فصلنامه پژوهش های فرسایش محیطی
سال دوم شماره 4 (پیاپی 8، زمستان 1391)

In addition to Erodibility of sediment particles in river increase river sediment load، they are important factors in morphological changes. In the rivers that erodibility is high، trend of morphological changes are intensive that in this case، river is unstable. On the contrary، it will lead stability and low changes of the river. Study area of this research is Saraskanchay that has been located in the Hashtrood. The aim of this paper is investigation resistance of sediment particle to erosion by analysis of the river sediments characteristics. For this purpose، Sampling performed from studied Course and then Erodibility calculated by Bed Shear Stress and the Relative Strength Index. Grain size sediments indicated that is not significant correlation between Grain diameters of sedimentary. Cause of this is Human factors in the natural composition of the sediment grain diameter. Results indicated the critical shear stress is more from total shear stress in most parts of the river. This is indicator of Resistance of deposited particles on the river bed rather than erosion. Therefore، the river is stability and its changes are low in future.

Infiltration is the process of water penetration from the ground surface into the soil and is an important process in the hydrological cycle by which surface runoff and groundwater recharge can be linked. Over the years، the importance of the infiltration process resulted in the development of several simplified analytical models for predicting infiltration. These infiltration models range from entirely empirical to physically based models. The most serious problem associated with infiltration modelling of a catchment is how to express the spatial soil variability. In the present study، various infiltration models were fitted to the observed infiltration data of 27 double ring infiltrometer tests and the best-fit infiltration model for Darabkola watershed was identified and evaluated. In addition، the spatial variability of the selected infiltration model parameters was analyzed using the geostatistical techniques. Results showed that among of four models، the Green - Ampt model could determine the infiltration rate with smallest values of RMSE. Hence، saturated hydraulic conductivity parameter (KS) and suction head at the wetting front (Sw) were estimated for all the test points. Evaluation of spatial variability of these parameters indicated that parameters KS and Sw had the spatial dependencies of 0. 49 and 0. 25 respectively، showing medium spatial dependencies of both parameters. Also، investigation of interpolation parameter maps showed that in the upland with forest land use، relative to other areas in the watershed، the saturated hydraulic conductivity (KS) and suction head at the wetting front (Sw) have larger (1. 57-2. 69 cm/hr) and smaller values (12. 12-1737 cm)، respectively.

The present study shows that very low erosion class (0. 23 to 8 tons per hectare per year) Romeshgan watershed، most of the area to be included in the attrition levels low، medium، large and have too much. In general we can say the area is low to moderate ability erodible. SLEMSA model for estimating erosion، environmental conditions are examined. These factors in watershed erosion rates in different influence، its role in the model represent different values. Overlapping layers، rainfall، slope classes، geology، the land user، land type and Revealed that the maximum rate of erosion in areas with average precipitation of 600 mm، a range of plains and mountains of the terrace deposits and alluvial fans new and old، marl، limestone، siltstone، sandstone، conglomerate، and gypsum contains be. The slope factor، too، lands with slopes of 25 to 45 percent are devoted to the highest degree of erosion. Results using TOPSIS model in the survey also shows that factor eroding Romeshgan basin topography (slope) over other factors، basin was effective in erodible and has a major role. This model is also based on 1 sub basins in the north basin (with the highest similarity to the positive ideal)، have the greatest vulnerability to erosion، then the sub basins 2، 4 and 3 are located. The reason for this can be achieved over all the heights and slopes of the basins is below. Looking at the situation of erosion and geomorphologic factors in the basin، we knew that the geomorphologic unit surface area plain، erosion of geological factors (alluvial deposits، marl، gypsum، shale، etc.) and land and units geomorphologic other variables in the same mountain slope، geology and rainfall is higher. Given the importance of the erosion zone and listed the conditions subject to wear and perform the necessary actions to protect resources and prevent soil erosion and loss it is necessary.

In long-term، wind erosion has considerable impacts in rangelands. The aim of this study is to understand the changes of Hanitiyeh rangelands in 30 kilometers of East of Ahvaz city and its function. In order to this، using two transects of 42 meters length in wind gradient، patch and inter patch with 5 repeat (including Shrub Log Complex، Bush، Grass، Shrub، Shrub-Grass and Bare open soil) were measured. In addition، the list of floristic and vegetation were measured. And then using Landscape Function Analysis (LFA) to measure the three indices of stability، infiltration and nutrient cycle، for each growth form with 11 soil surface indices. MANOVA and correlation analysis showed that Bush form more increase soil surface stability to other forms. And also indicates that soil of grass growth form showed higher nutrients cycle index. Infiltration Index showed no significant differences among the five growth forms. Evaluating a rangeland، helps expert to recognize rangeland changes and evaluating it. Wind erosion control is carried out on increasing soil cohesion، thus improving soil resistance to wind. Also the studies about rangeland function with simple index in soil surface reflect of management and natural changes.

The lack of sediment gauging stations in the process of wind erosion، caused of estimate of sediment be process of necessary and important. Artificial neural networks can be used as an efficient and effective of tool to estimate and simulate sediments. In this paper two model multi-layer perceptron neural networks and radial neural network was used to estimate the amount of sediment in Korsya of Darab city. The simulations were performed with two methods common artificial neural network Initially، the sediment was sampled with sediment traps afterward by climatic factors such as average wind speed، evaporation، precipitation، relative humidity، minimum temperature، maximum temperature، average temperature and Percentage of vegetation، respectively، as the dependent variable and independent input to the model was chosen to simulate the sediment. The Results of the performance model show that MLP neural network (feedforward Back propagation algorithm) with learning technique of Calibrated dual gradient Compared to radial Neural Network Respectively with coefficient of determination. 95، Roots mean square error. 02 and coefficient of determination. 90، Roots mean square error. 40 for estimate of wind deposits were the higher efficiency and accurate. Course، it should be noted that an important advantage of the artificial neural network Multilayer Perceptron to Neural Network Radial is more flexibility.

Changes in river geomorphologic pattern would be considered in all environmental planning’s because this change have special consequences on land ownership properties، using cultivable lands on the rivers bank and supply of constructional materials. Sand and gravelmining of the river beds are among factors that lead to changes in river beds pattern. In This research، we investigate geomorphological changes in parts of Kashkan River in Khoramabad County from KashkanAncent Bridge to Cham Davood village، in a length about 14 km. There are three sand and gravel mining site in this short length of river which caused a major changes in the bed and banks of the case study river. We used a temporal resolution aerial photos of 1381 (A. H.)، ، Cartosat images of IRS by 5 meter resolution of 2009 of the study region، and used ARC/GIS، AutoCAD، Global mapper to calculate and measuring geometrical parameters that changed during this time period. By comparing spatio- temporal changes، results show that sand and gravel mining is a major factor of about 50 percent of changes occurred in the study area. River dynamic، bridge and curving dams’ construction in the river cours are other factors of changes، too.

Metropolises of today، in different parts of the world for various reasons، are often prone to damage from natural hazards، one of the slope instability that cause to plenty financial and human losses in each year on the systems of socio - economical and environment is landslide. We also have tens of landslides occur in different parts of country each year، and it led to more residential areas، roads and facilities are threatened. Research method is descriptive - analytical with using a library and field study and AHP-Fuzzy models and GIS to Landslide risk zonation، in region 1 of metropolitan Tehran. And try to answer this question that landslide processes and geomorphological hazards that limiting development and safety in Region1 of Tehran metropolitan which are they? Landslide risk zonation map shows، areas with low and very low risk، includes 50% of the study area، located in the urban area of Region1 and valley talwegs of its basin. But areas with much and very much risk located in northern parts of the area and dominated slopes. In general، whatever we goes to the upstream and the downstream of basins of the watershed area the rate of landslides risk will reduce. With consideration of final Landslide risk map zonation in order to development and safety urban should be prevent of constructions in much and very much areas of Landslide risk that located in streams margin and stream-valleys and areas that have potential of Landslide in Region1 of Tehran، and should be all urban land uses includes residential land uses with engineering techniques are stable.