جستجوی مقالات مرتبط با کلیدواژه « transect method » در نشریات گروه « جغرافیا »

Morphological Assessment will be necessary to understand the current situation and the potential for possible river changes in the future. Natural factors such as floods, soil erosion, landslides and human factors such as land use change and sand removal from the riverbed affect the morphology. River systems have always been of interest to humans as one of the most vital elements of the Earth's surface. Humans also change the face of the earth by changing their use, destroying natural resources, plowing the land in the direction of the slope, planting trees in the riverbeds. Any Manipulation into the riverbed will change the process of erosion and sedimentation along the river. Understanding the characteristics of flow and sediment is the basis for evaluating the behavior of rivers and deciding on engineering activities. Therefore, it is necessary to obtain the necessary information on how they work before starting engineering projects for rivers.

In this study, geological maps at a scale of 1: 100000 of the Geological Organization, topographic maps at a scale of 1: 50,000 digits of the Geographical Organization of the Armed Forces, Landsat satellite images, 2020 April, November 1995, Climatic data Temperature and precipitation (1399-1374) of Lorestan Meteorological Organization and Digital elevation model of 30 meters has been used. Arc GIS software was used for spatial analysis and ENVI software was used for processing satellite images. The normalized water difference index is the first index of water extraction in images and remote sensing data. In this indicator, two green and infrared bands are used. Positive values of this index indicate water and negative values indicate phenomena other than water. Researchers have proposed different methods for studying changes in river channels. The transect method is used to evaluate changes and displacements in river channels. In this method, lines with specific distances on both sides of the river route are drawn as baselines. These lines are constant for the time periods studied. River channel displacements relative to these lines are quantified. To further evaluate the Kahman River canal, the canal migration rate method was used. The Kahman river Canal was divided into two areas, mountainous areas and plain and agricultural areas, based on topography and land use.

To calculate the area to the right and left of the transects, the Kahman river channel was cut separately with a transect layer in 1995 and 2020. Calculation of changes in the area of transects shows that about 185.85 hectares of land adjacent to the Kahman river (1995-1999) have been eroded. On average, about 7.43 hectares of these lands have been destroyed annually. The maximum value of this index in transect 30 is calculated at 8.27 hectares. In order to better understand the changes and dynamics of the Kahman river Canal, the migration rate index (Rm) was also used. First, two fixed lines were drawn around the Kahman river channel. The area between the two was calculated using Arc GIS software functions. The average migration rate of Kahman river (1399-1374) was 2.51 meters per year. The lowest level of this index occurred in Trasket 49 at 0.18 meters per year. The mountain factor and stabilization operations along the river have been the most important reasons for its control and stabilization. The highest rate of migration occurred in transects 4, 32 and 30 at 4.80, 5.5 and 6.12, respectively. Shortcuts and land use changes have been the main reasons for the high rate of duct migration in these transects. The largest amount of lateral changes in the Kahman river route occurred in parts of the plain and agricultural areas, including transects 30 to 35. The most important factor was the high lateral changes of the Kahman river route in the plain area due to the high erosion of the coastal and floodplain materials. Most of the constituents of the bed and banks of the Kahman river in these periods are from fine to coarse sands.

Duct migration rate index showed that the average displacement of Kahman river canal (1374-1399) was 2.51 meters per year. The lowest value of this index was 0.18 meters per year and the maximum value was 6.12 meters per year. Calculation of changes in the area of transects showed that about 185.85 hectares of land adjacent to the Kahman River (1374-1399) has been destroyed. On average, about 7.43 hectares of these lands are lost every year. In the mountainous area, the effects of the mountains were the most important factor in determining the morphological changes of the Kahman River channel. The presence of erodible materials along the Kahman River in the plains and agricultural areas has increased the lateral migration of meanders and the width of the valley and floodplains adjacent to the river has increased significantly. Therefore, it can be said that the Kahman River has had more geometric changes in the plains and agricultural lands.

River and river processes are considered as the most significant geomorphic systems which are active on the earth’s surface (Bag, 2019). Over time, many changes in the morphology and dynamics of the river system can occur. The effects of river adjustment caused by the natural factors require much longer time span to be revealed. However, there are few exceptions that the natural factors such as river floods, landslide or earthquake can induce channel adjustments in a very short time (Chaiwongsaen et al., 2019). On the contrary, human activities can have a significant and rapid impact on natural processes and trends, resulting in a compressed time scale for river adjustments (Rinaldi & Simon, 1998). Morphological responses may include subtle shifts in cross-sectional stream channel geometry or widespread landscape transitions, involving progressive or abrupt change over daily to millennial timescales. In order to sustainably manage river systems, it is necessary to further investigate the characteristics of variation in river morphology at various temporal and spatial scales (Minh Hai, 2019). Givi Chay River is one of the permanent rivers of Ardebil province in northwest of Iran and there is still no comprehensive study on this river. This study attempts to investigate the changes of morphological of the Givi Chay River over the time period 2000-2019.2. Study AreaGivi Chay River with almost 54 kilometers is one of the permanent rivers of Ardabil province. Two rivers of Hiro (which is emanated from Khalkhal altitudes) and Arpa chay(which is emanated from north to south), are linked to each other in downstream and the stream around Inalava village is departed toward westward and between altitudes of Khalkhal and Givi reaches to Givi city through a narrow valley. In this area, that river is called Givi Chay. The river flows into Ghezelozan after crossing the city of Givi and joining the Firoozabad River.

In this research, the topography map with a scale of 1:50000, geology map with a scale of 1:100000, and google earth and Landsat Eight images, including OLI sensor (2019), Landsat seven including ETM + sensor (2000), bedrock maps and the Givi Chay River privacy at a scale of 1:2000 hydrological data and field data were used. Moreover, to control the results obtained by quantitative methods it is used from field studies for confirmation and verification. ENVI 5.3, Arc GIS 10.5 and Excel software were also used for image processing and data analysis. The geomorphological parameters of the river and their variations including bending coefficient and central angle were measured. The curvature coefficient is one of the few criteria used in river shape segmentation using s=1/ (y.2), i.e., by dividing the valley length by wavelength for each arc (Pitts coefficient) which was calculated. The central angle of the arcs on each of the intervals was calculated using the relation A=180L/Rπ, where A is the central angle, R, of the fitted circle radius (Kornias coefficient). The lateral changes of the canal were investigated using transect method and calculation of river migration rate. According to the Transect method, lines with distinct distances from both sides of the duct are depicted as baselines. These lines are constant for the time periods studied and hence can be calculated quantitatively for duct movements relative to these lines. When the conduit is moved in the right direction, the area of the right-hand transect of the conduit decreases and is added to the area of the left-hand transect of the conduit, and vice versa. In this study, the Givi Chay River channel was divided into 23 transects based on morphology and channel change trends and quantitative indices were calculated for each transect. The Rm = (A/L)/Y relation was also used to calculate the channel displacement rate. In this respect, RM stands for transverse displacement intensity, A for area between two centerline lines, L is centerline length at time t1 and Y is number of years.

The mean curvature coefficient for the first period in 2000 was 1.48 and decreased to 1.40 in 2019. But in other periods from 2019, the bending coefficient has increased compared to 2000, as the bending coefficient from 1.23 to 1.25 in the second period and from 1.85 to 1.86 in the third period and from 1/15 to 1/18 in the fourth quarter it increased. In general, the lowest bending coefficient for each period is in the fourth interval and in a finite amount. In the first, second, and fourth intervals, most of the intervals in both study periods have a curvature coefficient of 1.5-1.5 and therefore the conduit plan is sinusoidal, but in the third interval more than 60% of the range has a curvature of 1.5 to 2 and therefore the interval pattern is in the form of a Meander. In the second and fourth intervals, the standard deviation of the bending coefficient is low and in the second interval is 0.19 in 2000 and 0.18 in 2019 and in the fourth interval is 0.14 in 2000 and 0.12 in 2019. In general, they indicate the existence of similar arcs. In the first and third intervals, the standard deviation is relatively high for both periods, indicating non-similar arcs.In both periods, the first and the third intervals were highly developed in the form of Meander and the fourth period were of the developed Meander type. However, during the second period during the period, the type of the rift from the developed meander changed to the highly developed meander and the central angle reached from 143.82 in 2000 to 163/50 in 2019. Due to the low valley bed and its alluvial slope, which is associated with complex mazes, and with increasing spiral arc and river energy concentration, the intensity of erosion reaches its maximum and where it is a maze arch, it is concentrated on both sides. A large amount of excipients flows into the bed. As the spiral energy intensifies, the width of the floodplain increases due to erosion. In the first interval, the central angle of the riverbed has decreased in 2019 compared to 2000, and with the decrease of the central angle of the river, the mean radius of tangent to the riverbed has also decreased and in other intervals has witnessed an increasing trend of the central angle during the study period. Increasing the central angle indicates that the river meanders are active and the morphology of the river has changed to a highly developed rudimentary twist, as well as a change in the central angle in bends that have not been removed and only changes have been made in it. In the third interval, the mean central angle in both periods is higher than other intervals. In fact, the river flows in a winding direction due to the geological resistance of the river and the low width resulting from this factor.The maximum amount of lateral changes in transect 12 was 1.51 m and in this transect during the study period 5.47 hectares decreased from left bank and added to right bank. The lowest location in Transect 20 is 0.54 meters, thus reducing the left bank to 1.13 hectares and adding to the right bank of the river. Transverse displacements have often occurred in parts of the river course where the riverbed has floodplains, and the riverbed in these areas is significantly wider and the slope greatly reduced and widened significantly. Agricultural lands and gardens are visible in these areas.

According to the results of the calculation of morphological indices, the average bending coefficient in the first period decreased in 2019 compared to 2000, but the coefficient of bending increased in the 2nd, 3rd and 4th intervals. The first, second, and fourth intervals have sinusoidal plans in both study periods, but in the third intervals in both periods, the interval pattern is a meander. In terms of the central angle index, in the second interval during the study period, the type of interval changed from extended to highly develop. However, the first and third intervals, in both study periods, are highly developed in the form of a meander and the fourth period are in the form of a developed meander. In the plain, the main factor affecting the river meandering is the alluvial formation, the slope is low and the meanders are inscribed and plain, whereas in the mountainous part the river changes are subject to valley changes and the meandering state is seen throughout the valley.The results of lateral conduit changes also showed that the average migration rate of the Givi Chay duct during the 19-year interval was about 0.87 m/year. It should also be noted that, during the period 2000 to 2019, approximately 39.52 hectares were generally added to the right bank of the river and 11.62 hectares decreased to the right bank.In general, changes in the Givi Chay River Plans have been attributed to the expansion of existing meanders, displacement of the river path, and increased curvature and formation of small meanders. Hydrological processes are caused by the process of supply of sediment and sediment discharge, dam construction and lithological resistance of the riverbed as well as human interference such as, encroachment of the riverbed, construction of bridges, sand harvesting.

The study of the urban texture highlights the density of built space and open spaces in the city and has an important role in the final decisions to optimize service distribution and improve the quality of urban spaces. This study aimed to investigate the urban texture of Urumia for assessing public open space and green spaces compared to built environments and masses. In order to analyze the data and the quantitative texture of Urumia, transect method was used. The study was a cross- functional one focusing on Urumia. The results showed that in the transect T1 from North-West to South- East of the city, the spaces ​​between 60 and 100 parts of density had been made. The lack of green spaces in parts 80 and 100 and the lack of open spaces in all parts except in parts 34 and 63 is visible. In the transect T2, from the West to the East of the city, the western part of the land had ​​the highest density and the eastern part had the highest density of agricultural land and orchards. In the central part, between parts 30 and 80, there is a deficit passage network. In the transect T3 from the south west to the north east of the city, the density of built spaces in the city center has increased to 85 percent, while the shortage of passage network, especially the shortage of agricultural land and green and open spaces is visible in the middle of the transects 15 to 76. In the transect T4 from the south to the north of the city, built-in compression spaces between parts of the central sections have increased from 40 to 60 and the lack of green and open spaces is clearly evident. In conclusion it can be said that Urumia landscape consists of three types of tissues: the central condensed texture of open green spaces with a minimum and maximum spaces; the edges of the tissue center where the density has somewhat reduced the construction of buildings, and the margin consists of barren land, gardens and agricultural land. In this way, the construction level has decreased from the center to the sides of the city