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Journal of Geographical Sciences >

2017 , Vol. 27 >Issue 11: 1376 - 1388

DOI: https://doi.org/10.1007/s11442-017-1441-1

Research Articles

Planform characteristics and development of interchannel wetlands in a gravel-bed anastomosing river, Maqu Reach of the Upper Yellow River

  • LIU Boyi , 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: Liu Boyi, Master Candidate, specialized in fluvial geomorphology. E-mail:

Received date: 2017-06-02

  Accepted date: 2017-07-06

  Online published: 2017-09-07

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

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 (Dl), and node density (Dn) 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 (Su) is highly correlated with other geomorphologic parameters. P increases with increasing Su, 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, Dl and Dn show a tendency to decrease with increasing Su 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.

Key words： channel planform; gravel-bed anastomosing river; interchannel wetland; geomorphologic parameter; Yellow River

Cite this article

LIU Boyi , WANG Suiji . Planform characteristics and development of interchannel wetlands in a gravel-bed anastomosing river, Maqu Reach of the Upper Yellow River[J]. Journal of Geographical Sciences, 2017 , 27(11) : 1376 -1388 . DOI: 10.1007/s11442-017-1441-1

1 Introduction

An anastomosing river is composed of interconnected channels that enclose vegetated interchannel wetlands (fluvial islands) or floodbasins (Schumm, 1968; Miall, 1977; Rust, 1978; Smith and Smith, 1980; Makaske, 2001; Wang et al., 2005). Multi-channels network and vegetated interchannel wetlands are two fundamental components of anastomosing rivers. The multi-channel network in anastomosing rivers is significantly different from the single channel in straight or meandering rivers. Furthermore, stable interchannel wetlands in anastomosing rivers are different from the midchannel bars of braided rivers. Since anastomosing rivers were recognized as an independent river pattern, their sedimentary and hydraulic properties have been extensively studied (Wang and Ren, 1999; Yin et al., 2000; Makaske et al., 2002; Tabata and Hickin, 2003; Wang, 2003; Wang et al., 2004; Abbado et al., 2005; Makaske, 2009; Makaske et al., 2017). In addition, the formation and stability of the multi-channel network within anastomosing rivers has also been investigated (Miller, 1991; Wang et al., 2000; Makaske, 2001; Wang, 2002; 2004; Wang et al., 2005; Roze et al., 2012). Previous studies have suggested that avulsions, primarily driven by aggrading channels, form new channels in anastomosing rivers (Bryant et al., 1995; Jones and Schumm, 1999, Makaske, 2001). Meanwhile, frequent avulsions combined with relatively slowly abandoned old channels help maintain the multi-channel network (Makaske, 2001; Abbado et al., 2005).
Previous research on the planform of anastomosing rivers has focused on the need to distinguish anastomosing rivers from other river patterns. Parameters including sinuosity index, braiding index (Brice, 1964), braiding parameter (Rust, 1978), and braid-channel ratio (Friend and Sinha, 1993) have been used in the identification of anastomosing rivers. However, few of those parameters represent the most significant characteristics of anastomosing rivers: the highly developed multi-channels and vegetated interchannel wetlands. A likely reason for this neglect is the lack of high-precision data, which could be used to describe the planform characteristics of complex multi-channel network in anastomosing rivers.
Both interchannel wetlands and multi-channels are crucial geomorphologic units in anastomosing rivers. Planform characteristics and the development of interchannel wetlands and multi-channels control the behavior of anastomosing rivers. In recent papers on the planform characteristics of other multi-channel rivers, researchers extracted interchannel wetlands, bars, and channels using historical maps and aerial photos ( Hooke and Yorke, 2011; Belletti et al., 2015), then addressed their formation and evolution (Zanoni et al., 2008; Church and Rice, 2009; Wyrick and Kingeman, 2011; Mikuś et al., 2013; Picco et al., 2014). Multi-channel rivers essentially form in two ways: (1) splitting of diverted avulsive flow, leading to the formation of new channels on floodplains or interchannel wetlands (e.g., Wang et al., 2000; Makaske, 2001); and (2) formation of new interchannel wetlands due to stabilization of sand or gravel bars, causing the diversion of the former channel (Osterkamp, 1998; Gurnell et al., 2001). Clearly, the evolution of interchannel wetlands and multi-channels are highly connected.
The Maqu Reach of the Upper Yellow River (MRUYR) is comprised of a single channel and multi-channel subreaches that alternate among anastomosing, anabranching, meandering, and braided river patterns (Wang, 2008; Li et al., 2013a). Previous work has demonstrated that the valley setting, channel gradient, riparian vegetation development, regional hydrology and sediment load conditions, and tributary confluences influence channel planform transformations (Wang, 2008; Li et al., 2013a, 2013b; Yu et al., 2013, 2014). The development of interchannel wetlands and multi-channels in an anastomosing subreach exhibit spatial variety due to these channel planform transformations. Moreover, the gravel-bed anastomosing subreach along MRUYR is significantly different from other sand-bed anastomosing rivers; the interchannel wetlands and anabranches in this anastomosing subreach appear in the form of interchannel wetland clusters (IWCs), a special combination of interchannel wetlands and gravel-bed anabranches.
Therefore, this area is a good example and study site to investigate planform characteristics of gravel-bed anastomosing rivers. Geomorphologic units, including channels, interchannel wetlands, and IWCs, were extracted using high resolution Google Earth images. Then, the size distributions of interchannel wetlands and IWCs were investigated. Finally, geomorphologic parameters, including the ratio of interchannel wetland area to IWC area (Zanoni et al., 2008), shoreline density (Kidová et al., 2016), and node density (Bertoldi et al., 2009) were used to analyze the planform characteristics of IWCs and development of channels in the study area.
The purpose of this paper is to describe the planform characteristics of interchannel wetlands in the anastomosing MRUYR. A particular focus is the relationship between IWCs and development of the multi-channels in anastomosing rivers.

2 Study area

The study area is located in Maqu County in southwestern Gansu Province, a marginal area in the eastern Qinghai-Tibet Plateau (Qi and Li, 2008). It has a humid alpine climate; annual precipitation is about 564 mm and mean annual temperature is about 1.1°C (Chu et al., 2014). Based on landform variability, Maqu County can be divided into three regions, the north-western mountain, middle-southern hill, and eastern valley plain regions (Liu et al., 2012). The MRUYR lies in the eastern portion of the Animaqing (Anyemaqen) Mountains, where the river turns nearly 180° in the ‘U-shaped’ form (Figure 1). This part of the river is about 270 km in length, from the entry location near Awancang Town in Maqu, to the exit in southwestern Maqu County. It consists of anastomosing, anabranching, meandering, and braided reaches (Wang, 2008; Li et al., 2013a). The particularly anastomosing reach is evident near Qihama and Cairima towns.
Figure 1 Overview of the location and topography of the study area; the left image is a digital elevation model that includes the tributaries of the Yellow River and the Maqu reach indicated in red
This study concentrates on the 65 km anastomosing reach with highly developed interchannel wetlands and multi-channel network, situated near Cairima and Qihama towns, which lies in the transitional area between the middle-southern hill and eastern valley plain regions. The land cover on the riversides and interchannel wetlands is clearly different. Alpine meadows cover most riverside areas (Jiang, 2008), while trees and shrubs grow on the interchannel wetlands (Chu et al., 2014). Sediment sizes are also different between riverside, interchannel wetlands, and channels. Riverside and interchannel wetlands are covered with fine sand sediment, while channels are mainly occupied by gravel, whose median grain size varies from 40 mm to 70 mm (Wang, 2008). The flow regime is dominated by precipitation and snow-ice meltwater. The discharge at the Maqu gauging station (1959-1989 and 2008-2013) usually reaches a maximum in July or September; the mean discharge in June and September is 1046.74 m3/s and 955.19 m3/s, respectively. While an extreme flood event (mean daily discharge of 4320 m3/s) occurred in September 1981, peak flow normally reaches a maximum of 2670 m3/s in July and 2870 m3/s in September. A minimum monthly mean discharge of 113.72 m3/s occurs in February, when ice covers most of the studied reach.

3 Materials and methods

Discharge data from the Maqu gauging station were obtained from the Hydrological Yearbook of the Yellow River. High resolution satellite images of the study reach with a resampling resolution of 0.59 m were extracted from Google Earth using the Google Satellite Map Downloader (Singh et al., 2015). Satellite images (Figure 2a; Images 1, 2, and 3 in Table 1) were acquired from two satellites on three different dates during the flood season (World-view-02 on August 27, 2011, GeoEye-01 on July 29, 2013, and August 1, 2013). All satellite imagery information is listed in Table 1. Considering that anastomosing rivers are relatively stable and there were no significant changes in the channel planform over these few years or at different water levels, these satellite images acquired on different dates can be used to quantify the planform of the study reach.
Figure 2 Satellite images of the study reach obtained from Google Earth. (a) Mosaic image of images 1, 2, and 3; (b) image 4, satellite image from Landsat 8; and (c) image 5, satellite image of part of the study reach during low flow
Table 1 Satellite imagery information
Image Satellite Date Covered reach (km) Discharge (m³/s)
1 Worldview-02 Aug. 27, 2011 0-13.34 627
2 GeoEye-01 Jul. 29, 2013 13.41-45.18 1640
3 GeoEye-01 Aug. 1, 2013 45.18-64.81 1920
4 Landsat 8 Jul. 23, 2013 0-64.81 1610
5 Worldview-02 Mar. 8, 2011 25.25-59.81 113
The images were projected to UTM 48N. Based on these images, geomorphologic units were digitized at a scale from 1:1000 to 1:2000 using ArcGIS 10.2. Interchannel wetlands were identified according to the standard proposed in Zanoni et al. (2008); only vegetation patches with vegetation coverage > 75% were identified. Generally, 90% of surfaces are usually covered by vegetation in the interchannel wetlands in the study reach. We compared the digitized channel boundary with image 4 (Figure 2b, Landsat 8 on July 23, 2013) and image 5 (Figure 2c, Worldview-02 on March 8, 2011 at low flow), and found no significant differences. Therefore, geomorphologic units extracted from the mosaic image of images 1, 2, and 3 can represent the planform characteristics of the study reach.

4 Results

4.1 Micro geomorphologic units and parameters

To investigate the channel planform, we first defined the typical micro geomorphologic units in the studied reach and chose parameters to describe their characteristics. The micro geomorphologic units (the definitions are listed in Table 2) include river corridor, principal channel, anabranches, interchannel wetlands, and IWCs (Figure 3).
Table 2 Definition of the micro geomorphologic units in the anastomosing Maqu reach
Micro geomorphologic units Definition
River corridor Area of all geomorphologic units in the anastomosing river, including all channels and interchannel wetlands
Principal channel The primary channel in an anastomosing river, which is usually the largest of all channels and has active water during low flow
Anabranches All channels other than the principal channel
Interchannel wetlands Vegetated land between channels
Interchannel wetland clusters A combination of interchannel wetlands that develop on the same gravel bar and anabranches separating those interchannel wetlands
Figure 3 Map of the Maqu reach showing the micro geomorphologic units and interchannel wetland clusters
We defined the river corridor, principal channel, and anabranches according to the classification of channels provided in Rice et al. (2009). The principal channel indicates the widest and deepest of all channels; here, all other channels are defined as anabranches. The term interchannel wetlands used here was previously applied in Wang (2000) to a study of anastomosing rivers; the definition is similar to that of established islands presented in Gurnell (2001), which includes vegetated islands developing on gravel bars and those excised from floodplains. The definition of IWCs is similar to compound bar presented in Rice (2009). The difference is that bar-top channels and unvegetated bars in compound bars were considered as channels in IWCs, because they are inundated during flood season, and gravel bars cannot separate channels while interchannel wetlands can.
We chose the area of IWC (Su) and number of interchannel wetland in IWC (I) to describe their size characteristics. Parameters, including the ratio of interchannel wetland area to IWC area (P), shoreline density (Dl, the length of total channel shoreline per km2), and node density (Dn, the intersection point of channels per km2) were chosen to analyze the development of IWCs.
The ratio of interchannel wetland area to IWC area (P) is defined as follows:
P = Si / Su (1)
where Si is the sum of the area of interchannel wetlands in an IWC and Su is the area of the IWC.
Shoreline density (Dl) is calculated according to the following formula:
Dl = Li / Su (2)
where Li is the sum of channel shoreline length in an IWC.
Node density (Dn) is calculated as follows:
Dn = N / Su (3)
where N is the sum of node numbers in an IWC.
The principal channel and IWCs separated by the principal channel are important geomorphologic units. Despite the few small interchannel wetlands in the principal channel, most are distributed in 30 IWCs, which are named U1, U2, …, to U30 from upstream to downstream. The spatial distribution of IWCs is shown in Figure 3 and their geomorphologic parameters are listed in Table 3.
Table 3 Geomorphologic parameters of the interchannel wetland clusters on the Maqu reach
Code Su (ha) I P (%) Li (km) Dl (km/km2) N Dn (node/km2)
U1 28.58 5 44.89 4.32 15.13 7 24.49
U2 63.51 16 65.40 8.08 12.72 33 51.96
U3 250.27 22 77.32 19.50 7.79 41 16.38
U4 404.15 47 73.51 43.70 10.81 83 20.54
U5 136.88 17 74.15 14.73 10.76 29 21.19
U6 44.21 15 66.02 6.93 15.67 24 54.29
U7 128.55 16 81.96 13.62 10.59 28 21.78
U8 25.31 9 37.56 3.94 15.58 12 47.42
U9 345.31 53 75.80 39.65 11.48 65 18.82
U10 331.36 44 71.27 32.82 9.90 64 19.31
U11 27.77 8 40.83 3.64 13.12 11 39.61
U12 163.57 28 73.58 21.67 13.25 36 22.01
U13 672.94 85 79.12 71.11 10.57 143 21.25
U14 54.45 14 50.81 7.75 14.23 28 51.42
U15 170.26 27 74.86 17.73 10.41 31 18.21
U16 119.13 15 70.07 13.97 11.73 16 13.43
U17 67.94 20 50.52 10.00 14.72 31 45.63
U18 1336.17 131 79.24 110.94 8.30 202 15.12
U19 177.93 48 63.95 24.47 13.75 56 31.47
U20 95.34 41 57.09 17.20 18.04 63 66.08
U21 321.44 54 78.85 35.77 11.13 67 20.84
U22 239.77 12 73.98 14.48 6.04 15 6.26
U23 6.46 2 33.25 0.82 12.66 3 46.47
U24 96.14 13 78.33 11.31 11.76 21 21.84
U25 70.64 4 71.70 5.92 8.37 7 9.91
U26 243.44 18 71.57 22.62 9.29 32 13.15
U27 183.42 26 83.21 18.86 10.28 45 24.53
U28 114.00 14 55.55 11.24 9.86 22 19.30
U29 260.51 29 73.11 20.06 7.70 40 15.35
U30 25.73 4 52.71 3.54 13.77 7 27.21

4.2 Size distribution of interchannel wetland areas

There is a significant size difference between the 848 interchannel wetlands in the studied reach. For example, the area of the smallest interchannel wetland is 0.0028 ha, while the largest one is 258.75 ha. According to differences in area, interchannel wetlands were divided into five size ranges: micro (< 0.1 ha), small (0.1-1 ha), middle (1-10 ha), large (10-100 ha), and mega (≥ 100 ha) (Table 4). The MRUYR contains 231 micro interchannel wetlands, 284 small interchannel wetlands, 232 middle interchannel wetlands, and 103 large-mega interchannel wetlands. The highest distribution is between the micro and middle sizes. Nevertheless, the large and mega interchannel wetlands have a larger total area. The total area of the 515 micro to small interchannel wetlands is only 117.62 ha, which accounts for 2.55% of the total area of all interchannel wetlands, while the total area of the 97 large interchannel wetlands is 2988.96 ha, accounting for 64.87% of the total area of all interchannel wetlands. The total area of four mega interchannel wetlands is 692.67 ha, which accounts for 15.03% of the total area of all interchannel wetlands (Table 4).
Table 4 Total number and total area of interchannel wetlands in different size ranges
Area (ha) Type Interchannel
wetlands number		 Interchannel wetlands
number frequency (%)		 Total area
(ha)		 Total area
frequency (%)
<0.1 Micro 231 27.24 8.70 0.19
0.1-1 Small 284 33.49 108.92 2.36
1-10 Middle 232 27.36 808.19 17.54
10-100 Large 97 11.44 2988.96 64.87
≥100 Mega 4 0.47 692.67 15.03

4.3 Size distribution of interchannel wetland clusters

Thirty IWCs were found in the studied reach, and their size varies significantly. The largest cluster size is 1336.17 ha, and it contains 1058.75 ha of interchannel wetlands. In contrast, the smallest cluster is only 6.46 ha, in which the interchannel wetlands is 2.14 ha. According to differences in area, the IWCs were divided into four size types (Table 5): small (< 100 ha), middle (100-200 ha), large (200-500 ha), and mega (≥ 500 ha) IWCs.
Table 5 Total area and total number of interchannel wetlands of interchannel wetland clusters with different sizes
Area (ha) Type Number Total area (ha) Total area frequency (%) Interchannel wetlands number Number Total number frequency (%)
<10 Small 1 6.46 0.10 < 10 6 5.14
10-50 5 151.59 2.44 10-20 10 20.31
50-100 6 448.02 7.22 21-50 10 36.80
100-200 Middle 8 1193.74 19.24 51-100 3 22.10
200-500 Large 8 2396.24 38.62 > 100 1 15.65
>500 Mega 2 2009.11 32.38
The total area varies significantly between different types of IWCs (Figure 4). Eighteen middle to mega sized IWCs have a total area of 5599.09 ha (90.34% of the total area of all IWCs). Notably, eight large IWCs have a total area of 2396.24 ha, accounting for 38.62% of the total area of all IWCs, which is more than any other type of IWCs. In addition, two mega IWCs have a total area of 2009.11 ha, accounting for 32.38% of the total area. The total number of interchannel wetlands also varies between IWCs. The cluster with the most has 131 interchannel wetlands, while the cluster with the least has only two interchannel wetlands. IWCs containing 21-50 interchannel wetlands occur with the greatest frequency, accounting for 39.67% of the total number of interchannel wetlands.
Figure 4 Statistical analysis of interchannel wetlands in interchannel wetland clusters with different areas (a. Total area and cumulative frequency; b. total number of interchannel wetlands and cumulative frequency)

5 Discussion

5.1 Relationship between the area of interchannel wetland clusters and geomorphologic parameters

P, the ratio of interchannel wetland area to IWC area, varies between IWCs with different areas. The P value increases with increasing Su, the area of the IWC (Figure 5a). When Su is less than 100 ha, P increases rapidly with increasing Su, until P reaches about 70%. When Su is between 100 and 500 ha, P increases slowly from 70% to about 80%. Noticeably, P reaches a stable value of about 80% when Su is > 500 ha.
Figure 5 Relationship between area and other geomorphologic parameters of interchannel wetland clusters, (a) area and ratio of interchannel wetland area to interchannel wetland cluster area, (b) area and shoreline density, and (c) area and node density
This relationship indicates that the development of interchannel wetlands in an IWC reaches a relative stable stage as P reaches 70%. The upper limit value of P is 80%, which indicates that the development of interchannel wetlands and anabranches in an IWC has entered the equilibrium stage; the interchannel wetlands occupied in the IWC maintain 80% and anabranches occupied in the IWC maintain 20%. This is the most stable stage for the development of interchannel wetlands and anabranches.
A relatively stable hydrological condition is one reason that P increases with increasing Su. In this condition, the total area of channels maintains a stable value, and the main process for IWC expansion is the growth of interchannel wetlands, which leads to an increase in P. An upper limit for P suggests that an equilibrium stage between the formation of new channels and extinction of old channels has been reached. Channel capacity reduces with increasing area of interchannel wetlands, which leads to avulsion and dissection of interchannel wetlands. In this case, the increase in P is limited.
Shoreline density (Dl) is highly correlated with Su (Figure 5b). Small interchannel wetlands, Su < 100 ha, have high shoreline density, an average of 13.81 km/km2. The average Dl value decreases by 17.89% to 11.33 km/km2 in the medium-sized IWCs, i.e., Su is 100-200 ha. In large-mega IWCs, Su > 200 ha, the average Dl value further decreases to 9.30 km/km2, which is 32.64% less than that of small IWCs (Table 6).
Table 6 Interchannel wetland cluster parameters categorized by area
Area (ha) P (%) Dl (km/km2) Dn (node/km2)
Avg. Min Max Avg. Min Max Avg. Min Max
<10 33.25 12.66 46.47
10-50 48.40 37.56 66.02 14.65 13.12 15.67 38.60 24.49 54.29
50-100 62.31 50.52 78.33 13.31 8.37 18.04 41.14 9.91 66.08
100-200 72.17 55.55 83.21 11.33 9.86 13.75 21.49 13.43 31.47
200-500 74.46 71.27 78.85 9.27 6.04 11.48 16.33 6.26 20.84
>500 79.18 79.12 79.24 9.43 8.30 10.57 18.18 15.12 21.25
The relationship between node density (Dn) and Su is similar to those between Dl and Su (Figure 5c). Dn decreases with increasing Su. Small IWCs have high node density, averaging 40.53 node/km2. When Su is 100-200 ha, the average Dn value decreases to 21.49 node/km2, which is 46.97% less than that of small IWCs. When Su is > 200 ha, Dn further decreases to 16.70 node/km2, 58.80% less than that of small IWCs (Table 6).
Clearly, Su at 100 ha and 200 ha are two important areas during the growth of IWCs. When Su is less than 100 ha, Dl and Dn maintain high values, when Su is between 100-200 ha, Dl and Dn decrease significantly, and when Su is > 200 ha, Dl and Dn maintain relatively low values.
The difference in development is due to the change in the principal developing process of interchannel wetlands and anabranches. In small IWCs, the increasing number of small anabranches and interchannel wetlands is the main process during growth. Thus, the increasing length and number of anabranches is clear, which leads to high Dl and Dn. In medium-sized IWCs, merging of interchannel wetlands causes the abandonment of some small anabranches. This abandoning process can reduce the rate of increasing number and length of anabranches during the growth of IWCs. Thus, Dl and Dn are significantly reduced, with Dn the most obvious. In large and mega IWCs, the merging of interchannel wetlands and abandoning of channels are more frequent; the development of small interchannel wetlands and anabranches is restricted. Instead, the development of middle and large interchannel wetlands and anabranches is more common. Thus, Dl and Dn maintain relatively low values.

5.2 Formation of interchannel wetland clusters

In the anastomosing MRUYR, the existence of IWCs composed of interchannel wetlands and anabranches is one of its most important characteristics. In this study, we present some preliminary theories to explain the formation of IWCs.
First, the meandering principal channel, as the main conduit for water and sediment transportation, plays an important role in the formation of IWCs. The multi-channel network in anastomosing rivers is usually composed of one principal channel and several anabranches. Due to its high stream power, the principal channel controls the change in channel planform in anastomosing rivers. In the studied reach, the main stream of the Yellow River, the controlling function of the principal channel is even clearer than other small to middle size anastomosing reaches. The hydraulic conditions vary on different sides of the meandering principal channel, which causes concentrated deposition in some areas near the principal channel and growth of interchannel wetlands. Large IWCs usually appear on the convex bank of the principal channel, while IWCs are less developed on the concave bank.
Second, the formation of a broad river corridor due to weakening structural control provides enough area to develop IWCs. The valley setting (Yu et al., 2013) is one reason for the channel transformation in MRUYR. Upstream of the reach is a narrow meandering one that is area limited, which essentially prevents the formation of IWCs. When the Yellow River flows from the middle-southern hill region to the eastern valley plain region (Figure 1), the weakening structural control leads to a widening of the river corridor and formation of IWCs, especially at the middle part of the studied reach where two mega IWCs formed.
Third, shrubs and trees growing on channel banks and interchannel wetlands favor the development and preservation of IWCs. Shrubs and trees growing on interchannel wetlands are clearly different vegetation from the alpine meadow covering other areas in this region (Chu et al., 2014). Shrubs and trees stabilize gravel bars (Gurnell et al., 2001) and lead to the formation of new interchannel wetlands or islands, which contribute to the development of IWCs. Furthermore, these shrubs and trees protect interchannel wetlands from lateral erosion (Miller, 1991), especially reducing lateral movement of the principal channel.

6 Conclusions

The anastomosing Maqu reach is composed of one meandering principal channel and various interchannel wetlands and anabranches. The interchannel wetlands and anabranches appear in the form of IWCs. Interchannel wetlands ranging in area from small to middle and IWCs in the large or mega area range are the most common in the Maqu reach.
P, the ratio of interchannel wetland area to IWC area, was used to evaluate the characteristic combination of interchannel wetlands and anabranches in this anastomosing river. P stabilized at 80%, indicating that the development of interchannel wetlands and anabranches in an IWC entered an equilibrium stage. At equilibrium, the formation of new channels and abandonment of old channels were in balance.
Shoreline density Dl and node density Dn represent the characteristics of anabranches in length and number. In the Maqu reach, Dl and Dn have a tendency to decrease with increasing Su due to diverse evolution processes in the IWCs with different sizes.
There are three primary reasons for the formation of IWCs in the anastomosing Maqu reach: the separating effect of the meandering principal channel, weakened structural control from mountains to valley, and preservation by shrubs and trees growing on interchannel wetlands.

The authors have declared that no competing interests exist.

References

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Abbado D, Slingerland R, Smith N D, 2005. Origin of anastomosis in the upper Columbia River, British Columbia, Canada. In: Blum M D, Marriott S B, Leclair S F. Fluvial Sedimentology VII. Oxford, UK: Blackwell Publishing Ltd., 1-15.Summary To understand the origin of anastomosis on the Columbia River between Spillimacheen and Golden, British Columbia, Canada, a geomorphological and sedimentological survey was undertaken during the summer flood of 2000. On the basis of these observations, the study reach can be divided into two subreaches: a highly anastomosed section with three to five channels, and a weakly anastomosed section with one to two channels. The highly anastomosed reach occurs immediately downstream from the Spillimacheen tributary and is characterized by a higher channel slope, a higher number of crevasse splays, a larger combined crevasse splay area, a wider valley and a coarser bedload. Higher rates of floodplain aggradation in the highly anastomosed reach are suggested by modern sediment budgets and radiocarbon dates. These geomorphological and sedimentary associations are consistent with the hypothesis that anastomosis of the Columbia River is maintained by a dynamic equilibrium between the rates of channel creation and channel abandonment. Rising base-level, fine bedload and low bed-slope are not necessary immediate conditions for anastomosis of the Columbia River.

DOI

[2]
Belletti B, Dufour S, Piégay H, 2015. What is the relative effect of space and time to explain the braided river width and island patterns at a regional scale?River Research and Applications, 31(1): 1-15.Abstract Several decades of human activities have severely impacted braided rivers worldwide. Despite their widespread disappearance, some remnant braided sectors are still held in the French Rhone basin, mainly in the south-east of France. In this paper, we analyse the evolutionary pattern of 53 braided reaches, focusing on the active channel width and island patterns, by comparing aerial photographs from the 1950s and 2000s (Institut G茅ographique National). Because different braided patterns exist (e.g. bar versus island-braided), we tested the relative effect of geographical and temporal factors. The hypothesis is that three main biogeomorphological braided types exist (i.e. defined through the presence, the amount and the relative size of vegetated islands), based on the combined effect of the following: (i) their position along the river network (i.e. river gradient, altitude and sediment regime) and (ii) the temporal effect represented by the time since the last large flood, that is, the recent flood history. Our results show that even if the regional context (climate and sediment regime mainly) plays a key role, the temporal factor, represented by recent flood history, seems to heavily influence the response of the width pattern and vegetation recovery. Local factors (i.e. topography and groundwater) may also have an impact, but their influence has no effect at the regional level. These results support braided river management (conservation and/or restoration actions) in the Rhone basin and provide a better understanding of the range of braided rivers' functioning. Further studies (e.g. multidate retrospective survey) are needed to better understand the role of flood events on braided pattern and vegetation recovery. Copyright 2013 John Wiley & Sons, Ltd.

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[3]
Bertoldi W, Zanoni L, Tubino M, 2009. Planform dynamics of braided rivers.Earth Surface Processes and Landforms, 34(4): 547-557.Abstract The high dynamism and complexity of braided networks poses a series of open questions, significant for river restoration and management. The present work is aimed at the characterization of the morphology of braided streams, in order to assess whether the system reaches a steady state under constant flow conditions and, in that case, to determine how it can be described and on which parameters it depends. A series of 14 experimental runs were performed in a laboratory physical model with uniform sand, varying the discharge and the longitudinal slope. Planimetric and altimetric configurations were monitored in order to assess the occurrence of a steady state. A set of parameters was considered, such as the braid-plain width and the number and typology of branches and nodes. Results point out that a relationship exists between braiding morphology and two dimensionless parameters, related to total water discharge and stream power. We found that network complexity increases at higher values of water discharge and a larger portion of branches exhibits morphological activity. Results are then compared to the outputs of a simple one-dimensional model, that allows to easily predict the average network complexity, once the bed topography is known. Model computations permit also the investigation of the effect of water discharge variations and to compare different width definitions. The at-a-station variability of planimetric parameters shows a peculiar behaviour, both regarding number of branches and wetted width. In particular, the analysis of the relationship between width and discharge highlighted relevant differences in comparison to single thread channel. Copyright 2009 John Wiley & Sons, Ltd.

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[4]
Brice J C, 1964. Channel patterns and terraces of the Loup Rivers in Nebraska. U.S. Geological Survey Professional Paper 422-D, Washington DC.Abstract: Genre: USGS Numbered Series ProdID: 32765 Citation Author: Brice, James Coble Citation Contributing Office: Citation Datum: Citation Day: Citation Edition: - Citation Editor: Citation End Page: Citation Issue: Citation Keywords: Citation Language: ENGLISH Citation Larger Work Title: Citation LatN: Citation LatS: Citation LonE: Citation LonW: Citation Month: Citation No Pagination: Citation Number Of Pages: Citation Online Only Flag: Citation Phsyical Description: iv, 41 p. *MISSING PAGES* Citation Projection: Citation Public Comments: Citation Publisher: U.S. Govt. Print. Off., Citation Series: Professional Paper Citation Series Code: PP Citation Series Number: 422-D Citation Search Results Text: Channel patterns and terraces of the Loup Rivers in Nebraska; 1964; PP; 422-D; Brice, James Coble Citation Start Page: Citation Volume: Citation Year: 1964 Type: citation/reference Text: Channel patterns and terraces of the Loup Rivers in Nebraska; 1964; PP; 422-D; Brice, James Coble URL (THUMBNAIL): <a href="http://pubs.usgs.gov/pp/0422d/report-thumb.jpg" target="_blank">http://pubs.usgs.gov/pp/0422d/report-thumb.jpg URL (DOCUMENT): <a href="http://pubs.usgs.gov/pp/0422d/report.pdf" target="_blank">http://pubs.usgs.gov/pp/0422d/report.pdf Date Other: Sat, 1 Jan 1994 00:00 -0600 Publisher: U.S. Govt. Print. Off.,

[5]
Bryant M, Falk P, Paola C, 1995. Experimental study of avulsion frequency and rate of deposition.Geology, 23(4): 365-368.In existing models of alluvial architecture it is typically assumed that mean avulsion frequency is independent of sedimentation rate. However, if avulsion is driven by superelevation of a river bed above its surrounding flood plain, one might expect avulsion rate to increase with sedimentation rate. We have carried out a series of experiments with laboratory-scale fluvial fans in which we measured the frequency of apical avulsions as a function of mean sedimentation rate on the fan. Avulsion frequency increased strongly with increasing sedimentation rate and then stabilized as mass flows began to influence deposition. In the regime of increasing avulsion frequency, the added volume of sediment needed to trigger an avulsion decreased with increasing sedimentation rate. Although our experimental results cannot simply be scaled up to natural rivers, they suggest the possibility of coupling between avulsion frequency and sedimentation rate that would be strong enough to change qualitatively the results of existing models of alluvial architecture. These models should be applied with caution until avulsion mechanics are better understood.

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[6]
Chu L, Huang C, Liu Get al., 2014. Changes in ecological patterns of Maqu alpine wetland in Yellow River Source Area during 2000-2010.Progress in Geography, 33(3): 326-335. (in Chinese)Wetland as a unique ecosystem has important environment regulating functions and irreplaceable role in maintaining regional ecological balance,conserving biodiversity,and providing food,materials and water resources to humans. The Maqu alpine wetland located in the northeast of the Tibetan Plateau is an important water conserving and supplying area to the upper reach of the Yellow River. In the past 30 years,global warming has led to significant vegetation changes on the Tibetan Plateau. The Maqu alpine wetland is undergoing a process of prominent warming and drying,and degradation of its water conservation function is very significant in recent years. Wetland vegetation dynamics,regional differentiation and causes of degradation of the alpine wetland ecosystem were investigated using multi-source remote sensing data in this study. Land use information and ecological patterns of Maqu were extracted via analyzing Landsat-5/TM and Landsat-7/ETM+ satellite images of 2000 and 2010,through visual interpretation and supervised classification using GIS techniques. NDVI(Normalized Difference Vegetation Index) was used as an indicator in monitoring vegetation changes. MODIS NDVI time series data of 2000-2010(after applying the S-G filtering method and MVC) were used to detect temporal and spatial variations and evolution trend of wetland ecosystems. Point data from weather stations was interpolated using Kriging interpolation method. Based on long-term observations from weather stations,the relationship between Maqu wetland changes and climatic factors(temperature and precipitation) was examined using the least squares method. The results show that areas of rivers,inland beaches,ponds,and swamp meadows were decreasing. Summer NDVI of 2000-2010 in the study area also decreased. Areas with significant decline in NDVI are located in Cairima,Manrima and Hequmachang. Changes in vegetation type also occurred,as signified by swamp meadows shifting to subalpine meadows. The warming and dry climate appears to be a critical factor contributing to the degradation of the Maqu alpine wetland. The changes of the Maqu alpine wetland are related to the inter-annual variability of precipitation and temperature,with 61% and 51% of the total area showing a positive correlation between NDVI and annual precipitation as well as between NDVI and mean temperature respectively. A stronger correlation exists between NDVI and annual precipitation,indicating that the vegetation growth is more sensitive to the inter-annual variability of precipitation.

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[7]
Church M, Rice S P, 2009. Form and growth of bars in a wandering gravel-bed river.Earth Surface Processes and Landforms, 34(10): 1422-1432.Abstract The changing form of developing alluvial river bars has rarely been studied in the field, especially in the context of the fixed, compound, mainly alternate gravel bars that are the major morphological feature of the wandering style. Century scale patterns of three-dimensional growth and development, and the consequent scaling relations of such bars, are examined along the gravel-bed reach of lower Fraser River, British Columbia, Canada. A retrospective view based on maps and aerial photographs obtained through the twentieth century shows that individual bars have a life history of about 100 years, except in certain, protected positions. A newly formed gravel bar quickly assumes its ultimate thickness and relatively quickly approaches its equilibrium length. Growth continues mainly by lateral accretion of unit bars, consistent with the lateral style of instability of the river. Bar growth is therefore allometric. Mature bars approach equilibrium dimensions and volume that scale with the overall size of the channel. Accordingly, the bars conform with several published criteria for the ultimate dimensions of alternate barforms. Sand bars, observed farther downstream, have notably different morphology. Fraser River presents a typical wandering channel planform, exhibiting elements of both meandered and low-order braided channels. Hydraulic criteria to which the Fraser bars conform illustrate why this planform develops and persists. The modest rate of bed material transfer along the channel typical of the wandering type determines a century-length time scale for bar development. This time scale is consistent with estimates that have been made for change of the macroform elements that determine the overall geometry of alluvial channels. Copyright 2009 John Wiley & Sons, Ltd.

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[8]
Friend P F, Sinha R, 1993. Braiding and meandering parameters. In: Best J L, Bristow C S. Braided Rivers. London, UK: Geological Society of London, 75: 105-111.

[9]
Gurnell A M, Petts G E, Hannah D Met al., 2001. Riparian vegetation and island formation along the gravel-bed Fiume Tagliamento, Italy.Earth Surface Processes and Landforms, 26(1): 31-62.

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[10]
Hooke J M, Yorke L, 2011. Channel bar dynamics on multi-decadal timescales in an active meandering river. Earth Surface Processes and Landforms, 36(14): 1910-1928.Occurrence and development of channel bars are major components of the morphodynamics of rivers and their relation to river meandering has been much explored through theory and experimentation. However, field and documentary data of characteristics and evolution over timescales from years to several decades are lacking. Four sets of aerial photographs in the period 1984–2007 were used to map and quantify bar numbers and areas in GIS on an active meandering reach. Bar types were classified. Additional temporal resolution was provided by annual ground photography and mapping for 1981–2010. Analysis was extended backward by use of large scale Ordnance Survey maps from 1873 onwards. As expected, point bars are the most common type but ‘free’ bars of several types are major components of bar deposition. Point bars and attached bars are significantly larger in size than mid-channel and side bars. Spatial distribution of bars varies down the reach and over time but is related to channel sinuosity, gradient and mobility and to bend evolution. Different types of bar occur in distinctive channel locations, with point and concave-bend bars in zones of high curvature. Bar activity shows a relation with discharge events and phases and possibly with changing riparian conditions, but superimposed on this is a common sequence of bar evolution from incipient gravel mid-channel bars to full floodplain integration. This life-cycle is identified as 7–965years on average. No evidence for mobility of free bars within the course is found. The results are compared with bar and bend theory; the bars are forced and conform in general to bend theory but detailed variation relates to geomorphic factors and to autogenic sequences of bends and bars. Mid-channel bars are width induced. Variability of bar occurrence needs to be taken into account in river management and ecological evaluation, including for the EU WFD. Copyright 08 2011 John Wiley & Sons, Ltd.

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[11]
Li Z,Wang Z, Pan Bet al., 2013a. Analysis of controls upon channel planform at the First Great Bend of the Upper Yellow River, Qinghai-Tibet Plateau.Journal of Geographical Sciences, 23(5): 833-848.中国科学院机构知识库(中国科学院机构知识库网格（CAS IR GRID）)以发展机构知识能力和知识管理能力为目标，快速实现对本机构知识资产的收集、长期保存、合理传播利用，积极建设对知识内容进行捕获、转化、传播、利用和审计的能力，逐步建设包括知识内容分析、关系分析和能力审计在内的知识服务能力，开展综合知识管理。

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[12]
Li Z, Wang Z, Yu Get al., 2013b. River pattern transition and its causes along Maqu reach of 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.

[13]
Liu H, Xu X, Wang Jet al., 2012. Type and distribution of aeolian geomorphology at Marqu Region of Upstream Yellow River.Arid Land Geography, 35(3): 348-357. (in Chinese)The Marqu with rangeland area of 8.57 107 hm2 is hailed as the first pasture of Asia.At present,the desertificated area is 0.6% of the total area of the Marqu county whith 7 136.77 hm2 of desertificated land and 3 600 hm2 of potential rangeland sandification,and has been expanding by the effect of climate change and people action.A field measure on eolian lanform will give reference to control the desertificated grassland of Marqu.In July and August of 2008,we investigated the grassland of Marqu county referrenced satellite image,and measured the eolian lanform,such as sand dunes and sandy blowouts and so on at plains and hills by GPS,compass and other instruments.The surveyed result shown as follows: the eolian lanform of Marqu might be classified in 17 classes or 4 grades by reference standards of dynamic factors,dynamic bed surfaces,activity and shape of sand dunes.The desertificated grassland centralized at terrace of Yellow River and middle or lower reaches of streams in Marqu,and there were also sandy grasslands on many of hills at Marqu.The sand dune was higher at first and second terraces of Yellow River than that of dunes at others places,and the highest sand dune was 12 m with the SSE direction of 64% of barchan dunes.Another place where many moving sand dunes distributed was the remaining delta including Yellow River and its branches.Most of shift and semi-shift sandy ridges with 3 m height hold the remaining delta,and prevail direction of sand ridges was NNW of 51 % of line ridge.At top of hill or adret,the line ridge and sand sheet usually was found,and distributed at the transition of landforms.The sandy grassland blowout and eolian bank were fund at fixed and semi-fixed sandy land and the transition zone between sandy land and grassland.The shapes of sandy blowout were roundness,oval,arch and horseshoe,while 60% of sandy blowouts,which connected with fixed or semi-fixed sandy dunes,were oval and horseshoe.It was direct proportional function as Y=0.49x-0.11(R2=0.899,and Y is depth,x is macro axis of blowout) which expressed the functional relation between depth and macro axis of blowout.The eolian bank with a shape as curtain usually distributed at transition zone between two landforms,such as shoulder of slope and passageway.The sedimentation of blown-sand from ancient to present supplied rich source of sand at the terraces for desertification grassland,as well as deposit rock.It was the active role that powerful wind with direction of NNW.The immense difference of physical property between surface and under layer,friable vegetation and people action accelerated differentiation and the desertification of grassland in Marqu.It is much important that the surface of grassland was prevented to destroy for controlling desertificted-grassland,while it is difficult that vegetation is destroyed to control grassland desertification with the more and more people actions at the grassland of Marqu.It is potential hazardous that surface of grassland is opened with sand under turf,while it will be much easier to prevent the land surface is destroyed for control grassland to desertify than that of improved and controlled desertificated grassland at Marqu grassland.There are mainly two deposit sandy landform which is like the general eolian-deposit morphology,such as dune and ridge which are fashioned into by wind with rich sand at Muqu region located at Tibet Plateau with cold climate,while the vegetation and local landform are special.The eolian landform,such as sandy grassland blowout and eolian bank is affected strongly by vegetation,structure of land,local morphology and cold climate,which is a characteristic of type and distribution of eolian landform at Muqu region with grassland,hill and cold climate.

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[14]
Jiang S, 2008. Analysis on variety trend of runoff between Dari and Maqu in the headwater region of Yellow River in the past 50 years.Geographical Research, 27(1): 221-228. (in Chinese)

[15]
Jones L S, Schumm S A, 1999. Causes of avulsion: An overview. In: Smith N D, Rogers J. Fluvial Sedimentology VI. Oxford, UK: Blackwell Publishing Ltd., 171-178.In braided streams, the term avulsion is sometimes used to describe the shift of the main threadof current to the other side of a mid-channel bar (Leedy et al., 1993; Miall, 1996, p. 317), but herethe term is restricted to the 171 Page 185. 172 LS Jones and SA Schumm Flow P r e

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[16]
Kidová A, Lehotský M, Rusnák M, 2016. Geomorphic diversity in the braided-wandering Belá River, Slovak Carpathians, as a response to flood variability and environmental changes.Geomorphology, 272: 137-149.61We assess the effect of different flood periods on river evolution during six last decades.61The post-flood period serial geomorphic analysis (POPSEGA) was used.61Decrease in active zone area and geomorphic diversity of the river was identified.61Increase in island area and reduction in river bank shift are related to changes in floods during last decades.

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[17]
Makaske B, 2001. Anastomosing rivers: A review of their classification, origin and sedimentary products.Earth Science Reviews, 53(3): 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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[18]
Makaske B, Smith D G, Berendsen H J A, 2002. Avulsions, channel evolution and floodplain sedimentation rates of the anastomosing upper Columbia River, British Columbia, Canada.Sedimentology, 49(5): 1049-1071.Abstract Ages of channels of the anastomosing upper Columbia River, south-eastern British Columbia, Canada, were investigated in a cross-valley transect by C dating of subsurface floodplain organic material from beneath levees. The avulsion history within the transect was deduced from these data, and morphological stages in channel development were recognized. Additionally, floodplain sedimentation rates were established. The new data demonstrate that the upper Columbia River is a long-lived, dynamic anastomosing system. Results show that anastomosis at the study location has persisted since at least 2700 cal. years BP, with avulsions occurring frequently. At least nine channels have formed in the studied cross-valley transect within the past 300065years. Channel lifetimes from formation to abandonment appear to be highly variable, ranging from approximately 800 to 300065years. Log jams provoking avulsions and/or silting up of old channels are proposed as reasons for this variability. Long-term average floodplain sedimentation rates appear to be significantly lower than previously proposed by Smith (1983, Int. Assoc. Sedimentol. Spec. Publ., 6, 155–168). A long-term (455065years) average of 1·7565mm65year(after compaction) was based on C dates, while a short-term sedimentation rate of 0·865mm was determined for a single, relatively small, seasonal flood in 1994 using sediment traps. However, short-term sedimentation rates vary considerably over the floodplain, with levees aggrading up to four times faster than floodbasins. Channels of the upper Columbia River anastomosed reach follow a consistent pattern in their development, with each stage being characterized by different morphology and processes. Channel evolution comprises the following succession: (1) avulsion stage, in which a crevasse splay channel deepens by scour and levee sedimentation; (2) widening and deepening stage, in which bank slumping and bed scouring dominates; (3) infilling stage, in which either channel narrowing (bank accretion) or channel shallowing (bed accretion) takes place; and (4) abandonment stage, in which the residual (remnant) channel is filled exclusively by silt, clay and organic material. Vertical stacking (super- imposition) of active channels on recent channel-fill sand bodies is a notable feature of the upper Columbia River, which suggests that reoccupation of residual channels is a common process.

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[19]
Makaske B, Smith D G, Berendsen H J Aet al., 2009. Hydraulic and sedimentary processes causing anastomosing morphology of the upper Columbia River, British Columbia, Canada.Geomorphology, 111(3/4): 194-205.The upper Columbia River, British Columbia, Canada, shows typical anastomosing morphology — multiple interconnected channels that enclose floodbasins — and lateral channel stability. We analysed field data on hydraulic and sedimentary processes and show that the anastomosing morphology of the upper Columbia River is caused by sediment (bedload) transport inefficiency, in combination with very limited potential for lateral bank erosion because of very low specific stream power (≤022.3W/m 2 ) and cohesive silty banks. In a diagram of channel type in relation to flow energy and median grain size of the bed material, data points for the straight upper Columbia River channels cluster separately from the data points for braided and meandering channels. Measurements and calculations indicate that bedload transport in the anastomosing reach of the upper Columbia River decreases downstream. Because of lateral channel stability no lateral storage capacity for bedload is created. Therefore, the surplus of bedload leads to channel bed aggradation, which outpaces levee accretion and causes avulsions because of loss of channel flow capacity. This avulsion mechanism applies only to the main channel of the system, which transports 87% of the water and >0290% of the sediment in the cross-valley transect studied. Because of very low sediment transport capacity, the morphological evolution of most secondary channels is slow. Measurements and calculations indicate that much more bedload is sequestered in the relatively steep upper anastomosing reach of the upper Columbia River than in the relatively gentle lower anastomosing reach. With anastomosing morphology and related processes (e.g., crevassing) being best developed in the upper reach, this confirms the notion of upstream rather than downstream control of upper Columbia River anastomosis.

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[20]
Makaske B, Lavooi E, De Haas Tet al., 2017. Upstream control of river anastomosis by sediment overloading, upper Columbia River, British Columbia, Canada.Sedimentology, doi: 10.1111/sed.12361.Anastomosing rivers, systems of multiple interconnected channels that enclose floodbasins, constitute a major category of rivers for which various sedimentary facies models have been developed. While the sedimentary products of anastomosing rivers are relatively well-known, their genesis is still debated. A rapidly growing number of ancient alluvial successions being interpreted as of anastomosing river origin, including important hydrocarbon reservoirs, urge the development of robust models for the genesis of anastomosis, to facilitate better interpretation of ancient depositional settings and controls. The upper Columbia River, British Columbia, Canada, is the most-studied anastomosing river and has played a key role in the development of an anastomosing river facies model. Two hypotheses for the origin of upper Columbia River anastomosis include the following: (i) downstream control by aggrading cross-valley alluvial fans; and (ii) upstream control by excessive bedload input from tributaries. Both upstream and downstream control may force aggradation and avulsions in the upper Columbia River. In order to test both hypotheses, long-term (millennia-scale) floodplain sedimentation rates and avulsion frequencies are calculated using 14C-dated deeply buried organic floodplain material from cross-valley borehole transects. The results indicate a downstream decrease in floodplain sedimentation rate and avulsion frequency along the anastomosed reach, which is consistent with dominant upstream control by sediment overloading. The data here link recent avulsion activity to increased sediment supply during the Little Ice Age (ca 1100 to 1950 ad). This link is supported by data showing that sediment supply to the upper Columbia study reach fluctuated in response to Holocene glacial advances and retreats in the hinterland. Upstream control of anastomosis has considerable implications for the reconstruction of the setting of interpreted ancient anastomosing systems. The present research underscores that anastomosing systems typically occur in relatively proximal settings with abundant sediment supplied to low-gradient floodplains, a situation commonly found in intermontane and foreland basins.

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[21]
Miall A D, 1977. A review of the braided river depositional environment.Earth Science Reviews, 13(1): 1-62.Generalized sedimentation models have been developed from a review of more than sixty recent papers on modern and ancient braided-stream deposits. Braided rivers consist of a series of broad, shallow channels and bars, with elevated areas active only during floods, and dry islands. There are three main bar types; longitudinal, comprising crudely bedded gravel sheets; transverse to linguoid, consisting of sand or gravel and formed by downstream avalanche-face progradation; and point or side bars, formed by bedform coalescence and chute and swale development in areas of low energy. Important sediment-forming processes include bar formation, channel-floor dune migration, low-water accretion and overbank sedimentation. Braided-stream deposits consist of up to three gravel facies, five sand facies and two fine-grained facies. Vertical sequences recorded in modern and ancient deposits are of several types: flood-, channel fill-, valley fill-, channel re-occupation- and point bar-cycles. Some of these fine upward and could be confused with meandering-river sequences. Facies assemblages and vertical sequences fall into four main classes, which are proposed as sedimentation models for the interpretation of ancient braided-river deposits in the surface and subsurface: (1) Scott type: consists mainly of longitudinal bar gravels with sand lenses formed by infill of channels and scour hollows during low water. (2) Donjek type: may be dominated by sand or gravel; distinguished by fining-upward cycles caused by lateral point-bar accretion or vertical channel aggradation. Cycles commonly are less than 3 m thick, but cycles up to 60 m may be present, representing valley-fill sequences. Longitudinal and linguoid-bar deposits, channel-floor dune deposits, bar-top and overbank deposits all may be important. (3) Platte type: characterized by an abundance of linguoid bar and dune deposits (planar and trough crossbedding). No well-developed cyclicity, probably owing to a lack of topographic differentiation in the river (no evidence of deep, primary channels, abandoned areas or overbank areas). (4) Bijou Creek type: consists of horizontally laminated sand plus subordinate amounts of sand showing planar crossbedding and ripple marks. Formed during flash floods and may be most typical of ephemeral streams.

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[22]
Mikuś P, Wyżga B, Kaczka R Jet al., 2013. Islands in a European mountain river: Linkages with large wood deposition, flood flows and plant diversity.Geomorphology, 202: 115-127.Vegetated islands are characteristic landforms of braided mountain rivers. Long-term observations and recent morphological and botanical surveys conducted in the gravel-bed Czarny Dunajec, Polish Carpathians, were used to determine the processes and patterns governing initiation and development of islands and their floristic complexity. Moreover, dendrochronologically estimated years of island inception were compared with the timing and magnitude of flood flows in the period 1970 2011 to infer about controls on the formation and persistence of islands in the river. In the high-energy, braided river, islands originate as a result of deposition of large vegetative particles, mostly large wood, on gravel bars and the associated vegetative regeneration of living wood or the growth of seedlings and saplings in the shelter of wood accumulations. Tree-ring dating of the largest trees growing in particular zones of building and established islands indicated a predominant upstream island growth in the river. It results from repeated accumulation of living wood on the head of islands and its subsequent regeneration and contrasts with the progressive downstream growth of islands in the rivers supplied with large, stable logs of the tree species without the capability to re-sprout. The lack of islands from the years 1982 1996 most likely reflects the removal of relatively young islands by two major floods in the 1990s which were, however, unable to destroy older and larger islands. After 1997 the occurrence of low to moderate floods facilitated the formation and persistence of islands. The plant inventory demonstrated that species richness increased non-linearly with the increasing age, area and shoreline length of islands. Islands supported more plant species than the riparian forest and attained comparable species richness at an early stage of development. Fast developing, dynamic and supporting rich plant communities, islands contribute highly to the overall floristic complexity of the river corridor and their re-establishment should be viewed as an important factor in the restoration of hydromorphologically degraded mountain rivers.

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[23]
Miller J R, 1991. Development of anastomosing channels in south-central Indiana.Geomorphology, 4: 221-229.Avulsion is typically associated with aggrading fluvial systems, but the investigated streams are undergoing an episode of degradation. Avulsion occurs because of localized deposition along concave-up channel segments. The concave-up channel reaches are spatially controlled by the occurrence of non-resistant strata that separate beds of resistant sandstone. Thus, the location of avulsion and anastomosing channels is predetermined by the lithology and stratigraphy of the underlying bedrock.

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[24]
Osterkamp W R, 1998. Processes of fluvial island formation, with examples from Plum Creek, Colorado and Snake River, Idaho.Wetlands, 18(4): 530-545.A fluvial island is a landform, elevated above and surrounded by stream-channel branches or waterways, that persists sufficiently long to establish permanent vegetation. Natural fluvial islands occur in any part of a drainage network but most commonly in montane, piedmont-valley, and coastal flood-plain environments. Processes, often interactive, by which islands form include avulsion (the sudden separation of land by a flood or by an abrupt change in the course of a stream), rapid and gradual channel incision, channel migration, dissection of both rapidly and slowly deposited bed sediment, and deposition of bed sediment on a vegetated surface or behind a channel obstruction. Products of high-energy conditions, fluvial islands typically lack stability over decades to millennia. Fluvial islands in Plum Creek, Colorado, USA, results of sorting processes following a recent high-magnitude flood, and in the Snake River, Idaho, USA, partly results of the Pleistocene Bonneville Flood, Illustrate how islands form, develop, and disappear. The examples consider differing conditions of island shape, size, height, sediment, and vegetation.

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[25]
Picco L, Mao L, Rainato Ret al., 2014. Medium-term fluvial island evolution in a disturbed gravel-bed river (Piave River, Northeastern Italian Alps). Geografiska Annaler: Series A,Physical Geography, 96(1): 83-97.lt;P>River islands are defined as discrete areas of woodland vegetation surrounded by either water-filled channels or exposed gravel. They exhibit some stability and are not submerged during bank-full flows. The aim of the study is to analyze the dynamics of established, building, and pioneer islands in a 30-km-long reach of the gravel-bed Piave River, which has suffered from intense and multiple human impacts. Plan-form changes of river features since 1960 were analyzed using aerial photographs, and a LiDAR was used to derive the maximum, minimum and mean elevation of island surfaces, and maximum and mean height of their vegetation. The results suggest that established islands lie at a higher elevation than building and pioneer islands, and have a thicker layer of fine sediments deposited on their surface after big floods. After the exceptional flood in 1966 (RI65>65200 years) there was a moderate increase in island numbers and extension, followed by a further increase from 1991, due to a succession of flood events in 1993 and 2002 with RI65>6510 years, as well as a change in the human management relating to the control of gravel-mining activities. The narrowing trend (1960–1999) of the morphological plan form certainly enhanced the chance of islands becoming established and this explains the reduction of the active channel, the increase in established islands and reduction of pioneer islands.</P>

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[26]
Qi D, Li G, 2008. Status, causes and protection counter measures of wetland degradation in Maqu County in the Upper Yellow River.Wetland Science, 5(4): 341-347. (in Chinese)Wetland is praised as"kidney of the earth" and regarded as one of three main ecosystems,besides forest and ocean on the earth.Apart from offering human being food,materials and water resources,wetland has important environment regulating function and irreplaceable effects on maintaining regional ecological balance,conserving biodiversity and precious species,etc..Maqu wetland in the upper Yellow River has special ecological function because of its special geographical location.However,it is very serious in drying,shrinking and degradation of wetland in Maqu county.Damages and causes of wetland degradation of Maqu county in the upper Yellow River were mainly expounded in the paper.The damages of wetland degradation in Maqu county mainly include rapidly decreasing of water conservation function,aggravating of soil erosion,sharply reducing of biodiversity,largely degrading of wetland grassland and increasing of ecological refugee.The causes of wetland degradation are the results of both natural factors and factitious factors.The natural factors mainly include climate warming,precipitation reducing,groundwater level declining and geological structure of soil changing;the influences of human activities mainly include overgrazing,excessively digging,frequently occurring of rats and pests disaster and increasingly enlarging of wetland grassland desertification area.The corresponding protection countermeasures of Maqu wetland were presented,including raising the environment protecting consciousness of local people,reinforcing lawmaking of wetland,perfecting wetland policy and law,increasing financing investment,enhancing wetland science and technology research and application,developing wetland ecological tourism resources,truly fulfilling grassland contract system and strictly controlling grazing intensity.With regard to protection of wetland,there need not only improving of rules and regulations,but mature control techniques as well and the regulations should be prior to the techniques.The degradation of wetland in Maqu county can not be solved drastically until the regulations are enhanced,legal system are perfected and the consciousness of people' improved continually.At the same time,it must be done for wetlands to adopt the advanced,operable in Maqu county,effective and feasible control techniques as well as long term control and protection.

[27]
Rice S P, Church M, Wooldridge C Let al., 2009. Morphology and evolution of bars in a wandering gravel-bed river; lower Fraser river, British Columbia, Canada.Sedimentology, 56(3): 709-736.A hierarchical typology for the channels and bars within aggradational wandering gravel-bed rivers is developed from an examination of a 50 km reach of lower Fraser River, British Columbia, Canada. Unit bars, built by stacking of gravelly bedload sheets, are the key dynamic element of the sediment transfer system, linking sediment transport during individual freshets to the creation, development and remoulding of compound bar platforms that have either a lateral or medial style. Primary and secondary unit bars are identified, respectively, as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels. The record of bar accretion evident in ground-penetrating radar sequences is consistent with the long-term development of bar complexes derived from historical aerial photographs. For two compound bars, inter-annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer-term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys. Annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel, indicating that relatively little bed material bypasses the bars. Bar construction and change are accomplished mainly by lateral accretion as the river has limited capacity to raise bed load onto higher surfaces. Styles of accretion and erosion and, therefore, the major bar form morphologies on Fraser River are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features. For example, 65-year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers.

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[28]
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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[29]
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.The classification can be applied to ancient alluvial deposits through an understanding of the processes that relate channel morphologies to their resulting sedimentary suites. As the processes are imperfectly understood, so the application to paleochannels is imprecise. However, it can be made satisfactorily in most cases, provided maximum use is made of the channel-process information in alluvial sedimentary models.

[30]
Schumm S A, 1968. Speculations concerning paleohydrologic controls of terrestrial sedimentation.Geological Society of America Bulletin, 79(11): 1573-1588.Abstract The relations that have been recorded among modern climatic, phytologic, and hydrologic data are used to speculate about the effects of evolving vegetation on the hydrologic cycle. At present the peak of erosion rates occurs in semiarid regions, whereas during prevegetation time erosion rates rose to a plateau, the magnitude of which depended upon the erodibility and weathering characteristics of the rocks. With the appearance of terrestrial vegetation and its colonization of the earth's surface, erosion rates decreased, as did runoff and flood peaks. A review of the relations existing between the morphologic and hydrologic characteristics of river channels demonstrates that fluvial sedimentary deposits are significantly different depending upon the nature of the sediment load moved through the channel. Combining the conclusions obtained from an analysis of hydrologic relations with conclusions concerning effects of type of sediment load upon river morphology, it is possible to speculate on the changing nature of the land phase of the hydrologic cycle before and during the colonization of the landscape by vegetation. During prevegetation time, bed-load channels moved coarse sediments from their sources and spread them as sheets on piedmont areas. With increased plant cover, alluvial deposits were stabilized, but large floods caused periodic flushing of sediment from the system, thereby creating cyclic sedimentary deposits. The influence of climate change on the volume and type of sediment moved from an erosional system became more pronounced as the effect of vegetation on the hydrologic cycle increased. Finally, with the appearance of grasses during the Cenozoic Era, the relations between climate, vegetation, erosion, and runoff became much as today except for the influence of man.

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[31]
Singh M, Evans D, Friess Det al., 2015. Mapping above-ground biomass in a tropical forest in Cambodia using canopy textures derived from Google Earth.Remote Sensing, 7(5): 5057-5076.This study develops a modelling framework for utilizing very high-resolution (VHR) aerial imagery for monitoring stocks of above-ground biomass (AGB) in a tropical forest in Southeast Asia. Three different texture-based methods (grey level co-occurrence metric (GLCM), Gabor wavelets and Fourier-based textural ordination (FOTO)) were used in conjunction with two different machine learning (ML)-based regression techniques (support vector regression (SVR) and random forest (RF) regression). These methods were implemented on both 50-cm resolution Digital Globe data extracted from Google Earth (GE) and 8-cm commercially obtained VHR imagery. This study further examines the role of forest biophysical parameters, such as ground-measured canopy cover and vertical canopy height, in explaining AGB distribution. Three models were developed using: (i) horizontal canopy variables (i.e., canopy cover and texture variables) plus vertical canopy height; (ii) horizontal variables only; and (iii) texture variables only. AGB was variable across the site, ranging from 51.02 Mg/ha to 356.34 Mg/ha. GE-based AGB estimates were comparable to those derived from commercial aerial imagery. The findings demonstrate that novel use of this array of texture-based techniques with GE imagery can help promote the wider use of freely available imagery for low-cost, fine-resolution monitoring of forests parameters at the landscape scale.

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[32]
Smith D G, Smith N D, 1980. Sedimentation in anastomosed river systems: examples from alluvial valley near Bannf, 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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[33]
Tabata K K, Hickin E J, 2003. Interchannel hydraulic geometry and hydraulic efficiency of the anastomosing Columbia River, southeastern British Columbia, Canada.Earth Surface Processes and Landforms, 28(8): 837-852.Abstract The morphodynamics of the anastomosing channel system of upper Columbia River in southeastern British Columbia, Canada, is examined using an adaptation of conventional hydraulic geometry termed ‘interchannel hydraulic geometry’. Interchannel hydraulic geometry has some of the characteristics of downstream hydraulic geometry but differs in that it describes the general bankfull channel form and hydraulics of primary and secondary channels in the anastomosing channel system. Interchannel hydraulic geometry generalizes these relationships and as such becomes a model of the geomorphology of channel division and combination. Interchannel hydraulic geometry of upper Columbia River, based on 03eld measurements of 04ow velocity and channel form at 16 test sections, is described well by simple power functions: w bf = 3·24 Q bf 0·64 ; d bf = 1·04 Q bf 0·19 ; v bf = 0·30 Q bf 0·17 . These results, with other related measurements of 04ow resistance, imply that channel splitting leads to hydraulic inef03ciency (higher 04ow resistance) on the anastomosing Columbia River. Because these 03ndings differ from those reported in studies elsewhere, we conclude that hydraulic ef03ciency does not provide a general explanation for anabranching in river channels. Copyright 08 2003 John Wiley & Sons, Ltd.

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[34]
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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[35]
Wang S, 2003. Architectures, relationships between discharges and width/depth ratios of stream cross profiles, and stream powers of anastomosing rivers.Acta Sedimentologica Sinica, 21(4): 565-570. (in Chinese)As a new type of rivers, anastomosing river has been concerned by researchers although some questions about it was not clear for understanding it. This paper discusses the river architectures, relationships between width/depth ratios of stream cross sections and discharges, and stream powers of anastomosing rivers according to references and obtained data recently. It is helpful to researchers who is interested in this river pattern to develop the theory for it. Many aspects of anastomosing river appear particular characteristics compared with other river patterns. In the planform architectures, the multiple channels joining each other enclose flood basins on which vegetation, swamps and lakes develop basically. Longitudinal gradients of the channels are very low while the channel width/depth ratios are smaller than 40. In the depositional architectures of cross profiles, some isolated sand bodies of channel deposits are "floating" in the mud bodies of flood basins. In the half logarithm diagram of width/depth ratios of stream cross profiles vs. discharges, the scatters of anastomosing rivers are below compared with that of other river patterns. The stream powers of anastomosing rivers are very low compared with the old trunk channel from which it diverted because the channel gradients and discharges of every anastomosing channel are smaller than that of the old trunk channel. The specific stream power of the anastomosing channels: eastern Songzi River, western Songzi River, Hudu River, Ouchi River, northern Ouchi River and Songliheliu River are 3.0 W/m 2, 5.5 W/m 2, 2.8 W/m 2, 6.4 W/m 2, 3.7 W/m 2 and 2.7 W/m 2, respectively. Obviously, all of them are smaller than 10 W/m 2. But the specific stream power of anabranched Changjiang trunk channel is 140 W/m 2. All of the characteristics of anastomosing rivers indicate that this river pattern is different from the anabranched rivers represented by the lower Changjiang River, especially from other river patterns.

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[36]
Wang S, 2004. Simulation experiment of anastomosing multiple channel formation. In: Hu C, Tan Y. Proceedings of the Ninth International Symposium on River Sedimentation. Beijing: Tsinghua University Press, 1747-1753.The anastomosing river is a fluvial river pattern that recently gets more and more attention from researchers. The hydrological, geomorphologic and sedimentological characteristics of some anastomosing rivers have been revealed. But the experiment simulation of anastomosing rivers is vacant hitherto. The flume simulation experiments are the reappearance of natural rivers under the condition of decreasing time and space. This work reports the formation and evolution of an anastomosing river simulated in the flume. The experimental beginning condition is: an artificial meandering channel in the assistant area of flume; a rectangle floodplain (4.5 m x 16.5 m) with concave cross sections is in the objective area and its stratum has a structure of double layers. The upper layer with a thickness of 1.5 cm consisted of Gaoling which median grain size is 0.013,2 mm; the under layer, consisted of fine sands which median grain size is 0.188 mm, has a thickness of 0.5 m. The mean longitudinal gradient of the floodplain is 0.005,8 from 5.5 m to 17 rn and 0.007,7 from 17 m to 22 m along the ordinate. Adoptive constant discharge is 3 L (.) s(-1). Suspended sediment discharge is 4.5 g (.) min(-1) in the primary 3 h and 1.2 g (.) s(-1) thereafter. The total time span of flume experiment is 50 h. In the initial stage of simulation sedimentation mainly occurred in the upper reach, random erosion occurred in the middle reach and the back-ward erosion mainly occurred in the lower reach of the objective area. A rudimental anastomosing river with multiple channels connected each other basically appears about 13.5 h. Hereafter, up to 25.5 h the evolution fashion of the anastomosing river changed from downcutting erosion to faint lateral erosion and the fall back of channel banks is not evident, it indicates that the anastomosing channels changes into its autumn. From 25.5 h to 50 h the abandonment or avulsion of an individual channel are the new evolution characteristics of the simulated anastomosing river. The whole flume experiment simulates successfully the formation and evolution of natural anastomosing rivers and proves that the anastomosing river is a new river pattern, which is different from anabranched river. This is a useful attempt to reveal the formation of anastomosing rivers via flume simulation and helpful to understand the characteristics of anastomosing rivers.

[37]
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.

[38]
Wang S, Chen Z, Smith D G, 2005. Anastomosing river system along the middle Yangtze River Basin, Southern China.Catena, 60(2): 147-163.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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[39]
Wang S, Ni J, Wang Get al., 2004. Hydrological processes of an anastomosing river system on the Zhujiang River delta, China.Journal of Coastal Research, 43(Special Issue): 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.

[40]
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】：

[41]
Wang S J, Li J S, Yin S P, 2000. Basic characteristics and controlling factors of anastomosing fluvial systems.Chinese Geographical Science, 10(1): 31-38.

[42]
Wyrick J R, Klingeman P C, 2011. Proposed fluvial island classification scheme and its use for river restoration.River Research and Applications, 27(7): 814-825.Abstract Fluvial islands are present in nearly all natural and regulated rivers. They are important from hydrological, biological, geopolitical and socio-economic points of view. As ubiquitous as islands are, consideration of islands is relatively absent in most river restoration concepts. The natural river processes that allow for island formation can easily be integrated into typical river classifications. To begin, an island classification scheme is proposed that can become a tool for improved river classifications and restoration projects. In developing an island classification scheme, the objectives are similar to those of previous river classification methods. By observing island characteristics, inductive generalizations may be made about the river's hydrologic and ecologic potential. In river hierarchies, the distinguishing variables used to describe streams were characteristics that could easily be discerned from their appearances, i.e. field-determinable features. A similar approach is sought for island classification. The distinguishing characteristics of any island may be sorted into three basic categories: those that can be measured from a topographic map or an aerial photograph; those that can be measured in situ at the island and those that can be inferred from either a known history of the island or from the other characteristics of the island. Once all the suitable characteristics were identified, a matrix for island classification was created which can be used to classify island origin and type. The better that the inter-relationship between island formation, channel processes and watershed processes are understood, the better the natural bio-physical regime of the river corridor can be identified and incorporated into restoration plans. Copyright 2010 John Wiley & Sons, Ltd.

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[43]
Yin S, Xie Q, Guan S, 2000. Study on anastomosed river with comparative sedimentology.Acta Sedimentologica Sinica, 18(2): 221-226. (in Chinese)Based on the theory of comparative sedimentology, this paper gives the detailed description of both the modern anastomosed river (Qiqihaer Nenjiang section) and the corresponding ancient ones(Huanghua depression and Qaidam basin). The paper presents the depositional processes,characteristics of sedimentary rhythm,geometry and heterogeneity of the modern anastomosed river with a reference material home and abroad, and generalizes the depesitiomal model. The river in Qiqihaer has the following features, that is, low slope gradient, small with/depth ratio, fast aggradation rate, the channel anastomosed, and confined lateral migration, and soon. The river can be divided into six sub-facies such as anastomosed channel, natural levee, crevasse splay, river beach, inter-river lake, and swamp. All provide the basis for the analysis of ancient corresponding reservoir quality sand bodies. The ancient anastomosed river, influenced by post-depositional physical or chemical reaction such as diagenesis, presents relative difference compared with the modern one, but both have similar sedimentary characteristics in morphology, environments, sand body structure, rhythm, and so on. It is this similarity that provides the basis of comparative sedimentology and its application. The authors discuss the formation mechanism on the anastomosed river so as to put forward a general discipline as a direction for further study. The river's formation is controlled by various factors, the authors explore that it is related to the low slope gradient, massive vegetation, flood development, and the uniform development. Sometimes the anastomosed river can be transformed from braided river. With the knowledge and comparative study on both the modern and ancient anastomosing river, we can analyse geometry, continuity, and heterogeneity of underground related sand bodies, which is very important in the course of exploration and development of petroleum.

[44]
Yu G, Brierley G, Huang H Qet al., 2014. An environmental gradient of vegetative controls upon channel planform in the source region of the Yangtze and Yellow rivers.Catena, 119: 143-153.中国科学院机构知识库(中国科学院机构知识库网格（CAS IR GRID）)以发展机构知识能力和知识管理能力为目标，快速实现对本机构知识资产的收集、长期保存、合理传播利用，积极建设对知识内容进行捕获、转化、传播、利用和审计的能力，逐步建设包括知识内容分析、关系分析和能力审计在内的知识服务能力，开展综合知识管理。

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[45]
Yu G, Liu L, Li Zet al., 2013. Fluvial diversity in relation to valley setting in the source region of the Yangtze and Yellow rivers.Journal of Geographical Sciences, 23(5): 817-832.The spatial distribution of valley setting (laterally-unconfined, partly-confined, or confined) and fluvial morphology in the source region of the Yangtze and Yellow Rivers is contrasted and analyzed.The source region of the Yangtze River is divided into 3 broad sections (Ⅰ, Ⅱ and Ⅲ) based on valley setting and channel gradient, with the upstream and downstream sections being characterized by confined (some reaches partly-confined) valleys, while the middle section is characterized with wide and shallow, laterally-unconfined valleys.Gorges are prominent in sections Ⅰ and Ⅲ, while braided channel patterns dominate section Ⅱ.By contrast, the source region of the Yellow River is divided into 5 broad sections (sections Ⅰ-Ⅴ) based on valley characteristics and channel gradient.Sections Ⅰ, Ⅱ and Ⅳ are alluvial reaches with mainly laterally-unconfined (some short reaches partly-confined) valleys.Sections Ⅲ and Ⅴ are mainly confined or partly-confined.Greater morphological diversity is evident in the source region of the Yellow River relative to the upper Yangtze River.This includes braided, anabranching, anastomosing, meandering and straight alluvial patterns, with gorges in confined reaches.The macro-relief (elevation, gradient, aspect, valley alignment and confinement) of the region, linked directly to tectonic movement of the Qinghai-Tibet Plateau, tied to climatic, hydrologic and biotic considerations, are primary controls upon the patterns of river diversity in the region.

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[46]
Zanoni L, Gurnell A, Drake Net al., 2008. Island dynamics in a braided river from analysis of historical maps and air photographs.River Research and Applications, 24(8): 1141-1159.Abstract An analysis of island and active corridor dynamics is presented for a 1665km island-braided reach of the gravel-bed Tagliamento River (Italy) based upon information extracted, geocorrected and registered to a common base from three map (1803, 1833, 1927) and nine aerial photograph sources (1944/6, 1954, 1970, 1986, 1991, 1996, 1997, 1999, 2005). The active corridor width showed a general decline over the study period but with some recent widening. Adjustments in active corridor width were achieved through processes of floodplain avulsion, island attachment and progressive encroachment of the edge of the active corridor across gravel areas. These adjustments were accompanied by the preferential creation of dissection (floodplain avulsion) islands during periods of widening and the construction of mid islands within the corridor during periods of narrowing. Changes in island extent were achieved by rapid island turnover, which reached a maximum rate of over 50% per annum when corridor narrowing was most rapid between 1970 and 1991. Very few island surfaces were found to persist for more than 24 years. Despite this enormous dynamism and apparent cyclic behaviour, between 1944/6 and 2005 the ratio of island area to active corridor area remained relatively constant at around 0.08 and supported a consistently high bankfull shoreline to downstream length ratio of around 665km65·65km 611 . These intrinsic properties of the dynamics of the study reach and other island-braided channels need to be recognized and maintained by river managers because they represent a characteristic habitat dynamism that is crucial to the maintenance of ecological integrity. Copyright 08 2008 John Wiley & Sons, Ltd.

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