Highlighting the meandering changes of the Karun River using multi-temporal Landsat and IRS images

Master's thesis in the field of geography, geomorphology

Abstract

Khuzestan's vast plain hosts important permanent rivers, the largest of which is the Karun River. The Karun watershed is one of the largest sub-basins of Iran and a part of the main watershed of the Persian Gulf and the Oman Sea. The Karun River is about 890 km long and consists of four main branches named Khorsan, Ab Vank, Ab Kiyar and Bazeft. It originates from the Sarhai spring at the foot of the Vank mountains and flows to the southeast under the name of Kohrang Ab and enters the Khuzestan plain near the city of Gatund. Near Shushtar, it is divided into two branches, Gargar and Shatit. These two branches join the Dez river in the place of Bituminous Dam and form the Great Karun. This river finally flows into the Persian Gulf. So far, many studies with different goals have been done on this river. The study section of the Karun River in this research is from the entrance to the Khuzestan Plain (in the city of Gatund) to the mouth of the river (where it joins the Persian Gulf). With reference to Bryce's method in introducing river meanders, we counted the Karun meanders for the first time in Iran, and the number of 149 river meanders was determined and the types of meanders were divided into two according to the geometric factors of radius of curvature and chord length. Simple and compound meanders were classified. Then, by forming a database composed of 1:50000 topographic maps, aerial photos from 1955 AD (1334 solar), Landsat satellite image from 1973 and IRS from 2006, we processed multi-temporal images and aerial photos in the environment of ER Mapper and GIS software. Considering that the basis of the work was to identify meanders based on 1:50,000 topographic maps prepared from aerial photos of 1955, we also included a part of the aerial photos of this year in the analysis process of meandering changes. This brought two advantages; Both the accuracy of work in detecting changes was increased and the time period of the study was increased to 51 years. The following results were obtained with the conducted studies:

Bryce method can be used to identify and count Karon meanders. In this thesis, while using Bryce method in the study of Karon river, 149 meanders were identified in this river. By comparing the images, photographs and topographical maps of the total 149 identified meanders, 54 cases of change were observed, among which 21 cases of change of meander type from simple to compound and reverse were observed.

Most of the changes in the studied time period are related to the conversion of the simple to compound pattern.

Another important change is related to the end part of the Karun route, which is the Bahmanshir river, in the order that in At the mouth of the river, two meanders have been added to the total number of meanders in the river.

The largest number of compound meanders have been seen in the Shatit and Karun rivers, especially from Weis to Ghazawieh Koch (meander 85). Most of the changes in the river in the time period under study correspond to these areas.

In addition to proving the importance of satellite images and the high accuracy of these images in showing meandering changes in a specific time period, the useful application of topographic maps 1:50000 was proven in a study of large rivers such as Karun. This combination was completed with the aerial photos taken from the area.

Key words: Karun - Meander - multi-time satellite images - Bryce method - remote sensing

Chapter 1                    

Research overview

1-1- Explanation of the research problem and its importance

The Khuzestan plain is a low-altitude plain with a gentle slope, where important rivers flow. Because Karun, Karkheh, Dez, Venus and Sarghar flow in it. These rivers have high mobility and dynamism, and over time, their landforms and their course have changed in the longitudinal and transverse directions. The Karun River is the longest and most watery river in Iran and is considered one of the meandering rivers of the Khuzestan Plain.

In a classification, rivers are divided into three groups: meandering, branching or arterial, and straight. According to the morphological characteristics, the Karun river shows arterial, meandering and straight characteristics in different longitudinal sections after entering the Khuzestan plain. By entering the plains of Khuzestan, the Karun River has been affected by important variables such as discharge, slope, sediment load, depth, width, and speed, and its longitudinal and transverse degrees have caused many changes from the past until now. Meanwhile, winding rivers are divided into two types: a) winding alluvial or regular rivers, b) winding valley rivers. Karun is a type of alluvial meanders, and its twists and turns are not subordinate to the main valley.

A meander itself is divided into three parts, which include the following: 1) Convex part: In this part, the speed decreases and sedimentation increases. 2) Concave part: In this part, the rate of increase and destruction expands. 3) Middle part: This part is the distance between the convex and concave parts. By carrying out these studies, it is possible to accurately and correctly understand the changes, behavior and principles governing the Karun River, determine the type of meandering changes, and finally take action to exploit the river's potential and apply proper management to its environment. In this thesis, we intend to analyze the form and changes of the meandering of the Karun River, in the area of ??Gatund (the entrance of the Karun to the Khuzestan Jalgahi) to the mouth by analyzing multi-temporal satellite images (Landsat) and IRS).

The importance and application of multi-temporal images in tracking changes in the meandering of the Karun River.

Combining remote sensing techniques and GIS in order to determine the changes in the meandering of the river.

Hypotheses

Multi-temporal satellite images and remote sensing techniques are highly capable in highlighting the meandering changes of the Karun River and determining the changes in the type of meanders.

Often, the change in the form of Karun meanders during the studied time period is related to the change in the type of meanders rather than the change in the river pattern.

Questions

1- Are remote sensing techniques and multi-temporal satellite images capable of highlighting the changes in river landforms, including meanders?

Which of the settlement centers may be displaced? Will the Caron meanders suffer?

Caron River is changing to what type of meanders in the course of its evolution in the studied time frame?

Research background

- Tourne (1991), in an article entitled coastal erosion and meander migration in the Mississippi and Red rivers in the United States of America, states that referring to the migration of bends Mississippi and Red Rivers in America, the importance of beach characteristics in beach retreat, channel geometry and meander shape change is clear, they say: historical evidence shows how the nature of the material on the outer beach affects both the speed and the distribution of beach erosion in a bend, the speed and direction of the bend migration together exerts many changes on the channel transformation pattern.

- Greco et al. (2007), have studied the middle part of the Sacramento River, which is an active meandering river channel, the sediments of this river have created a low-slope front in a new and separate area from the alluvial land, this recently formed land has undergone primary succession by forest species such as willow and other trees and has provided important habitat for maintaining certain species in California. The land surface (formation of the flood plain in the Meander river system)" and "Analysis of the land formation and specific distribution of gravel deposits, riverside plant communities, forest structure formed in relation to the slope of the area" and it comes to the conclusion that: 71% of the Meander riverside vegetation was formed in the region during 101 years, and the highest percentage of canopy covered in these lands is related to willow trees (18%) and Cottonwood (31-43%) is 1-9 and 10-44, respectively.