عنوان مقاله [English]
Introduction:Urban Change Effects More Than Any Other Human Factor on River Systems. River Channel Changes are very Significant due to Urban Development. So Today, River Geomorphology is the Base for Studying Environmental Changes that are used for River Channel Management.
Materials and methods:The Purpose of this Study was to Evaluate the Effects of City's Physical Expansion on Hydrological Characteristics, Discharge and River Sediment and Features of Channel River Including Platform or Spatial Pattern of River, Lateral and Longitudinal Profile, Number of Meanders, Curvature, Width to Depth Ratio and River Geomorphic Forms The Evin Watershed is in the Period of 20 years (1998-2018). This Research was Carried out in Three Steps: the First Step was Hydrological Studies Using the Semi-Distributed SWAT Model in two Sections of the 20 years (1998) and (2018) in the Evin-Darake Basin, the Second Step of the Study of Discharge and River Sediment in the Basin. The Sediment and Discharge Data During the Statistical Period of 1361-1391 was used for the Hafthouz Station. the Changes were analyzed in the Pre and Post Urban Development Period. Finally, the Third Step of Geomorphological Studies of the Basin was studied. Due to Geomorphology Studies, Aerial Photos and Satellite Imagery were used to Document Land Cover, Drainage Network and Urban Extension, and then each Channel was Divided into Intervals. Field Studies in each Range include Measuring Channel Dimensions, Sediment Characteristics, Geomorphic Forms, and other Items Mentioned in this Research.
Results and discussion, Conclusion: The Results of the Simulation of Precipitation Process-Runoff Based on the City's Physical Development Scenario indicate that the Average Rainfall in Evin Watershed is equal to 4,430 mm, of which this amount of Rainfall in the Previous Period is 142.6 mm and in By 2018, 146.8 mm is Evaporated in the form of Actual Evapotranspiration from the surface of the earth and plant. Also, the mean Curve Number (CN), which indicates the amount of Water retained on the Catchment, is in the Simulation Process, this amount is 84.01 in 1998 and (in 2018), this amount has increased to 76.78 and the Runoff rate The Surface area in the Previous Period (1998), 106.66 mm and (2018) increased to 126.88 mm. According to the Results of the Sediment Evolution Process before Urban Development, the amount of Sediment has Risen over time, which subsequently shows an increase in Discharge. On the other hand, the Results of the Study of the trend of Changes in the amount of Sediment in the Post-Urban Development Period compared with the Previous Period, decreased significantly In Discharge and as a Result of Sediment Production. Based on the results of the SWAT Model, the Urban Development Factor and Human interference have shown increased Runoff Production Capability and reduced permeability of the Basin.
The results in the discussion of geomorphological studies showed that with the development of urbanization and development of human activities within the studied area, the river system has changed. The survey of aerial photos and Google Earth suggests that changes in the river's path as the river has undergone erosion and lateral changes over the course of twenty years of study, the riverbank on the right bank of the river. In general, in the sections of the route, the rivers are limited by resistant outcrops and formations, the Meander movements are minimized, there is no possibility of lateral displacement and displacement of the waterway bed and limits the river's potential for change. Also, the longitudinal profile of the Evin River in the Upper and Upper Mountain Range has undergone less urbanization and expansion. In the longitudinal profile of the river Darake, there are dysfunctional and uplifting phenomena, which is due to the bending of the river and indicates the sedimentation and erosion in these parts of the river. In the convexity of the sedimentation process and at concave points, erosion is performed. over the course of twenty years, with increasing flow rate and urban development, river profiles in the previous period tend to be submerged and the sections are shaped like V. But in the new period, the profile of the plate has expanded due to increased runoff and lateral erosion of the river bank, and the profiles of the sections have changed in shape U. The largest change in the number of Meanders in range 1 is observed in 1998, with 4 twists and in 2018 it has increased to 10 twists. During the period from 1998 to 2018, the Range of 1 From the direct to sinusoidal pattern, the Range of 2 From the sinusoidal pattern to Meander and the range 4 from the direct pattern to the sinusoidal pattern. In the range of 5, the pattern change was not observed due to direct channeling and fixation of the channel and river bank walls using concrete walls. In range 1, the Curvature of the channel increased from 1.7 in 1998 to 1.13 in 2018. In range 2, the Curvature from 1.24 in 1998 to 1.31 in 2018, shows an incremental trend. Also, in the range of 3, the Curvature increased from 1.25 in 1998 to 1.29 in 2018, but the pattern pattern did not change over the course of twenty years and was observed as a Meandering. Due to the presence of natural obstacles (outbreak of resistant formations), in range of 3, the pattern is dominant. In the ranges of 4 and 5 of the river, the difference in Curvature is not very different. The results of the measurements of the depth-to-width ratio indicate that the width of the river has increased over the course of twenty years by the width of the Channel in the range of intervals due to the erosion of the banks. No variation in the width of the river has been made at range of5 (urban area). The area around Watercourse and river in the form concrete channels is restricted and restored.