فصلنامه پژوهش های فرسایش محیطی
پیاپی 4 (زمستان 1390)

One of the sensitive systems in geomorphology is the coastal system in which rapid change is noted due to the collision of the two dynamic environments of sea and land. Coastal lines can record evidence of geomorphological alterations. Due to various reasons such as environment changes، global warming، and issues regarding human activities، studies and quantitative measurements from periodic changes are beneficial for the environmental management of shores. Remote sensing data and satellite images are considered to be reliable، concise sources for investigation and interpretation of the coastal line and for performing quantitative measurements. In this study we have used the TM-5 satellite images from 1986 and 2010، in a 24-year schedule to monitor the costal changes of Eastern Hormoz، based on the maximum likelihood method. Then، by using quantitative measurements، we analyzed coastal line changes according to pixel points، percentage of changes and amount of changed area. In addition، we investigated the trend in changes in the width and coastal line for a two-year period. In order to evaluate in a wider spectrum، we studied four sectional samplings. The results of this study revealed that in the 24-year this area has undergone considerable coast line changes، such that the changes reached to 2. 8 kilometers in some areas، which may represent the fact that the hot line of water in 1986 progressed more toward the beach when compared to the 2010 data. In consideration of the coastal line changes and the 2010∕1986 ratio، the level of changed area is 29،320،200 m2، and the percent change is 5،6% of the investigated coastal line which was prone to periodical changes.

Rivers are one of the most important، common supplies for drinking water، agriculture and industry. The water passes through different regions and by direct contact with the surrounding environment large fluctuations in water quality occur. Excessive exploitation of soil، continuous use of surface and underground water resources، and use of agricultural chemicals (fertilizers and pesticides) cause significant negative effects on the environment. Various uses for land by humans causes changes to the physical، chemical and biological components of water resources. These changes are generally negative، restricting water resource usage. This article examines the impact of different land uses on surface water quality.

In this study undertaken in Babolroud Basin، seven models that included MPSIAC، EPM، Fournier، Douglas، Kirkby، Geomorphology and Hydrophysical were evaluated to determine the best model for estimation of soil erosion and sediment yield. These models have not been previously compared together. The zoning soil erosion intensity map was prepared from each model by using GIS. The estimated sediment yield was compared with the observed data (43 years of data from Ghorantalar Station) by using the statistical evaluation criteria such as relative and absolute difference، and correlation coefficient. Results showed that the MPSIAC model in the Lowland and Azar sub-basins، the Geomorphology model in the Karsang and Esklim Sub-basins، and the EPM model in the Babolak Sub-basin were more precise and efficient than the other models. By investigating the observed sediment data in Babolroud Basin، the MPSIAC model was used with a relative difference of 7. 932% (76659. 896 ton/y) and correlation coefficient of 0. 86، which was the most appropriate model to estimate soil erosion rate and sediment yield in this basin.

This study used the MPSIAC and EPM models as a comparison to estimate erosion and sediment in the Poorahmadi Watershed Basin. Required data regarding the natural characteristics of studying the watershed basin was provided from comprehensive studies of this in addition to digital image processing and preparation ofthe required maps using the joint capabilities of RS and GIS. By using the required factors، the amount of erosion was calculated in both the MPSIAC and EPM models. In the MPSIAC model، erosion was calculated to be 1903. 72 m3/km2/y، whereas sediment was calculated as 616. 03 m³/km²/y. However، the rate of erosion in the EPM model was estimated to be 1093. 5 m³/km²/y and for sediment، it was 1015. 8 m³/km²/y. The results showed that in some sub-basins there was good correlation between the MPSIAC and EPMmodels،however in areas with high erosion the EPM model has less certainty than the MPSIAC model.

In the Summer of 2001، an intense thunderstorm in the southeastern Caspian Sea triggered a catastrophic flood in the Madarsoo Basin. Methods that included high-resolution aerial photographs، interpretation of satellite images، multi-date mapping، hydraulic calculations and field observations enabled documentation of the geomorphic impact of this flood on the Madarsoo River and its tributaries. Geomorphologic effects of this catastrophic flooding included the uprooting of trees up to 2 m in diameter from the main river channels; locally as much as 80% of the tree crown cover was removed from the riparian zones. Uprooting of the trees exposed the underlying flood plain to macro turbulent scour، leading to extensive removal of flood plain sediments that had accumulated over centuries. Other hydro-geomorphic impacts of this flood have been drainage network modifications، the creation of new alluvial fans، and a new meandering pattern and gully development، all of which have been documented. Subsequent to the mentioned flood، two other extreme floods have also affected this basin in August of 2002 and 2005. In addition to causing further landform modifications، these floods wiped out the infrastructure which had been reconstructed after 2001. All three floods were of the same conditions based on their time، climatic and triggering characteristics. The peak flood was estimated to be 700m3/s in August 2002 and 1060 m3/s in August 2005. The occurrences of the two above mentioned catastrophic floods and related processes were the result of triggering variables and the formation new dynamic environments by the main event (August 2001 flood)، which prolonged the required time for recovery of the stream channels. Geomorphic instabilities lead to consecutive crises in this new environment. This condition accelerated geomorphic hazards in combination with the effects of the recent climate.

Rivers have a complicated، various condition in the diverse environment as studied by hydrology، geomorphology، hydraulics، ecology and engineering. River geomorphology studies the river process and landforms and examines the evolution of the river''s landscape، which can play an important role in identifying river channel characteristics and behavior. Designs with river engineering enable precise examinations of rivers leading to declines in property damage. In this study we initially determined the type of river style. Then، with three degrees of freedom، the channel morphology، plan form، river bed characteristics، capacity for adjustment، and relevant geoindicators for each degree of freedom for each river style were determined. Next، we interpreted the river''s evolution by using ergodic reason to assess whether irreversible geomorphic change occurred. The geomorphic recovery potential of each reach was determined by assessing the connectivity of the reaches and interpreting limiting factors and pressures. In the LavijRud catchment eight river styleswere identified. More steep headwaters have intact condition and gorges، low sinuosity planform with discontinuous floodplain and high energy with gravel bed river styles have a high river recovery potential. Cut-fill، bedrock controlled with discontinuous floodplain and confined with occasional pocket floodplain river styles have moderate river recovery potential. Confined with slump bank river style have a low river recovery potential and their conditions are degraded. Results show that river styles in this catchment also have respectively 65% high، 28% moderate and 7% low river recovery potential. Management prioritization of each river style observed the river''s geomorphic conditions and recovery potential.

The purpose of the current study is to investigate the effects of some environmental factors on erosion value, to determine the most important governing factors and the relation between erosion of working units and environmental factors (soil characteristics, slope, aspect, elevation, lithology, geomorphology faces and vegetation cover percentage). We used the geomorphology method to prepare a working units map. This map was derived by overlaying slope, aspect, elevation, lithology andgeomorphology face maps.In order to study plant cover, random-systematic sampling in each working unit was conducted in ten plots.Regarding the species type and distribution, the area of each plot was determined based on the minimal area method. Canopy cover of species was determined in each plot. Furthermore, five profiles were sampled within the working units to study soil characteristics at depths of 0-50 cm. Subsequently, the texture, percent of lime, organic matter, gravel, pH and EC were measured. Erosion value was determined in each working unit by the E.P.M. method.Statistical analysis was performed using Principal Components Analysis (PCA) through the PC-ORD4 software program.The results showed that among environmental factors, the vegetation cover, lime percentage, face and organic matter were the first set of factors that determined the change in erosion value by 33.99%.The second set of factors that included loam,stone resistance and clay percentage play contributed to the change by 17.295%. These two sets of factors altogether explain 51.288% of the erosion value variation in VarkeshBasin.