin management planning. However, due to the lack of accurate statistics on erosion and sediment amounts, it becomes necessary to utilize estimation models for assessing erosion and sedimentation. These models are often region-specific and may have a wide range of uncertainty in different areas. One notable benefit of modeling, regardless of its type, is its ability to analyze natural processes within the basin. On the other hand, understanding erosion and sedimentation processes in a region can be an effective step in managing, planning, and prioritizing available resources. In this research, the aim was to determine the sensitivity of the MPSIAC model to the relationships among its parameters. Additionally, the goal was to assess the model's sensitivity to changes in these parameters and their impact on sedimentation. By identifying the influential ground and atmospheric parameters, it becomes possible to prioritize their effect on water sedimentation in the region.

Through the sensitivity analysis of the model, it is possible to identify the flexibility of the model to the changes of its various parameters. It is also possible to determine the relationships between model variables and prioritize the parameters affecting the model output. Sensitivity analysis can be used in the calibration stage, in such a way that results are accurate, and time and cost are saved. In this study, to analyze the sensitivity of the MPSIAC model, first, the nine parameters of the model were examined. Then, according to the arrangement of different parameters in the structure of this model, the parameters were numbered from X1 to X9. Then, the score range of each parameter was entered in its calculation table according to the modified model of PSIAC. In this step, the average of each parameter was calculated according to its upper and lower limits. To achieve this, the nine parameters of the model were standardized, and the sedimentation rate was estimated by varying each parameter within its lower and upper limits while keeping the other parameter(s) fixed at their averages. With each change, the sediment discharge was calculated.

In the analysis of the results, the slope of the curves of the standardized parameters relative to the dependent variable (specific sediment) is considered. So that, any part of the curve that has more slope changes means that the model is more sensitive to minor changes in that parameter in that interval. In this study, the results of this sensitivity analysis reveal that the slope factor and runoff volume have a considerable influence on sediment yield. For slopes up to approximately 15%, the slope parameter has a relatively smaller impact compared to other parameters. However, as the slope value increases, its effect becomes more pronounced, indicating that high slopes (greater than 15%) have the greatest impact on sedimentation. The runoff factor exhibits a sudden increase in sensitivity at higher flow rates.

In examining the effect of different parameters on the model performance, the parameters that had the largest slope of changes can be considered as the most effective parameters in sedimentation of the basin. In other words, the model demonstrates high sensitivity to slight changes in specific peak discharge values above 20 m³/s/km2. Therefore, implementing integrated (biomechanical) management measures to control slope steepness and reduce runoff volume can be an effective strategy for mitigating sedimentation. Therefore, based on the results, the role of land factors is very important, such as slope and then runoff, in the erodibility and sediment production in basins. Of course, it should be noted that climatic parameters directly and indirectly affect the amount of peak flood discharge and should not be neglected for their importance and influence in flooding and subsequently the erodibility of the watershed.

Today, soil erosion has become one of the biggest problems in the world, especially in arid and semi-arid areas, which affects environmental, agricultural and food security issues. On the other hand, the growth and development of human activities along with land use change and resource destruction are among the factors affecting the intensity of erosion. Soil erosion in Iran has intensified due to the destruction of natural resources in recent years, and land use changes have played a significant role in this process. However, until now, preventive approaches based on soil erosion hazard assessment to adopt correct management measures have received less attention, which is mostly due to the lack of necessary statistics and information in the basins. Therefore, in any case, it is necessary to identify the areas prone to erosion and sediment production in the internal sub-basins of Iran, which lead to the loss of thousands of tons of fertile soil every year. To achieve this objective, models have been presented, each of which has strengths and weaknesses. By organizing the information related to the decision-making process and simulating the factors affecting the decision, as well as by simplifying the relationships in nature, the models lead to the understanding natural systems. Models are tools that are used in combination with many other assessment methods, so it can be said that modeling is the best option for the initial assessment of watersheds without statistics or with limited statistics. Therefore, the present study was conducted with the aim of investigating the hazard and identifying the areas sensitivity to soil erosion in the sub-basin of the Chehelgazi watershed of Kurdistan province using the Fargas model.

Chehelgazi sub-basin as one of the sub-basins of Qeshlaq dam is located in Sanandaj province. Considering the natural and weather conditions, it is considered representative of mountainous areas (27,233 hectares and equipped with a hydrometric station). The average height of the mentioned sub-basin is about 2200 meters above the sea level, and also the average annual rainfall in this sub-basin is 294.2 mm, the area of pastures is 23465 and the total of irrigated and rainfed agriculture is 3768 hectares. Fagas model was used in order to investigate the hazard and identify the areas sensitive to soil erosion in the mentioned sub-basin. In determining the hazard of erosion, the Fargas model considers two factors of erodibility of rocks and drainage density in each rock unit. In this research, by using maps of rock units, drainage density and scoring tables related to the model, a soil erosion hazard map of the basin was prepared. In the first step, the rock units of the basin were determined using the geological map, and based on the model guide, the rock resistance to erosion was evaluated. In the second step, the drainage network map of the studied basin was prepared and integrated with the stone unit map, and after integration, the drainage density of each stone unit was determined and based on the model valuation guide, the drainage density of each stone unit was valued. Finally, the erodibility hazard map of the basin was prepared in five categories (low to very severe) by multiplying the value number of rock erosion resistance and drainage density in each rock unit.

The results of the Fargas model analysis showed that 0.48, 36.15, 15.35 and 48% of the sub-basin are in low, medium, severe and very severe erosion hazard, respectively. In other words, 63.35% of the sub-basin is in a state of severe and very severe erosion hazard. Comparing the results of the model with various studies in the basin and other similar basins showed that the Fargas model estimates the erosion hazard more than the actual value, which can be caused by the valuation of rock units. However, the existence of shale and its high sensitivity to erosion in the basin and the confirmation of the model in determining its erosion hazard can be a confirmation of the efficiency of the model.

The results of the present study indicate the hazard of high erodibility of the sub-basin. Because of the the sub-basin's position in the water supply of Qeshlaq Dam, it is suggested, while examining other quantitative and qualitative models and their results, to provide evaluation and planning models, to make management decisions, and to promote, train, and implement useful projects related to reducing the rate of displacement and loss of the soil at the basin level. Because in order to increase the life and efficiency of dams, the entry of sediment into the dam should be as low as possible to be a small step towards reducing the rate of soil erosion and wastage. However, according to the results of the model, it can be observed that the studied area is under severe hazard of soil erosion, and these results are useful for researchers and planners to control erosion; but due to the limited number of studies in the region, other studies should be conducted in the region for more certainty.

Due to the logistical challenges of large-scale rainfall simulator, most studies to date have used small scale rainfall simulator with a nozzle height of less than 3 m and a plot area of less than 5 m 2. Performing such small-scale studies is valuable for investigating the rate of soil erodibility, soil infiltration, the impact of herbaceous and shrub cover on water erosion and runoff. But there is a need for larger rainfall simulator to better understand and deepen the water cycle process and the interactions that occur on a larger scale. The rainfall simulator should be designed to simulate rain from top of canopy. In this case, raindrops can reach their final speed. For this purpose, a 15-meter anchored tower (controlling tower by several cable is called anchoring) with multiple nozzles is need. The most important component of any rainfall simulator is the type of nozzle used. The most common type of nozzle is a rotating plate nozzle with a 360 ° rotation angle in two linear mounting patterns and H mounted on top of the mast. The nozzles are connected vertically to a water tank and pump motor via a plastic pipe. After setting up the system and calibrating the rainwater, a windmill collector with a radius of 5 meters (about 80 m 2) of thick nylon, thin rods and zippers is used to collect throughfall, interception, and stemflow. In water erosion of soil, the most important stage that the soil is washed is rutting stage. In small-scale rainfall simulator, the low dimensions of plots causes runoff doesn’t have enough time to rut the soil, so in this condition true knowledge about soil erodibility cannot be achieved.

Gully erosion is one of the most important advanced (accelerated) forms of water erosion; so, identification and consideration of effective factors and its zoning is one of the important tools for controlling this phenomenon. The main purpose of the present study is spatial modeling and assessment of gully erosion using a probabilistic Weights-of-evidence (WofE) model and its different scenarios for selecting the location of gullies identified in Maharloo Watershed, Fars Province. For this aim, first, using extensive field observations, points of headcut, end, and also the boundary of the gullies (gully polygons) were identified and the gully inventory map for the study area was prepared. Then, thematic layers such as percent slope, slope aspect, plan curvature, elevation, Topographic Wetness Index, average annual precipitation, NDVI, land use, lithological units, distance from river, distance from road, drainage density, and some soil characteristics (percent silt, percent clay, EC and pH) were identified as effective factors on gully occurrence and their maps were prepared and classified in GIS environment. In the next step, using WofE algorithm, the relationship between effective factors and three different scenarios according to gully locations (head, end and gully polygons) were determined and the weight of each factor's classes was calculated. Ultimately, gully erosion zonation maps were prepared in the ArcGIS software environment. Evaluation of three gully erosion zoning maps using the ROC curve and 30% of unused gullies in the modeling process indicated that the accuracy of the models prepared based on three scenarios are 0.847, 0.861 and 0.792, respectively. Also, results of layer weighting using WofE model indicated that rainfall increasing, high drainage density, high silt percentage, low altitudes, southern directions, low distances from roads and river, Asmari, Aghajari, Razak, Gachsaran, Mishan and Sachun geological formations, as well as bare lands, have played an effective role in the occurrence of gully erosion in the study area. In order to control and prevent this kind of erosion in the Maharlo Watershed, the protective measures and watershed management were performed in the early stages.

One of the important reasons of soil erosion and sediment production in irrigation and drainage canal networks is the soil instability. Erosion mechanism in this type of channel starts with the impact of raindrops and soil aggregation, so that broken fine particles lead to blockage the pores. In this condition, soil permeability is reduced compared to the initial state and runoff that is increasing. Increased runoff on slopes of moderate to steep, rises shear stress sharply which causes soil destruction and produces sediment production. To overcome this problem, suitable vegetation cover deployment is appropriate, but in some situations, vegetation cover establishment is not possible simply due to special circumstances and it is not the best solution in the short term as well. One of the ways of controlling erosion on slopes is the use of various mechanical structures, commonly used in engineering projects, that is associated with expensive costs. Another solution that was tested in this research, is the use of natural corrective materials such as organic mulch and natural rectifier materials. In this study, by using four types of various organic mulch, soil erosion resistance of various parameters of the drain canal bank was studied using simulated rainfall in the rainfall laboratory of Soil Conservation and Watershed Management Research Institute. In this article, the results of using bio mulch for erosion control, on the drainage channel bank are provided. This study aimed to determine the most appropriate type and density of different mulch on canal bank erosion reduction for irrigation and drainage network channel project that is located in Arayez plain of Khuzestan. With the use of four organic mulch, at least 40 experiments on soil samples were done. For the all laboratory tests, 25 kg soil samples were pressed inside the steel basins, to imply the bulk density of soil in nature. Treatments in the flume with a slope of 1 to 1.25, similar side slope drains, in both 30 and 80 mm per hour rainfall intensity were simulated. Each treatment was applied at three densities. The results showed that all mulch treatments compared with control samples had a significant effect on sediment and it confirmed that the bio mulch are effective in the erosion control of the bank drainage channel. The results showed that the mulch will lead to reduce sediment more than 90 percent. Therefore, the use of mulch 1 and 4 in the highest density, have the greatest impact on the rate of erosion. It was also found that by increasing density of mulch, the amount of sediment reduced significantly.

Investigation of sediment particle size distribution (SPSD) was considered as a new science to investigate the SPSD interactions in fluvial systems by hydrologists, geomorphologists and geochemists since 1980s. Accurate understanding of complexities of SPSD behavior in different environments will help overcoming management problems in soil and water conservation as well as pollutants transferring in the environment. This study was conducted to provide comprehensive information about the importance and application of SPSD in different spatial and temporal scales. The present study at first provided the definition of SPSD from different perspectives of scientists, then introduced the SPSD measurement methods and finally, investigated SPSD variation at different spatial and temporal scales. Such information could be used for better understanding and management of transport of sediment and sediment-associated nutrients as well as contaminants such as phosphorus, pesticides, heavy metals and pathogenic agents. In addition, the results are useful in engineering projects such as drinking water, wastewaters and rivers and is valuable to identify the soil erosion processes.

Recognition and evaluation of influencing factors on desertification as well as determination of influenced area with this problem is necessary. The method of FAO-UNEP is one of the proper methods to evaluating the desertification which into study the different factors and process. Vegetation distraction, water and wind erosion, decreasing the quality and quantity of water supply, saltification of soil together with animal pressure and human population on the environment were the main factors and processes investigated in this research. A period time of 20 years (1989-2008) choose for assessment of desertification in this study and data were collected with considering the aerial photograph and remote sensing images. For investigation of each processes were evaluated several indices and scoring with field sampling and library studies. Four class of poor, moderate, intense and very intense were determined for discrimination of desertification levels. Each process was investigated from 3 aspects such as existing condition, speed and natural capability of desertification. Desertification maps was constructed in GIS and integrated for final desertification map. Base on the result were classified 116466ha (%20) in low, 273240ha (%48) in intermediate and 179123ha (%32) in severe class of desertification in Shazand watershed. Intense desertification were observed mainly in mountainous and rocky area with slop higher than %40 and poor vegetation. Severe desertification was observed mainly in mountainous ranges with slop higher than 15-30 percent and poor vegetation. Water erosion and vegetation destruction were the main factors of desertification in this watershed and whereas the animal pressure was the main factor of desertification intensity.

One of the important factors affecting on the erosion is lithological characteristics in the watershed. Due to the characteristics of the watershed can be considered reaction of rock to the process of weathering and erosion in the study. In the research of erosion and soil conservation investigate the lithological characteristics of the study area is very important. According to the study area (north of the Darab city) is located in arid and semi-arid and it is able to water erosion, the aim of the study area is investigation the characteristics geological formations, determination of sensitive the area to water erosion in the northern of Darab city. Also in the research, relationship between lithological characteristics and Normalized Difference Vegetation Index (NDVI) was determined. After preparing the geology map and determining the type of formations in the region, based on resource was obtained sensitivity of formations in the study area. Finally, relationship between NDVI and sensitivity of geological formations to water erosion using Landsat 8 images in 2015 was determined. Also for preparing the landform map used topography position index (TPI) in the study area. The inputs data for preparing the TPI was slope, min curvature, max curvature, plan and profile. The results showed that there were 4 classes of sensitivity that consist of low sensitivity, medium sensitivity, high sensitivity and very high sensitivity in the study area. So that 40.22, 26.81, 20.11 and 13.41 km2 were in classes of low sensitivity, medium sensitivity, high sensitivity and very high sensitivity to water erosion respectively in the study area. Also the results showed that EMas-ja with low sensitivity had the highest NDVI (0.457). So the EMas-ja was suitable for growing of vegetation and had low erosion in the study area. The results showed that the study area was classified ten classes that consist of canyons, deeply incised streams, midslope drainages, shallow valleys, upland drainages, headwaters, u-shaped valleys, plains small, open slopes, upper slopes, mesas, local ridges/hills in valleys, midslope ridges, small hills in plains, mountain tops, high ridges. The highest area of landform was canyons, deeply incised streams (44.36%) and mountain tops, high ridges (33.38%). While the lowest area of landform was plain small (0.12%)

Soil is one of the main non-renewable natural resources in the world and its degradation is considered as a major threat around the globe because it reduces the productivity capacity of soil variability and makes the environment instable in the long turn. Soil degradation has three different aspects: Physical، Chemical and Biological degradation. If any of these aspects of the destruction of the soil can be estimated in an equation، assessment and estimation of the soil degradation can be done easily. To achieve this goal extensive efforts have been made in various parts of the world and different methods for assessing soil degradation have been suggested. In this research latest guideline of soil degradation assessment presented by Land Degradation Assessment in Aridlands is used to desert region of the east of Esfahan and different aspects of soil degradation is assessed by that. According to the findings of this research، LADA methodology of soil degradation easily can be used by most users within the country because the method is simple and provides results as fast as possible. Comparing the results of this method and photos of relative the sampling sites has shown the model is reasonably accurate.

Rainfall erosivity as one of the major factors of soil erosion is expressed as indexes. The objective of this study is determining the appropriate rainfall erosivity index in Iran and generalizes it by its estimation from more readily available indexes to stations without rainfall intensity data and to determine the most accurate interpolation method for preparation of its map. For this reason, necessary data were collected from seven soil erosion research plots in Western Azerbyjan, Khorasan Razavi, Zanjan, Semnan, Mazandaran, Markazi, and Yazd provinces, respectively. The rainfall intensities were recorded, as was the sediment yield associated with storm events, and 64 different erosivity indices based on rainfall intensity were computed for these soil erosion research stations. Our founding shows that were the best correlated with sediment than other erosivity index. Further, rainfall erosivity indices, based on the amount of rainfall, were also computed for all soil erosion research plots and synoptic and climatic stations. The results showed that the modified Fournier index had a significant correlation with After normalizing the primary data, semi-variograms were determined and the best model was obtained. Then, different interpolation methods were compared and spline was chosen for drawing the rainfall erosivity map. The output map showed a decreasing trend from west and north to east and south of the country and this trend was correlated with climatic change from humid to semiarid regions.

The aim of this research is to describe the development of a methodology based on present knowledge and available data for evaluation of water erosion behavior and risk as well as modeling and estimation of soil erosion، which is compatible for other similar areas of Iran. Accordingly، the conducted research was based on four major types of water erosions including: sheet، rill، channel and riverbank which have considerable role on sediment yields of Baleghli Chay Watershed، Ardebil Province، were separately and spatially studied. In order to determine the inter-effects of effective factors، the study was conducted using stepwise multivariate statistical tests. For each erosion type، an individual model was then presented. In the next step، after determining of relations between sediment yield and environmental factors (fixed & variable) through statistical analyses and selecting of effective factors on erosion and sediment yields، was created an empirical structure for modeling erosion and sediment yields based on MPSIAC erosion model. In formulation of the new model، were used of eight effective factors on erosion in the area. These factors are susceptibility of geological formation، soil erodibility، rainfall erosivity، runoff erosivity، topography، hydrographic drainage، Normalized Difference of Vegetation Index (NDVI) and field conditions of erosion features. In the presented model، with summation of the scores of mentioned eight factors، obtains the M value، which can estimate the amount of erosion and sediment yields of the area، using exponential formula between sediment yield and M values. In addition، in order to obtain the confidence of presented model، it was used in «Nir» catchment for evaluation the precision. The results showed 11 percent difference. With accepting of this error value، the water erosion hazard map of the area was provided and presented using new model.

Soil erosion is a main hazard in most area of the country specially in arid and semi-arid regions and it is very important because of sedimentation, pollution, increased flooding and its negative effects on soil productivity. One of the features of arid and semi-arid areas is the presence of low cover of vascular plants. These empty spaces are usually good niches for biological soil crusts or cryptogams like mosses. These crusts contribute to a variety of ecological functions and have different effects on soil features and vascular plants. The present study was carried out in the rangelands of Torogh dam basin of Khorasan- Razavi province in order to find the effects of such kind of plants (mosses) on water erosion. For this purpose, artificial runoff streams in plots with two intensity (low and high) for 30 minutes. In order to study the effects of different amount of mosses on sedimentation and specific erosion, four different density of mosses in the same experimental situation were studied: high (60- 75% of plot), medium (35-50% of plot), low (10-20% of plot) and control (0%). The results of analysis of variance and tukey method by the use of Minitab software showed a significant difference in 95% level between the four considered density of mosses and the two intensity of water. As mosses density decrease, sedimentation and specific erosion increased consequently. But there were no significant differences in infiltration between the different treatments.

Desertification is a global problem and most of arid and semi-arid countries of the world including Iran face the phenomenon. Desertification causes many limitations in terms of agriculture, food supply, livestock farming, industry development and so forth. The phenomenon is a process that has gradually developed and intensified and the costs of modifications increase exponentially. Therefore, identification and assessment of factors effective in desertification, and determining the regions affected by this disaster are necessary for each region. FAO and UNEP method is considered as one of the best methods to evaluate desertification in which several processes are investigated. Vegetation degradation, water erosion, wind erosion, decline in the quality and quantity of water resources and soil salinization as well as livestock and population pressure on the environment are considered as the main processes in this study. This study was carried out in a twenty-year period with considering the oldest data, aerial photographs and satellite images. To evaluate each process, several indicators were considered and selected indicators were evaluated by field and library work. Four classes of low, moderate, severe and very severe were also selected for separation of desertification intensity. Each process was studied from three aspects i.e. current situation, velocity and the potential of desertification. Desertification maps were generated in GIS and then integrated to produce final map of desertification. According to the results, 125853 ha (%23), 251504 ha (%45), and 158819 ha (%29) were classified in classes of low, moderate, severe and very severe, respectively. Severe desertification mainly was observed in mountainous areas with slopes over 60 percent, and in saline and sodic marginal lands of Kavire-e-Meighan basin. Vegetation degradation and water erosion were identified as the main factors of desertification in this basin and livestock grazing was the main cause of worsening desertification. Obtained results provide a basis for better recognition and proper combating desertification in this area.

Determining the relative sensitivity of land to erosion and its factors، could be the basis of soil conservation programs. The aim of this study is to compare water and wind erosion functions in land degradation of Dasht-e-Jeihoon using PSIAC and IRIFR. EA models and the source studying of aeolian sediments in geomorphologic facieses as homogeneous units. The results indicate that in Dasht-e-Jeihoon، water erosion has been transferred fine and coarse grained sediments to the center of plain. In fact، in this region wind erosion fulfills the effect of water erosion in center of the plain. Erosion estimation shows that 50. 3 percent of the region includes the mountain facieses)erosional or bare pediment (which water erosion is moderate to high، have minute to low wind erosion and 49. 7 percent of the region includes the facieses of Epandage and covered pediment which water erosion is low while wind erosion has moderate to high effects. Water erosion not only results 39. 7 percent of the Dashte-Jeihoon sedimentation، but also it has a significant role to supply erodible particles in downstream of the region. Observations and the results showed that for estimating the erosion in dry areas such as Dashte-Jeihoon، we need to use water and wind erosion estimator models as supplements.

Gully erosion is a type of water erosion which causes degradation in both agricultural fields and rangelands as well in arid and semi-arid areas. According the role of soil degradation due to erosion، research objectives were to find out investigation causes gully erosion in Robat Tork Watershed. In this research three representative gullies were selected in agriculture and rangeland working units. In each working unit، samples taken from nine soil profiles were analyzed for texture، organic matter، gypsum، total lime، pH، EC and SAR. Soil infiltration rate was measured where were drilled profiles in each working unit too، In addition، morphometric characteristics of gullies including length and lateral profiles، top and down width، depth of gully، the cross section، width to depth ratio، the slope of bed، gully length were studied. Results of the study showed that SAR and sodium cation are caused dispersion of soil particles and increasing gully erosion. percentage of clay and silt is 11% and 29% in surface layer representative head cut gully and organic matter is between 0. 30% to 1. 82% in agriculture unit. In rangeland unit، percentage of clay and sand is 41% and 43% in surface layer representative head cut gully and organic matter is between 0. 29% to 0. 99%. In rangeland unit، in a specified level، the number of gully is more than agriculture unit. Furthermore، the results showed that TNV in agriculture unit and pH، EC in rangeland unit is more than. In both units depth to wide ratio is more than 1 in every gully. Permeability of soil is 4. 25 cm and 3. 45 cm in agriculture and rangeland units respectively.

Desertification process as a continuous and destructive phenomenon and as a global scourge, not only developing countries but also developed countries threatens. Successful projects and control desertification and reduce risk factors inhibit desertification requires proper understanding of cause and effect relationship between desertification and existing processes, but it is obviously what the process and accelerate out of its normal effect of making human factors.In The case study Desertification procesure in the framework of work units assessed applying different valuable and available indexes of erosion including: kind and density of water erosion, drainage net density, major landuses, green cover, appearance of erodiblity formations, soil cover, number of days with dust storm. Map of desertification map for the watershed generated and overlayed with current landuse map. Finaly desertification procesure involving landuse were assessed in categorized geomorphological units; mountain, pedimont and playa. Results showed that the dominant form of erosion in mountain is water one. Over the pedimont and playa, because of erosion activities in highlands and focusing land exploitations in lowlands, desertification is more intense and both water erosion and wind erosion are active.

Many studies have been carried out to assess and prepare desertification map in the world. In order to develop a regional model and quantitatively assess the present situation of desertification، a study was carried out in an area of 88350 hectares in Zahak region of Sistan. In this study، at first by combining information extracted from topographic and geologic maps، air photos and field survey، the area was divided into 11 geomorphologic facies; each of which was considered as the main unit for evaluation of the present situation of desertification. Considering to FAO-UNEP and MICD models are the most famous models of desertification intensity assessment in Iran and world. In this study، based on land use، effective indices emphasizing water erosion criterion were identified using to FAO-UNEP and MICD models. Then، the most effective of indexes was selected and a desertification area model was allocated. Also، the numerical value of indices was analyzed in each work unit and after all area. Finally، the present situation of desertification intensity of the study area emphasize of water erosion criterion in four classes of insignificant and low، medium، intense and very intense was estimated. The results indicate that in the developed regional model، the study area with respect to intensity of desertification is placed in about 4915 hectare (5. 9 %) in the low class and about 78599 hectare (94. 1 %) in the medium class. also the weight medium of quantities valuation estimated in the total area DS=15. 19. That، it indicated the intensity of desertification medium class in the total area.

Gully erosion is one of water erosion types that happen due to improper management of agricultural lands. The main objectives of this research are zonation and characterisation of gully erosion. For this purpose، affected areas by gully erosion were noticed in Arial photographs and satellite images. Areas with more than 500 ha and their dominant climates were specified with climate map and for each climate two areas in which one representative gully and two repetition gullies were chosen. Morphology characteristics، soil sampling and other related studies were performed in each gully. Consequently، according to the main characteristics، such as climate and view plan، these gullies were classified by cluster analysis and their digitized zonation maps were provided. According to the results، six regions with a total area of 7437. 3 ha were affected by gully erosion with three different types of climates، from which، three regions had moderately arid climate (Qeshlagh Alborz and Naizar) and warm semi-arid (Rahjerd) with more than 500 ha. These regions that are classified in two classes based on cluster analysis، have lateral gullies which are developed beside the natural drainages and are classified as un continuous gullies. The texture of soil surface is usually sandy-loam and in some cases loam and silty-loam and sandy-loam and silty-loam in the subsurface layer. Highly sensitive lands، flood occurrence، past heavy rainfalls and high amount of salts in some areas، are from the most morpho-climatic factors causing gully erosion in dry regions and deserts of Qom province.