پديد آورندگان :
حجازي، اسداله نويسنده , , برومند، ريحانه نويسنده دانشجوي دكتري ژيومورفولوژي، دانشگاه تبريز ,
چكيده لاتين :
Nowadays it is useful for managers and planners to have some information about erosion and its resulted changes in order to protect soil and water. So since soil erosion is considered as one of the main problems of the country basins, it can be treated as the most important barrier to achieve sustainable development. Faroob Rooman basin is located in the Dasht-e-Kavir drainage basin, Neshabour town. The experimental model EPM was used in the area studied to examine erosion and sediments considering cold, semiarid and mountainous situation and unstable condition in view of flooding and lack of statistic and information about quantitative evaluation of sediments. So the basin is divided into 22 sub-basins and annual sediment estimation of the basin is relied on these 22 sub-basins. It was estimated that the sub-basin F5 equal to 10.75T/h/y has the most amount among the others. It was also calculated that specific erosion of the total drainage basin is 20.58 to 3.01 ton per hectare per year and specific sediment rate 8.69 to 4.15 ton per hectare per year. Average specific erosion of the total basin was estimated 8.64 ton per hectare per year. According to studies and investigations, constituents sensitive to erosion and usage type are the most important effective factors of erosion affecting other factors. So the best options for controlling erosion and sediments in the regions are as pasture management, land management and technical structural operation suggested depending on the conditions of each sub-basin.
Methodology
In the present paper, the methodology is based on experimental method, qualitative and quantitative analyses and field study. Having performed preliminary studies, the cases required for studying erosion and sediments were evaluated considering the experimental model EPM. At first the statistics regarding sediments measuring stations of the area studied were derived and then analyzed. So considering statistics available and using the EPM model (in this model multiple factors are used described in the form of usage in the area studied) the map of working units was prepared to identify erosion and sediment situation and prepare different types of water erosion in the area studied by matching geologic, geomorphologic, agrologic, vegetation, land use and …maps in GIS setting (ILWIS, 2001). Then by interpreting aerial photographs, erosion types of the area were identified and its initial map was prepared. In this step by visiting the area, different types of erosion in working units were identified and the final map of erosion types of the area was prepared considering different types of erosion such as superficial, groove and...
Findings and discussion
In Farob drainage basin, presence of constituents sensitive to erosion and usage type are the most important effective factors of erosion affecting other factors. Extending dry farms and cultivating annual plants such as wheat in steep lands, early exploitation of pastures, constructing roads without observing technical points for extracting mines in steep and mountainous regions are some examples of wrong utilization in this region. Also special geomorphologic features such as stone projections concentrating wastewater and aggravating erosion in downstream regions are also some examples.
Estimating the rate of erosion and sediment produced by the basin
Considering its importance, it is necessary to know the rate of erosion and sediment for controlling it. Since erosion and sediment size change annually, its calculation and estimation are of importance to plan for reduction and minimize damages of erosion, determining effective factors on erosion and constructing structures controlling and protecting water and soil. Faroob Roman drainage basin, Neishabour, was used to estimate sediment rate from statistics available in Faroob Roman hydrometric station (measuring suspensions). Having gathered statistics and information regarding water flow rate of each sample in m3/s and sediment size in ton/d, the software Excel was used to obtain the best equation between data. Since the relationship between flow rate of water and that of sediment is exponential Qs = a* Qwb, in this equation y is sediment in ton/d and x is flow rate of water in m3/s. constants of a, b and r are 25.69, 1.90 and 0.86 respectively. Knowing average daily flow rate of water in the station, average suspension is calculated in ton/d and finally for different months for each year separately.
Conclusion
Erosion is resulted from interaction of natural and human factors. Physiologic and topographic, geologic, geomorphologic, soil, climatic and hydrologic properties, vegetation, type of exploitation and generally exploiters and residents of the basin,… all interactionally affect on erosion (Ale Sheikh, 52, 2001). However one or more factors are considered as the main ones regarding special condition of the region so it is necessary to identify their effects appropriately for planning and applying management. In Faroob Roman drainage basin, presence of constituents sensitive to erosion and usage type are the most important effective factors of erosion affecting other factors so that about 2.3% of Faroob drainage basin account for water lands and gardens located frequently in the margin of the main canal and especially in the basin exit. The basin exit is almost alluvial and low steep. The respective lands were divided for irrigation so a relative management was applied. These lands are of low sedimentation however it is obvious that the part of lands directly located on the river margin is subjected to the river erosion and wastewater of submerged irrigation also causes erosion. Also less than 0.5% of Faroob Roman basin areas consist of dry farms. These lands are located in the river margins and low steep regions their erosion of which can be observed after harvest and baring the land. About 90% of the basin surface is pasture. Suggestions for protecting water and soil and controlling erosion and sedimentation of the drainage basin should be offered as pasture management, dry and water farmland management, mechanic and biologic operations.
