Geomorphic changes of the Cheshmeh Kileh River in the coastal plain of Western Mazandaran between 2014 and 2022

Introduction



In coastal plains, rivers are very important geomorphological elements. Changes and evolutions of their morphology in different periods have a great impact on human settlements. River ecosystems are constantly changing, and these changes over time create different landscapes. Geomorphological Changes can negatively impact agricultural, irrigation, and drainage network infrastructure riverbanks. Therefore, detecting environmental changes is important in proper planning for sustainable development and rational utilization of natural facilities. Understanding these river dynamics is essential for effective management practices in reducing flood risks and maintaining ecological integrity. By focusing on the relationship between discharge changes and morphological evolution, researchers can develop more effective strategies for managing river systems during continuous environmental changes over periods. Historical environmental changes have a profound impact on current river morphology and shape the physical characteristics and dynamics of river systems. Understanding these impacts is very important, especially in the context of ongoing environmental changes driven by natural processes and human activities. This study aimed to investigate morphological changes in the Cheshmeh Kileh River over different periods and also contribute to a more comprehensive understanding of river dynamics in coastal areas.

Materials and methods

The Cheshme Kileh River Basin is located in the western part of Mazandaran Province, between Abbasabad and Ramsar Cities. This River is the largest in the western parts of Mazandaran provinces and has the maximum discharge in this region. The average annual discharge of the Cheshme Kileh River in the 18-year statistical period is 12.25 cubic m per second. The Cheshme Kileh originates from the Do-Hezar and Se-Hezar basins in the Takht-e- Soleyman and the Alamut Mountains. The river is 80 kilometers long and flows into the Caspian Sea after passing through Tonekabon city. The study area in this study is the coastal plain section of the Cheshme Kileh River, which is divided into five sections according to River patterns. Geologically, the mountainous section of the basin is located in the Alborz zone. The predominant sediments in the plain section are alluvium deposits. This study the changes in the Cheshmeh Kileh River channel in western Mazandaran evaluated between 2014 and 2022. to assessments of this river channel change satellite data available in the Google Earth system was used and the river banks were extracted in different periods. Quantitative analysis of river bank changes over periods was performed using DSAS software and ARC GIS 10.5 software. This plugin determines the rate of changes in the right and left banks of the river using the distance of each measured point to the baseline and the date of the extracted shorelines. In this study, Net shoreline movement (NSM), Shoreline change envelope (SCE), Liner regression rat (LRR), and endpoint rate (EPR) indices were used to quantitatively assess the changes in the river bank. The method of Magdanloo and Fernandez (2011) was used to assess the Channel Activities (CA). In this method, to identify and measure the lateral migration rate of the Cheshmeh Kileh River between 2014-2022, the centerline of the river was drawn for years, and then by superimposing layers.

Results and discussion

The results indicate that the pattern of the river despite changes in the curvature coefficient, the overall pattern of the river has not changed between 2014 and 2022. The results of the channel activity revealed that the highest channel activity was between 2014 and 2015 and the lowest was between 2015 and 2019. Data obtained from the changes in the left and right banks of the Cheshmeh Kileh River separately in different periods from 2014 to 2022 showed that in the NSM index on the left bank of the Cheshmeh Kileh River, the maximum retreat (bank erosion) was -113.05 m, the maximum prograde (sedimentation and land formation on the bank) was 31.78 m, the average bank changes were -35.8 m. In the SCE index, the maximum retreat of -113.05 m and the average of these changes of -23.82m occurred during 8 years. The highest rate of bank prograte occurred in the central part of the river. The dominant trend on the left bank of the Cheshmeh Kileh River during this period was the retreat and erosion of the bank. According to the EPR index, the maximum retreat rate was -14.1 m/year, the maximum prograde rate was 10.35 m/year, and the average bank changes were -1.03 m/year. According to this index, the maximum retreat rate was -12.96 m/year, the maximum prograde rate was 8.63 m/year, and the average bank changes were -1.34 m/year. Based on the average NSM index data on the right bank of the Cheshmeh Kileh River in the period 2014 to 2022, the maximum prograde was -108.36 m, the maximum retreat was 48.44 m, and the average bank change was -85.7 m. The dominant trend on the right bank of the Cheshmeh Kileh River in the 8 years was the type of prograde and occurrence of sedimentation on the bank. According to the (EPR) index, the maximum advance rate was -13.56 m/year, the maximum retreat rate was 60.06 m/year, and the average bank changes were -0.99 m per year. According to the (LRR), the maximum advance rate was -14.45 m/year, the maximum retreat rate was 6.02 m/year, and the average bank changes were -1.03 m/year.

The results of this research indicates that, due to the general convexity of the river towards the west, the dominant bank erosion has occurred on the left side of the river. The results of the study of the changes of the left and right banks of the channel in the studied periods show that the process of changes is not the same and due to changes in the river discharge, the processes of prograde and retreat of the channel can change simultaneously with erosion and sedimentation. In these periods when the river discharge decreases, the sedimentation processes intensify and provide the basis for the progression of the channel banks and lead to a decrease in the channel width. When the river discharge increases or extreme floods occur in the river, the process of changes in the river will be erosive.

Conclusion

The results indicate that the channel dynamics in Cheshmeh Kileh River with a sinusoidal pattern are more than in straight rivers. The effect of floods in these rivers increases in the width of the rivers, and this effect is more noticeable in sinusoidal rivers. The evaluation of the values obtained from the model data also showed that at all times, river bank recession and erosion occurred on the left bank. The average rate of these changes along the river was approximately 1 m/year. The intervals located in the middle and upper parts of the plain had more suitable conditions for bank erosion and channel instability due to the greater slope.