In this study, the factors affecting the formation of channel patterns and dynamics in the Givi-chay River during the period 2019–2000 were analysed. To evaluate the river strength, flaw stress and its effects on channel morphology, Landsat 7 and 8 images, topographic maps, geology, and hydrological and field data were used. According to the results of the calculation of hydrological indicators, in terms of 15, the index, a significant difference is seen among upstream and downstream stations. Therefore, it can be found that the presence of the Givi Dam has created a good platform for intensifying the hydrological and morphological changes of the river plan. The particular strength of the river in all parts of the fourth interval and the ninth, 12th, eighth (second interval) levels causes the erosion threshold to soar. The highest amount of shear stress was observed in the second interval at 12, 13, and 9, respectively. Generally, the changes of the Givi River Plan include expansion of existing meanders, displacement of paths, increase of curvature and formation of small meanders and formation of channel pattern and dynamics, affected by discharge provision, sediment discharge due to dam construction, lithological resistance of the riverbed and human interference.

  • Factors affecting the formation of channel patterns were analysed.

  • Givi Dam has created a good platform for intensifying hydrological changes.

  • Highest amount of shear stress was observed in the second interval at 12, 13, and 9, respectively.

  • Givi-chay River Plan includes expansion of existing meanders.

  • Formation of channel pattern and dynamics, affected by discharge provision, sediment discharge due to dam construction.

NDWI

Normalized Difference Water Index

MNDWI

Modified Normalized Difference Water Index

AWEI

Automated Water Extraction Index

WRI

Water Ratio Index

Q5

Equal to the amount of flow that is equal to or greater than the mentioned amount in 5% of the days of the flow year

Q10

Equal to the amount of flow that is equal to or greater than the mentioned amount in 10% of the days of the flow year

Q15

Equal to the amount of flow that is equal to or greater than the mentioned amount in 15% of the days of the flow year

Q25

Equivalent to a flow rate which is a flow that is equal to or greater than 25% of the flow's annual volume

Q35

Equal to the flow rate, which is equal to or greater than the mentioned amount in 35% of the days of the flow year

Q45

Equal to the flow rate, which is equal to or greater than the mentioned amount in 45% of the days of the flow year

Q50

Equal to the flow rate, which is equal to or greater than the mentioned amount in 50% of the flow year

Q55

Equal to the flow rate, which is equal to or greater than the mentioned amount in 55% of the days of the flow year

Q65

Equal to the rate, which is equal to or greater than 65% of the flow year

Q75

Equivalent to a flow rate which is a flow that is equal to or greater than that in 75% of the flow year

Q85

Equivalent to a flow rate which is a flow that is equal to or greater than 85% of the flow's annual volume

Q90

Equal to the rate of flow which is equal to or greater than 90% of the flow year

Q95

Equivalent to a flow rate which is a flow that is equal to or greater than 95% of the flow's annual volume.

River and river processes are considered as the most significant geomorphic systems which are active on the earth's surface (Bag et al. 2019). Over time, many changes in the morphology and dynamics of a river system can occur (Kondolf & Piégay 2003). Metamorphosis of rivers can be gradual and continuous in the long-term approach, or it can be periodic and sudden if considered under certain circumstances in the short-run (Remondo et al. 2005; Garde 2006). The effects of river adjustment caused by natural factors require a much longer time-span to reveal. However, there are the few exceptions that natural factors such as river floods, landslides, or earthquakes can induce channel adjustments in a very short time (Chaiwongsaen et al. 2019). In contrast, human activities can have a significant and rapid impact on natural processes and trends, resulting in a compressed timescale for river adjustments (Rinaldi & Simon 1998). Since these disturbances cause substantial changes to flow and sediment structures, at present few rivers are in a natural or semi-natural condition (Surian & Rinaldi 2003). Consequently, the flow structure of many rivers has been dramatically altered from their natural flow structure (Nanson & Hickin 1986; Oorschot et al. 2018).

Therefore, it can be said that several factors are involved in river morphology and researchers have pointed to them in various studies. These factors include the following: lithology of wall and bed materials (Schumm 1985; Jain & Sinha 2005; VanLaningham et al. 2006; Petrovszki & Timár 2010; Pike et al. 2010; Ziyad 2014; Falkowski et al. 2017; Batalla et al. 2018), urbanization and sand harvesting (Gregory 2006; Surian et al. 2011; Mandal et al. 2016), anthropogenic effects such as flood deflection, waste dumping, residential construction, docks and bridges (Debnath et al. 2015; Bandyopadhyay & Kumar De 2018), dam construction (Brandt 2000; Snoussi et al. 2002; Grant et al. 2003; Richard et al. 2005; Gordon & Meentemeyer 2006; Graf 2006; Bisantino et al. 2010; Ollero 2010; Shin & Julien 2011; Ashouri et al. 2014; Casado et al. 2016; Yang et al. 2018; Chen et al. 2019; Hammerling et al. 2019), and climate change (Zhou et al. 2012; Zhang et al. 2017). 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 (Slater et al. 2019). The changes in river morphology may cause many problems, such as changing the river course, flooding of nearby areas, and damage to hydraulic structures, as well as having some environmental impact (Chinnarasri et al. 2008). 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 et al. 2019).

Givi-chay River is one of the permanent rivers of Ardabil, in the northwest of Iran. The main issues related to the Givi-chay River are bed changes over time, river instability, river departure and erosion along the river, and the existence of different river patterns in different parts of it has led to different processes in different parts of the river. In addition, the Givi Reservoir Dam has been constructed on the Givi-chay River to regulate river water to control floods and also to supply drinking water, industry, and land improvement in the region. The construction of the dam and its related consequences can provide a very good basis for intensifying the hydrological and morphological changes of the river. Researchers have not yet done a comprehensive study on this river. This study attempts to investigate the changes of geomorphological indices of the Givi-chay River over the period of time 2000–2019, and considering that dams affect the flow structure and sediment load (Nelson et al. 2013; Overeem et al. 2013), one of the factors that can strongly disrupt the stability of rivers is the construction of dams (Liaghat et al. 2017). Evaluation of hydrological conditions, especially regarding the construction of Givi Dam and its effects on conduit morphology, is also discussed. As stream power can be an extremely useful index of fluvial sediment transport, channel pattern, river channel erosion, and coastal habitat development (Barker et al. 2009), changing river power causes changes in sediment transport balance and sediment load rate, which causes morphological forms that are found in the riverbed; specific power and total power have been estimated for different return periods. In order to determine whether the increase in river specific power will have the same effect in different regions or whether the parameters of each section are the most important factor in determining the type of cross-section and the number of cross-section changes, a calculation of the shear stress was performed. Determining and identifying morphological parameters, hydrological indicators, power status, and shear stress and studying the geological conditions and land use status along the Givi-chay River route, while being aware of the river behavior, can be used to deal with the river and management, and the implementation of the reorganization plans in them was quite conscious and based on the rules governing the river.

Study area

Givi-chay River, of almost 54 km, is located in Ardabil province, in the northwest of Iran. The two rivers of Hiro (which emanates from Khalkhal altitudes) and Arpachay (which emanates is from north to south) are linked to each other in the downstream and the stream around Inalava village departs westward and between the altitudes of Khalkhal and Givi reaches to Givi city with 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 (Figure 1). Givi Reservoir Dam is generated between 37° 25′ to 37° 55′ north latitude and 48° 45′ east longitude to regulate river water for flood control and also to provide drinking water, industry and land improvement. The total volume of the Givi Dam reservoir is 57 million m³ and its regulatory volume is 76 million m³. The study area consists mainly of Tertiary volcanic and pyroclastic formations, especially Eocene, Oligocene, and Miocene, which have been associated with the sedimentation of rocks such as conglomerate, sandstone, marl, gypsum and lime layers. In addition, the Quaternary sediments of the range consist of coarse-grained alluvial deposits, debris and domain sediments, and river deposits (Figure 2).
Figure 1

Location map of the area under study.

Figure 1

Location map of the area under study.

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Figure 2

Geological map of the area under study.

Figure 2

Geological map of the area under study.

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Materials

In this research, a topography map with a scale of 1: 50,000, geology map with a scale of 1:100,000, and Google Earth and Landsat 8 images, including OLI sensor (2019), Landsat 7 including ETM+sensor (2000), bedrock maps and the Givi-chay River at a scale of 1:2,000, hydrological data from the two stations of Abegharm (upstream of the dam) and Firoozabad (downstream of the dam) and field data are used. The maps for determining the limits of the Givi-chay River bed and boundaries with a scale of 1:2000 were prepared by the regional water organization of Ardabil province, including physiographic information (measurement curves), the distribution of urban and rural points in the bed, and the river boundary is the location of existing constructions on the river bed and boundary (bridges, diversion dam). Also, to control the results obtained by quantitative methods it is used from field studies for confirmation and verification. ENVI 5.3, ArcGIS 10.5, HEC RAS, Smada, Excel and SPSS software were also used for image processing and data analysis.

Water indices and river extraction

Atmospheric correction was performed by FLAASH on satellite images first, and then using water indices, including NDWI (Green−NIR)/(Green+NIR), MNDWI (Green−MIR)/(Green+MIR), AWEI_ no shadow (4×(Green−SWIR1) −(0.25×NIR+2.75×SWIR2)), AWEI_shadow (Blue+2.5×Green−1.5×(NIR+SWIR1)−0.25×SWIR2)) and WRI (Green+Red)/(NIR+SWIR1), respectively, by McFeeters (1996), Xu (2006), and Feyisa et al. (2014); the river route was extracted from the images. According to the kappa coefficient (0.98 for 2000 and 2019) and overall accuracy (99.05% for 2000 and 99.42% for 2019), the river path extracted by the AWEI_sh index for both periods of 2000 and 2019 was confirmed and used. After river extraction according to water spectral indices, in the next step, the Givi-chay River route was initially divided into two upstream and downstream sections of the dam. Then, based on various variables such as geological and topographic control, flood plain width, and anthropogenic effects, according to field observation and use of Google Earth images and Landsat satellite, it was divided into four intervals for the more accurate and scientific study of the river: interval 1 (upstream dam interval, from the junction of the Hirochay and Arpachay to the dam), and the downstream dam intervals of interval 2 (lowland), 3 (mountainous) and 4 (sub-mountainous).

Hydrological conditions

The morphological parameters of the river are influenced by several factors and the hydrological parameters are the driving force for performing and causing morphological changes. In this regard, methods based on hydrological indicators are the simplest and most widely used methods of assessing the hydrological regime and estimating the flow worldwide. In the present study, to investigate the hydrological changes, the data between the two stations of Abegharm and Firoozabad were examined using 27 hydrological indicators. The first groups of indicators used are discharge values with different probability percentages (Q5, Q10, Q15, Q25, Q35, Q45, Q50, Q55, Q65, Q75, Q85, Q90, and Q95). Another group of indicators that were examined in the present study are as follows: normal flow in high water condition (the amount of current that is equal to or higher than 1.4 days of the year in 91 days of the year flow), normal discharge in dehydration mode (normal discharge in the state of water shortage is the amount of flow that is equal to or higher than it in 3/4 of the days of the year (274 days). To calculate the mentioned index, the flow data related to the hydrometric stations in the study area, which are daily, should be arranged and sorted for each year (from the highest to the lowest). In the next step, using the Vibol formula, the probability of occurrences is determined, and then the values available on the 274th day of the year are considered as the normal flow in the state of water shortage), normal flow (the amount of current that is equal to or higher than it in half of the days of the year, i.e. 182 = 365*2. The hydrometers available in the study area, which are daily, should be arranged and sorted for each year (from the most to the least). In the next step, using the Vibol formula, the probability of occurrences is determined, and then the values available on the 182nd day of the year are considered a normal discharge) average flow (Q=∑v/t; where Q: average flow, v: total water volume, t: time), mode flow (the amount of flow or range of flow that has the highest frequency of occurrence during the year), mean flow (if we lower the flow every year, flow will be in the middle of 182 and 183 flow), minimum flow (the lowest flow during the year is obtained by arranging the flow for each year), maximum flow (the most flow located during the year, which is achieved by arranging the flow for each year), annual flow (the total flow over a year), days with zero flow (the number of days of data that flow is zero), zero flow % (by taking the percentage of data from flow zero, from the ratio of the percentage of flow zero=flow zero/366×100, it is obtained), standard deviation of current flows from Equation (1):
formula
(1)
where Xi: daily flow values, X: average flow values and n: the number of data in the statistical period (Curtis & Whitney 2003; Dadaser-Celik & Stefan 2009; Wu et al. 2012; Berhanu et al. 2015; Uday Kumar & Jayakumar 2018; Owolabi et al. 2020). It should be said that first the daily data of the two upstream and downstream stations were arranged yearly (from the beginning of the water year to the end of it). Then the probability of occurrence was determined in descending order (from maximum current to minimum current) using Equation (2):
formula
(2)
where M is the sorted columns, and N is the number of days in the year, i.e. 365. Then, a paired t-test was used for statistical analysis of indices in order to study the significance of indices changes between the upstream and downstream dam and consequently study the effect of dam construction.

Geomorphological parameters

Then the geomorphological parameters of the river and their variations including the bending coefficient and central angle were measured (Mohammadi et al. 2008; Magshoudi et al. 2017; Esfandiary & Rahimi 2019). The curvature coefficient is one of the few criteria used in river shape segmentation and was calculated using Equation (3) and by dividing the valley length by wavelength for each arc:
formula
(3)
where S is the curvature coefficient, L is the arc length and λ/2 is half the wavelength (Pitt's coefficient). The central angle of the arcs on each of the intervals was calculated using Equation (4):
formula
(4)
where A is the central angle and R is the fitted circle radius (Kornis coefficient). The direction of the river and the circles fitted to the rivulets in the two periods studied are shown in Figure 3.
Figure 3

(a)–(d): The river path and the circles fitted to the rivulets in the first, second, third, and fourth intervals, respectively. Boxes 1–6 show more clearly the portions of the river changes. Red is used for the river in 2000 and green for the river in 2019.

Figure 3

(a)–(d): The river path and the circles fitted to the rivulets in the first, second, third, and fourth intervals, respectively. Boxes 1–6 show more clearly the portions of the river changes. Red is used for the river in 2000 and green for the river in 2019.

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Flow power

Flow power is one of the important river parameters that can be used in morphological analysis and is one of the important theoretical discussions in sediment transport studies (Ferguson 2005; Parker et al. 2011; Lecce 2013; Phillips & Desloges 2014; Bizzi & Lerner 2015; Sholtes et al. 2018). Next, total river power was calculated using Equation (5):
formula
(5)
where Ω: total river power (in watts per metre), γ: specific gravity of water (9,810 N/m2), Q: discharge (m3/s based on data from Abgarm and Firoozabad hydrometric stations), and S: slope of the bed (using longitudinal mapping of the studied intervals and then calculated by dividing the difference in height of the upstream and downstream of the intervals along its length). The river power can also be expressed per unit area per square metre in the riverbed unit (Equation (6)):
formula
(6)
where ω is the river specific power per unit area per square metre, which is the average. The transverse section of the river's power is expressed per unit of river width (or river power per unit of bed area, square metres). The annual mean flow was used to determine the river specific power under normal flow conditions and monthly peak discharge and peak instantaneous discharge data were used to determine the maximum river power at a given point in time. It should be noted that different return periods were obtained using Smada software and Gamble distribution (Table 1). Finally, given that boundary shear stress indicates the initiation of deposition of sediment particles by the flow of water in the riverbed, the shear stress (boundary) was obtained using Equation (7):
formula
(7)
where τ: boundary shear stress in newtons/m2, ρw: specific gravity in kg/m3, g: gravity acceleration (equal to 9.81 metres per square second), R: hydraulic radius or water depth in metres (in the present study, water depth was considered, which was also taken when water was collected from laboratory samples), and S: the bed slope.
Table 1

Average annual discharge and return period of monthly peak and maximum discharge, by Gamble distribution method

DischargeReturn periodQ2.3325102550100200500
Monthly peak discharge Abegharm Station 18.38 14.88 33.63 46.04 61.73 73.37 84.92 96.43 111.62 
Firoozabad Station 23.04 19.86 36.88 48.16 62.40 72.97 83.46 93.91 107.70 
Maximum discharge Abegharm Station 51 46 80 104 136 161 187 214 251 
Firoozabad Station 82 69 117 148 189 219 250 281 323 
DischargeReturn periodQ2.3325102550100200500
Monthly peak discharge Abegharm Station 18.38 14.88 33.63 46.04 61.73 73.37 84.92 96.43 111.62 
Firoozabad Station 23.04 19.86 36.88 48.16 62.40 72.97 83.46 93.91 107.70 
Maximum discharge Abegharm Station 51 46 80 104 136 161 187 214 251 
Firoozabad Station 82 69 117 148 189 219 250 281 323 

Average annual discharge of Abegharm Station: 2.07. Average annual discharge of Firoozabad Station: 3.26.

Investigation of hydrological indicators of Givi-chay River in 2000–2019 and analysis of Dam impact

According to the results of calculation of hydrological indices and analysis of the statistical t-test (Table 2), between the two stations of Abegharm (upstream) and Firoozabad (downstream), it can be said in terms of indices that there is a significant difference between the two stations, Q5, Q10 and Q15, and changes in flows (Q5, Q10, Q15) can affect the frequency of sedimentary regime changes and changes in moisture content. Also, in the indicators, Q35, Q45, Q50, Q65, and Q90, there is a significant difference between the two stations. It is also worth mentioning that for these indices from a geomorphological point of view, minimal discharge can affect the abundance of sediment regimes in the river, storage and sediment transport, and the time required for canal stability along the river (Curtis & Whitney 2003; Uday Kumar & Jayakumar 2018; Owolabi et al. 2020) (Figure 4(a) and 4(b)). Also, at times of low flow, shear stress is weak in the pools allowing transitory accumulation of fine deposits and pebbles (Petit 1987). But with respect to the Q25 and Q55, Q85, and Q95 indices, there was no significant difference between the two stations over the 19-year period. There was a significant difference between normal discharge indices of stations. Therefore, it can be concluded that the amount of flood flow during the statistical period downstream of the dam was more than upstream, indicating the regulatory effects of water, and this factor contributes to the possibility of river erosion (Figure 4(c)–4(e)) and the formation of longitudinal barriers and sedimentary islets is enhanced by sediment deposition in the river (Figure 4(g) and 4(h)) and it can be said that the overall canal morphology and flood changes downstream of the dam will be affected by the dam construction (Uday Kumar & Jayakumar 2018). The maximum discharge was also increased at the downstream station and there was a significant difference between the two stations. According to the theory of Graf (2006) flow maximizes the frequency of canal bed mobility and inbound load, river erosion, and overall canal morphology and changes the number and size of functional surfaces (Graf 2006) (Figure 4(f)). There is also a significant difference between the two stations with respect to the mean discharge index, and according to the study of Graf (2006), it can be said that the average or average flow, the volume of sediment accumulation processes, low flow canal size (usually active), and canal pattern affect the geomorphic complexity (Graf 2006).
Table 2

Hydrological indices at the two stations of Abegharm (upstream) and Firoozabad (downstream)

IndicesStationMeanMean differenceMaxMinStd deviationStd error meantdfsig
Q5 Abegharm 7.475 −5.764 19.6 2.4 4.928 1.195 −2.314 24.786 0.031 
 Firoozabad 13.239  34.4 2.14 9.011 2.185    
Q10 Abegharm 5.456 −4.245 14.1 2.14 3.341 0.81 −2.385 23.828 0.043 
 Firoozabad 9.701  27.7 1.92 6.535 1.585    
Q15 Abegharm 4.248 −3.975 11.5 1.32 2.666 0.646 −2.716 23.33 0.027 
 Firoozabad 8.224  22 1.5 5.414 1.313    
Q25 Abegharm 2.617 −0.768 5.64 0.96 1.403 0.34 −1.432 30.82 0.27 
 Firoozabad 3.386  7.27 1.33 1.711 0.415    
Q35 Abegharm 1.58 −0.67 2.8 0.8 0.571 0.138 −2.494 26.246 0.048 
 Firoozabad 2.25  4.35 0.7 0.949 0.23    
Q45 Abegharm 1.279 −0.502 2.35 0.66 0.449 0.109 −2.296 25.534 0.041 
 Firoozabad 1.782  3.62 0.66 0.782 0.189    
Q50 Abegharm 1.169 −0.432 1.83 0.66 0.373 0.09 −2.141 23.562 0.024 
 Firoozabad 1.602  3.45 0.65 0.745 0.18    
Q55 Abegharm 1.056 −0.322 1.63 0.6 0.339 0.082 −1.604 22.219 0.009 
 Firoozabad 1.378  3.28 0.57 0.755 0.183    
Q65 Abegharm 0.847 −0.063 1.4 0.22 0.342 0.083 −0.365 24.603 0.009 
 Firoozabad 0.91  1.96 0.04 0.633 0.153    
Q75 Abegharm 0.493 −0.108 1.12 0.08 0.327 0.079 −0.709 26.329 0.027 
 Firoozabad 0.601  1.65 0.01 0.541 0.131    
Q85 Abegharm 0.244 −0.021 0.76 0.01 0.247 0.06 −0.236 31.716 0.584 
 Firoozabad 0.265  0.84 0.272 0.066    
Q90 Abegharm 0.155 −0.031 0.43 0.133 0.032 −0.494 26.132 0.044 
 Firoozabad 0.186  0.76 0.223 0.054    
Q95 Abegharm 0.083 0.002 0.38 0.111 0.027 0.066 31.242 0.997 
 Firoozabad 0.08  0.34 0.095 0.023    
Normal high water discharge Abegharm 2.349 −1.1 3.88 0.96 1.001 0.242 2.241 25.371 0.007 
 Firoozabad 3.45  7.27 1.33 1.76 0.426    
Normal dehydration discharge Abegharm 0.5 −0.011 1.15 0.08 0.333 0.08 −0.078 28.487 0.071 
 Firoozabad 0.511  1.62 0.01 0.481 0.116    
Normal discharge Abegharm 1.169 −0.432 1.83 0.66 0.373 0.09 −2.141 23.562 0.024 
 Firoozabad 1.602  3.45 0.65 0.745 0.18    
Average discharge Abegharm 2.073 −1.191 4.69 0.81 1.059 0.256 −2.034 23.208 0.008 
 Firoozabad 3.265  7.31 0.89 2.171 0.526    
Mean discharge Abegharm 1.168 −0.427 1.83 0.66 0.374 0.09 −2.108 23.539 0.023 
 Firoozabad 1.595  3.45 0.65 0.747 0.181    
Mode discharge Abegharm 0.59 −0.601 1.47 0.52 0.126 −1.968 22.338 0.005 
 Firoozabad 1.191  3.82 1.146 0.278    
Minimum discharge Abegharm 0.043 0.01 0.31 0.076 0.018 0.461 29.276 0.446 
 Firoozabad 0.033  0.2 0.055 0.013    
Maximum discharge Abegharm 13.84 −8.92 37.4 4.84 9.681 2.348 −1.997 26.666 0.046 
 Firoozabad 22.76  60.07 8.8 15.665 3.799    
Annual discharge Abegharm 727.38 −377.384 1,712.72 295.12 356.55 86.476 −2.137 25.181 0.05 
 Firoozabad 1,104.7  2,669.94 323.86 634.83 153.97    
Zero to percent discharge Abegharm 2.86 1.719 13.66 4.996 1.211 1.084 31.134 0.067 
 Firoozabad 1.141  17.49 4.221 1.023    
Days with zero discharge Abegharm 10.47 6.294 50 18.286 4.435 1.084 31.134 0.067 
 Firoozabad 4.176  64 15.452 3.747    
Standard deviation Abegharm 2.891 −1.123 7.9 0.85 2.146 0.52 −1.255 28.972 0.386 
 Firoozabad 4.014  11.9 0.88 3.002 0.728    
Q90/Q50 index Abegharm 0.093 0.008 0.31 0.09 0.022 0.267 31.428 0.908 
 Firoozabad 0.084  0.42 0.104 0.025    
Lin index Abegharm −0.621 0.135 −0.384 −0.776 0.118 0.032 2.562 22.825 0.383 
 Firoozabad −0.756  −0.417 −1.074 0.149 0.041    
IndicesStationMeanMean differenceMaxMinStd deviationStd error meantdfsig
Q5 Abegharm 7.475 −5.764 19.6 2.4 4.928 1.195 −2.314 24.786 0.031 
 Firoozabad 13.239  34.4 2.14 9.011 2.185    
Q10 Abegharm 5.456 −4.245 14.1 2.14 3.341 0.81 −2.385 23.828 0.043 
 Firoozabad 9.701  27.7 1.92 6.535 1.585    
Q15 Abegharm 4.248 −3.975 11.5 1.32 2.666 0.646 −2.716 23.33 0.027 
 Firoozabad 8.224  22 1.5 5.414 1.313    
Q25 Abegharm 2.617 −0.768 5.64 0.96 1.403 0.34 −1.432 30.82 0.27 
 Firoozabad 3.386  7.27 1.33 1.711 0.415    
Q35 Abegharm 1.58 −0.67 2.8 0.8 0.571 0.138 −2.494 26.246 0.048 
 Firoozabad 2.25  4.35 0.7 0.949 0.23    
Q45 Abegharm 1.279 −0.502 2.35 0.66 0.449 0.109 −2.296 25.534 0.041 
 Firoozabad 1.782  3.62 0.66 0.782 0.189    
Q50 Abegharm 1.169 −0.432 1.83 0.66 0.373 0.09 −2.141 23.562 0.024 
 Firoozabad 1.602  3.45 0.65 0.745 0.18    
Q55 Abegharm 1.056 −0.322 1.63 0.6 0.339 0.082 −1.604 22.219 0.009 
 Firoozabad 1.378  3.28 0.57 0.755 0.183    
Q65 Abegharm 0.847 −0.063 1.4 0.22 0.342 0.083 −0.365 24.603 0.009 
 Firoozabad 0.91  1.96 0.04 0.633 0.153    
Q75 Abegharm 0.493 −0.108 1.12 0.08 0.327 0.079 −0.709 26.329 0.027 
 Firoozabad 0.601  1.65 0.01 0.541 0.131    
Q85 Abegharm 0.244 −0.021 0.76 0.01 0.247 0.06 −0.236 31.716 0.584 
 Firoozabad 0.265  0.84 0.272 0.066    
Q90 Abegharm 0.155 −0.031 0.43 0.133 0.032 −0.494 26.132 0.044 
 Firoozabad 0.186  0.76 0.223 0.054    
Q95 Abegharm 0.083 0.002 0.38 0.111 0.027 0.066 31.242 0.997 
 Firoozabad 0.08  0.34 0.095 0.023    
Normal high water discharge Abegharm 2.349 −1.1 3.88 0.96 1.001 0.242 2.241 25.371 0.007 
 Firoozabad 3.45  7.27 1.33 1.76 0.426    
Normal dehydration discharge Abegharm 0.5 −0.011 1.15 0.08 0.333 0.08 −0.078 28.487 0.071 
 Firoozabad 0.511  1.62 0.01 0.481 0.116    
Normal discharge Abegharm 1.169 −0.432 1.83 0.66 0.373 0.09 −2.141 23.562 0.024 
 Firoozabad 1.602  3.45 0.65 0.745 0.18    
Average discharge Abegharm 2.073 −1.191 4.69 0.81 1.059 0.256 −2.034 23.208 0.008 
 Firoozabad 3.265  7.31 0.89 2.171 0.526    
Mean discharge Abegharm 1.168 −0.427 1.83 0.66 0.374 0.09 −2.108 23.539 0.023 
 Firoozabad 1.595  3.45 0.65 0.747 0.181    
Mode discharge Abegharm 0.59 −0.601 1.47 0.52 0.126 −1.968 22.338 0.005 
 Firoozabad 1.191  3.82 1.146 0.278    
Minimum discharge Abegharm 0.043 0.01 0.31 0.076 0.018 0.461 29.276 0.446 
 Firoozabad 0.033  0.2 0.055 0.013    
Maximum discharge Abegharm 13.84 −8.92 37.4 4.84 9.681 2.348 −1.997 26.666 0.046 
 Firoozabad 22.76  60.07 8.8 15.665 3.799    
Annual discharge Abegharm 727.38 −377.384 1,712.72 295.12 356.55 86.476 −2.137 25.181 0.05 
 Firoozabad 1,104.7  2,669.94 323.86 634.83 153.97    
Zero to percent discharge Abegharm 2.86 1.719 13.66 4.996 1.211 1.084 31.134 0.067 
 Firoozabad 1.141  17.49 4.221 1.023    
Days with zero discharge Abegharm 10.47 6.294 50 18.286 4.435 1.084 31.134 0.067 
 Firoozabad 4.176  64 15.452 3.747    
Standard deviation Abegharm 2.891 −1.123 7.9 0.85 2.146 0.52 −1.255 28.972 0.386 
 Firoozabad 4.014  11.9 0.88 3.002 0.728    
Q90/Q50 index Abegharm 0.093 0.008 0.31 0.09 0.022 0.267 31.428 0.908 
 Firoozabad 0.084  0.42 0.104 0.025    
Lin index Abegharm −0.621 0.135 −0.384 −0.776 0.118 0.032 2.562 22.825 0.383 
 Firoozabad −0.756  −0.417 −1.074 0.149 0.041    
Figure 4

(a) Low flow and poor shear stress caused vegetation to expand as perennial shrubs along the river, (b) bed widening and reduced river discharge caused vegetation growth in the riverbed, resulting in low flow power and poor shear stress, (c)–(e) subduction and erosion along the river, (f) channel bed mobility and change in functional levels, (g) and (h) deposition of sediments and formation of longitudinal barriers.

Figure 4

(a) Low flow and poor shear stress caused vegetation to expand as perennial shrubs along the river, (b) bed widening and reduced river discharge caused vegetation growth in the riverbed, resulting in low flow power and poor shear stress, (c)–(e) subduction and erosion along the river, (f) channel bed mobility and change in functional levels, (g) and (h) deposition of sediments and formation of longitudinal barriers.

Close modal

There is also a significant difference between the two stations in terms of normal discharge, moderate discharge, and annual discharge, which can lead to the frequency of sediment regimes in the canal and canal bed loading and erosion (Figure 4(c)–4(e)) and (Figure 4(g) and 4(h)).

According to the results of the study, there is a significant difference between a number of indicators between the upstream and downstream stations and it can be stated that the construction of Givi Dam in 2013 and the changes in the flow by the dam can affect the amount and timing, and it affects the duration of upstream and downstream currents and can provide suitable bedding for intensifying hydrological changes and, subsequently, river morphological changes (Liaghat et al. 2017; Oorschot et al. 2018). Behind the dam, sedimentation activity is dominant due to dewatering, volume, and high-water content, and downstream of the dam, all inbound and all or part of the suspended load in the reservoir is deposited (Nelson et al. 2013; Overeem et al. 2013). Downstream changes include sedimentation and erosion in parts of the river, displacement of meanders, flooring, and wall demolition. To investigate the impact of dam construction, a flow duration curve at the downstream dam (Firoozabad) station was prepared separately for two periods before and after dam construction (Figure 5). By examining the flow duration curve, we can see that before the construction of the dam, high slope discharge (33% probability) is 2.42, moderate slope discharge (66% probability) is 0.947 and low slope discharge (probability of occurrence 100%) is 0.038, and after construction of the dam, flow or high slope discharge (33% probability) equals 2.09, moderate slope discharge (66% probability) is 0.657 and low slope discharge (100% probability) is 0.020. Therefore, the greatest impact of dam construction on maximum flow changes was that it reduced the peak discharge after dewatering. Therefore, decreasing the peak discharge will change morphological indices such as transverse and longitudinal profile and hydraulic indices such as water depth and flow rate (Brandt 2000; Snoussi et al. 2002; Grant et al. 2003; Richard et al. 2005; Gordon & Meentemeyer 2006; Graf 2006; Bisantino et al. 2010; Ollero 2010; Shin & Julien 2011; Ashouri et al. 2014; Casado et al. 2016; Yang et al. 2018; Chen et al. 2019; Hammerling et al. 2019).
Figure 5

Flow duration curve (FDC) before and after dam construction.

Figure 5

Flow duration curve (FDC) before and after dam construction.

Close modal

Investigation of morphological indices of Givi-chay River in 2000–2019

The results show that the bights increased from 75 to 100 during this time, indicating morphological and instability changes in the river (Mohammadi et al. 2008; Esfandiary & Rahimi 2019). According to Table 3, the mean curvature coefficient for the first period in 2000 was 1.48 and decreased to 1.40 in 2019. But in other periods in 2019, the bending coefficient increased compared with 2000, with the bending coefficient from 1.23 to 1.25 in the second period and from 1.85 to 1.86 in the third period, it increased from 1/15 to 1/18 in the fourth quarter. 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 1.5–1.05 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 it is 0.19 in 2000 and 0.18 in 2019, and in the fourth interval it 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 (Mohammadi et al. 2008). In the first and third intervals, a severe meander pattern is also seen in the intervals (Table 3).

Table 3

Curve coefficient and central angle river characteristics of Givi-chay River

Curve coefficient characteristics
IntervalYearRiver segmentation by curve coefficient
MinMaxMeanMean differenceStd deviation
1–1.051.05–1.51.5–2>2Interval pattern
2000 – 66.67 20 13.33 1.06 2.35 1.48 0.08 0.39 sinusoidal  
 2019 6.25 68.75 6.25 17.75 1.01 2.29 1.4  0.43 sinusoidal  
2000 – 88.89 11.11 – 1.06 1.99 1.23 −0.02 0.19 sinusoidal  
 2019 – 87.5 12.5 – 1.05 1.9 1.25  0.18 sinusoidal  
2000 – 12 60 28 1.24 2.98 1.85 −0.01 0.39 meander  
 2019 – 9.68 64.52 25.8 1.2 2.99 1.86  0.46 meander  
2000 25 75 – – 1.03 1.49 1.15 −0.03 0.14 sinusoidal  
 2019 – 100 – – 1.06 1.47 1.18  0.12 sinusoidal  
Central angle river characteristics
IntervalYearRiver segmentation by central angle (°)
MinMaxMeanMean differenceStd deviationInterval pattern
0–4141–8585–158158–296296>
2000 – – 33.33 66.67 – 126.46 292.17 219.99 30.26 63.2 highly developed 
 2019 – – 43.75 56.25 – 112.91 294.7 189.73  63.69 highly developed 
2000 – 7.41 70.37 22.22 – 84.64 269.01 143.82 −19.68 40.92 developed 
 2019 – – 47.5 52.5 – 91.74 294.81 163.5  47 highly developed 
 2000 – – 96 – 157.04 295.69 254.6 −0.52 36.74 highly developed 
2019 – – 3.23 96.77 – 143.16 295.92 255.12  42.71 highly developed 
 2000 – – 100 – – 105.15 157.41 129.6 −28.24 18.19 developed 
2019 – – 76.92 23.08 – 106.23 247.81 157.84  35.57 developed 
Curve coefficient characteristics
IntervalYearRiver segmentation by curve coefficient
MinMaxMeanMean differenceStd deviation
1–1.051.05–1.51.5–2>2Interval pattern
2000 – 66.67 20 13.33 1.06 2.35 1.48 0.08 0.39 sinusoidal  
 2019 6.25 68.75 6.25 17.75 1.01 2.29 1.4  0.43 sinusoidal  
2000 – 88.89 11.11 – 1.06 1.99 1.23 −0.02 0.19 sinusoidal  
 2019 – 87.5 12.5 – 1.05 1.9 1.25  0.18 sinusoidal  
2000 – 12 60 28 1.24 2.98 1.85 −0.01 0.39 meander  
 2019 – 9.68 64.52 25.8 1.2 2.99 1.86  0.46 meander  
2000 25 75 – – 1.03 1.49 1.15 −0.03 0.14 sinusoidal  
 2019 – 100 – – 1.06 1.47 1.18  0.12 sinusoidal  
Central angle river characteristics
IntervalYearRiver segmentation by central angle (°)
MinMaxMeanMean differenceStd deviationInterval pattern
0–4141–8585–158158–296296>
2000 – – 33.33 66.67 – 126.46 292.17 219.99 30.26 63.2 highly developed 
 2019 – – 43.75 56.25 – 112.91 294.7 189.73  63.69 highly developed 
2000 – 7.41 70.37 22.22 – 84.64 269.01 143.82 −19.68 40.92 developed 
 2019 – – 47.5 52.5 – 91.74 294.81 163.5  47 highly developed 
 2000 – – 96 – 157.04 295.69 254.6 −0.52 36.74 highly developed 
2019 – – 3.23 96.77 – 143.16 295.92 255.12  42.71 highly developed 
 2000 – – 100 – – 105.15 157.41 129.6 −28.24 18.19 developed 
2019 – – 76.92 23.08 – 106.23 247.81 157.84  35.57 developed 

According to Table 3, in both periods, the first and the third intervals were highly developed in the form of meander and in the fourth period were of the developed meander type. However, during the second period during the study 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. In this interval, the heavy ravine is due to its low bedrock and alluvial slope and the meanders are free and plain, and with increasing meandering arch and concentration of river energy at a given point, the erosion intensity reaches its maximum and somewhere as the meander arch is concentrated to the sides and tangential to the bed wall, large amounts of side material flow into the bed and as the meandering energy intensifies over the bending and meander arch, floodplain width is increased due to erosion (Figure 6(a) and 6(b)). In the first interval, the central angle of the riverbed decreased in 2019 compared with 2000, and with the decrease of the central angle of the river, the mean radius of the tangent to the riverbed also decreased, and in other intervals an increasing trend of the central angle during the study period was witnessed. Increasing the central angle indicates that the river meanders are active and the morphology of the river has changed to a highly developed meander, as well as there being a change in the central angle in bends that have not been removed and only in which changes have been made. In the third interval, the mean central angle in both periods is higher than the other intervals, and 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 (Figure 6(c) and 6(d)). The rate of development of the meander rotation is completely influenced by the bedrock lithology (Lecce 2013), and the expanded riffle rotations are spread in low-strength, high-strength hydraulic shear formations. But because the topography of the area is very rough and the river is enclosed in a deep valley, the stage does not become a horseshoe.
Figure 6

(a), (b) River erosion due to loose and erodible materials, (c) and (d) the geological strength of the riverbed and the low width resulting from this factor.

Figure 6

(a), (b) River erosion due to loose and erodible materials, (c) and (d) the geological strength of the riverbed and the low width resulting from this factor.

Close modal

The decreasing trend of wavelengths at all intervals in 2019 relative to 2000 indicates a decrease in the number of successive meanders, meaning that the number of meandering streams has increased, as the number has increased. The decrease in wavelength should be accompanied by an increase in the number of meanders, and in the present study, the number of meanders has also increased. The meandering of the rivers at all intervals confirms this. The wavelength and valley length decreased in the second period compared with the first period, indicating a decrease in erosion processes and the superiority of sedimentation processes and a downstream flow force. In general, the average arc radius declined throughout the years from 2000 to 2019. But when comparing the intervals with each other, in the third interval the radius of curvature of the curves in both periods is smaller than the other intervals and is an indication of the pressure and instability of the arc and the greater twisting energy for erosion. That is, the curvature of the flow path in the third interval is greater for shear and displacement. In the second interval (plain interval), due to the presence of erodible formations on the banks of the river, the freedom of action and power of the river movement is high, and as a result of faster movement and high erosion, the radius of the rings from the other study interval is increased. Therefore, the larger arc radius is due to riverbed erosion and lower radius due to mountains and lithology, and the change in river radius can be due to engineering actions and human interference along the river path and reduced river sedimentation due to construction of a dam that has severely affected the morphological behavior of the river (Surian & Rinaldi 2003).

Estimation of total power, specific power and shear stress

Channel bed morphology arises as a function of local shear stress and specific stream power (Flores et al. 2006), which are determined by both channel slope and unit discharge. Determining the erosive power for each of the sections is important from the point of view that it is possible to evaluate the conditions and hydrodynamic power of the flow and judge the forms and factors involved in each section. These minimum thresholds tentatively correspond to 100 N/m2 or 300 W/m2 for shear stress and unit stream power, respectively (Magilligan 1992; Hafez 2000), and as the river strength exceeds the erosion threshold, the amount of change imaginable for the cross-section will increase. Figure 7 shows the cross-sections examined.
Figure 7

Position of the investigated sections along the river path with schematic representation of a number of transverse sections.

Figure 7

Position of the investigated sections along the river path with schematic representation of a number of transverse sections.

Close modal

According to studies (Magilligan 1992; Hafez 2000; Flores et al. 2006), it can be said that the factors affecting river power are the width of the channel and the slope. In the first interval, the slope of the riverbed is high. However, downstream of the Givi Reservoir Dam where the river enters the flood side, especially in the area of Saidabad, the slope of the riverbed decreases up until Firoozabad, causing the alluvial materials to be deposited and the width of the riverbed to rise. In the interval after Firoozabad, the river gets steeper because of the folds of the river banks, forming a rocky and bare riverbed. The area under study is made up of metamorphic and volcanic rocks alternately placed between sedimentary layers. The oldest area has been formed by biosparite lime and siliceous limestone up to a thick layer as the youngest layer, which is the sediments of present-day rivers. Tertiary rocks are mainly the result of extensive volcanic activity, especially in the Eocene, Oligocene and Miocene, followed by the deposited conglomerate, sandstone, marl, gypsum, and limestone layers. The present-day sediments include fine and coarse alluvial material, sediments, and river deposits. In the first period, the river flows into a valley bed, and in parts formed by erodible formations and at sections close to the dam, the river width is generally increased. In addition, in the parts that are composed of the porphyry and megaporphyritic layers of the Eocene, these layers lose their resistance when exposed to water and then they become erosional. However, the erosion rate of these rocks is low compared with the amount of erosion in alluvial layers or alluvial terraces. In the second interval and immediately after the Givi Dam, the river passes through the valleys overlooking Givi town, and in this area the width of the bed due to the nature of the bank decreases and the riverbed has coarse sediments and is covered with broken stones resulting from falling from the banks and being transported from upstream (sections 8 to 10). Turning away from the dam and crossing the Givi River, the Givi Plain downstream of the main flood plain is entered, with a width of between 500 and 1,000 m and more than 12 km to Firoozabad (sections 11 to 20) and most of the arable lands. The gardens in this area are located in the flood plain of the river, and due to the passage of the river through erodible formations such as marl, especially near Sekerabad and Mikailabad, widespread riverbeds and young gullies are observed (VanLaningham et al. 2006; Pike et al. 2010; Lecce 2013). Large volumes of flanking material (especially during floods) are eroded and loose flanks lead to the widening of canals and intra-channel ridges, and these sediments are clearly visible in bends, middle islands, and marginal lands and steep banks, which are constantly displaced and eroded by currents, and the bed morphological variations in this range are high. Decrease in width at section 14 is due to occupation by debris from gardens and construction. At the beginning of the third period, the Firoozabad area is in the continuation of the flood of the previous interval and by joining Sanghorchay, the river enters the mountainous part and the coastal areas have deep valleys with steep slopes along the river due to encountering high altitudes and rocky outcrops, and the alternative route has a meander and river changes that are subject to valley changes and the meandering state is seen throughout the valley (sections 21 to 28). The course of the river in this period corresponds to the Ean geological unit (an alternation of andesite lava, andesite basalt, and basalt with andesite-shaped glass tuff), Ngms (alternation of gray and red gypsum marls with gray sandstone in layers of micro-coagulation) and Ngc (red conglomerate). In the fourth period, the river width is reduced and the riverbed is covered with coarse sediments, which extends to Ghezelozan, in some areas due to rock material loss from canal-fill elevations and redirection. During this period, the formation of sections is subject to lithological resistance of the riverbed and no agricultural uses are observed (Schumm 1985; VanLaningham et al. 2006; Pike et al. 2010; Lecce 2013; Falkowski et al. 2017; Batalla et al. 2018). Therefore, the low river width in the fourth interval (sections 29 to 32) is due to lithological resistance and from Firoozabad to the River Ghezelozan river-crossing corresponds to the Ean geological unit with a north–south trend, and this periodic unit of andesitic lava, andesite basalt, and basalt is associated with andesitic glass tuff.

In the first and second periods, a large part of the river route passes through the use of gardens. In the first period, due to the reduction of the width of the valley, these uses on the steep banks of the river are limited and include lands in the terraces and gardens that extend in the narrow strip of the river valley. The second range of the Givi River area is one of the most important parts of the river in terms of the exploitation and use of lands and gardens and villages. Givi River, after passing through narrow and rocky valleys downstream of Givi Dam, flows into Givi plain in the downstream of the city, and has a sedimentary alluvial catchment area with a lower slope compared with the upstream and general conditions for harvesting river materials. Thus, in past years, river sand materials have been harvested from the area of Gargabad village (Saeed Abad) and Mikael Abad, as well as in the lower part of it (before Firoozabad), to connect and build a reservoir dam. In some parts of the river, this has disrupted the bed and section, and in some areas, it has destroyed and eroded the banks and bridges (Gregory 2006; Surian et al. 2011; Mandal et al. 2016; Koehnken et al. 2020). The third and fourth periods (from Firoozabad to the annexation to GhezelOzan) show the lowest amount of land use and exploitation along the river compared with other areas, and there is no agricultural use in these periods. Other examples of human interference in the Givi-chay River, especially in the downstream areas of the dam, include the construction of bridges (Debnath et al. 2015; Bandyopadhyay & Kumar De 2018) (such as the bridges in the village of Ilvanagh, the stone bath, the downstream of the Givi Dam, Korpoqolaghi, the village of Mikael Abad and Firoozabad village). The foundations of the bridges act as a dam or floodgate, causing water to recede and sediment to rise. Other human factors include the creation of walls and fences for separation of private property, as well as the creation of restaurants, encroachment on the river, and the narrowing of the riverbed. It can be said that the twists and turns of the river, the high speed of the water flow and the aggression of the farmers towards the river have caused the sidewalks to be washed away and foaming, and in some other areas the water level has risen and water enters the lands and gardens along the river. At the site of the screws (meander twists), gardens and lands on the outside shore of the screw are more prone to erosion and destruction due to the centrifugal force caused by the movement of water and must be protected in terms of resistance to erosion. Pumping river water to irrigate agricultural lands and orchards around the river (Debnath et al. 2015; Bandyopadhyay & Kumar De 2018) and draining construction debris are other human activities on the banks of the Givi-chay River (Figure 8).
Figure 8

Examples of human intervention downstream of the dam: (a) construction of bridges that cause water retention and sediment upstream; (b) creation of walls and fences, for the separation of personal property and also creating restaurants and consequently narrowing the river; (c) pumping river water.

Figure 8

Examples of human intervention downstream of the dam: (a) construction of bridges that cause water retention and sediment upstream; (b) creation of walls and fences, for the separation of personal property and also creating restaurants and consequently narrowing the river; (c) pumping river water.

Close modal

Therefore, considering the width and slope parameters of the river and the calculation of total power and specific power (Table 4) and based on the power of 300 watts, as erosion power, it can be said that in terms of total river power and the cross-sections of the first interval (upstream of the dam), it does not have much erodible power. But in the downstream part of the dam, in the second interval (sections 11, 12, and 13), it has a total power of 799.515 W/m2 and then (sections 8, 9, and 10) a total power of 575.651 W/m2. In the third interval, in sections 25 to 28, the total power is 351.787 W/m2, and in the fourth interval the river power is 671.593 W/m2 and beyond the erosion threshold. In terms of specific river power at the average annual flow rate, the river does not perform major erosion work at any of the sections, except where the stream is directly impacted by the river banks and performs scouring or cutting or sanding of the shores, or where the current hits a screw directly. In terms of the average annual flow, the lowest specific power of the river was in the 19th and 20th sections. The base flow (Q2.33) plays the greatest role in the shape, pattern, and variability of the river sections, and in the active sections, the riverbed undergoes major changes and changes due to the base flow (Magilligan 1992; Hafez 2000; Flores et al. 2006), the fourth interval sections and sections 9, 12, 8 and 13 will have the highest potential for cross-section deformation and shoreline deformation, and at different return periods the erosive strength of the river will be high, and sections 20, 19, 15, 18 and 17 will have the least potential. The specific power of the river in different return periods based on monthly peak and maximum instantaneous flow for sections is shown in Tables 5 and 6, respectively. According to the indices of width, slope, and depth of water, the highest amount of shear stress was also in the second interval and in sections 12, 13, 9, 8,11 and the fourth interval sections, and the lowest shear stress was in sections 19 and 20. Therefore, the specific power and shear stress are directly related.

Table 4

Hydrological parameters of flow in selected sections and calculation of river specific power and shear stress of each section

SectionIntervalWidth (m)Slope (%)Depth of water (m)Total power (W/m2)Specific power (W/m2)Shear stress (N/m2)SectionIntervalWidth (m)Slope (%)Depth of water (m)Total power (W/m2)Specific power (W/m2)Shear stress (N/m2)
22.19 0.014 0.5 284.29 12.81 68.67 17 25.92 0.007 0.52 223.86 8.63 35.7 
19.09 0.014 0.52 284.29 14.89 71.41 18 25.81 0.007 0.53 223.86 8.67 36.39 
18.8 0.014 0.54 284.29 15.12 74.16 19 31.6 0.004 0.48 127.92 4.04 18.83 
17.93 0.014 0.56 284.29 15.85 76.91 20 40.54 0.004 0.4 127.92 3.15 15.69 
26.92 0.014 0.45 284.29 10.56 61.8 21 13.2 0.008 0.63 255.84 19.38 49.44 
25.93 0.014 0.47 284.29 10.96 64.54 22 8.75 0.008 0.67 255.84 29.23 52.58 
35.81 0.014 0.4 284.29 7.938 54.93 23 9.15 0.008 0.65 255.84 27.96 51.01 
10.81 0.018 0.65 575.65 53.25 114.77 24 8.44 0.011 0.66 351.78 41.68 71.22 
5.19 0.018 0.77 575.65 110.91 135.96 25 16.22 0.011 0.54 351.78 21.68 58.27 
10 13.86 0.018 0.63 575.65 41.53 111.24 26 8.13 0.011 0.64 351.78 43.27 69.06 
11 24.13 0.025 0.54 799.51 33.13 132.43 27 9.32 0.011 0.61 351.78 37.74 65.82 
12 16.58 0.025 0.6 799.51 48.22 147.15 28 14.32 0.011 0.56 351.78 24.56 60.42 
13 21.97 0.025 0.58 799.51 36.39 142.24 29 10.71 0.021 0.58 671.59 62.7 119.48 
14 15.37 0.007 0.6 223.86 14.46 41.2 30 8.69 0.021 0.6 671.59 77.28 123.6 
15 28.58 0.007 0.5 223.86 7.83 34.33 31 8.34 0.021 0.6 671.59 80.52 123.6 
16 14.4 0.007 0.61 223.86 15.54 41.88 32 7.93 0.021 0.61 671.59 84.69 125.66 
SectionIntervalWidth (m)Slope (%)Depth of water (m)Total power (W/m2)Specific power (W/m2)Shear stress (N/m2)SectionIntervalWidth (m)Slope (%)Depth of water (m)Total power (W/m2)Specific power (W/m2)Shear stress (N/m2)
22.19 0.014 0.5 284.29 12.81 68.67 17 25.92 0.007 0.52 223.86 8.63 35.7 
19.09 0.014 0.52 284.29 14.89 71.41 18 25.81 0.007 0.53 223.86 8.67 36.39 
18.8 0.014 0.54 284.29 15.12 74.16 19 31.6 0.004 0.48 127.92 4.04 18.83 
17.93 0.014 0.56 284.29 15.85 76.91 20 40.54 0.004 0.4 127.92 3.15 15.69 
26.92 0.014 0.45 284.29 10.56 61.8 21 13.2 0.008 0.63 255.84 19.38 49.44 
25.93 0.014 0.47 284.29 10.96 64.54 22 8.75 0.008 0.67 255.84 29.23 52.58 
35.81 0.014 0.4 284.29 7.938 54.93 23 9.15 0.008 0.65 255.84 27.96 51.01 
10.81 0.018 0.65 575.65 53.25 114.77 24 8.44 0.011 0.66 351.78 41.68 71.22 
5.19 0.018 0.77 575.65 110.91 135.96 25 16.22 0.011 0.54 351.78 21.68 58.27 
10 13.86 0.018 0.63 575.65 41.53 111.24 26 8.13 0.011 0.64 351.78 43.27 69.06 
11 24.13 0.025 0.54 799.51 33.13 132.43 27 9.32 0.011 0.61 351.78 37.74 65.82 
12 16.58 0.025 0.6 799.51 48.22 147.15 28 14.32 0.011 0.56 351.78 24.56 60.42 
13 21.97 0.025 0.58 799.51 36.39 142.24 29 10.71 0.021 0.58 671.59 62.7 119.48 
14 15.37 0.007 0.6 223.86 14.46 41.2 30 8.69 0.021 0.6 671.59 77.28 123.6 
15 28.58 0.007 0.5 223.86 7.83 34.33 31 8.34 0.021 0.6 671.59 80.52 123.6 
16 14.4 0.007 0.61 223.86 15.54 41.88 32 7.93 0.021 0.61 671.59 84.69 125.66 
Table 5

River specific power rate (W/m2) in different return periods based on monthly peak flow in study sections

Return periods
22.335102550100200500
SectionInterval
First 92.096 113.759 208.145 284.954 382.064 452.107 525.593 596.832 690.847 
First 107.054 132.232 241.946 331.228 444.107 527.849 610.944 693.75 803.033 
First 108.703 134.272 245.678 336.337 450.957 535.991 620.368 704.452 815.42 
First 113.987 140.787 257.599 352.657 472.839 651.999 650.469 738.633 854.986 
First 75.914 93.77 171.537 234.886 314.933 374.318 433.243 491.965 569.461 
First 78.812 97.35 178.124 243.854 326.957 388.609 449.785 510.748 591.203 
First 57.068 70.491 128.979 176.575 236.749 281.392 325.689 369.832 428.09 
Second 324.411 376.356 602.43 786.688 1,019.3 1,191.96 1,363.31 1,534.01 1,759.27 
Second 675.699 783.893 1,254.77 1,638.55 2,123.04 2,482.67 2,893.57 3,195.11 3,664.29 
10 Second 253.022 293.536 469.861 613.571 794.992 929.657 1,063.3 1,196.44 1,372.13 
11 Second 201.851 234.172 374.837 489.484 634.215 741.645 848.262 954.473 1,049.63 
12 Second 293.767 340.806 545.526 712.379 923.016 1,079.37 1,234.53 1,389.11 1,593.09 
13 Second 221.696 257.194 411.69 537.608 696.568 814.56 931.66 1,048.31 1,202.25 
14 Second 88.73 102.938 164.772 215.169 278.79 326.015 372.882 419.571 481.181 
15 Second 47.718 55.358 88.612 115.715 149.93 175.327 200.352 225.64 258.774 
16 Second 94.707 109.872 175.872 229.663 297.57 347.976 398 447.833 513.594 
17 Second 52.615 61.04 97.706 127.559 165.317 193.32 221.111 248.796 285.33 
18 Second 52.839 61.3 98.122 128.134 166.021 194.144 222.053 249.857 286.546 
19 Second 24.661 28.61 45.796 59.803 77.486 90.612 103.638 116.615 133.739 
20 Second 19.223 22.301 35.697 46.615 60.399 70.63 80.783 90.898 104.246 
21 Third 118.077 136.983 219.268 286.333 370.996 433.84 496.208 558.338 640.325 
22 Third 178.127 206.649 330.782 431.954 559.675 654.478 748.565 842.292 965.977 
23 Third 170.34 197.615 316.322 413.071 535.208 625.867 715.841 805.471 923.748 
24 Third 253.921 294.579 471.531 615.752 797.818 932.961 1,067.08 1,200.69 1,377 
25 Third 132.127 153.283 245.359 320.404 415.141 485.462 555.251 624.774 716.517 
26 Third 263.603 305.811 489.511 639.231 828.239 968.535 1,107.77 1,246.47 1,429.51 
27 Third 229.946 266.765 427.009 557.612 722.488 844.87 966.327 1,087.32 1,246.99 
28 Third 149.657 173.621 277.913 362.915 470.222 549.874 628.922 707.67 811.586 
29 Fourth 382.013 443.181 709.398 926.373 1,200.28 1,403.6 1,605.38 1,806.39 2,071.64 
30 Fourth 470.812 546.199 874.298 1,141.71 1,479.29 1,729.87 1,978.55 2,226.28 2,553.2 
31 Fourth 490.571 569.121 910.989 1,189.62 1,541.37 1,802.46 2,061.58 2,319.71 2,660.34 
32 Fourth 515.934 598.546 958.089 1,251.13 1,621.06 1,895.66 2,168.17 2,439.65 2,797.89 
Return periods
22.335102550100200500
SectionInterval
First 92.096 113.759 208.145 284.954 382.064 452.107 525.593 596.832 690.847 
First 107.054 132.232 241.946 331.228 444.107 527.849 610.944 693.75 803.033 
First 108.703 134.272 245.678 336.337 450.957 535.991 620.368 704.452 815.42 
First 113.987 140.787 257.599 352.657 472.839 651.999 650.469 738.633 854.986 
First 75.914 93.77 171.537 234.886 314.933 374.318 433.243 491.965 569.461 
First 78.812 97.35 178.124 243.854 326.957 388.609 449.785 510.748 591.203 
First 57.068 70.491 128.979 176.575 236.749 281.392 325.689 369.832 428.09 
Second 324.411 376.356 602.43 786.688 1,019.3 1,191.96 1,363.31 1,534.01 1,759.27 
Second 675.699 783.893 1,254.77 1,638.55 2,123.04 2,482.67 2,893.57 3,195.11 3,664.29 
10 Second 253.022 293.536 469.861 613.571 794.992 929.657 1,063.3 1,196.44 1,372.13 
11 Second 201.851 234.172 374.837 489.484 634.215 741.645 848.262 954.473 1,049.63 
12 Second 293.767 340.806 545.526 712.379 923.016 1,079.37 1,234.53 1,389.11 1,593.09 
13 Second 221.696 257.194 411.69 537.608 696.568 814.56 931.66 1,048.31 1,202.25 
14 Second 88.73 102.938 164.772 215.169 278.79 326.015 372.882 419.571 481.181 
15 Second 47.718 55.358 88.612 115.715 149.93 175.327 200.352 225.64 258.774 
16 Second 94.707 109.872 175.872 229.663 297.57 347.976 398 447.833 513.594 
17 Second 52.615 61.04 97.706 127.559 165.317 193.32 221.111 248.796 285.33 
18 Second 52.839 61.3 98.122 128.134 166.021 194.144 222.053 249.857 286.546 
19 Second 24.661 28.61 45.796 59.803 77.486 90.612 103.638 116.615 133.739 
20 Second 19.223 22.301 35.697 46.615 60.399 70.63 80.783 90.898 104.246 
21 Third 118.077 136.983 219.268 286.333 370.996 433.84 496.208 558.338 640.325 
22 Third 178.127 206.649 330.782 431.954 559.675 654.478 748.565 842.292 965.977 
23 Third 170.34 197.615 316.322 413.071 535.208 625.867 715.841 805.471 923.748 
24 Third 253.921 294.579 471.531 615.752 797.818 932.961 1,067.08 1,200.69 1,377 
25 Third 132.127 153.283 245.359 320.404 415.141 485.462 555.251 624.774 716.517 
26 Third 263.603 305.811 489.511 639.231 828.239 968.535 1,107.77 1,246.47 1,429.51 
27 Third 229.946 266.765 427.009 557.612 722.488 844.87 966.327 1,087.32 1,246.99 
28 Third 149.657 173.621 277.913 362.915 470.222 549.874 628.922 707.67 811.586 
29 Fourth 382.013 443.181 709.398 926.373 1,200.28 1,403.6 1,605.38 1,806.39 2,071.64 
30 Fourth 470.812 546.199 874.298 1,141.71 1,479.29 1,729.87 1,978.55 2,226.28 2,553.2 
31 Fourth 490.571 569.121 910.989 1,189.62 1,541.37 1,802.46 2,061.58 2,319.71 2,660.34 
32 Fourth 515.934 598.546 958.089 1,251.13 1,621.06 1,895.66 2,168.17 2,439.65 2,797.89 
Table 6

River specific power rate (W/m2) in different return periods based on maximum moment flow in the study sections

Return periods
22.335102550100200500
SectionInterval
First 284.707 315.635 495.142 643.685 841.741 996.473 1,157.39 1,324.5 1,553.51 
First 330.94 366.911 575.547 748.212 978.431 1,158.29 1,345.34 1,539.59 1,805.78 
First 336.045 372.571 584.426 759.753 993.523 1,176.16 1,366.09 1,563.34 1,833.64 
First 352.25 390.649 612.783 796.618 1,041.73 1,233.23 1,432.38 1,639.19 1,922.61 
First 234.682 260.191 408.143 530.585 693.842 821.387 954.033 1,091.78 1,280.55 
First 243.642 270.125 423.725 550.843 720.333 852.747 990.458 1,133.47 1,329.44 
First 176.421 195.597 306.819 398.865 521.593 617.474 717.19 820.742 962.646 
Second 1,127.11 1,339.46 1,911.18 2,384.89 3,087.29 3,577.34 4,083.72 4,590.1 5,276.16 
Second 2,347.6 2,789.9 3,980.71 4,967.38 6,430.37 7,451.06 8,505.87 9,560.5 10,989.5 
10 Second 879.078 1,044.7 1,490.61 1,860.08 2,407.91 2,790.12 3,185.06 3,580.01 4,115.1 
11 Second 701.295 833.423 1,189.15 1,483.9 1,920.94 2,225.85 2,540.92 2,856 3,282.87 
12 Second 1,020.64 1,212.94 1,730.65 2,159.62 2,795.67 3,239.43 3,697.98 4,156.53 4,777.79 
13 Second 770.244 915.362 1,306.07 1,629.79 2,109.8 2,444.69 2,790.74 3,136.79 3,605.63 
14 Second 308.278 366.359 522.732 652.298 844.413 978.447 116.95 1,255.45 1,443.1 
15 Second 165.788 197.024 281.119 350.798 454.116 526.198 600.682 675.167 776.082 
16 Second 329.044 391.038 557.94 696.238 901.294 1,044.36 1,192.19 1,340.02 1,540.31 
17 Second 182.802 217.243 309.969 386.799 500.719 580.198 662.326 744.455 855.726 
18 Second 183.581 218.169 311.29 388.447 502.853 582.671 665.149 747.628 859.373 
19 Second 85.682 101.825 145.287 181.299 234.695 271.948 310.43 348.938 401.092 
20 Second 66.787 79.37 113.248 141.318 182.939 211.977 241.983 271.989 312.642 
21 Third 410.236 487.527 695.618 868.036 1,123.69 1,302.05 1,486.36 1,670.67 1,920.38 
22 Third 618.871 735.47 1,049.39 1,309.49 1,695.17 1,964.24 2,242.29 2,520.33 2,897.03 
23 Third 591.816 703.318 1,003.51 1,252.25 1,621.06 1,878.37 2,144.26 2,410.15 2,770.39 
24 Third 882.203 1,048.41 1,495.91 1,866.69 2,416.47 2,800.03 3,196.39 3,594.74 4,129.73 
25 Third 459.05 545.538 778.389 971.323 1,257.4 1,456.98 1,663.22 1,869.46 2,148.89 
26 Third 915.841 1,088.39 1,552.95 1,937.87 2,508.61 2,906.8 3,318.27 3,729.73 4,287.2 
27 Third 798.905 949.423 1,354.66 1,690.44 2,188.3 2,535.65 2,894.58 3,253.51 3,739.8 
28 Third 519.957 617.92 881.667 1,100.2 1,424.23 1,650.3 1,883.9 2,117.51 2,434 
29 Fourth 1,327.24 1,577.29 2,250.53 2,808.35 3,635.47 4,212.53 4,808.82 5,405.12 6,213 
30 Fourth 1,635.75 1,943.94 2,773.67 3,461.16 4,480.54 5,191.74 5,926.64 6,661.54 7,657.22 
31 Fourth 1,704.4 2,025.52 2,890.07 3,606.41 4,668.57 5,409.62 6,175.36 6,941.1 7,978.56 
32 Fourth 1,792.52 2,130.24 3,039.49 3,792.87 4,909.95 5,689.31 6,494.64 7,299.98 8,391.08 
Return periods
22.335102550100200500
SectionInterval
First 284.707 315.635 495.142 643.685 841.741 996.473 1,157.39 1,324.5 1,553.51 
First 330.94 366.911 575.547 748.212 978.431 1,158.29 1,345.34 1,539.59 1,805.78 
First 336.045 372.571 584.426 759.753 993.523 1,176.16 1,366.09 1,563.34 1,833.64 
First 352.25 390.649 612.783 796.618 1,041.73 1,233.23 1,432.38 1,639.19 1,922.61 
First 234.682 260.191 408.143 530.585 693.842 821.387 954.033 1,091.78 1,280.55 
First 243.642 270.125 423.725 550.843 720.333 852.747 990.458 1,133.47 1,329.44 
First 176.421 195.597 306.819 398.865 521.593 617.474 717.19 820.742 962.646 
Second 1,127.11 1,339.46 1,911.18 2,384.89 3,087.29 3,577.34 4,083.72 4,590.1 5,276.16 
Second 2,347.6 2,789.9 3,980.71 4,967.38 6,430.37 7,451.06 8,505.87 9,560.5 10,989.5 
10 Second 879.078 1,044.7 1,490.61 1,860.08 2,407.91 2,790.12 3,185.06 3,580.01 4,115.1 
11 Second 701.295 833.423 1,189.15 1,483.9 1,920.94 2,225.85 2,540.92 2,856 3,282.87 
12 Second 1,020.64 1,212.94 1,730.65 2,159.62 2,795.67 3,239.43 3,697.98 4,156.53 4,777.79 
13 Second 770.244 915.362 1,306.07 1,629.79 2,109.8 2,444.69 2,790.74 3,136.79 3,605.63 
14 Second 308.278 366.359 522.732 652.298 844.413 978.447 116.95 1,255.45 1,443.1 
15 Second 165.788 197.024 281.119 350.798 454.116 526.198 600.682 675.167 776.082 
16 Second 329.044 391.038 557.94 696.238 901.294 1,044.36 1,192.19 1,340.02 1,540.31 
17 Second 182.802 217.243 309.969 386.799 500.719 580.198 662.326 744.455 855.726 
18 Second 183.581 218.169 311.29 388.447 502.853 582.671 665.149 747.628 859.373 
19 Second 85.682 101.825 145.287 181.299 234.695 271.948 310.43 348.938 401.092 
20 Second 66.787 79.37 113.248 141.318 182.939 211.977 241.983 271.989 312.642 
21 Third 410.236 487.527 695.618 868.036 1,123.69 1,302.05 1,486.36 1,670.67 1,920.38 
22 Third 618.871 735.47 1,049.39 1,309.49 1,695.17 1,964.24 2,242.29 2,520.33 2,897.03 
23 Third 591.816 703.318 1,003.51 1,252.25 1,621.06 1,878.37 2,144.26 2,410.15 2,770.39 
24 Third 882.203 1,048.41 1,495.91 1,866.69 2,416.47 2,800.03 3,196.39 3,594.74 4,129.73 
25 Third 459.05 545.538 778.389 971.323 1,257.4 1,456.98 1,663.22 1,869.46 2,148.89 
26 Third 915.841 1,088.39 1,552.95 1,937.87 2,508.61 2,906.8 3,318.27 3,729.73 4,287.2 
27 Third 798.905 949.423 1,354.66 1,690.44 2,188.3 2,535.65 2,894.58 3,253.51 3,739.8 
28 Third 519.957 617.92 881.667 1,100.2 1,424.23 1,650.3 1,883.9 2,117.51 2,434 
29 Fourth 1,327.24 1,577.29 2,250.53 2,808.35 3,635.47 4,212.53 4,808.82 5,405.12 6,213 
30 Fourth 1,635.75 1,943.94 2,773.67 3,461.16 4,480.54 5,191.74 5,926.64 6,661.54 7,657.22 
31 Fourth 1,704.4 2,025.52 2,890.07 3,606.41 4,668.57 5,409.62 6,175.36 6,941.1 7,978.56 
32 Fourth 1,792.52 2,130.24 3,039.49 3,792.87 4,909.95 5,689.31 6,494.64 7,299.98 8,391.08 

One can say that the existence of vegetation in the riverbed and along the river increases the roughness of the flow path, wastes water energy, slows the flow, and reduces the shear velocity and stress of the flow. In other words, the water energy is dissipated at the site of the wall by the aerial organs of the plant. The plant stems through which the flow passes bear the highest tensile force and as density increases, the roughness coefficient also increases. Hydraulic resistance also causes the suspended sediments along the riverbed to be absorbed and deposited, thus controlling the width and increasing the stability of the walls. In the fourth interval, where the level of vegetation is very low, the shear stress is also high; this is while in parts of the river path with dense vegetation, the vegetation acts as a protection and prevents erosion of the margins, reducing shear stress (Van De Wiel & Darby 2007; Eaton & Millar 2017; Zhu et al. 2018).

According to the results, it can be said that with the construction of Givi Dam, the fundamental changes in river flow regime are in the form of decreased downstream discharge in a high water season, increased downstream discharge in a low water season, downstream reduced sediment, sedimentation of suspended matter, and increase in riverbed level. This causes the natural balance of the river to be changed. These changes have also affected the geometrical and geomorphological features of the river.

This study shows that the sections and regions with fine-grained and alluvial bed materials are more sensitive to discharge changes and sediment load; generally, in the Givi-chay River, in the sections that the river passes from alluvial barracks, the riverbed is unstable. The most important factor in the meandering of the river, in the plain region where meanders are free, is its alluvial formation type and low slope. In contrast, in the mountainous regions, the river changes follow the valley changes.

Considering the parameters of width, depth, and slope of the river and calculation of total power, specific power and shear stress, the maximum amount of total river power is in the second interval, in sections 11, 12, and 13. In terms of river-specific power, the fourth interval sections, and the 9th, 12th, 8th, and 13th sections, have the most potential for deformation and coastal deformation, and at different return periods the erosive power of the river will be high, in the 20th, 19th sections, while sections 15, 18, and 17 have the least potential. The highest amount of shear stress was observed in the second interval, at 12, 13, 9, 11, and the lowest at 19 and 20.

In particular, the changes in the Givi-chay River plan are the developing of existing meanders, river route displacement, increasing curvature, and creating of small meanders. Pattern formation and morphological changes of the Givi-chay River are affected by hydrological processes induced by the construction of the Givi-chay dam, lithological resistance of the riverbed and river banks, and human interventions such as encroachment on land, the riverbed, bridge construction, and sand mining. In general, river management and water resource strategies should consider the styles and magnitude of channel changes, to avoid or mitigate their adverse effects on present and future human activities. In order to adopt principled methods and sustainable environmental management, the results of the present study can be considered by the Regional Water Organization, Watershed Management and Natural Resources, farmers and residents around the Givi-chay River.

The authors would like to thank the regional Water Company of Ardabil for providing the hydrology data for this study. We also acknowledge the support from Mohaghegh Ardabili University.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.

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