فصلنامه پژوهش های فرسایش محیطی
سال دوم شماره 1 (پیاپی 5، بهار 1391)

Analysis and Investigation of Landslide Hazard Zoning using HyIdentification of susceptible areas to landslide occurrence is one of the basic measures for reduction of the possible risk and hazard management. The main goal of this research is to compare the applicability of two statistical landslide hazard zonation models، valuing area accumulation and Analytical Hierarchy Process (AHP)، in Ziarat Watershed، Gorgan، Golestan Province. In a review of previous works and field works، we chose nine factors of slope، aspect، elevation، lithology، landuse، river distance، road distance، fault and rainfall distance، and identified effective factors in landslide hazard، and used them to conduct an analysis risk by GIS software. Data from previous land slidesin the study area were collected and GPS. Thesenine maps were crossed with the map of previous landslides. Theamount of landslides and their areas were computed in each class. After determining the rate of each factor (element)، we performed landslide zonation in GIS by combining density levels and AHP models. Theefficiency of output results of the models was assessed by Drand QS indices. The results of Drindex showed that the combination of both models was more efficient in recognizing the hazard classes with high danger (Qs=1/81) compared to those of low danger (Qs=0/78). brid Model of Hierarchical Analysis and Surface Density

Past decades damage by floods in Iran and on the other of the world has shown that we have still much work to do to cope with this problem. Hence، the study of these events and development of more effective adaptation and mitigation policies has become a priority، in other parts of the globe. First step in achieving flood risk assessment is data collection. Availability، suitability and quality of hydrological، meteorological، topographic and management data is discussed. This study combines a hydrologic and geomorphic data with aim of geographical information system to delineate the extent of a flood event in the Ojan Chay basin (98،227 km2)، one of the river system draining into the Aje Chay River. For This purpose، the 16- information layer has been prepared for overlaying using fuzzy sum and classified using Fuzzy C mean on the geomorphology data. The main objective of this research is to assess the flood hazard that affects Ojan Chay river basin، in order to develop a basis for further vulnerability and risk analysis. Flood hazard risk presented in the map because that give a more direct and stronger impression of the spatial distribution of the flood risk than other forms of presentation. The results of this study show that more than 70% accuracy (Kappa coefficient 0. 7502459) compared with reference data، indicating the acceptability of this method is the mapping of flood hazards.

The use of new methods of Remote Sensing (RS) and Geographical Information System (GIS) in zoning the flooding potential and its variations in a particular geographical area (Tang-e-Bostanak Catchment Area) constitutes the main subjects of this study. In this regard، the production، combination، and composition of effective information layers such as K index and run off in identifying these zones have been noted، highlighting the capacity of GIS. Theaim is the identification and percent of flood zoning and their variations within an 18-year period by RS and land use variation maps. In this study، we have observed excess rainfall under the curve number (CN). According to the results، the above mentioned area isexperiencing a 15% increase in flooding during the 18-year period.

In Iran. one of the extensively used methods for determine the values of erosion and sediment is Model EPM. But according to the reports، So، in this study attempted to determine the values of erosion intensity and erosion intensity mapping two methods based on Fornier and factorial scoring method to compare the EPM in Mazlqan watershed semiarid have been done. The results of the investigation indicate that factorial scoring method due to the relative difference to compare with EPM model with 25 percent of watershed management in the filed of study towards Fornier study method are appropriate، differences between relative amounts of the test methods can be in the structure therefore recommended to the method of mapping and prioritizing watershed areas critical of the country’s semi-arid gully erosion are lacking about are used.

When aerial parts of the plants capable of storing absorbing mineral salts in their leaves fall، these dissolved materials are transferred to the soil surface، changing its physical and chemical properties. In this study، we have investigated the influence of the Haloxylon tree on the physical and chemical properties، and also humidity of the soil using two، 300 m long transects; one canopy of the trees (1. 5 m distance from the tree trunk) and another one used as the reference located at a distance five times as long as the tree’s height (almost 50 m away from the tree trunk). Thirty points were selected on each transect، and samples were taken from depths of 0-10، 10-20، and 20-30 cm of the soil. Measurements were taken with respect to Ca+، Mg+، K+، Na+، pH، EC، biomass and volume humidity.

Rapid urban development in recent decades، has affected various aspects of social، economic، cultural، political and human environment. Negative environmental effects of urban growth have increased to such extent that is the largest threat in front of the ecosystem. One of the consequences of these negative environmental effects is ecological and biological capacitance reduction، also referred to as desertification. Currently، the desertification، with human intervention، is more technogenic desertification and is beyond salinity، wind erosion، and other parameters that were previously considered. The main aim of the present study is to survey the effect of urban and industrial development (technogenic desertification) in the desertification of the East region of the Esfahan province. In this study we tried to determine and prepare plan of potential situation of land desertification، caused by urban and industrial development، which is one of the most important human-caused criteria in the assessment of areas affected by desertification within the Isfahan Province eastern region. For this purpose، in addition to information on land use map and work unit map of study area، the visual interpretation of satellite images are also used to identification and spatial adaptation of desertification assessment indices with land realities. Arc GIS and ILWIS software are applied to use digital files and presented maps. Review and comparison of criteria scores of technogenic desertification in the study area indicated that low-intensity desertification is expanded at about 284،451 hectares of the area (82. 3%)، moderate-intensity desertification is expanded to approximately 59187 hectares of the area (17. 2%)، and severe desertification of land is expanded to about 1883 hectares of the area (0. 5%). Land with very severe desertification in the area is not observed.

The sediment load that is transported by rivers can create numerous problems such as sedimentation in the reservoir and storage capacity reduction، developed load in the rivers، destruction of structures along the river and transfer of pollution. Therefore، an accurate estimate of the sediment load in rivers is absolutely essential for river engineering، reservoir design، sediment transportation، measuresof environmental damage caused by deposition. Due to the fact sediment load is measured at different times in addition to the lack of reliable observational data in the watershed، empirical equations are used to estimate the sediment load. In this study،to determine the most suitable method for estimating the suspended sediment in Roodak Hydrological Station، we have collected and analyzed data from flow and sediment discharge during the years1972-2008. By the correlation between flow and sediment discharge onthis station of six statistical methods، we chose the best method to estimate suspended load. In a comparison of the accuracy of these methods، we used the statistical indices، RME، MAE and standard deviation. The resultsshowed that the multi-linear (two curves) method wasthe mostaccurate method. Therefore it was selected as the most appropriate method for estimating suspended load in Roodak Station.