فصلنامه پژوهش های فرسایش محیطی
سال چهارم شماره 1 (پیاپی 13، بهار 1393)

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.

One of the main types of water erosion is gully erosion in which a large volume of soil is washed away. Gullies، in addition to producing a large amount of sediment and consequently filling dams and tanks، make a vast area of lands unusable and change the overall appearance of the earth. In this study، considering the importance of gully erosion in Ilam province، effects of environmental and biological factors on this kind of erosion in three areas of Dehloran، Mehran (Saleh Abad) and an area near to Ilam city (Chawar) were investigated. For field studies، after detecting the major gully areas، in these areas different types of gullies were identified. Gullies were classified into three groups of linear، bulbous، claws. Then slope، geographical position، total size of the area، altitude، land use، vegetation and gravel percentage factors، and gully features including: length، depth، upper and lower widths، gullies’ head height were identified. Collecting soil samples from both surface and deep walls of the gullies was done. To investigate the influence and the relationship of various factors on the gully erosions under the study from the results of field visits، laboratory operations and data analysis we used Duncan Polynomial Test and Pearson; besides، for determining the most important factors affecting gully erosion analysis of the main components is used. Results showed that slope and altitude had a significant impact on Gully erosion in such a way that the maximum erosion was on a slope of 10-15%، and at lower altitudes، but geographical position has not such an impact. In addition، the maximum erosion was for agricultural land use and the minimum was for forest land use، and among physical and chemical parameters surface sand، total size of the area، superficial EC were positively correlated and vegetation percentage was negatively correlated with gully erosion. Based on the results، superficial sand، and depth of the gullies and total size of the area were the most affecting factors on gully erosion.

Soil organic carbon (SOC) content plays a key role in soil biological، chemical and physical behavior and knowledge about its state and distribution is essential for the effective and sustainable use of soil. Laboratory measurements of SOC are costly and time consuming and have not the possibility to extend the results to similar areas. Recently، the use of remote sensing data for evaluation of SOC as a simple، rapid، inexpensive and even accurate have attracted the attention of researchers. The aim of this study was to evaluate the efficiency and accuracy of ETM+ satellite images for estimating SOC using artificial neural network and regression models. In this way، the digital number values in different bands of ETM+ satellite images have been used. Both regression and neural networks were used to develop the models between organic carbon measured in the laboratory and satellite data. Finally the accuracy of these models was evaluated with R2 and RMSE indices. The statistical analysis shows that these models was fitted using digital number values in the visible and mid- infrared bands of satellite images have the highest coefficients of determination. Moreover، the neural network models have the higher accuracy and. less error than regression models.

Dust storms are one of damaging climatic phenomena on the synoptic maps that are affected from the elements of pressure، cloudiness، precipitation، relative humidity، wind، temperature، and evaporation. According to Kermanshah province is one of the areas that is affected by the storms، the aim of this study is synoptic analysis of extreme dust storms in Kermanshah Station in 54-year period (1951-2005). First، the number of extreme dust days was identified according to the horizontal visibility index of 100 meters or less. Then، for recognition of transporting atmospheric system of dust، the synoptic patterns of sea level pressure، 500 hPa geopotential، wind direction، omega، surface temperature and profile of subtropical Jetstream from 1000 to 100 hPa were plotted using climate data of upper and middle atmosphere. The results show that the isoheight lines of 500 hPa geopotential have the west - east orientation in both days، and are condensed in the study area. The SLP maps represent the high pressure systems in the West (Iraq، Syria، Europe and Africa) and low pressure systems in the East (Eastern neighbors) that are the cause of western winds and dust storms. Sea level winds are the northern and western winds in both days. Center of Subtropical Jetstream has been formed in the levels higher than 400 hPa. Its tongues have arrived to the ground surface، and have developed in the latitudes of 50 to 65 degrees. Isothermal maps have a similar pattern in both days، and lines 30 to 36˚C have expanded on Iraq، Syria and Iran. Also، Omega maps indicate the descending motions of the air that increases the dust in the study area.

One of the types of water erosion and land degradation which causes imbalance in the area of natural resources and agricultural land and gives heavy losses، is the gully erosion phenomenon. To control this phenomenon، It is important to understand the influence factors on the geometry specification. land degradation، a broken ecological balance of the land and landscape and risk of falling at biological resources in these areas، among other things، the study of the gully، is inevitable and necessary especially in the Darrehshahr township. In this regard، Gully 36 number were selected in Darrehshahr area in the ilam province. To this end، were identified environmental factors، Physical - Chemical Soil properties، cover and hydrological properties of gullies tested using aerial photography، the digital maps and field operations. Results of statistical analysis using multiple regression (stepwise method) revealed that length of gully with upstream area of the gully، top and bottom width and cross section of the Gully with basin elongation، deep gully with basin elongation and slope curvature، high of head Gully with local slope of the gully and steep walls of gully with percentage cover have a significant relationship. So could be concluded that characteristics of geometry gully in the study area would be a function of the upstream، basin elongation، curvature slope، local slope of the gully head and the percentage of canopy cover catchment area of gully.

The instability and mobility of sand dunes is a major concern of planning and management in arid coastal plains. The aim of this study is to identify morphogenetic characteristics of sand masses and their locations، as well as to identify the processes that formed and transported them in the western part of the Makran coastal plain. Research data and tools were including spatial distributions of landforms، the morphologic and stretch of sand dunes، sedimentologic characteristics including granolometric and morphoscopic indicators، the velocities and directions of winds، Geologic and topographic maps، satellite images، aerial photos and computer''s software including ArcGIS، WRPLOT View and Gradistat. By using data from local meteorological stations، wind characteristics were studied and wind roses were plotted، also. Maps of aeolian landforms and general morphology of sand masses were plotted by using aerial photographs، satellite images and field controls. Elongation of sand masses was investigated، too. The results indicate that from sediment sources aspect، Coastal Plain sand masses are divided to interior sand masses that are originated from removing plain surface and coastal sand masses that are originated from tidal ranges. Also، where removal landforms are widely absent، no interior masses were formed and only coastal sand masses and barriers were formed.