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Journal of Geographical Sciences >

2019 , Vol. 29 >Issue 2: 306 - 320

DOI: https://doi.org/10.1007/s11442-019-1598-x

Research Articles

Evolution of the gravel-bedded anastomosing river within the Qihama reach of the First Great Bend of the Yellow River

  • GAO Chao , 1, 2 ,
  • WANG Suiji , 1, 2
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  • 1. Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
  • 2. College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
* Corresponding author: Wang Suiji, PhD and Associate Professor, specialized in fluvial geomorphology and fluvial sedimentology. E-mail:

Author: Gao Chao, Master Candidate, specialized in fluvial geomorphology. E-mail:

Received date: 2017-12-15

  Accepted date: 2018-03-09

  Online published: 2019-02-25

Supported by

National Natural Science Foundation of China, No.41571005, No.41271027

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Journal of Geographical Sciences, All Rights Reserved
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Abstract

The anastomosing river that is present within the First Great Bend of the Yellow River is different from other sand-bedded rivers of this type because it contains gravel-bedded materials. It is therefore important to determine whether, or not, the specific characteristics of this anastomosing river are similar to those seen in sand-bedded forms, including the characteristics of erosion and deposition, and the stability of channel and interchannel wetlands. Four Landsat images from 1990, 2001, 2013, and 2016 alongside two Google Earth (GE) images from 2011 and 2013 were utilized in this study in tandem with field sampling and observations to select a 12 km main channel length section of the Qihama reach anastomosing river. This section was then used to determine variations in channel planform and sedimentary characteristics over a 26 year period. The results of this study show that this gravel-bedded anastomosing river has exhibited a high degree of stability overall, and that there has been no obvious channel and wetland bank erosion and deposition. Data also show that over the 26 years of this study, anastomosing belt area increased by 2.43%, while the ratio of land to water area remained almost equal. The number of wetlands has also increased along this river section at a rate as high as 62.16% because of the fragmentation of some small interchannel examples, while the talweg has alternately migrated to either the left or right over long periods of time at a relatively stable rate. Indeed, as a result of the migration of this line, there has been significant turnover in the number of islands within the main channel while bank shift has occurred at a rate of about 5 m/yr. The numerous anastomosing channels within this river section remained very stable over the course of this study, characterized by a mean annual migration rate of just 1 m/yr, while the sediments in bank columnar sections are mainly composed of fine sands or silts with a relatively high clay content. The sediment grain-size distribution curve for this river section contains multiple peaks, distinct from the muddy sediments within bank columnar sections from sand-bedded anastomosing rivers. The dense vegetation within riparian and interchannel wetlands alongside this river reach has also protected anastomosing channels from erosion and maintained their stability, a key feature of this gravel-bedded system.

Key words： gravel-bedded anastomosing river; anastomosing belt; wetlands; talweg; sediments; Yellow River

Cite this article

GAO Chao , WANG Suiji . Evolution of the gravel-bedded anastomosing river within the Qihama reach of the First Great Bend of the Yellow River[J]. Journal of Geographical Sciences, 2019 , 29(2) : 306 -320 . DOI: 10.1007/s11442-019-1598-x

1 Introduction

Anastomosing rivers are stable and interconnected multi-channel systems that differ from other waterway patterns and have attracted an increasing amount of research attention over recent decades. In his early work, Schumm (1968) was the first to differentiate anastomosing rivers from their braided counterparts, noting that the former are stable and comprised of low gradient multichannel systems that form on alluvial plains because of low water transport capacity which leads to riverbed deposition and branching. Although Rust (1978) later differentiated anastomosing rivers from other forms using the braided index and their degree of sinuosity, later workers have noted severe limitations in the use of these semi-quantitative indexes (Wang et al., 2002). Smith and Smith (1980) subsequently published a more detailed analysis of this type of watercourse, noting that an anatomosing river comprises a stable multichannel system with a low gradient, a medium amount of bending, and a series of interconnected channels separated by wetlands that themselves contain vegetation. Building on this early study, a detailed series of studies on anastomosing rivers have resulted from subsequent research (e.g., Schumm, 1985; Selby, 1985; Knighton and Nanson, 1993; Wang and Ren, 1999; Wang et al., 1999, 2004, 2005; Wang and Yin, 2000; Makaske, 2001; Wang, 2002) leading to classifications that are mainly based on traditional geomorphological methods. Thus, although anatomosing rivers have traditionally been classified based on the degree of sediment transport, sedimentation rate, and the presence and shape of channel planforms, technological developments and the emergence of computational mathematics has enabled simulation-based research on river networks. In this context, Wang (1990) first introduced the concept and method of applying fuzzy mathematics to problems in river classification, presenting analyses of some examples, while Shi et al. (2007a) classified the different watercourse types present within the lower reaches of the Yellow River by applying fuzzy clustering and discriminate analyses. Indeed, by making a number of improvements to the application of fuzzy clustering, these workers were able to conclude that some discriminants and criteria used in river classification established via these statistical methods were invalid (Shi et al., 2007b, 2009; Xu and Shi, 2009). At the same time, other researchers have also applied the cellular automata method to simulate the processes of braided river formation (e.g., Murray and Paola, 1994, 2015; Thomas and Nicholas, 2002). These methods, however, rely excessively on computer analyses while the index they utilize to generate models is relatively simple because the interactions between various factors are ignored. Some studies in this area have also been focused solely on the pattern of single rivers, so cannot be more widely applied in fluvial geomorphology.
A number of typical anastomosing rivers are known globally, including the lower reaches of the Saskatchewan River, the upper reaches of the Columbia River, the Wakool River in Canada, Cooper’s Creek in Australia, and the Rhine-Meuse Delta in the Netherlands (Smith and Putnam, 1980; Rust, 1981; Smith, 1983; Tornqvist, 1993). Rivers of this type within China are most obvious in the section between Songzikou and other estuaries that divert the Yangtze River and Dongting Lake, the reach adjacent to the confluence of the Heilong and the Songhua rivers, and in the waterway section within the Pearl River Delta (Wang et al., 1999). Although these waterways have commonly been referred to as “sandy anastomosing rivers” because of the presence of sediments of this size within their channel beds, Wang (2008) identified a new sub-type when studying river transformation patterns within the Yellow River Basin. This new sub-type does not differ from more common sandy anastomosing rivers in planform, micro-geomorphology, and other features other than in the presence of a gravel bed; these rivers are therefore considered to belong to a new subclass of anastomosing river, distinct and worthy of study in terms of scouring and silting characteristics, the causes underlying their formation, and the maintenance of channel and interchannel wetlands. All of these aspects are interesting in the context of current fluvial geomorphological and river sedimentological research.
The First Great Bend within the Maqu reach of the Yellow River formed as a result of uplift of the Qinghai-Tibet Plateau and has been less influenced by human activities because of its unique geographical location and environmental characteristics. This region is therefore ideal to study the evolution of rivers under natural conditions. Indeed, previous research that has evaluated the fluvial geomorphology of the Yellow River on the Qinghai-Tibet Plateau has mainly been focused on its formation, development, and evolution over geological time scales (e.g., Yuan and Wang, 1995; Li et al., 1996; Yang and Wang, 1996; Zhang et al., 2003), and more recent processes and characteristics have rarely been investigated (Wang, 2008; Li et al., 2013). Recently, however, Liu and Wang (2017) discussed variations in interchannel wetlands within the Maqu anastomosing river reach of the Upper Yellow River. The results of this study revealed the spatial distribution and level of interchannel wetland development within this gravel-bedded anastomosing river for the first time. Four Landsat images (1990, 2001, 2013, and 2016) and two Google Earth (GE) images (2011 and 2013) of a 12-km main channel length section of the Qihama anastomosing river reach are used in this study, in combination with field observations and sampling, to analyze variations in channel planform and sedimentary characteristics over a 26-year period. The objective of this study is to explore the evolutionary characteristics of a gravel-bedded anastomosing river under natural conditions in order to enhance our understanding of this new river sub-pattern, and enrich the theoretical basis of fluvial geomorphology.

2 Study area and methods

2.1 Study area

The study area discussed in this paper has an elevation of about 3400 m and is located in the vicinity of Qihama Town (33°N, 102°E) at the start of the First Great Bend of the Yellow River (Figure 1), in the southwestern Gannan Grassland. The mean annual precipitation in this region is 520 mm, mean annual temperature is 2°C, and the frost-free period is 120 days. The main channel selected for analysis is about 12 km in length, has a mean gradient about 0.60‰ (Li et al., 2013), and a mean channel width of about 200 m. The main channel and anabranches with varying degrees of sinuosity and width are connected to one another along this section; ratios of their width to depth are all below 40 and sometimes about 20. Dense trees, shrubs, and grasses grow on interchannel wetlands around this river section, have a surface sediment thickness between 1 m and 2.3 m, and are mainly comprised of mud and silt. The sediment that makes up the river bed is mostly gravel that has a median grain size between 4 cm and 7 cm (Wang, 2008). Hydrological data recorded at the Maqu gauging station adjacent to the study area shows that mean annual runoff is 14.4 billion m3; runoff between June and October accounts for about 73% of the annual volume, and peak flow normally reaches a maximum in July and September when mean monthly values are 1046.74 m3/s and 955.19 m3/s, respectively. Data also show that the mean annual suspended sediment load is 4.47 million tons, and the period between May and October accounts for about 95% of the annual total.
Figure 1 Map showing the location of the river reach discussed in this study

2.2 Methods

Satellite image analysis is an important and powerful tool used to obtain channel planforms that has been widely applied in fluvial geomorphological research (e.g., Wang et al., 2014; Mei and Wang, 2016). The Landsat images of the study area used in this research comprise 30 m resolution TM data (captured on July 8th, 1990), 15 m resolution ETM data (captured on August 15th, 2001), and 15 m resolution OLI data (captured on July 23rd, 2013, and July 15th, 2016). All of these satellite images were downloaded from the United States Geological Survey (http://glovis.usgs.gov/) and were used in combination with two GE images (captured on August 27th, 2011, and July 29th, 2013) that have 0.5 m resolution. All images were collected during the flooding season between June and September in order to facilitate the use of vegetation boundaries to delineate channels and to accurately extract their spatial distributions (Wang et al., 2014; Gurnell, 2015; Mei and Wang, 2016).
Image geometric correction was performed using the software ENVI5.1, and the 30 m resolution TM data was resampled using cubic convolution to enhance its resolution to 15 m. All images were then loaded into the software Arcgis10.2 for vectorization and to enable a channel planform to be generated for each year (Figure 2).The TM and ETM data were then processed using standard false color synthesis of bands 4, 3, and 2 while the OLI data were processed using bands 5, 4, and 3 to highlight channel boundaries. A talweg is the line of maximum velocity within each channel section and also delineates the deep connection that forms during interactions between water flow and the river bed. These lines are therefore drawn according to the principle that the deeper the water, the higher grayscale value an image will exhibit (Yan et al., 2013).The geometric parameters of channel planforms between 1990 and 2016 were therefore calculated quantitatively using the software Arcgis10.2 (Table 1).
Figure 2 Channel planforms in different years within the river reach studied in this paper
Table 1 Geometric parameters of channel planforms in different years
Date of image captured Talweg length (km) Sinuosity Area of the anastomosing belt (km2) Land area (km2) Water area (km2) Number of wetlands
July 8th, 1990 11.43 1.21 16.89 8.12 8.77 37
August 15th, 2001 12.83 1.36 17.00 8.27 8.73 40
July 23rd, 2013 12.72 1.35 17.17 9.12 8.05 60
July 15th, 2016 12.18 1.29 17.30 9.11 8.19 60
A 12 day field survey was also carried out between April 24th, 2016, and May 5th, 2016, and a number of bank columnar sections were sampled. These samples were analyzed at the Institute of Geographic Sciences and Natural Resources Research, CAS, using a Mastersizer 2000 laser particle size analyzer with a measurement range between 0.01 μm and 2000 μm and an error less than 2%. Particle size (dm) was transformed into φ value using the formula proposed by Udden (1914) and Wentworth (1922), as follows:
$\varphi =-\text{lo}{{\text{g}}_{2}}{{d}_{m}}$ (1)
Results were then scaled so that values between 1 φ and 2 φ denote coarse sand, while values between 2 φ and 3 φ denote fine sand, values between 3 φ and 4 φ denote very fine sand, values between 4 φ and 8 φ denote silt, values greater than 8 φ denote clay, and values greater than 8 φ denote muddy sediment.

3 Results

3.1 Variation in channel planform parameters

The data presented in Figure 3a show that the ratio between water and land areas within the anastomosing belt of this river reach remained almost equal over the course of this study and did not change significantly. Results show, for example, that water and land area percentages were 52% and 48% in 1990, 51% and 49% in 2001, 53% and 47% in 2013, and 53% and 47% in 2016, respectively. This means that the area of the anastomosing belt (i.e., water area plus land area) increased slightly between 1990 and 2016 from 16.89 km2 to 17.30 km2, a rate of just 2.43% (Figure 3b), while the length of the talweg increased between 1990 and 2001 and then decreased; the maximum and minimum recorded values were 12.83 km in 2001 and 11.43 km in 1990, respectively. The length of the talweg followed the same increasing trend as the anastomosing belt area between 1990 and 2001, while the opposite trend was seen between 2001 and 2016.
Figure 3 The relative proportions of water and land area (a), variations in anastomosing belt area and talweg length (b), variations in the number of interchannel wetlands (c), and the area of interchannel wetlands within the river reach studied in this paper (d)
The results of this study show that 37, 40, 60, and 60 interchannel wetlands were present within the river reach in 1990, 2001, 2013, and 2016, respectively (Figure 3c). These correspond to the number and rate increases of 3 and 8.11% between 1990 and 2001, and 20 and 50% between 2001 and 2013, respectively. Data show that while the number of interchannel wetlands greatly increased between 2001 and 2013 (Figure 3c), the corresponding increase in area was very small (Figure 3a); this suggests that the interchannel wetlands within the river reach were partially fragmented, a phenomenon that is also reflected by the data presented in Figure 3d. These data (Figure 3d) show that mean areas of interchannel wetlands were 0.22 km2, 0.21 km2, 0.15 km2, and 0.15 km2 in 1990, 2001, 2013, and 2016, while median areas were 0.11 km2, 0.09 km2, 0.05 km2, and 0.05 km2, respectively, all significantly decreasing trend. In addition, abnormal values (maximum and minimum) and lower quartiles for these years remained almost unchanged, while the upper edges and quartiles in this box-plot gradually reduced so that the latter was equal to the mean value in 2013 and 2016 (i.e., 75% of wetland area is at the mean level). All these data show that interchannel wetlands within the river reach fragmented overtime; this change is particularly evident for interchannel wetlands with areas between 0.1 km2 and 0.8 km2, while not obvious for those with areas less than 0.1 km2 or greater than 0.8 km2. This increase in the number of interchannel wetlands indicates that some new small channels were formed via flood avulsion on original surfaces, a result that is consistent with the developmental model for sandy anastomosing channels on floodplains (Wang, 2002; Wang et al., 2005).

3.2 Talweg migration rate and anastomosing belt symmetry index

The rate of talweg migration can be used to quantitatively reveal some of the characteristics of channel evolution and is calculated (Giardino and Li, 2011), as follows:
${{R}_{m}}={\frac{A}{L}}/{y}\;$ (2)
In this expression, Rm denotes the annual talweg migration rate, A is the area surrounded by these lines in two years (i.e., the combined left and the right change area in the latter year relative to the earlier year), while L is length in an earlier year, and y denotes the number of interval years (Figure 4).
Figure 4 Cartoon showing change in area with talweg migration to either the left or right over time
Annual talweg migration rates for the six time periods considered in this study are shown in Figure 5; data for the three successive periods between 1990 and 2001, 2001 and 2013, and 2013 and 2016 are shown in Figure 5a, while Figure 5b shows data for the three longer time periods between 2001 and 2016, 1990 and 2013, and 1990 and 2016.
Figure 5 Changes in area caused by talweg migration within different time periods and the mean annual rate of change within the river reach studied in this paper
Data show that the size of the talweg change area on the left and right changed alternately over the three successive periods. The total change area and the annual change rate initially decreased and then increased, with the smallest values, 0.57 km2 and 3.75 m/yr, recorded between 2001 and 2013, and the largest values, 0.96 km2 and 25.06 m/yr, recorded between 2013 and 2016, respectively. Results also reveal that some parts of the talweg underwent discontinuous change between 2013 and 2016 (Figure 2) which led to a much larger change area and rate.
In contrast, the area of total change was larger over the three longer time periods than that in the three successive periods, and annual rates of change were 6.45 m/yr, 3.37 m/yr, and 4.63 m/yr, respectively. Recorded rates of change were relatively smaller over longer time periods; the talweg rate of change was 3.37 m/yr between 1990 and 2013, the smallest of all periods, but was larger between 1990 and 2016 than between 1990 and 2013 because of the discontinuous change to this line that occurred between 2013 and 2016.
The watershed symmetry index (Rs), the ratio between the right and left side areas of the talweg within a basin, was proposed by Qian et al. (1987) as a proxy for watershed symmetry. Building on this, we propose use of the anastomosing belt symmetry index (SIa) in this study, the ratio between right and left side areas divided by the talweg within an anastomosing belt. The index comprises a dimensionless number and can be used to reflect either the symmetry of an anastomosing belt or trends in the relative migration of the talweg. Thus, when SIa increases, the talweg migrates to the left, while when SIa decreases, the talweg migrates to the right.
The data presented in Figure 6 show that right side area remained consistently greater than left side area divided by the talweg within the river anastomosing belt. Thus, measured values of SIa ranged between 1.59 and 1.70 over the course of this study; SIa increased from 1.69 to 1.70 between 1990 and 2001 which means that the talweg migrated to the left, while because this index decreased from 1.70 to 1.59 between 2001 and 2013, the talweg migrated to the right. In contrast, SIa values increased from 1.59 to 1.65 between 2013 and 2016, indicating that this line migrated to the left. These data accord with the observation that the area of left talweg change was greater, smaller, and greater than that seen on the right over the three successive time periods of this study (Figure 5).
Figure 6 Comparison of symmetry index values for the anastomosing belt in different years

3.3 The influence of talweg migration on interchannel wetlands and river banks

The data presented in Figure 7a show that the talweg migrated to the right between 1990 and 2016, up to a maximum distance of about 270 m. Although the boundaries of the anastomosing belt did not change significantly, associated interchannel wetlands and islands did vary a great deal; as the talweg migrated to the right between 1990 and 2001, island D1 was eroded upstream and deposited downstream, amalgamating with the S1 interchannel wetland. At the same time, the upstream side of island D2 was also eroded but because this corresponded with no obvious downstream side deposition, the whole area was reduced by almost a half. As island D1 was strongly influenced by water flow because of its elevated situation on the talweg curve, sediments in this case were easily blocked by southeastern wetland S1 before being re-deposited.
Observations show that the talweg continuously migrated to the right between 2001 and 2013 causing erosion on the northern side of interchannel wetland S1 and the continuous retreat of the northwestern side of island D1. Erosion also occurred on the upstream side of island D2 over the time period of this study and deposition took place downstream side, with the area of the latter much larger than the former. Similarly, although the upstream side of island D2 only experienced a small amount of erosion between 2001 and 2013, its downstream side was extended about 200 m to the southwest because of sedimentation while the southeastern side of wetland S2 also experienced deposition.
The field data incorporated in this study (Table 2) show that the interchannel wetland to the right of sampling site QP26 is 2 m high and incorporates an uppermost 1 m mud layer and a basal 1 m gravel layer. Field observations show that about 1 m of the southeastern part of the interchannel wetland S2 has been deposited over the last decade, and that because a new island (D3) is developing between wetlands D2 and S2, the channel between the two must have been deposited between 2001 and 2013. Observations also show that the right side of the main channel was relatively higher in the past, and that a gravel bar extended upstream to the north of QP27 (Table 2). A large number of fallen trees within interchannel wetland S2 were also recorded to the west of QP28; this is consistent with the presence of a branching node that diverted more water flow to the right as the talweg migrated in this direction which led to erosion of the right bank of the main channel. The topography downstream of QP28 was also higher in the past which means that less sediments have been transported in this direction than have been deposited due to a backwater effect. At the same time, the water flow is weaker on the downstream side of island D3 because of this backwater effect, which has also led to deposition on both side of QP26; thus, three new islands (D4, D5, and D6) appeared on the left side of the talweg causing its migration to the right and deposition on the side of these new features.
Table 2 The locations of field work sites and the characteristics of columnar sections on the channel banks of the Qihama reach of the anastomosing river in 2016
Site Observation date Latitude Longitude Channel and sediment characteristics
QP25 April 26th 33°22′51″N 102°01′20″E The upper layer of the left main channel bank at this site is composed mainly of fine sand and silt, while the lower layer below 75 cm is gravel.
QP26 April 30th 33°22′33″N 102°00′36″E The width of the right anastomosing channel is 60 m, the water width is 30 m, and the water depth is 1 m at this location. The bank height is 2 m, with 1 m mud layer on the top and 1m gravel layer on the bottom. The mean size of gravel is between 6 cm and 7 cm, ranging up to a maximum of 10 cm.
QP27 April 30th 33°22′43″N 102°00′40″E The main channel width at this site is about 200 m and comprises two gravel bars in the center and one gravel bar adjacent to the right bank which had been eroded about 1 m.
QP28 April 30th 33°22′46″N 102°00′36″E The width of the anastomosing channel adjacent to the main channel at this site is 15 m and an upward extending gravel bar with a maximum width of 30 m is next to the left bank of the main channel. The right bank at this site is about 1.6 m high and has a 1 m mud layer on the top and a 0.6 m gravel layer on its base. A large number of trees on the right bank were fallen, indicating that this right bank was washed back.
In addition, although the talweg significantly migrated to the right between 2013 and 2016, no significant changes were seen in the adjacent interchannel wetlands. This means that it is difficult to erode the channel bank over the short-term process of talweg migration.
The area where the anastomosing belt changed most obviously is shown in Figure 7b. These data show that the right side of the main channel encompasses the S1 interchannel wetlands, while the left side comprises the margin of the anastomosing belt or the bank of the main channel on this side. No anastomosing channel developed on the left concave bank of the main channel while it was subject to strong erosion while its boundary also did not significantly change. Observations show that the maximum migration distance of this bank between 1990 and 2016 was about 130 m, while the annual rate of change was 5 m/yr; similarly, the width of the anastomosing belt within this region was about 2000 m, corresponding with an approximately 0.25% annual rate of change. Although the main bank of this channel has been strongly affected by water flow, its retrogradation rate has nevertheless been very slow, indicating that the margin directly affected by talweg migration is also very stable.
Figure 7 Changes in the talweg, interchannel wetlands, and banks within typical sections of the study river reach

3.4 The evolutionary characteristics of anastomosing channels

Because of the issues inherent to studying the evolution of a single small anastomosing channel using Landsat images that have resolutions of either 15 m or 30 m, two high resolution GE images (0.5 m resolution) for 2011 and 2013 were also utilized in this study to vectorize and analyze the four anastomosing channels (lower right corner of Figure 7).
Changes in the area, length, sinuosity, and mean width of the four anastomosing channels within the river reach studied in this paper between 2011 and 2013 are shown in Figure 8. Data show that the areas of channels 1, 2, and 3 slightly decreased over this time period by 6.57%, 6.06% and 6.38%, respectively, while the area of channel 4 increased by 1.24% (Figure 8a). Similarly, the lengths of channels 1 and 2 also increased slightly (by 1.47% and 1.20%, respectively) while the lengths of channels 3 and 4 decreased slightly (by 0.60% and 0.64%, respectively) (Figure 8b). At the same time, the mean widths of channels 1, 2, and 3 also decreased slightly (by 7.92%, 7.18%, and 5.82%, respectively), while the mean width of channel 4 increased by 1.89% (Figure 8c). The corresponding lateral accretion rates of these four channels were 1 m/yr, 1.5 m/yr, 1 m/yr, and -0.5 m/yr, respectively, while variations in their sinuosity were very small, all rates less than 2.73% (Figure 8d).
Figure 8 Comparison of the four anastomosing channel planforms within the river reach of the study area between 2011 and 2013

4 Discussion

The avulsion model for the formation of anastomosing rivers was summarized in three successive stages by Smith (1989) and Wang (2002) as comprising initial multi- and anastomosing-channelization followed by the development of a regular anastomosing channel. Observations show that the river reach studied here developed during the third of these stages because the entire anastomosing belt is adequately developed, the locations of channels are basically stable, and the ratio between water and land area maintained relatively constant throughout the study period. The total area of the anastomosing belt also increased slightly while interchannel wetlands became fragmented.
The results of this study show that while the talweg migrated alternately to the left and right over time, its rate of change remained relatively stable over a longer period and exerted little influence on the entirety of the anastomosing belt. Indeed, because of the stability of the anastomosing belt, recorded SIa values generally ranged between 1.60 and 1.70; this variation reflects the fact that actual trends in talweg migration are consistent with relative trends. The recorded migration rate of the main channel is also visibly larger than that of the anastomosing ones based on talweg data, a characteristic that is more reminiscent of meandering than anastomosing rivers. Previous studies (e.g., Smith et al., 1989; Mccarthy, 1992; Wang et al., 2004, 2005) have noted that anastomosing rivers form via early channel avulsion; indeed, rivers of this type within the Jingjiang reach of the Yangtze River and within the middle reaches of the Amazon River all developed via an avulsed channel splitting from the meandering river (Wang, 2002; Soares et al., 2010; Rozo et al., 2012). The research presented here on the anastomosing river within the Jingjiang reach of the Yangtze River demonstrates that some anastomosing channels can be very stable and that lateral migrations are not obvious; this contrasts with the main Yangtze River channel that is very unstable and exhibits a lateral migration rate greater than about 30 m/yr (Wang et al., 2005). The mean annual migration rate of the left bank of the meandering-similar main channel reported in this study was less than 5 m/yr, much smaller than that of the Jingjiang meandering channel. At the same time, however, the migration rate of anastomosing channels within the Qihama river reach reported here is almost equal to that seen in the Yangtze where the rate is 1 m/yr (Wang et al., 2005). This suggests that the anastomosing channels within the Qihama river reach are at least as stable as their counterparts within the Yangtze.
The typical sediment characteristics of this river section are epitomized by data from sampling point QP25 on the left bank and sampling point QP27 on the right bar of the main channel (Figure 7). Samples were taken at these points from the surface and at depths every 15 cm at QP25 and every10 cm at QP27 and show that sediments from below a depth of 75 cm in QP25 and 120 cm in QP27 are gravel layers (Figure 9). Thus, comparing the data presented in Figures 9a and 9b, it is clear that the sediments that comprise the bar and the bank of this channel are mainly composed of fine sand and silt, while the clay content is high and there is a multi-peak grain-size distribution curve. The mean clay content at these two sampling sites is about 10%, although the value (14.90%) at QP27 is higher than that at QP25 (8.01%) and there is also a clear difference in sand content. Similarly, the mean fine sand content (50.64%) is higher than the silt content (34.68%) in sample QP25, while the mean silt content (53.97%) is higher than the fine sand content (29.67%) in sample QP27, and mean coarse sand content (10.92%) is higher in QP25 but much smaller (1.40%) in QP27. These data show that the sediment characteristics of the channel bank and the bar are similar, but the materials within the latter are finer because of the deposition of suspended sediment.
Figure 9 Percentage distribution curves for different grain sizes within the bank columnar sections QP25 (a) and QP27 (b)
The data presented in this paper show that while the riverbed within anastomosing channels consists of gravel, sediments on top are mainly silt and mud, a minor difference from the clay that makes up sand-bedded anastomosing channels, including those within the Yangtze River. The presence of dense vegetation within riparian and interchannel wetlands protects these anastomosing channel banks from erosion, and maintains their stability. Thus, the high lateral migration rate that characterizes the main channel is the result of strong stream power and the relatively lower cohesiveness of bank sediments. It is also the case, however, that many of these anastomosing channels remain in active for some months of the year or even operate at a low flow rate; combined with a narrow channel and vegetation-covered midchannel wetlands, this results in high stability and limited lateral migration. Although the crust within the study area is the result of tectonic uplift, anastomosing reach is nevertheless in subsidence relative to the surrounding high ground, and generally illustrates that the main channel is slightly eroded surrounding anastomosing channels and interchannel wetlands are more obviously the result of deposited. It is noteworthy that Makaske et al. (2009) noted in earlier work that the anastomosing section in the upper reaches of the Columbia River formed via avulsion due to river bed sedimentation. The gravel-bedded anastomosing river studied in this paper also exhibits a number of similarities to sandy-bedded rivers of this type in terms of channel planforms and stability. However, an increase in the number of interchannel wetlands with time indicates that some small new channels formed within individual midchannel wetlands via the avulsion of old channels; this observation, combined with hydrodynamic conditions and sedimentary characteristics, highlight clear differences from sandy-bedded anastomosing rivers. Further research will therefore be required to determine the specific processes that led to the formation of this river channel.

5 Conclusions

A number of clear conclusions regarding the characteristics and evolution of the gravel-bedded anastomosing river within the Qihama reach of the First Great Bend of the Yellow River over the last 26 years can be presented based on the channel planform and sediment composition analyses presented in this paper.
(1) Gravel-bedded anastomosing channels tend to exhibit a high degree of stability. Data show that over the last 26 years, the area of the anastomosing belt of this river channel has increased from 16.89 km2 to 17.30 km2, an annual rate of increase of 2.43%, while the ratio of land to water area has remained almost equal. At the same time, the number of interchannel wetlands that comprise small areas between ​​0.1 km2 and 0.8 km2 has markedly increased, at a rate as high as 62.16%. Although this anastomosing belt fragmented over time, changes in the areas of larger interchannel wetlands were not obvious.
(2) The main channel talweg migrated alternately to the left or right over the time period of this study, at a rate that remained relatively stable. Data show, however, that the trend in talweg migration remained consistent with the actual trend at least on the basis of SIa changes. Indeed, because of the influence of talweg migration, large changes to the islands within the main channel have been seen while the maximum annual change rate of the outer bank has remained around 5 m/yr, similar to the characteristics of a meandering river. The numerous anastomosing channels have remained very stable with a mean annual migration rate about 1 m/yr.
(3) The surface sediments that comprise midchannel bars and river banks are mainly fine sands and silts. These sediments have a relatively high clay content (about 10%) and exhibit a multi-peak grain-size distribution curve. At the same time, gravel makes up the beds of anastomosing channels, a significant difference from sand-bedded rivers of this type. Bank sediments, however, are mainly silt and clay, another slight difference from the clay banks of sand-bedded anastomosing rivers, while the presence of dense vegetation on riparian and interchannel wetlands protects these anastomosing channels from erosion and maintains their stability. These sediments are also an important factor contributing to the high stability of this gravel-bedded anastomosing river system.

The authors have declared that no competing interests exist.

References

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Knighton A D, Nanson G C, 1993. Anastomosis and the continuum of channel pattern.Earth Surface Processes and Landforms, 18(7): 613-625.Anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain. Their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables - flow strength, bank erodibility and relative sediment supply. Using an ordinal scaling (L(ow)-M(oderate)-H(igh)), the traditional forms of straight, meandering and braided have respective representations of (L,L,L), (M,L/M,L/M) and (H,H,M/H) in terms of those variables. The anastomosing pattern is on average represented by (L,L,M/H) but not so definitively as other forms. Specification of the third element (sediment supply) is particularly hampered by the paucity of data but aggradation, a characteristic of many anastomosing rivers, can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport. A sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and/or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches. A flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity. Anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems.

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Li Z, Wang Z, Yu Guoan et al., 2013. River pattern transition and its causes along the Maqu reach of the Yellow River source region. Journal of Sediment Research, (3): 51-58. (in Chinese)The river channel of the Yellow River source region near Maqu County is a special alluvial plain channel,which continuously appears anastomosing river,anabranching river,meandering river and braided river,occuring 4 times of river pattern spatial transition phenomena in 270 km long flowing distance.Based on remote sensing images and 2011-2012 field investigation,the river pattern diversity and the basic feature of Maqu river channel are described,and the causes of river pattern spatial transition phenomena are analyzed simultaneously.It is distinct that the river pattern transition of Maqu channel happens four times,which are anastomosing-anabranching,anastomosing-meandering,meandering-braided and braided-meandering transition.The causes of anastomosing-anabranching transition are landform control,sand bars formation by sediment deposit and vegetation growth.The causes of anastomosing-meandering transition are landform control,channel slope changing from high to low and the longitudinal river bank sediment grain becoming finer.The causes of meandering-braided transition are the Baihe River confluence and channel slope changing from low to high.The causes of braided-meandering transition are the river incision of downstream valley and the Heihe River confluence.

[6]
Liu B, Wang S, 2017. Planform characteristics and developing of interchannel wetlands in a gravel-bed anastomosing river, Maqu reach of the Upper Yellow River.Journal of Geographical Sciences, 27(11): 1376-1388.Both interchannel wetlands and multi-channels are crucial geomorphologic units in an anastomosing river system. Planform characteristics and development of interchannel wetlands and multi-channels control the characteristics of anastomosing rivers. To understand the role that interchannel wetlands play in the development of anastomosing rivers, a study was conducted on the Maqu Reach of the Upper Yellow River (MRUYR), a gravel-bed anastomosing river characterized by highly developed interchannel wetlands and anabranches. Geomorphologic units in the studied reach were extracted from high resolution satellite imagery in Google Earth. The size distributions of interchannel wetlands and interchannel wetland clusters (IWCs), a special combination of interchannel wetlands and anabranches, were investigated. Geomorphologic parameters, including the ratio of interchannel wetland area to IWC area (P), shoreline density (D l ), and node density (D n ) were used to analyze planform characteristics of IWCs and the development of multi-channels in the studied reach. The results suggest that small or middle sized interchannel wetlands and large or mega sized IWCs are more common at the study site. The area of IWC (S u ) is highly correlated with other geomorphologic parameters. P increases with increasing S u , and the upper limit is about 80%, which indicates that the development of interchannel wetlands and anabranches in the IWC is in the equilibrium stage. In contrast, D l and D n show a tendency to decrease with increasing S u due to diverse evolution processes in IWCs with different sizes. There are three main reasons leading to the formation of IWCs: varying stream power due to the meandering principal channel; development of the river corridor due to the weakening of geologic structure control; and high stability of interchannel wetlands due to conservation by shoreline vegetation.

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[7]
Makaske B, 2001. Anastomosing rivers: A review of their classification, origin and sedimentary products.Earth Science Reviews, 53(3/4): 149-196.Anastomosing rivers constitute an important category of multi-channel rivers on alluvial plains. Most often they seem to form under relatively low-energetic conditions near a (local) base level. It appears to be impossible to define anastomosing rivers unambiguously on the basis of channel planform only. Therefore, the following definition, which couples floodplain geomorphology and channel pattern, is proposed in this paper: an anastomosing river is composed of two or more interconnected channels that enclose floodbasins. This definition explicitly excludes the phenomenon of channel splitting by convex-up bar-like forms that characterize braided channels. In present definitions of anastomosing rivers, lateral stability of channels is commonly coupled with their multi-channel character. Here, it is suggested that these two properties be uncoupled. At the scale of channel belts, the terms ‘straight’, ‘meandering’ and ‘braided’ apply, whereas at a larger scale, a river can be called anastomosing if it meets the definition given above. This means that, straight, meandering and braided channels may all be part of an anastomosing river system. Straight channels are defined by a sinuosity index; i.e., the ratio of the distance along the channel and the distance along the channel-belt axis is less than 1.3. They are the type of channel that most commonly occurs in combination with anastomosis. The occurrence of straight channels is favoured by low stream power, basically a product of discharge and gradient, and erosion-resistant banks. Anastomosing rivers are usually formed by avulsions, i.e., flow diversions that cause the formation of new channels on the floodplain. As a product of avulsion, anastomosing rivers essentially form in two ways: (1) by formation of bypasses, while bypassed older channel-belt segments remain active for some period; and (2) by splitting of the diverted avulsive flow, leading to contemporaneous scour of multiple channels on the floodplain. Both genetic types of anastomosis may coexist in one river system, but whereas the first may be a long-lived floodplain-wide phenomenon, the latter only represents a stage in the avulsion process on a restricted part of the floodplain. Long-lived anastomosis is caused by frequent avulsions and/or slow abandonment of old channels. Avulsions are primarily driven by aggradation of the channel belt and/or loss of channel capacity by in-channel deposition. Both processes are favoured by a low floodplain gradient. Also of influence are a number of avulsion triggers such as extreme floods, log and ice jams, and in-channel aeolian dunes. Although some of these triggers are associated with a specific climate, the occurrence of anastomosis is not. A rapid rise of base level is conductive to anastomosis, but is not a necessary condition. Anastomosing rivers can be considered an example of equifinality, since anastomosis may result from different combinations of processes or causes. Anastomosing river deposits have an alluvial architecture characterized by a large proportion of overbank deposits, which encase laterally connected channel sand bodies. Laterally extensive, thick lenses of lithologically heterogeneous, fine-grained avulsion deposits can be an important element of the overbank deposits of anastomosing rivers. These deposits may also fully surround anastomosing channel sandstones. Anastomosing channel sand bodies frequently have ribbon-like geometries and may possess poorly developed upward-fining trends, as well as abrupt flat tops. The overbank deposits commonly comprise abundant crevasse splay deposits and thick natural levee deposits. Lacustrine deposits and coal are common in association with anastomosing river deposits. None of these characteristics is unique to anastomosing river deposits, and in most cases, anastomosis (coexistence of channels) cannot be demonstrated in the stratigraphic record.

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[8]
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[10]
Murray A B, Paola C, 1994. A cellular model of braided rivers.Nature, 371(6492): 54-57.A BROAD sheet of water flowing over non-cohesive sediment typically breaks up into a network of interconnected channels called a braided stream (Fig. 1). The dynamics of such networks are complex; channels migrate laterally, split, rejoin and develop bars, with the flow shifting unpredictably from one part of the network to another. Many processes are known to operate in a braided river 1 3 , but it is unclear which of these are essential to explain the observed dynamics. We describe here a simple, deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers. The patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge. Although the morphology of the resulting network depends in detail on the sediment-transport rule used in the model, our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free-surface flow.

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Murray A B, Paola C, 2015. Properties of a cellular braided-stream model.Earth Surface Processes and Landforms, 22(11): 1001-1025.

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Rozo M G, Nogueira A C R, Truckenbrodt W, 2012. The anastomosing pattern and the extensively distributed scroll bars in the middle Amazon River.Earth Surface Processes and Landforms, 37(14): 1471-1488.Abstract The middle Amazon River, between the confluences of the Negro and Madeira Rivers in Brazil, shows an anastomosing morphology with relatively stable, multiple interconnected channels that locally enclose floodbasins. Additionally, this system is characterized by sinuous secondary channels with meander development, discontinuous natural levees concentrated on the concave banks and extensively distributed scroll bars mainly in the islands, related to subrecent and present‐day migration of mainly secondary channels. This distinguishes the Amazon from many other anastomosing rivers that have laterally stable, non‐meandering channels. We analyzed sedimentary processes using field data, morphology and channel changes trough a temporal analysis using remote sensing data and obtained optically stimulated luminescence (OSL) dating to understand the genesis of this large anastomosing river and the development of its meandering secondary channels. Scroll bars have developed in a multichannel river system at least since 7.5 ± 0.85 ka. Avulsion is inferred to have played a minor role in the formation of this anastomosing system, with only one documented case while mid‐channel bar formation and chute cut‐offs of the main and secondary channels are the main formative mechanisms of anastomosis in this system. Differences in resistance to erosion control the relatively straight main channel and allow secondary channels to develop a meandering platform. Vegetation contributes to the relative stability of islands and the floodplain. Low gradient and high average aggradation rate (1.1 mm yr611) are conditions which favor the development of anastomosis. Additionally, stable external conditions, low abandonment rate of older channels and independence from high avulsion frequency suggest a long‐lived, semi‐static type of anastomosing river in this reach of the Amazon. Copyright 08 2012 John Wiley & Sons, Ltd.

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[14]
Rust B R, 1978. A classification of alluvial channel systems. In: Miall A D. Fluvial Sedimentology. Canada Calgary: Canadian Society of Petroleum Geologists, 187-198.

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[19]
Shi C, Wu B, Ma J, 2007a. Cause of formation and discrimination of channel patterns for alluvial rivers.Journal of Hydroelectric Engineering, 26(5): 107-111. (in Chinese)The analysis presented in this paper indicates that there is a correspondence relationship between the equilibrium degree of sediment transport and the complete channel characteristics.The classification and discrimination of river types are based on the complete channel characteristics,the formation of river types is based on the equilibrium degree of sediment transport.The channel patterns formed in alluvial rivers lie in the variable equilibrium degrees of sediment transport.A dimensionless parameter is derived based on theoretical formulas that describe the flow,sediment and riverbed conditions by strong equilibrium sediment transport.This dimensionless parameter is viewed as the channel stability parameter,based on which a channel pattern discrimination procedure is developed.Test of the procedure in the lower Yellow River and the Wei river indicates that the computation results are consistent with the field observations and the fuzzy cluster method is applicable in practical use.

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[20]
Shi C, Wu B, Ma J, 2007b. Classification and discrimination of channel patterns in the Lower Yellow River.Journal of Sediment Research, (4): 53-58. (in Chinese)In this paper,a method for the classification and discrimination of channel patterns for the Lower Yellow River was developed by using fuzzy cluster and discrimination analysis.The calculations were carried out based on a stability function that was derived from theoretical formulations of mechanics of sediment transport,fluvial processes,and strong equilibrium sediment transport for alluvial rivers.The calculated results using 11 years' data of the Lower Yellow River indicate that the proposed method can be used for the analysis and prediction of channel patterns in the Lower Yellow River after the use of Xiaolangdi reservoir.Moreover,the proposed method is of importance for the classification and discrimination of channel patterns of other alluvial rivers.

[21]
Shi C, Wu B, Ma J, 2009. Natural classification of river patterns based on clustering method with fuzzy equivalent matrices.Journal of Hydroelectric Engineering, 28(5): 215-220. (in Chinese)This paper assumes that any set of river patterns can be considered as a fuzzy river set and that the relation between river patterns is a fuzzy relation.From this concept,a method for natural classificaiton of river patterns based on clustering method with fuzzy equivalent matrices is proposed.The method is based on the hypothesis and formula of equilibrium degree of sediment transport for the alluvial river patterns.Test based on 20 years' data of the Yellow River show that the channel patterns can be well distinguished and predicted by the proposed method.The clustering results can effectively reveal the relation and difference between river patterns.

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[22]
Smith D G, 1983. Anastomosed fluvial deposits: Modern examples from western Canada.Modern and Ancient Fluvial Systems, 155-168.Summary Facies of two Canadian modern anastomosing river systems are discussed, the upper Columbia and lower Saskatchewan Rivers, which occur in intermontane and plains settings respectively. Both systems contain aggrading, multiple, low gradient, sand bed channels with adjacent splay, levée, and shallow wetland environments, all aggrading in accordance with channel sedimentation. While aggrading cross-valley alluvial fans or subsidence tend to control sedimentation rates in intermontane valleys, basin subsidence and/or regional tilting controls deposition rates in plains settings. Sedimentation style in the upper Columbia River valley (120 × 1·5 km) consists of low-sinuosity, stable channels, depositing multi-storied channel sands and numerous sandy crevasse splay deposits. Channel deposits form as sand stringers laterally contained by deposits of levée silt and lacustrine mud. Aggrading at an average rate of 60 cm per 100 years over the past 2500 years, the anastomosing system is very dynamic, exhibiting avulsions and channel fills. Deposition in the lower Saskatchewan River valley (120 × 80 km) a much wider basin with slower aggradation rates (29 cm 100 yr 611 , C-14 date on peat buried beneath a levée) results in laterally extensive sheets of overbank levée deposits of fine sand which grade into even more laterally extensive thick deposits of peat. With time, some dominant channels become highly sinuous, thus causing increased flow resistance, major avulsions upriver and eventual channel filling and abandonment. Facies differences of the two anastomosed river systems are believed to be caused by both the rate of sedimentation and width of the sedimentary basin.

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[23]
Smith D G, Putnam P E, 1980. Anastomosed river deposits: Modern and ancient examples in Alberta, Canada.Canadian Journal of Earth Sciences, 17(10): 1396-1406.ABSTRACT The anastomosed fluvial system is proposed as an environment of deposition for some over-bank deposits, coal, and coarse channel sediments (sandstone and conglomerate) in the Rocky Mountain molasse (Mesozoic ertiary) of Alberta and British Columbia. The system consists of rapidly aggrading channels and adjacent wetlands, caused by a rising local base level downriver (i.e., alluvial fans) or basin subsidence. Multiple, multi-storied anastomosed channel deposits generally have low gradients, variable sinuosities, and low width/depth ratios.Anastomosed fluvial facies are similar to some river-dominated low energy deltaic facies; therefore, many of the deposits and facies geometries are similar. Similarity occurs because the fluvial processes and morphologies are similar. For example, as with lower deltaic plains, stable anastomosed channels are related to gentle gradients and high amounts of silt, clay, and vegetation in the banks. Channel stability subsequently accounts for a stable deposition environment favourable for the accumulation of organic material. Wetland environments cover the largest area (estimated 60 90%) of anastomosed systems, while channels, levees, and crevasse splays are minor in extent.Modern and ancient examples of anastomosis are described to provide a basic depositional framework. The lower reach (valley fill) of the modern Alexandra River in Banff Park is the modern example described. In east-central Alberta and southwest Saskatchewan, the hydrocarbon-bearing channel sandstones of the upper Mannville subgroup (Vigrass) are interpreted as an ancient (Lower Cretaceous) anastomosed system of very large scale (80 km 300 km).We believe that the interpretation of environments of deposition in some ancient fluvial sequences of molasse deposits has been limited. This is due to the fact that anastomosed systems have only recently been understood as a unique fluvial style related to specific causal conditions. We suggest that the rapid subsidence along the western margin of the molasse foreland, coupled with high sediment loads from nearby mountain building (i.e., Rocky Mountains), would represent suitable conditions for anastomosis as well as graded meandering or aggrading braided fluvial styles. These same conditions would also apply to molasse deposition in intermontane basins.

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[24]
Smith D G, Smith N D, 1980. Sedimentation in anastomosed river systems: Examples from alluvial valleys near Banff, Alberta.Journal of Sedimentary Research, 50(1): 157-164.ABSTRACT 3 anastomosed river systems are described. Each reach consists of an interconnected network of low-slope, narrow and deep, straight to sinuous, stable channels that transport coarse sand and gravel. Channels are separated by levees and wetlands composed of silt/mud and vegetation. Gravel-bed braided channels occur upstream from each anastomosed system, joined by a transitional reach comprising stable, elongate, silt islands within braided channels. The 3 anastomosed reaches have formed upstream from elevating base levels caused by deposition of alluvial fans across trunk valleys. -from Authors

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[25]
Smith N D, Cross T A, Dufficy J P et al., 1989. Anatomy of an avulsion.Sedimentology, 36(1): 1-23.

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Soares E A A, Tatumi S H, Riccomini C, 2010. OSL age determinations of Pleistocene fluvial deposits in central Amazonia.Anais Da Academia Brasileira De Ciências, 82(82): 691-699.

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[27]
Thomas R, Nicholas A P, 2002. Simulation of braided river flow using a new cellular routing scheme.Geomorphology, 43(3-4): 179-195.Results are presented from a numerical simulation of two-dimensional flow patterns in a braided river using a simple cellular routing scheme. The results of the routing scheme are compared with field measurements of discharge per unit width obtained within the study reach at low flow and, for higher flows, with the predictions of a more sophisticated hydraulic model that solves the two-dimensional shallow water form of the Navier tokes equations. An assessment is made of the sensitivity of the routing scheme to variations in the values of its main parameters, and appropriate values are determined based on the physical characteristics of the study site and available flow measurements. It is shown that despite the simple approach adopted by the cellular routing scheme to simulate processes of water redistribution, it is able to replicate accurately both the field data and the results of the more sophisticated hydraulic model. These results indicate that the routing scheme outlined here is able to overcome some of the limitations of previous simple cellular automata models and may be suitable for use in modelling bedload transport and channel change in complex fluvial environments. As such this research represents a small and ongoing contribution to the field of numerical simulation of braided river processes.

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[28]
Tornqvist T E, 1993. Holocene alternation of meandering and anastomosing fluvial systems in the Rhine-Meuse delta (central Netherlands) controlled by sea-level rise and subsoil erodibility.Journal of Sedimentary Research, 63(4): 683-693.

[29]
Udden J A, 1914. Mechanical composition of clastic sediments.Geological Society of America Bulletin, 25(1): 655-744.Not Available

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[30]
Wang P, 1990. A fuzzy mathematical method on the classification of river patterns.Journal of Chengdu University of Science and Technology, (1): 83-93. (in Chinese)

[31]
Wang S, 2002. Comparison of formation model and channel stability between two different sorts of multiple channel river patterns.Acta Geoscientia Sinica, 23(1): 89-93. (in Chinese)In multiple channel rivers, anastomosing rivers as a new river pattern differing from anabranched and braided rivers have aroused much attention. Nevertheless, the difference between the anabranched and the anastomosing rivers is frequently ignored. Some researchers even think that they are of the same channel pattern according to channel planform. To explain their fundamental differences, this paper focuses on the multiple channel formation models of the two river patterns. Based on the study of the anabranched channel reach of Lower Changjiang River and the anastomosing Jingjiang distributaries, it is held that the anabranched multiple channel forms with appearance of one or more mid channel lands, which have two layers of sediments whose grains are thin and fine in the upper part and thick and coarse in the lower part, whereas the anastomosing multiple channel forms with appearance of one or more stable channels on the floodplain surrounded by coherent fine grained sediments. Anastomosing multiple channels show higher stability than anabranched ones.

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[32]
Wang S, 2008. Analysis of river pattern transformations in the Yellow River basin.Progress in Geography, 27(2): 10-17. (in Chinese)The Yellow River is famous in the world because of its high-concentrated flow and high sedimentary rate on the channel bed of the lower reach.The study on the Yellow River,hereinto,is mainly on erosion,hydrology,sediment delivery and channel bed evolution in the middle-lower reaches.It has not been sufficient to pay attention to the river pattern transformations in the main or tributary channels of the Yellow River.Frequent,various and complicated transformations of river patterns in different reaches of the Yellow River are scientific problems which cannot be blench for researchers.This study focuses on the river pattern transformations and their influence factors in the selected river reaches: Maqu reach,the first curve in the upper reach,Tuoketuo reach in the end of the upper reach,and Gaocun reach in the lower reach of the Yellow River.The river pattern transformations in the Maqu reach show changes from anastomosing to meandering and from meandering to braiding.The series transformations present a tend from very stable to very unstable channel patterns that is reverse to the normal trend from unstable to stable channel patterns in the world.These transformations are influenced by crustal rise,restriction of the gorges in upper and lower reaches,hydrodynamic characteristics,sediment characteristics of channel boundary and regional distribution of vegetation cover.The river pattern transformations in the Tuoketuo reach show changes from meandering to straight.That is the transformation from relative stable to very stable channel patterns.It is mainly influenced by the sediment characteristics of channel boundary and hydrodynamic characteristics.The river pattern transformations in the Gaocun reach show changes from braiding to meandering channel patterns.It presents a trend from very unstable to relative stable channel patterns.It is mainly influenced by the sediment characteristics of channel boundary and hydrodynamic characteristics.The artificial levees only restrict the maximum range of the lateral migration of the channel but not influence the channel pattern.The reservoirs built in the upper reach of the braiding reach lead to increase of river flow erosion and sediment coarsening in the braiding channel reach,contemporarily,resulting in a great deal of fine muddy sediments deposit in the meandering channel reach.Obviously,the reservoirs facilitate the river pattern transformation.

[33]
Wang S, Chen Z, Smith D G, 2005. Anastomosing river system along the subsiding middle Yangtze River basin, southern China.Catena, 60(2): 147-163.The study focuses on the formation processes of the uprivermost (Jingjiang reach) of three anastomosing river reaches along the middle Yangtze River, downstream of the Three Gorges Dam site and 1700 km upriver from the seacoast at Shanghai in southern China. The Jingjiang reach consists of large anastomosing channels: the Songzi, Hudu, Anxiang and Ouchi rivers, which depart from the Yangtze trunk channel and flow southward and southeastward up to 200 km into the Dongting basin and lake; the lake rejoins the Yangtze at Chenglingji. The 7000 km anastomosing reach is characterized by multiple, stable, low gradient channels (0.00004 m/m, 4 cm/km), with low width/depth ratios () with very high sedimentation rates (33.5 123.3 mm/year) in some channels. Tectonic subsidence, caused by the Himalayan Orogeny, is thought to be the primary forcing mechanism in causing the anastomosing channel processes and deposition.Historical documents have shown that the Jingjiang channels were caused by repetitive avulsions southward from the Yangtze channel. The earliest recorded avulsion occurred in a high flood period before 1644, and subsequent avulsions have continued to modify the topography. Three major avulsion channels have diverted 14 33% of the discharge and 17 47% of suspended sediment load from the Yangtze channel. These channels have remained laterally stable, a characteristic of anastomosing rivers due to their low gradient, silt-clay banks, densely vegetated natural levees and stable interchannel islands consisting of clayey-silt that supports dense riparian vegetation. Data derived from hydrological gauging stations over the last 45 years demonstrate that total discharge and sediment load of anastomosing channels has decreased by two thirds, largely due to sediment aggradation on channel beds. Reduced sediment load and discharge, and human-caused channel modification were more pronounced in the eastern channels.With the completion of the 3-Gorges Dam in 2009, the anastomosing channels will cease to carry significant quantities of water and sediment to maintain fluvial vigor. In the next 100 years, the Yangtze main channel may become the only active channel as the anastomosing channels slowly will be infilled.

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[34]
Wang S, Li J, Yin S, 1999. Basic characteristics and controlling factors of anastomosing fluvial systems.Scientia Geographica Sinica, 19(5): 422-427. (in Chinese)Although anastomosing fluvial rivers are given much attention recently by some research workers because the result channel sandstone of which is one typical primary reservoirs of petroleum and natural gas, of which the flood plains and the interchannel wetlands are pay zones where coals had formed, the comprehension of anastomosing river is some extent limited at present. Some researchers regard that the anastomosing river river and the anabranched river are the same kind of rivers. In this paper, the sedimentary, geomorphic and hydraulic characteristics and the main controlling factors of anastomosing fluvial system are summarized systematically. Some of the characteristics are compared with others fluvial rivers. Humid climate is suitable to form anastomosing channel systems, in arid semiarid regions anastomosing river maybe develop if many befitting factors combine together. The authors of the paper think that anastomosing river is one typical channel pattern and is dissimilar to anabranched channel pattern.

DOI

[35]
Wang S, Li L, Cheng W, 2014. Variations of bank shift rates along the Yinchuan Plain Reach of the Yellow River and their influence factors.Journal of Geographical Sciences, 24(4): 703-716.It is important to examine the lateral shift rate variation of river banks in different periods. One of the challenges in this regard is how to obtain the shift rate of river banks, as gauging stations are deficient for the study of river reaches. The present study selected the Yinchuan Plain reach of the Yellow River with a length of 196 km as a case study, and searched each point of intersection of 153 cross-sections(interval between two adjacent cross-sections was 1.3 km) and river banks in 1975, 1990, 2010 and 2011, which were plotted according to remote sensing images in those years. Then the shift rates for the points of intersection during 1975–1990, 1990–2010 and 2010–2011 were calculated, as well as the average shift rates for different sections and different periods. The results show that the left bank of the river reach shifts mostly to the right, with the average shift rates being 36.5 m/a, 27.8 m/a and 61.5 m/a in the three periods, respectively. Contemporarily, the right bank shifts mostly to the right in the first period, while it shifts to the left in the second and third periods, with the average shift rates being 31.7 m/a, 23.1 m/a and 50.8 m/a in the three periods, respectively. The average shift rates for the left and right banks during the period 1975–2011 are 22.3 m/a and 14.8 m/a, respectively. The bank shift rates for sections A, B and C are different. The shift rate ratio of the left bank in the three sections is 1:7.6:4.6 for shift to the left and 1:1.7:3.8 for shift to the right, while that of the right bank is 1:1.8:1.2 for shift to the left and 1:5.6:17.7 for shift to the right during the period 1975–2011. Obviously, the average shift rate is the least in section A, while it is maximum in section B for shift to the left and in section C for shift to the right. The temporal variation of the shift rate is influenced by human activities, while the spatial variation is controlled by the local difference in bank materials.

DOI

[36]
Wang S, Mei Y, 2016. Lateral erosion/accretion area and shrinkage rate of the Linhe reach braided channel of the Yellow River between 1977 and 2014.Journal of Geographical Sciences, 26(11): 1579-1592.Quantitative studies on river channel lateral erosion/accretion area changes over time can reveal the characteristics of channel evolution. Taking the 213-km-long Linhe reach braided channel of the Yellow River as an example, area changes in channel bank erosion/accretion in four sub-reaches (S1, S2, S3 and S4) over 19 different periods were evaluated on the basis of remote sensing images captured since 1977. Mean channel shrinkage rate for the whole river reach was also obtained. Results show that the left and right banks of the Linhe reach were dominated by lateral net accretion between 1977 and 2014. The channel area of this section of the Yellow River was characterized by reduction between 1977 and 2001, while periods of alternate erosion and accretion occurred subsequent to 2001. Mean channel shrinkage rate in the Linhe reach braided channel was 6.15 km 2 /yr between 1977 and 2014, while the most remarkable changes in channel planform occurred in the 1990s. Compared to 1995, channel length and sinuosity increased by 5.8% and 6.6% by 2000, while channel area and mean width decreased by 39.4% and 42.8%, respectively. Significant changes in channel planform and shrinkage of the Linhe reach occurred in the 1990s, mainly as a result of the joint-operation of the Longyangxia and Liujiaxia reservoirs since 1986, which caused substantial reductions in runoff and sediment flux during the annual flooding season. In addition, bank erosion/accretion in the four sub-reaches was affected by the physical properties of local banks, engineering emplaced to protect channel banks, and hydrodynamic differences. However, since the implementation of integrated river management measures from 2000 onwards, these changes have been significantly mitigated and the health of the Linhe reach braided channel of the Yellow River has been restored.

DOI

[37]
Wang S, Ni J, Wang G et al., 2004. Hydrological processes of an anastomosing river system on the Zhujiang River Delta, China.Journal of Coastal Research, 124-133.The interconnected channels of the Xijiang and Beijiang rivers on the Zhujiang River delta and the flood basins surrounded by the channels form an anastomosing river system. The system can be divided into three zones (A, B and C) that are influenced mainly by river current, tidal current or both. To reveal the differences and the similarities between the two rivers and among the three zones in the system, six representative gauging stations were chosen to collect relevant data, such as the stream mean velocity, discharge, width, suspended sediment concentration, water level elevation and the width/depth ratio (W:D). Statistical relationships between these parameters were established. Although the planforms of both rivers on the delta show multiple channels, there are some differences in hydrological processes and channel morphology between the two rivers and among the three zones. The Xijiang channels are more efficient in hydraulic geometry than the Beijiang channels especially in Zone A. In Zone A, the channel W:D of the Beijiang River (about 80) exceeds 40 (the upper limit for an anastomosing river), but the Xijiang River W:D (30.4) is in the range. In zones B and C, the W:D of both rivers is in the range for an anastomosing river pattern. The channel gradient of the Xijiang River is lower than that of the Beijiang. The formation of the anastomosing system, and the differences between the two rivers and among the various channel reaches resulted from river self-adjustment; in this case human activities are not a factor.

[38]
Wang S, Ren M, 1999. A new classification of fluvial rivers according to channel planform and sediment characteristics.Acta Sedimentologica Sinica, 17(2): 240-246. (in Chinese)Key Words】：

[39]
Wang S, Xie X, Cheng D, 2002. The progress in the research of anastomosing river.Progress in Geography, 21(5): 440-449. (in Chinese)Anastomosing river, as a new fluvial river pattern, has attracted more and more attention of geomorphologists, hydraulic engineers and sedimentologists. Research on anastomosing river is in great demand of the geomorphology, hydraulic engineering and sedimentology. In this paper, after introduction of the basic concept of anastomosing river, the channel plantform and boundary condition, sedimentary characteristics, hydraulic condition of this river pattern are reviewed based on comprehensive references. Furthermore, in the same fluvial system the spatial transformation between anastomosing and another river patterns is also discussed. Some weaknesses and aspects needing more attention on study of anastomosing river are pointed out. These aspects are mainly following. (a) The dynamical mechanism of the avulsion for anastomosing river formation has not studied clearly till now. It needs theoretical explanation and simulation in laboratory or digital model. Obviously, there have some difficulties. (b) The hydraulic dynamics of anastomosing rivers are still unclear because few study has been actualized on fluvial dynamics for multiple channel rivers, especially for anastomosing rivers. Besides, the hydraulic characteristics have some differences between multiple channels. The explanation to every channel of an anastomosing river system is not the same always. The stream power (including gross stream power and specific stream power) is also different between different channels of an anastomosing river system. (c) The scatter values of channel slope and bankfull discharge for anastomosing rivers have not a clear law. One of the causes is that the river number studied fully by researchers is few and distributed in different climate zones. This demands researchers to study much more anastomosing rivers.

DOI

[40]
Wang S, Yin S, 2000. Discussion on channel patterns of anastomosing and anabranched rivers.Earth Science Frontiers, (s2): 79-86. (in Chinese)According to channel planforms in the world,there are many classification schemes of fluvial rivers in which the scheme proposed by Rust (1978) received extensive attention from many sedimentologists because one of its river types is classied as the anastomosing. While hydrologists and geomorphologists pay more attention to the classification scheme derived by Qian Ning (1987) because one of its river types is noticed as the anabranched. The two classification schemes were considered actually as one type by many researchers. Whether the anastomosing and the anabranched rivers belong to the same type of channel patterns is still questionable. In this paper some characteristics, such as definitions, channel planforms, interchannel subdeposits, hydraulics, formation mechanisms of a new channel and geomorphological location, etc. of the anastomosing and the anabranched rivers are compared. It is concluded that the type of the anastomosing river is different from that of the anabranched one. So for the sake of convenience to exchange the achievements in river research among sedimentologists, hydrologists and geomorphologists, a new classification scheme of fluvial rivers is possibly required.

[41]
Wentworth C K, 1922. A scale of grade and class terms for clastic sediments.The Journal of Geology, 30(5): 377-392.

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[42]
Xu X, Shi C, 2009. Analysis on basis and mathematical method of channel classification of alluvial river.Journal of Yellow River Conservancy Technical Institute, 21(1): 7-9. (in Chinese)The different classifications of channel bring a lot of inconvenience to study it.Based on the dynamics of river,basic theory of fluvial process and mathematics,with the forming reasons of river channel to classify the channel and explain the principle of the fluvial process.Because of the fuzziness feature of channel classification problem,the channel classification problem should be studied by the fuzzy mathematics method.

[43]
Yan M, Wang S, Yan Y et al., 2013. Planar changes of upper alluvial reaches of the Yellow River in recent thirty years.Journal of Arid Land Resources and Environment, 27(3): 74-79. (in Chinese)Based on the data of remote-sensing images,geomorphologic and geologic maps and hydrological data,the Ningxia-Inner Mongolia reaches is divided into four sections.According to planar characteristics,four sections are corresponding to compound of wandering river pattern and branching river,nearly straight river,braided river and meandering river.Comparison of river channel planform from 1978 to 2010 showed that change of river channel width and mainstream length were not monotone increasing or decreasing.As for river mainstream,the mainstream length of branching and nearly straight river had a little change,wandering river reach was decreased in earlier stage and then gradually increased,meandering channel was increased gradually.With respect to river average width,nearly straight river and sinuosity river were firstly widening and then narrowing,process of wandering river width was opposite,only branching river was narrowing gradually.Central shoal quantity changes of different river channel pattern could be divided into two types: one had a little change including Shizuishan-Bayangaole and Sanhuhekou-Toudaoguai;the other one was increasing firstly and then decreasing including Qingtongxia-Shizuishan and Bayangaole-Sanhuhekou.These changes was closely related to reservoir controls in the upstream of Yellow River.

[44]
Yang D, Wang Y, 1996. On river terraces of the upper reaches of the Huanghe River and change of the river system.Scientia Geographica Sinica, 16(2): 137-143. (in Chinese)The upper reaches of the Huanghe (Yellow) River, a length of 1350 km from Gyaring Lake to Guide county, cuts through the great slope of the northeast part of the Qinghai-Xizang (Tibet) Plateau and it runs through a few of Mesozoic-Cenozoic depositional basins, for example, Guide basin, Gonghe basin, Xinghai basin, Zoige basin, Ngoring-Gyaring basin etc. , the sections between them are a series of gorges of the Huanghe Riv-er.Based on author's investigation, there is a terrace of 7 steps in the Huanghe River val-ley by Guide county, a terrace of 3 steps being formed by the ancient Huanghe River and 7 steps in Gonghe basin, 6 steps by Gamao Yangqu town, 5 steps by Tangnaihai town, Xinghai County, 3 steps by Maqu town, Gansu Province, and one step by Ngoring-Gyaring Lake.The overall upper reaches of the Huanghe River was linked up by a series of the stream captures occurred after strongly uplifting of the Qinghai-Xizang area into a plateau. A section of the ancient Huanghe River through the place Gahaitan located on northeastern Gonghe basin towards east into Guide basin was developed during the end of Middle Pleistocene to the middle of the Late Pleistocene, and then it migrated towards southeast to the place Longyangxia Gorge about 60000 years ago. And the gorge from Maqu to Tangnaihai was linked up about 20000 years ago.

[45]
Yuan B, Wang Z, 1995. Uplift of the Qinghai-Xizang Plateau and the Yellow River physiographic period.Quaternary Sciences, (4): 353-359. (in Chinese)The Qinghai-Xizang Plateau came into being as early as in the middle Himalayan movement in Late Miocene. After that, the earth crust had kept a secular steady state for 10 Ma, and a peneplain surface with an elevation about 1 000 metres formed.The Qinghai-Xizang Plateau was mainly formed in Quaternary. It rose to 2 000m in Early Pleistocene, and reached an elevation of more than 4 500m in Late Pleistocene. And it rose about 300-500m during Holocene. Recently, Ding Lin et al.calculated the elevation rate of the Qinghai-Xizang Plateau according to the result of ages by fission-track dating:12-11 Ma B.P. 0.06mm/a11-8 Ma B. P. 0.18mm/a8-3 Ma B. P. 0.1mm/a3 Ma B.P. 1.5mm/a0.31 Ma B. P. 14.19mm/aDing Lin's calculating results show that the Qinghai-Xizang Plateau has risen about 1 900 metres since 0.3Ma B. P. The data also show that its uplift had been a fluctuation process in which uplift sometimes were fast and sometimes were slow.The Uplift of the Qinghai-Xizang Plateau obviously affected its periphery areas and resulted in the changing of the pattern, speed and direction of tectogenesis and the alternation of erosion and sedimentation.Recent study shows that the development history of the Yellow River was obviously affected by the uplift of the Qinghai-Xizang Plateau, especially in its middle reaches. There were closely relationship between the developing of the river terraces and the stages of the uplift.According to the study on the river terraces, the development history of the Yellow River may be tentatively divided into three stages:1. The Embryonic Period The old broad valley formed in the Baode period was still retained in the Shanxi-Shaanxi segment of the Yellow River to the Shanmen gorge. It may be said that this segment formed at least in Pliocene and even in Late Miocene. In that period, the crust was stable and lateral erosion was dominant so as to form a broad river plain far to the Yinchuan basin. The paleoclimate was hot and humid but the division of arid and humid seasons was very obvious. So the sediment strata mainly characteristic of brown clay were formed. Though the Yellow River at that time was only at its initial stage, it was the largest river in North China.2. The Coexistence Period of Rivers and Lakes As a result of the uplift of the Qinghai-Xizang Plateau, a violent erosion occurred in the middle reaches of the Yellow River in Late Pliocene. It was the so-cal-led Fenhe Erosion Period. Both the Shanxi-shaanxi segment gorges and the Shanmen gorge were formed in this period. And the Yellow River from the Gonghe basin downward was formed.In the same period, on the other hand, some area sagged and formed lakes, such as the Gonghe paleolake, the Yinchuan paleolake, the Hetao paleolake, the Shanmen paleolake and the Fenhe paleolake. All of these paleolakes were distributed along the trunk stream and greater tributaries of the Yellow River, appearing a landscape of the coexistence of rivers and lakes. These lakes were different in lasting time. Some researchers thought that they were salt-water inland lakes without linking each other. The Yellow River in this period might be a continental river.Further study are needed to determine the characters and the development history of these lakes.3. The Large River Period A violent dissection occurred before accumulation of the Malan Loess in North China. It was the so-called Qingshui Erosion Period in physiography. In this period terraces with the height of 20 to 50m along the Yellow River formed and most of large lakes disappeared. The geoworphologic landscape which has now emerged along the Yellow River from the Gonghe basin to the river mouth has basically formed. All these are results of an important geological event in North China, which corresponded to the acceleration of uplift of the Qinghai-Xizang Plateau since 0.3-0.2Ma B. P. While the Yellow River was in downcutting, a landscape of crisscrossed gullies and ravines appeared in the Loess Plateau, especially west of the Liupan Mountains.

[46]
Zhang Z, Yu Q, Zhang K et al., 2003. Geomorphological evolution of a Quaternary river from the upper Yellow River and geomorphological evolution investigation for 1:250000 scale geological mapping in Qinghai-Tibet Plateau.Earth Science-Journal of China University of Geosciences, 28(6): 621-626. (in Chinese)

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