Investigating the Effect of Flood Flows on Morphological Changes Using a Series of Satellite Images: Rapid Changes in Morphology of Bazoft River

doi:10.21203/rs.3.rs-3749894/v1

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Research Article

Investigating the Effect of Flood Flows on Morphological Changes Using a Series of Satellite Images: Rapid Changes in Morphology of Bazoft River

https://doi.org/10.21203/rs.3.rs-3749894/v1

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Morphology is one of the most important branches of river engineering science. Examining the changes in the geometry of sections in rivers that feed large dams is of particular importance. In fact, gaining a better understanding of the river's behavior will reduce potential damages to hydraulic structures and public infrastructure. In this regard, in this research, the morphological changes of Bazoft River, one of the sub-basins of North Karun, which enters the Karun 4 Dam at the end, have been investigated. In this study, using 26 Landsat + ETM and OLI satellite images, the displacement pattern of the main river channel, along with the changes in width and sinuosity resulting from sedimentation and erosion processes in long and short-term intervals leading to the year 2015 and caused by large floods in this period of time was investigated. The results showed that the average displacement of the main channel of the river leading to erosion (sedimentation) for the right and left banks is 14 (15) and 14 (14) percent of the average width of the river, respectively. Also, the net area change rate due to the displacement of the main channel of the river for the right and left banks was obtained as -1.8 and 0.3 hectares per year, respectively. By examining the effect of floods, it was found that the amount of erosion is higher than sedimentation on both coasts, and the left coast is more dynamic than the right coast. The average width of the river in the 30-year period for the four investigated periods is 33.8, 44.7, 40.2, and 38.6 meters, respectively. Also, the width of the Bazoft River did not change much before the biggest flood in 2009 and its value did not exceed 40 meters. But after the flood, the width of the river suddenly increased and these changes seem obvious. The maximum increase in width is related to the second span of the river and its value is equal to 70 meters. Investigations related to four longitudinal intervals along the river's path showed that the sinuosity value in all years in the first interval had an almost constant trend, but in the second and third intervals, its value is higher, so these two intervals are more active than the other two intervals be in the fourth span, which leads to the Karun Dam 4, changes in sinuosity have a downward trend. Also, the results showed that the dewatering of the Karun 4 dam had a significant effect on all the morphological parameters of the Bazoft River in the fourth period. The results of this study perfectly indicated the capability of revealing the river form changes using Satellite Images Time Series (SITS). This homogeneous result indirectly shows that the erosion rate of the upstream basin and the sediment load of the river increased during this period. Therefore, while updating the status of rivers, the effects of protective and structural measures in such rivers can be evaluated in this way and corrected for improvement.

Agricultural Engineering

Marine and Freshwater Ecology

Hydrology

Plant Physiology and Morphology

Geomorphology

Remote Sensing

Water Indicators

Erosion and Deposition

Floods

Satellite Images Time Series

Morphology

Hydraulic Structures

OLI Satellite Images

Public Infrastructure

Morphology is the knowledge of the river network from the point of view of its general shape and form, river border and boundary, dimensions and geometry, hydraulic characteristics, direction and longitudinal profile, and the process of its changes. In fact, in order to have a scientific and logical approach to the various problems of rivers, providing solutions, proper planning and designing water resources projects and related structures, and creating a correct understanding of the morphology and behavior of the river is a prerequisite. Therefore, river morphology studies play an important role in the planning, design, and maintenance of water structures and, in particular, reservoir dams. In recent years, the information that can be extracted from remote sensing images has been widely used for the preparation of the spatial information database, in order to investigate the morphological changes and engineering studies of rivers (Seif and Najmi, 2013 Arshad et al., 1386). Remote Sensing (RS) technique, with its special capabilities to produce repeated images in a wide area, has provided the possibility of monitoring the temporal and spatial changes of rivers, and along with that, the Geographical Information System (GIS) facilitates their processing and accelerated. Landsat's multispectral products, having the record of the longest sampling of the continental surface, medium spatial resolution, and public access level, are considered one of the best options for examining the morphological changes of the river (Baki and Gan, 2012). Fisher et al., 2016). Automatic classification by making a mask of water pixels is the basis of most digital image processing methods for surface water investigation. With this method, water is separated from other effects and the dynamics of water effects in different periods of time can be monitored using the change detection method (Fisher et al., 2016). In fact, there are three main methods to separate surface water from other effects:

A) Using the information of spectral bands (Rundquist et al., 1987)

B) Supervised and unsupervised classification (Otukei and Blaschke, 2007)

C) Using water indicators (Jiang et al., 2014).

The ease of implementation and the accuracy of the results obtained from water indicators are more than other methods. This method is very accurate in separating water pixels from other pixels in multispectral images. NDWI index was first presented by McFeeters (1996) to identify lakes and wetlands. The sensitivity of this index to moisture content has caused it to be used in the determination of vegetation stress, leaf area index studies, and modeling of agricultural products in addition to identifying water sources. The value of this index ranges from + 1 to -1 and higher values indicate more water content (Alavi Panah, 2019). Ji et al. (2009) by examining the accuracy of the water resources map prepared using the NDWI index, showed that this index has a good ability to separate surface waters, but it mainly faces two basic problems. The first case of extracting the index using different bands (Visible, Near-Infrared, or Mid-Infrared) gives different results, and in the case of other thresholds of this index, it is largely dependent on the proportion of water in each pixel. Xu (2006) modified the NDWI index by replacing the mid-infrared band instead of the near-infrared band and called it MNDWI. This modified index has more stable thresholds than the NDWI index. After that, Feyisa et al. (2014) developed two different versions of an automatic water extraction index called AWEIno shadow to increase the ability to separate surface water in images without shadows and AWEishadow for images with shadows of mountainous areas, buildings, and clouds. Presented Indicator Enhanced Water Index, abbreviated as EWI, is another index presented by Wang et al. (2015). This index uses the information of four spectral bands and has the ability to estimate the percentage of pixels occupied by water. Fisher et al. (2016) presented an index named WI2015 for separating surface water from other features in satellite images using the spectral information of five Landsat satellite bands. In recent years, according to the unique characteristics of remote sensing techniques and satellite images, many studies have been conducted in the field of investigating the morphological changes of rivers, which can be mentioned below.

Researchers investigated the changes in river borders and morphology by using different sensors of Landsat images and geographic information systems. (Haque (2023) and Hassan et al. (2023) and Rahman (2023) and Khatun et al. (2022)). In 2023, Haque will use low- and medium-resolution satellite data as well as remote sensing and geographic information system (GIS) skills to identify features of river displacement, erosion, and sedimentation between 1972 and 2013 to assess spatio-temporal changes. They paid the Jamuna River. In this study, LANDSAT satellite images with (MSS), (TM) and (OLI) (TIRS) sensors were used. The results show that total erosion from 1972 to 2013 was 3356 ha, while deposition was 5342 ha. Erosion and sedimentation cause shoreline displacement, river widening and sediment displacement. Thus, this study will be earnest in assisting the environmental management and associated planning including necessary measures.

During a study, Rahman (2023) investigated the morphological changes of the Jamuna River in Bangladesh in a 46-year period, from 1973 to 2019. About 240 km of Jamuna river course was evaluated using remote sensing and GIS. The main objective of this study was to understand the movement pattern of Jamuna River bed. River dynamics were evaluated based on beach erosion, accretion, shoreline displacement, channel width, and river course and confluence change. The results showed that the area of the river has increased by 48% in 46 years. The total eroded area was about 1038 square kilometers, with 35.40% more erosion on the left bank than on the right. Due to more erosion than sedimentation, the river widened. The average width of the river increased by 56.40% during this period. The average displacement rate on the left bank was higher than on the right bank, which indicates the eastward movement of the river. Hassan et al. (2023) using image analysis techniques on Landsat satellite data (ETM+, OLI), identified the nature of shoreline changes, erosion-accretion, and lobe displacement from 2003 to 2021 in the morphology of Nijhum Dwip Island. The findings show that since 2013, the morphology and geographical extent of the island have undergone significant changes and have gradually reached its current stable state in the Bay of Bengal. Compared to its 2003 extent, it has lost approximately 2.57 square kilometers by 2021, with more erosion and accretion in the southern part, which geometrically transformed the island from a rectangular to a sub-round shape. Khatun et al. (2022) in a study of spatial and temporal changes of riverbanks assessed the change of the Ganges River channel of Bangladesh for the period 1980–2020. For this purpose, Landsat images with a spatial resolution of 60/30 meters were used to determine the borders of the river bank. The results indicated a significant shift of the river bank to the left side in the direction of the flow. The total erosion and accretion of the studied area from 1980 to 2020 were estimated to be 250.82 and 236.75 square kilometers, respectively. Several studies investigated the morphological changes of the river using water indices (NDWI), some of which are mentioned below. (Arefin et al. (2021) and Saleem et al. (2020) and Hasanuzzaman and Mandal (2020) and Yousefi et al. (2020)). Arefin et al. (2021) examined changes in the boundary of the Padma River in Bangladesh from 1955 to 2016 using the normalized difference water index. Their findings indicate that during the period from 1955 to 1973, two sections of the river's right bank experienced the highest erosion levels. Conversely, a portion of the river's left bank underwent sediment deposition from 1973 to 2016, leading to the formation of new land areas and an increase in the width of the river bank. Hasanuzzaman and Mandal (2020) examined the morphology of the Raidak River over a span of 44 years (1972–2016), encompassing both short and long time intervals. Their findings revealed a general decrease in erosion and deposition rates, except for a specific 6-year period. As a result of these changes, the river channel exhibited increased activity and dynamism. Raj and Singh (2020) conducted a study on the spatio-temporal changes of the Ganga river spanning from 1973 to 2019. To ensure precision, they divided this period into five distinct intervals. Their findings indicated that the left bank of the river experienced erosion, while deposition increased in the river's bed. Additionally, the construction of the Farakka dam had an impact on the upstream region of the river. Saleem et al. (2020) conducted an analysis of the Padma River in Bangladesh, revealing that the left bank of the river experienced higher erosion compared to the right bank. Yousefi et al. (2020) employed the NDWI index to study the effects of extreme floods on the shape of the Karun River, as well as the consequent erosion and deposition. Their research highlighted the pivotal role of extreme floods in the deposition and morphological evolution of meandering rivers. Rezaeian et al. (2017) studied the morphological changes in the Karun River using four series of satellite images (Landsat TM and ETM + satellites) and concluded that the length of the river increased from 1958 to 1989, but from 1989 It has decreased until 2010. Li et al. (2016) investigated coastline changes in West Florida over a 30-year period at Sub-pixel spatial and annual temporal scales using Landsat data from 1984 to 2013. The results showed that the average rate of change is 0.42 ± 0.05 square kilometers per year on the west coast of Florida during three decades. This study shows that the time series of Landsat data is suitable for investigating the morphological changes of the coast. Petropoulos et al. (2015) investigated the changes in the Axios and Aliakmonas rivers over a 25-year period (1984 to 2009) by interpreting four Landsat TM satellite images. The amount of sedimentation and erosion was measured in different scales in the desired time period. Using the geographic information system, they concluded that the erosion rate was higher between 1990 and 2003, but the sedimentation rate was higher between 2003 and 2009. Dhari et al (2014) analyzed the Ganges using topographic maps and various Landsat images from 1972 to 2005. It was found that the coast west of the Ganges River has more erosion and the river is shifting to the west, and it was suggested that flood protection structures be built for the west coast. Penn (2013) investigated the changes in the Bankra River in West Bengal using topographical data, MSS, and ETM + Landsat images on different dates along with Google Earth images from 2011. The results of the research have shown changes in various morphological parameters of waterways such as sinuosity index and Pichan-Rudi ratio. Baki et al. (2012) studied the Jamuna River, which regularly undergoes significant erosion. Using thirteen Landsat MSS and TM images from 1973 to 2003, river change patterns that were affected by sedimentation and erosion processes were investigated for 30 years. The result is that the average erosion and sedimentation rates are 227 and 271 m/year for the long-term period (1973 to 2003), 90 and 104 m/year for the short-term period (from 1973 to 2003 annually) on the left bank, and so on. 187 and 148 m/year for the long term and 75 and 50 m/year for the short term on the right bank of the river. Sarkar et al. (2011) investigated the morphological changes of the Brahmaputra River in India in a 620 km span between 1990 and 2008. These researchers first used Landsat satellite images, and IRS images as a ground reference and determined the main channel of the river using the NDWI index. The observations of these researchers indicate the erosion of both sides of the river in the studied area. Sarma et al. (2007) investigated the 220 km stretch of the Burhi Dlhing River which is affected by many tributaries. Using topographic maps from 1934 to 1972 and satellite images from 2001 to 2004 as well as geographic information systems, these researchers evaluated the changes in coastlines caused by river erosion. The result of this research is that the highest average annual rate of erosion and sedimentation was observed on both coasts during the periods of 2001–2004 and 1972–2001. According to the scope of studies, there is still a need to investigate morphological changes in shallow and narrow mountain rivers, as well as the influence of water structures on morphological changes and the role of floods in the stable regime of rivers. Therefore, in this research, morphological changes in the Bazoft mountain river due to floods of recent years have been investigated. The central idea of this study revolves around the investigation of water extraction from Landsat images at the pixel level and further sub-pixel processing to separate water content for each pixel. The necessity for sub-pixel processing arises from the need to enhance the accuracy in determining the river boundary, given the narrow nature of the river under study. The issue of river bank erosion has significant consequences, leading to the displacement of numerous people, the loss of homes, agricultural lands, and resources, resulting in extreme poverty in the affected region. Despite these challenges, there is still a lack of sufficient erosion management plans in place. Despite the extensive capabilities of remote sensing technology and the discovery of basic laws of physics to understand the behavior of physical phenomena, natural systems have complex structures and behavior so their qualitative analysis is still a challenge. In the present study, an accurate model based on the sub-pixel method is needed to extract the river boundary to determine the morphological changes of the desired river. In fact, what makes micro-pixel processing necessary in this study is the need to increase the accuracy in determining the river border due to the small width of the studied river.

Study area

In this study, the morphological changes of the Bazoft River have been investigated. The Bazoft River is located in the Bazoft sub-basin with a length of 132 kilometers. It originates from the southern slope of Zardkoh Bakhtiari and then flows through the Bazoft Valley to the southeast and finally flows into the Karun 4 dam. Bazoft sub-basin with an area of over 2180 square kilometers in the form of a narrow strip (16 kilometers) but relatively long (about 135 kilometers) is located in the north to southwest part of Chaharmahal and Bakhtiari province and extends in the northwest-southeast direction. Is. The Bazoft sub-basin is located between the longitudes 49.81 and 53.53 degrees east and latitudes 31.63 and 32.48 degrees north. This basin is a completely mountainous region and morphologically it is in the form of large valleys that are located among the towering mountains. The height of its points varies from 840 meters at the exit point to 4420 meters and its average height is 2156 meters. In the Bazoft catchment basin, the Bazoft River has an altitude of 1600 to 1800 meters, which occupies the largest area in the upstream basin, Marghak station, and more than 14.5% of the basin's area is in this altitude category. Also, 65.7% of the area of this basin is between 1600–2600 meters high; is placed. The amount of precipitation in the highlands of Chaharmahal and Bakhtiari province, which in some areas is more than 1000 mm per year, as well as the topography of the region, has caused the Bazoft River to face large floods every year. Floods that, in addition to the destructive effect, cause changes in the morphology and morphology of the river. Table (1) shows the time and maximum flow of flood in the last 15 years of Bazoft River based on the hydrometric statistics of the Marghak and Landi stations. Karun 4 dam with a height of about 230 meters from the foundation and a normal level of 1028 meters above sea level is located four kilometers downstream from the confluence of Armand and Bazoft rivers, which was officially watered in April 2009. Figures (1) shows the location of the Bazoft River, the catchment area, and the location of Karun Dam 4. The Karun 4 dam was built with the aim of regulating the water of the rivers of the Upper Karun basin at the rate of 3.7 billion cubic meters per year, controlling the flooding and destructive floods of the rivers in the region, and producing electric energy at the rate of 2107 million kilowatt hours. The construction of this dam is located in Chaharmahal and Bakhtiari province, 180 km southwest of Shahrekord city and 11 km from Lordegan city, in a valley with a width of 40 meters. Karun 4 dam with a height of about 230 meters from the foundation and a normal level of 1028 meters above sea level is located four kilometers downstream of the confluence of the Armand and Bazoft rivers (670 kilometers from the outlet of the Karun River to the Persian Gulf).

Table 1

Characteristics of some floods of Bazoft River, Marghak and Landi hydrometric stations
Hydrological year	Frequency of flooding	The history of flow	Peak flow (cms)	Average flood discharge (cms)
2001–2002	35	2001-12-20	846.2	234
2002–2003	42	2002-12-10	782.8	196.3
2003–2004	33	2004-01-05	574.6	193.8
2004–2005	32	2005-03-12	1808.5	262.5
2005–2006	38	2006-02-09	1303.3	261.6
2006–2007	26	2007-03-27	675.8	233.6
2007–2008	15	2007-12-08	638.8	127.9
2008–2009	17	2009-04-10	197.4	117.8
2009–2010	22	2010-05-03	334.1	133.1
2010–2011	19	2011-03-12	842.1	191
2011–2012	10	2012-02-02	383.5	190.6
2012–2013	28	2012-12-22	485.1	141.2
2013–2014	14	2014-03-12	742.6	315.4
2014–2015	32	2015-03-23	1033.6	183.3
2015–2016	54	2016-04-13	560.1	148.7

The annual average of the basin is about 96 mm, the annual average is equal to 10.4 degrees Celsius and the average slope of the basin is about 45%. In terms of soil science, the dominant textures of the basin include Silty loam and clay loam, and other textures such as clay, loam, and sandy loam are also observed in this basin. The predominant use of the basin is pasture and the use of forest and agricultural land is also one of the major uses of this basin. The height of its points is from 840 meters to 4420 meters and its height is 2156 meters. In this catchment area of the Bazoft River, an altitude of 1600 to 1800 meters has occupied the largest area in the upstream basin of Marghak station, and more than 14.5% of the area of the basin is located in this altitude category. Also, 65.7% of the area of this basin is between 1600–2600 meters high; is placed. (Description in Fig. 2)

Investigation of river flow changes

There are four hydrometric stations of Shahid Khedari, Mavarz, Landi, and Marghak in the main course of the Bazoft River, and Marghak station has statistics until the water year 2017–2018, and it has become unavailable due to the water intake of Karun Dam 4. The annual statistics of Marghak station were reconstructed using Landi station statistics until 2015. The general characteristics of the hydrometric stations located in the study area are presented in Table (2). Based on the statistics of the mentioned stations on the dates when the satellite images are processed and used, the daily discharge of the river is extracted and these results are used to determine the flow conditions. Figures (3) also shows the average annual runoff of Marghak and Landi stations in the 48 years ending in 1995, along with the moving average of three, five, and seven years, based on which the average annual runoff is estimated to be about 66 cubic meters per second. As can be deduced from the moving average charts, the last 48 years include periods of drought and drought. According to the average annual water flow chart, the highest flow of Bazoft River occurred in the water year of 1992–1993 with a flow of about 156 cubic meters per second. The three-year moving average graph shows that the amount of discharge has an increasing trend from 1988 to 1992 and then it is a decreasing trend until 1998. Then, it increased from 1998 to 2004, and again from 2004 to 2016, the three-year moving Dubai had a decreasing trend.

Table 2

General characteristics of hydrometric stations in the study area
UTM (m)			Station type	Basin name	Station name	Row
Elevation sea level	Y	X	Station type	Basin name	Station name	Row
1899	3584695	391538	Hydrometry	Bazoft	Shahid Khedri Bridge	1
2377	3521604	434336	Hydrometry	Bazoft	Landi	2
2192	3559908	412857	Hydrometry	Bazoft	Mavarz	3
980	3477470	433474	Hydrometry	Bazoft	Marghak	4
1679	3563138	409314	Pluviometry	Bazoft	Chaman goli	5

The amount of precipitation in the highlands of Chaharmahal and Bakhtiari province, which reaches more than 1000 mm per year in some areas, as well as the topographical area, causes large floods in open rivers every year. Floods that, in addition to the destructive effect, cause changes in the morphology and morphodynamics of the river. Table (1) shows the time and maximum discharge of some Bazoft river floods based on the statistics of the regional water company of Chaharmahal and Bakhtiari province. Due to the fact that the Bazoft River is placed in two separate frames in satellite images, in this research, 26 frames of Landsat satellite images are used as the main data and 1:25000 coverage maps of the country along with Google Earth images. The ground reference data were used to investigate the changes in the boundary and the rate of erosion and sedimentation of the Bazoft River bank in the last 30 years. All the images were collected between the middle and the end of August according to the dry season of the region. The selection of images in the dry season is because at this time the vegetation cover and other land conditions, especially the water level, can be better evaluated. In addition, during the dry season, the probability of images without cloud cover is higher, and the border and pattern of the river can be recognized better. In this research, in addition to examining the annual images, the images before and after the flood of March 2019 were also evaluated in order to investigate the direct effect of the flood. The specifications and time of taking the images used can be seen in Table (3).

Table 3

Landsat images used
Data Pickup					Spatial resolution (meter)	Sensor	Data Pickup					Spatial resolution (meter)	Sensor
Row	Path	Year	Month	Day	Spatial resolution (meter)	Sensor	Row	Path	Year	Month	Day	Spatial resolution (meter)	Sensor
38	164	1985	8	2	30	Landsat-TM	38	164	2009	8	4	30	Landsat-TM
37	165	1985	6	22	30	Landsat-TM	37	165	2009	7	26	30	Landsat-TM
38	164	1987	8	24			38	164	2010^*	8	31	30	Landsat-ETM⁺
37	165	1987	8	15					2010	8	15
38	164	1994	8	27	30	Landsat-TM	37	165	2010^*	7	21
37	165	1994	8	38	30	Landsat-TM			2010	8	6
38	164	2005^*	8	1	30	Landsat-ETM⁺	38	164	2011^*	8	2	30	Landsat-ETM⁺
38	164	2005	8	17					2011	8	18
37	165	2005^*	8	8			37	165	2011^*	8	9
37	165	2005	8	24					2011	8	25
38	164	2006	9	5	30⁺	Landsat-ETM⁺	38	164	2012	8	4	30	Landsat-ETM⁺
38	164	2006^*	9	21					2012^*	8	20
37	165	2006^*	8	11			37	165	2012	8	11
37	165	2006	8	27					2012^*	8	27
38	164	2007^*	8	7	30⁺	Landsat-ETM⁺	38	164	2013	8	15	30	Landsat-OLI
38	164	2007	8	23			37	165	2013	8	22	30	Landsat-OLI
37	165	2007	8	14			38	164	2014	8	18	30	Landsat-OLI
37	165	2007^*	8	30			37	165	2014	8	25	30	Landsat-OLI
38	164	2008	8	1	30	Landsat-TM	38	164	2015	8	21	30	Landsat-OLI
37	165	2008	7	23	30	Landsat-TM	37	165	2015	8	28	30	Landsat-OLI

Extraction of the river border

The general description of this research is presented in Figure (2) in the form of a flow diagram. In this method, after calculating the most useful water indices, the optimal index was selected using the ROC diagram. The ROC curve is one of the appropriate methods to evaluate the results of the thresholding algorithm and to evaluate the ability of different thresholds in differentiating the desired phenomenon. This curve shows the relationship between correctly classified cells and incorrectly classified cells. If the rate of correctly classified cells is plotted on the horizontal axis and the rate of incorrectly classified cells is plotted on the longitudinal axis, the optimal threshold is the point that is more to the left and top of the graph than the other points (Fawcett, 2006). In fact, the highest rate of correct classification and the lowest rate of incorrect classification are seen at this point. The results of the examination of the total validity factors along with the stability of the thresholds made the MNDWI index to be chosen as the best index to determine the river border. Based on the optimal index, the location of the river is determined at the pixel level. Then, in order to verify the determined boundary, the optimal index's micro-pixel capability was used to estimate the water content of each pixel. After that, the edge highlighting process was used to eliminate the effect of classification error in the border areas of the river. Classification error occurs when a pixel (complex) belonging to one category is assigned to another category. All image processing steps were done in the ENVI software environment. In the following, the border of the river in different years was investigated with proper accuracy using ArcMap 10.3 software. So that 507 cross-sections perpendicular to the flow path with 250 meters intervals were used to investigate the changes in morphological parameters. In fact, the difference between the river border on the left and right bank on the cross-section in two different years was meant as the river border shifting in that time period. In this study, positive and negative values were considered for erosion (loss of land) and sedimentation (land formation), respectively. In the following, according to the changes in the river border, the area of erosion and deposition in the distance between two cross-sections was obtained. Also, the width of the river was extracted based on the distance between the left and right borders and its intersection with the cross-section line in each image. Changes in sinuosity were obtained at different times and in four intervals of the Bazoft River.

In this research, the morphological parameters of Bazoft River were investigated using Landsat satellite images in long and short periods from 1364 (1985) to 1394 (2015), and the results are presented in detail below. Also, the changes in width and sinuosity in case floods from the Bazoft River were evaluated. The results section is divided into three parts: findings, research limitations, and suggestions for future research.

Validation

Validation is an important and decisive part of the image processing operation, which can show a little understanding of the amount of error in the image processing process. The areas where the possibility of changes in the river bank reaches zero are used for the verification process in such studies. Extreme topography is one of the factors that limit bank erosion. Examining the number of changes in river bank displacement during different years by using the image processing method in these areas leads to the quantification of the error amount of the method. Feyisa et al. (2014); Dong et al. (2016); Jiang et al. (2014) have used Google Earth images as a verification reference in their studies. According to Google Earth images and field visits, the studied area of Bazoft River was divided into four separate areas. It should be mentioned that there are rocky walls in the Bazoft River so that in some areas of the river, access is only possible to one of the right or left banks. Three areas with rocky walls were identified in the studied area, and the error rate was obtained by comparing the extraction boundary in different years and the reference boundary, the results of which are presented in Table (3). As can be seen, the average absolute error is 1.1 meters, of course, it should be kept in mind that in the investigation of changes in morphological parameters, the river border is measured in two consecutive years relative to each other, which in this case. The average relative error was about 0.6 meters.

Table 3

Shifting of the river border in the surveying stations
Average	Border difference (meters)			Year
Average	Section three	Section two	Section one	Year
1.1	1.2	0.9	1.2	2005
1.3	1.3	1.2	1.4	2006
1.2	1.4	0.7	1.5	2007
1.1	1.1	1.0	1.2	2008
1.4	1.4	1.2	1.6	2009
1.2	1.2	1.0	1.4	2010
0.8	0.9	0.7	0.8	2011
1.1	1.0	1.0	1.3	2012
0.8	0.8	0.6	1.0	2013
1.2	1.2	1.1	1.3	2014
0.9	0.9	0.8	1.0	2015
1.1	1.1	0.9	1.2	Average

Displacement of the border

In order to determine the sedimentation and erosion intervals, the diagram of the displacement changes of the left and right banks of the entire river span was drawn in the long term, which can be seen in Figure (3). Based on the results of Figure (3), Bazoft River was divided into four separate areas. The first interval is from the origin to the distance of 47 km from the main section of the river, the second interval is from the distance of 47 km to 62 km, the third interval is from the distance of 62 km to 84 km and finally, the fourth interval is from the distance of 84 km to the end of the river (127 km) is the criteria for choosing the target ranges are river bank changes, mountainous and access to the area and the presence of natural complications.

Table 4

Average short-term displacement rate * Bazoft River (meters per year)
left bank			Right bank			Time period
Net rate	Deposition rate	Erosion rate	Net rate	Deposition rate	Erosion rate	Time period
-0.4	6.6	6.2	1	5.4	6.4	2005–2006
-0.6	7.6	7.0	-2.6	9.1	6.5	2006–2007
-0.1	5.8	5.7	1.7	4.9	6.6	2007–2008
-0.6	6.6	6.0	-1.4	6.3	4.9	2008–2009
1	3.5	4.5	0.2	4.2	4.3	2009–2010
0.8	5.4	6.2	-0.3	6.2	5.9	2010–2011
-1.7	3.9	2.2	-0.7	4.3	3.6	2011–2012
1.9	4.0	5.9	-0.8	5.1	4.4	2012–2013
1.3	4.2	5.5	0.1	5.1	5.2	2013–2014
-0.7	6.3	5.6	2.0	5.3	7.3	2014–2015
0.1	5.4	5.5	-0.1	5.6	5.5	Average
1.1	1.4	1.2	1.4	1.4	1.2	standard deviation
3.6	4.1	4.8	4.6	5.0	3.7	Range
0.1			-0.1			Net
* Positive values indicate erosion and negative values indicate deposition

The average displacement of the main channel for the left and right banks of Bazoft River with one-year time intervals is presented in Table (4). The results show that the average displacement leading to erosion in a ten-year period for the left and right banks is 5.5 meters per year. The average sedimentation rate was 5.6 meters on the right bank and 5.4 meters on the left bank per year. Considering the average width of the river, which is about 37.78 meters, the displacement of the main channel leading to erosion (sedimentation) for the right and left banks is 14 (15) and 14 (14) percent of the average width of the river respectively.

Area changes

Figures (4) and (5) show the area of erosion and sedimentation zones on the left and right banks of the river between 1384 and 1395, respectively. As can be seen, except for the years 1389 to 1390 and 1391 to 1392, when the amount of erosion is not much different from the amount of deposition, in most years deposition is more than erosion. The largest area of sedimentation and erosion (about 44 hectares) is from 1385 to 1386, which according to the information in table (1) can be related to the flood that occurred in Bazoft River in this year. The maximum difference between erosion and sedimentation is related to the years 1385 to 1386 on the right bank and 1390 to 1391 on the left bank, and in these years, the amount of sedimentation is 2.14 and 2.16 times the erosion, respectively. In the years 1389 to 1390 and 1391 to 1392, the amount of erosion in the left bank is 1.4 times and 1.7 times the sedimentation, respectively. Also, the least amount of erosion and sedimentation occurred in the years 2008 to 2010 and 2010 to 2011, respectively. The results show that there is no big difference between the average sedimentation and erosion of the right bank, and on this coast, the area of sedimentation is about 8% more than erosion. Meanwhile, on the left bank, erosion is about 1% more than sedimentation. Also, the results showed that the maximum amount of erosion occurred in 2005 to 2006, equivalent to 34.9 hectares, and the maximum sedimentation occurred in 2005 to 2006, equivalent to 44.18 hectares. Meanwhile, the minimum amount of sedimentation from 2009 to 2010 and the minimum amount of erosion from 2011 to 2012 are estimated to be 10.17 and 7.09 hectares, respectively. As can be seen in figures (4) and (5), in some years the changes in erosion and sedimentation in the right and left banks are different (for example, from 2019 to 2019, the erosion of the left bank is more than the amount of sedimentation, but it is the opposite in the right bank). As stated before, the amount of displacement of the river border in each section and the changes in the area between the two sections according to the difference in the border of the river in the considered years, and finally the values of erosion, sedimentation, and The net rate of changes for each beach is calculated based on the results of all sections; Therefore, the inconsistency of the changes of the river bank in different years can be caused by the difference in the area of sedimentation and erosion in different periods. In other words, it is possible for sedimentation or erosion to happen within the distance between two sections in consecutive years, and at other times, the discharge and the number of floods will cause a reverse process in the same area, which will ultimately affect the area of erosion and sedimentation in the length of the river is impressive.

Effect of floods on morphological parameters

In this research, in order to evaluate the effects of floods on the morphological parameters of the Bazoft River, and considering that the water intake of the Karun Dam was carried out in 1389, the biggest flood of the water year was 1389 to 1390 with a peak discharge of 1.842 cubic meters. Per second was examined. Figures (6) shows the results of the displacement of the main channel of the river for the flood of 1389 and the long-term average of 30 years (1365 to 1395). In March 2019 flood, the average displacement leading to erosion on the right and left banks is 14 and 13.1 meters per year, respectively, and the average sedimentation is 2.4 and 1.3 meters per year. Also, for the 30-year (long-term) period, for the left bank, the amount of erosion and sedimentation is 5.8 and 10 meters, respectively. These values for the right bank are 1.8 and 8 meters per year. As it is known, in the long-term period, the erosion and sedimentation values are close, in other words, the changes are insignificant in the 30-year perspective. Based on the average width of the river before the flood (about 35.8 meters), the displacement ratio of the river bank, which led to the erosion of the river bank, is 35 and 36 percent of the average width for the right and left banks, respectively. It is about three times the average displacement of ten years. As it is clear from the figure, it happened due to flood, in both coasts, the amount of erosion is more than sedimentation, but in the 30-year period, the left bank was sedimenting, and the right bank was slightly more eroded than sedimentation. In each considered period, the right bank is more eroded. Figures (7) shows a schematic view of these changes.

Table (5) shows the area of eroded and sediment areas of the river bank caused by the flood of March 2019 and during the period from 1985 to 2015. In the flood of 2019, the net rate of changes in the length of the river was about 195 hectares of erosion, of which the share of the right bank is 95 and the left bank is about 100 hectares. While in the long term, the trend of change is the opposite. So that the net rate of changes is due to sedimentation and is equivalent to 43 hectares, of which about 46 hectares of sedimentation occurred on the right bank and 3 hectares of erosion occurred on the left bank (it should be noted that the net rate of the difference between the average erosion rate of the average sedimentation rate was determined.

Table 5

Area of erosion and deposition caused by flood and 30-year period (hectares)
Period from 1985 to 2015	Flood in March 2019	Year
79.77	46.58	Deposition of the right banks
101.31	32.47	Deposition of the left banks
82.93	140.85	Erosion of the right banks
55.41	133	Erosion of the left banks
181.08	79.05	Total deposition
138.34	273.85	Total erosion
− .42.74	194.8	Net rate
3.16	94.27	Right bank net rate
-45.9	100.53	Left bank net rate

The results of area changes caused by floods also indicate that the left bank is more dynamic than the right bank, and its changes are more erosion-type. The left-to-right bank erosion ratio for the flood of 1389 was obtained as 1/06, which, of course, considering the flood debt, this issue is not far from expected, because the erosion is primarily affected by the flow. With a more detailed investigation, it has been determined that the changes in the average width of the river before and after the flood in 1389 have been accompanied by an increase of 32%, on average, compared to the flood of March 1389, it has reached from 35 meters to 52 meters. According to the time interval between the examined images before and after the flood (34 days for the flood of 2019) and the subsidence of the flood hydrograph in this time period, it can be shown that these changes are not after the flow on the flood plains, but in reality. The flood debt has partially caused the erosion of the flood plains and turned it into the main channel of the river. Figures (7) shows a schematic view of the changes in the main channel of the river in a period of the study area for the flood of March 2019. In Figure (7), blue and red colors show the right and left banks of the river before and after the flood, respectively, which in fact, the difference of the main channel in these two states indicates the changes in the morphological parameters of the studied area.

River width changes

Changes in river width are one of the most important and influential parameters in river morphology, which is discussed below. Based on the investigations and changes of the river bank, as mentioned in the previous part, the Bazoft River was divided into four sections. Therefore, width changes are introduced in the mentioned four intervals. It should be mentioned that the width of the river was extracted based on the distance between the left and right borders and its intersection with the cross-section line in each image. In order to compare, the changes in latitude in the 30-year period and long-term and short-term periods were investigated. The long-term periods are 10 years and respectively 1364-74, 1374-84, 1384-94 and the 30-year period is 1364–1394. Also, short-term courses with one-year intervals were determined from 1384-85 to 1394-95. Finally, the changes in latitude before and after the flood of 1389 were investigated and the results were compared with the long-term average of 10 years. Figures (8) and (9) show the changes in the width of the river in the long-term periods of 10 and 30 years, respectively. As it is known, in both time periods considered, the width of the river increased between the first and second periods, and the width of the river decreased in the second and third periods. At the end of the change, the width is almost the same as the previous interval. The average width of the river is 33.8, 44.7, 40.2, and 38.6 meters in the four periods of 1364-94, respectively. The smallest width of the river is at the beginning, which seems reasonable considering the mountainous conditions and the region. Table (6) shows the average width of the river in one-year periods ending in 2015. According to the results of Table (6), it can be concluded that the maximum width is in the second span (47 to 62 km) of Bazoft River and its value is equal to 41.8 meters. Also, the maximum values in the first, third, and fourth intervals are equal to 29.2, 38.4, and 38.3 meters, respectively. The range of changes in the width of the river, which is the distance between the maximum and the minimum, is greater in the fourth interval than in the other three intervals. This span is from 84 km to the end of the river (127 km). Due to the fact that the end of the river eventually becomes the Karon 4 dam reservoir, it can be said that these changes are due to the presence of the Karon 4 dam and its water intake.

Table 6

Annual average in four river sections (meters)
84Km to the end	62 to 84 km	47 to 62 km	First up to 47 km	Year
37.2	38.4	37.7	28.6	2005–2006
38.3	36.2	39.9	28.4	2006–2007
32.5	34	36.3	28.6	2007–2008
31.8	36.1	41.8	29.1	2008–2009
32.2	34.1	35.2	28.4	2009–2010
32.6	34.6	37.4	28.5	2010–2011
31.9	35.8	36.5	28.7	2011–2012
30.5	35	35.3	28	2012–2013
31.4	35.5	38.8	28.1	2013–2014
33.1	35.6	40.9	29	2014–2015
33.4	36.8	40.1	29.2	2005–2006
33.2	35.7	38.1	28.6	Average
38.3	38.4	41.8	29.2	Maximum
7.8	4.3	6.2	1.2	Range

Figure (10) shows the changes in the width of the river before and after the flood of 1389 and the 10-year average of the river. As it is known, the width of the river did not change much during the years 1384-85 to 1394-95 and also before the flood of 1389, and its value did not exceed 40 meters. But after the flood, the width of the river suddenly increased and these changes seem obvious. The maximum increase in width is related to the second span of the river and its value is equal to 70 meters. Therefore, in this period, the most changes in morphological parameters are expected. The minimum width of the river in the first period is an average of 10 years with a value of about 28 meters. This interval before and after the flood also has the minimum width, which is due to the mountainous nature of the initial interval. The remarkable thing about the first span, after the flood, the changes in its width were noticeable and its value increased by 6 meters. The sudden increase in the second period, in addition to the occurrence of floods, can be related to the presence of side branches in the path.

River sinuosity changes

Apart from the changes in the river border and erosion and sedimentation in it, sinuosity is also considered another important parameter in river morphology studies, which describes the dynamic nature of the river system. Sinuosity has no unit and is equal to the ratio of the length of the river to the straight length. What is certain is that sinuosity changes with time and place, therefore, in this research, sinuosity changes were obtained at different times and in four target intervals, the results of which can be seen in Figures (11) and (12). Figures (11) shows the changes in the sinuosity parameter in the 10-year period ending in 2015. As it is clear, in the second and third intervals, the sinuosity value is higher than in the other two intervals. In the first period, the sinuosity has a constant trend, which is due to the conditions of the river in this period and the mountainous nature of the region. Considering that the sinuosity shows the dynamics of the river system, it can be said that the river is more dynamic in the second and third periods. In other words, morphological changes are more in these two periods. In the third to fourth period, the sinuosity values have been decreasing. The effects of dewatering the Karun 4 dam are also evident, especially in the last years in the fourth period.

Figure (12) shows the change of sinuosity in the long-term intervals of 10 and 30 years. According to the figure, in all four investigated periods, sinuosity has increased between the first and second intervals. In the second and third intervals, the sinusoid is almost the same and the slope of the line is constant. At the open end, in each time period, the slope of the line has a downward trend and the value of sinuosity has decreased. In the 10-year periods, except for the period from 1365 to 1375, when the sinuosity was almost constant, in other periods compared to the 30-year period, the slope of the inter-increasing line is higher, in other words, in the long-term perspectives of 30 years, changes in sinuosity Ratio. It is less than 10 years. The maximum value of sinuosity is in the second and third periods of the river and the time periods 1385 to 1395 and 1375 to 1385 and its value is equal to 1.30.

Next, the changes of sinuosity before and after the flood of 1389 were investigated and the results were compared with the values of the 10-year period from 1385 to 1395. As shown in Figure (13), the sinuosity values before and after the flood were similar and the slope of the line did not change much in each interval. In other words, the flood has no effect on the sinuosity parameter of the river. Also, in the case of the 10-year period from 1385 to 1395 until the beginning of the fourth interval, the changes were similar to before, but in the fourth interval until the beginning of the reservoir of Karun 4 dam, the sinuosity value decreased more steeply, which could be the reason for the water intake of Karun 4 dam

Based on the findings of this research, it can be said that by using the analysis of temporal and spatial sequential satellite images, it is possible to analyze the morphological changes of rivers in different stages and events with appropriate accuracy. As a case study of the application of this method, the morphological changes of the Bazoft River from the tributaries of the Karun Bazoft basin located in Chaharmahal and Bakhtiari province, which due to its mountainous nature and the occurrence of large floods, have a large sediment load into the dam reservoir. Caron Chahar is transferred, and it was investigated. The results showed that the average displacement of the main channel of the river due to erosion in a ten-year period for both banks is about 14% of the width of the river, and the investigation of some floods showed that these values are up to 47 and 50% according to the flood damage. The width of the river reaches for the left and right banks. The evaluation of the net rate of changes in the area of deposition-deposition and erosion zones along the river showed that this rate is about 194 hectares of erosion in relation to the intended flood. Therefore, by extracting this information from the analysis of satellite images, it is possible to provide management solutions for rivers and water structures built with acceptable accuracy. This technique is also effective for analyzing the stability and stability of hydraulic and geometric characteristics of sections. As an example, this research showed that the width of the Bazoft River was decreasing from the beginning to the end of the period. This is despite the fact that after the flood, the river has increased in width. Based on the average width of the river before the flood (about 35.8 meters), the displacement ratio of the river bank, which led to the erosion of the river bank, is 35 and 36% of the average width for the right and left banks, respectively, which are three times the average displacement It is ten years old. The results showed that the value of sinuosity is higher in the two middle intervals. In the first period, the changes in sinuosity are constant, which is due to the mountainous nature of the region. In the last section of the river, the sinuosity has decreased compared to the previous section. In general, this research shows that by using the analysis of satellite images, it is possible to study the trend of morphological changes in rivers and evaluate the number of changes in the width and shorelines of rivers before any construction operations such as building a dam or bridge and take them into account in the design considerations. According to the results of this research, it can be stated that the morphological changes of the Bazoft River are insignificant in terms of quantity compared to the big rivers of the world; However, due to the mountainous nature of this river and the location of the Karun 4 Dam in its downstream, as well as taking into account the fact that large floods and subsequent sediment loads are high in mountainous rivers, morphological changes can affect the performance and provide management solutions. Karun Dam 4 is effective.

Automatic Water Extraction Index - Unshaded Areas	AWEI_{no shadow}
Automatic water indicator - shaded areas	AWEI _shadow
Advanced water index	EWI
The name of the Landsat satellite sensor	ETM⁺
The series of Indian satellites	IRS
Modified normal water index	MNDWI
The name of the Landsat satellite sensor	MSS
Normal water difference index	NDWI
The name of the Landsat satellite sensor	OLI
System performance characteristic	ROC
The name of the Landsat satellite sensor	TM
Water index	WI₂₀₁₅

Data Availability Statement

All the data, including the experimental measurements, the data used for formulating empirical relations, and the code processing the data that support the findings of this study, are available from the corresponding author upon reasonable request.

Author’s Contributions

Arash Koohizadeh Dehkordi, Rouhallah Fatahi Nafchi, Hossein Samadi-Boroujeni, Milad Khastar Boroujeni and Kaveh Ostad‑Ali‑Askari designed the study, collected data, wrote the manuscript and revised it

Funding

Funding information is not applicable. No funding was received. No grants were received.

Competing Interests

There is no competing of interest.

Consent to Participate

All authors designed the study, wrote the manuscript and revised it.

Conflict of Interest Statement

There is no conflict of interest.

Ethical Approval

The present Study and ethical aspect was approved by Water Engineering Department, College of Agriculture, Shahrekord University, Shahrekord, Postal Code: 8818634141, Iran.

Acknowledgment

Not applicable.

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Investigating the Effect of Flood Flows on Morphological Changes Using a Series of Satellite Images: Rapid Changes in Morphology of Bazoft River

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Abstract

Figures

Introduction

Materials and methods

Study area

Investigation of river flow changes

Extraction of the river border

Results and Discussions

Validation

Displacement of the border

Area changes

Effect of floods on morphological parameters

River width changes

River sinuosity changes

Conclusions

List of symptoms

Declarations

References

Additional Declarations

Supplementary Files

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