Journal of Geographical Sciences >
Bank and point bar morphodynamics in the Lower Jingjiang Reach of the Yangtze River in response to the Three Gorges Project
Wang Hongyang, PhD, specialized in hydraulics and river dynamics. E-mail: 861309583@qq.com |
Received date: 2021-09-03
Accepted date: 2021-12-29
Online published: 2022-10-25
Supported by
Key Program of National Natural Science Foundation of China(U2040219)
National Natural Science Foundation of China(51579015)
Program of National Key Research and Development Plan of China(2016YFC0402108)
Program of National Key Research and Development Plan of China(2016YFC0402103)
Geomorphic dynamics of alluvial rivers in response to upstream damming have substantial impacts on navigation, habitat protection, and channel stability. The purpose of this study was to determine how flow and sediment regimes, and meander characteristics affect the morphological adjustment of bends in the Lower Jingjiang Reach (LJR) before and after the Three Gorges Project (TGP). Based on detailed field measurements and hydrological and topographic datasets from 1991 to 2016, banks and point bars morphodynamics of 12 continuous bends in the LJR were comprehensively analyzed. Point bars in the LJR mainly experienced a net deposition before the TGP operation, but substantially deteriorated with a net erosion rate of 4.6 million m3 yr‒1 in the post-TGP periods (2003-2016), and erosion on heads and upstream margins of point bars was a general adjustment pattern in the 12 bends. The most significant morphological changes of point bars and banks occurred in 2006-2011, indicating a delayed response of the channel evolution of the LJR to damming. Detailed observations suggested that the medium discharges (16,000-18,000 m3 s‒1) were the most contributive discharges in shaping the morphology of point bars and banks in the LJR after damming. In addition, we revealed the importance of sediment supply on meander deformation of the LJR, driven by sediment exchange over point bars, and more upstream planform deformation tended to occur in bends with high sinuosity (>2.0) in the LJR after damming. The relationship between meander deformation and sinuosity was manifested through the geometric adjustment range of point bars. The morphological adjustments of point bars in the highly curved or compound bends of the LJR were more conducive to cause flow deflections, leading to form concave-bank bars after the TGP operation.
WANG Hongyang , LU Yongjun , YAO Shiming , ZUO Liqin , LIU Huaixiang . Bank and point bar morphodynamics in the Lower Jingjiang Reach of the Yangtze River in response to the Three Gorges Project[J]. Journal of Geographical Sciences, 2022 , 32(8) : 1530 -1556 . DOI: 10.1007/s11442-022-2009-2
Figure 1 Sketch maps of the study area: (a) Yangtze River Basin and (b) Lower Jingjiang Reach with locations of measured cross sections and Jianli hydrological station |
Table 1 Sources of data |
Data type | Station | Period | Sources |
---|---|---|---|
Daily discharge | Jianli | 1991-2016 | CWRC |
Daily water level | Jianli | 1991-2016 (excluding 1996 and 1997) | CWRC |
Daily suspended sediment concentration | Jianli | 1991-2016 | CWRC |
Topographic data | Topographic digital mapping | 1991, 1996, 1998, 2002, 2006, 2011, 2016 | CWRC |
Note: The topographic data source of this paper was the digital AutoCAD mapping (1:10 000) of the LJR measured and drawn by the Hydrology and Water Resources Survey Bureau of Jingjiang River. |
Figure 2 Variations of daily discharge, water level, and suspended sediment concentration at the Jianli hydrological station from 1991 to 2016 |
Table 2 Characteristics of the 12 consecutive bends in the Lower Jingjiang Reach |
Bends | Length of protected bank (km) | Chord length (m) | Thalweg length (m) | Sinuosity | Radius of curvature at the apex (m) | Planform type of meander morphology |
---|---|---|---|---|---|---|
Bend 1 | 9.4 | 7012 | 8895 | 1.27 | 1450 | Simple asymmetric |
Bend 2 | 9.5 | 4071 | 10650 | 2.62 | 1030 | Compond asymmetric |
Bend 3 | 2.8 | 4723 | 7322 | 1.55 | 1220 | Compond asymmetric |
Bend 4 | 10.2 | 8330 | 9210 | 1.11 | 2840 | Simple asymmetric |
Bend 5 | 31.7 | 8755 | 11684 | 1.33 | 2360 | Simple asymmetric |
Bend 6 | 5.2 | 6591 | 6808 | 1.03 | 4340 | Simple asymmetric |
Bend 7 | 8.1 | 5186 | 5710 | 1.10 | 3530 | Simple symmetric |
Bend 8 | 11.1 | 5541 | 6240 | 1.13 | 1920 | Simple asymmetric |
Bend 9 | 10.6 | 4423 | 9066 | 2.05 | 957 | Simple asymmetric |
Bend 10 | 6 | 8361 | 12417 | 1.49 | 1810 | Simple asymmetric |
Bend 11 | 16.1 | 2197 | 8773 | 3.99 | 707 | Compond asymmetric |
Bend 12 | 3.4 | 2906 | 7752 | 2.67 | 722 | Elongated simple asymmetric |
Note: The planform type of meander bends is defined based on Hooke (1984). |
Table 3 Elevation accuracy values for the annual digital terrain models (DTM) with a 5 m × 5 m cell size |
DTM | Elevation error (m) | ||
---|---|---|---|
SE | RMSE | MAE | |
1991 | 0.003 | 0.120 | 0.066 |
1996 | 0.003 | 0.110 | 0.059 |
1998 | 0.003 | 0.160 | 0.071 |
2002 | 0.003 | 0.224 | 0.104 |
2006 | 0.003 | 0.167 | 0.094 |
2011 | 0.003 | 0.173 | 0.106 |
2016 | 0.003 | 0.154 | 0.082 |
Note: The analysis was performed separately each year for the point bars, and concave banks. SE is standard error of mean, RMSE is root mean square error, and MAE is mean absolute error. |
Table 4 Reach-averaged hydraulic characteristics obtained from the field campaigns |
Campaign | Date | Reach | Transect | Q | H | W | D | U | J |
---|---|---|---|---|---|---|---|---|---|
m3 s‒1 | m | m | m | m s‒1 | ×10‒5 | ||||
1 | 2016/06/24 | Bend 2 | CS1, CS6 | 18,000 | 31.74 | 1118 | 14.87 | 1.16 | 6.2 |
Bend 3 | CS2, CS7 | 31.27 | 1006 | 15.03 | 1.23 | 4.2 | |||
2 | 2016/10/19 | Bend 2 | CS1, CS6 | 8340 | 25.04 | 940 | 10.03 | 1.01 | 6.3 |
Bend 3 | CS2, CS7 | 24.65 | 779 | 11.61 | 0.98 | 4 | |||
3 | 2019/07/26 | Bend 2 | CS1, CS6 | 23,700 | 33.57 | 1128 | 17.03 | 1.33 | 6.4 |
Bend 3 | CS2, CS7 | 33.09 | 1060 | 16.29 | 1.41 | 5.2 |
Note: Flow discharge (Q); Water level (H); Width of the water surface (W); Hydraulic depth (D); Reach-averaged velocity (U); Slope of the water surface (J). |
Table 5 Annual average erosion and deposition of the 12 consecutive bends in the Lower Jingjiang Reach from 1991 to 2016 |
Years | Bankfull channel | Point bar | Relative error (%) | ||||
---|---|---|---|---|---|---|---|
Deposition volume (106 m3 yr‒1) | Erosion volume (106 m3 yr‒1) | Erosion volume as proportion of total volume change (%) | Deposition volume (106 m3 yr‒1) | Erosion volume (106 m3 yr‒1) | Erosion volume as proportion of total volume change (%) | ||
Before TGP | |||||||
1991-1996 | 44.6 | 32.9 | 42.4 | 8.4 | 8.4 | 50.0 | 1.10 |
1996-1998 | 113.9 | 72.5 | 38.9 | 28.9 | 15.5 | 34.9 | -0.15 |
1998-2002 | 60.0 | 43.4 | 42.0 | 10.6 | 9.3 | 46.6 | -0.29 |
1991-2002 | 34.6 | 16.3 | 32.1 | 7.4 | 4.4 | 37.5 | 0.06 |
After TGP | |||||||
2002-2006 | 27.0 | 61.2 | 69.4 | 2.8 | 14.1 | 83.6 | -0.16 |
2006-2011 | 34.9 | 39.1 | 52.8 | 8.9 | 8.7 | 49.2 | -0.27 |
2011-2016 | 18.3 | 38.3 | 67.7 | 4.9 | 9.3 | 65.3 | -0.15 |
2002-2016 | 10.9 | 29.3 | 73.0 | 2.7 | 7.3 | 73.0 | -0.09 |
Note: The relative error was the comparison of interannual change volumes of these bends in the LJR, which were calculated by the trapezoidal rule and simpson's rule in the software Surfer, respectively. |
Figure 3 Variations in shape and width to depth ratio (WDR) of the typical transects from 1991 to 2016 |
Figure 4 Temporal variations of geometry in typical Bend 2 during both pre- and post-TGP |
Table 6 Annual average erosion and deposition of each point bar and concave bank in bends 1-12 from 1991 to 2016 |
Years | Point bar | Concave bank | |||||
---|---|---|---|---|---|---|---|
Deposition volume (106 m3 yr‒1) | Erosion volume (106 m3 yr‒1) | Erosion as proportion of total volume change (%) | Deposition volume (106 m3 yr‒1) | Erosion volume (106 m3 yr‒1) | Erosion as proportion of total volume change (%) | ||
Bend 1 | |||||||
1991-1996 | 0.56 | 1.19 | 67.9 | 1.67 | 0.34 | 17.1 | |
1996-1998 | 1.49 | 1.07 | 41.9 | 4.75 | 0.21 | 4.2 | |
1998-2002 | 0.21 | 1.52 | 88.1 | 2.22 | 0.15 | 6.4 | |
1991-2002 | 0.30 | 0.98 | 76.9 | 2.12 | 0.003 | 0.1 | |
2002-2006 | 0.27 | 0.83 | 75.3 | 0.43 | 1.10 | 72.1 | |
2006-2011 | 0.33 | 0.88 | 72.5 | 0.62 | 0.23 | 27.0 | |
2011-2016 | 0.12 | 0.78 | 86.9 | 0.27 | 0.47 | 63.5 | |
2002-2016 | 0.03 | 0.62 | 95.4 | 0.20 | 0.33 | 61.9 | |
Bend 2 | |||||||
1991-1996 | 1.14 | 0.48 | 29.9 | 0.32 | 0.59 | 64.6 | |
1996-1998 | 2.10 | 2.62 | 55.6 | 3.02 | 0.44 | 12.8 | |
1998-2002 | 1.67 | 0.52 | 23.9 | 0.57 | 1.29 | 69.2 | |
1991-2002 | 0.78 | 0.16 | 17.2 | 0.27 | 0.21 | 44.1 | |
2002-2006 | 0.18 | 1.97 | 91.8 | 0.65 | 0.58 | 47.5 | |
2006-2011 | 0.73 | 1.92 | 72.5 | 21.54 | 2.22 | 9.3 | |
2011-2016 | 0.90 | 0.60 | 40.0 | 2.61 | 20.67 | 88.8 | |
2002-2016 | 0.18 | 1.01 | 85.1 | 0.60 | 0.13 | 17.3 | |
Bend 3 | |||||||
1991-1996 | 0.34 | 0.14 | 29.8 | 0.27 | 0.28 | 51.7 | |
1996-1998 | 0.89 | 1.15 | 56.4 | 1.58 | 0.66 | 29.4 | |
1998-2002 | 0.58 | 0.15 | 20.3 | 0.70 | 0.22 | 23.9 | |
1991-2002 | 0.28 | 0.08 | 22.6 | 0.37 | 0.06 | 14.6 | |
2002-2006 | 0.13 | 0.62 | 82.4 | 0.17 | 0.44 | 72.6 | |
2006-2011 | 0.29 | 0.79 | 73.5 | 0.40 | 0.11 | 20.9 | |
2011-2016 | 0.65 | 0.12 | 15.9 | 0.09 | 0.32 | 77.5 | |
2002-2016 | 0.08 | 0.21 | 73.1 | 0.08 | 0.14 | 62.5 | |
Bend 4 | |||||||
1991-1996 | 0.58 | 0.60 | 51.2 | 0.74 | 0.09 | 11.0 | |
1996-1998 | 1.71 | 0.82 | 32.5 | 1.70 | 0.09 | 5.0 | |
1998-2002 | 0.30 | 1.02 | 77.3 | 0.47 | 0.46 | 49.4 | |
1991-2002 | 0.39 | 0.49 | 56.0 | 0.61 | 0.01 | 1.8 | |
2002-2006 | 0.07 | 1.72 | 95.9 | 0.12 | 0.41 | 77.0 | |
2006-2011 | 0.73 | 0.50 | 40.9 | 0.31 | 0.08 | 19.8 | |
2011-2016 | 0.16 | 0.71 | 81.6 | 0.18 | 0.16 | 46.9 | |
2002-2016 | 0.15 | 0.74 | 82.9 | 0.09 | 0.09 | 48.0 | |
Years | Point bar | Concave bank | |||||
Deposition volume (106 m3 yr‒1) | Erosion volume (106 m3 yr‒1) | Erosion as proportion of total volume change (%) | Deposition volume (106 m3 yr‒1) | Erosion volume (106 m3 yr‒1) | Erosion as proportion of total volume change (%) | ||
Bend 5 | |||||||
1991-1996 | 0.73 | 2.86 | 79.8 | 1.49 | 0.34 | 18.7 | |
1996-1998 | 7.40 | 2.41 | 24.6 | 3.17 | 0.84 | 21.0 | |
1998-2002 | 3.10 | 1.41 | 31.3 | 1.61 | 0.71 | 30.6 | |
1991-2002 | 1.00 | 0.67 | 40.3 | 1.42 | 0.16 | 10.0 | |
2002-2006 | 0.73 | 1.29 | 63.7 | 0.52 | 0.88 | 63.1 | |
2006-2011 | 0.60 | 0.61 | 50.4 | 0.84 | 0.33 | 28.1 | |
2011-2016 | 1.28 | 0.37 | 22.7 | 0.26 | 0.75 | 74.5 | |
2002-2016 | 1.07 | 0.18 | 14.4 | 0.32 | 0.42 | 56.6 | |
Bend 6 | |||||||
1991-1996 | 0.70 | 1.00 | 58.7 | 0.37 | 0.13 | 26.1 | |
1996-1998 | 1.20 | 1.72 | 59.0 | 0.70 | 0.03 | 4.5 | |
1998-2002 | 0.40 | 1.24 | 75.7 | 0.30 | 0.11 | 26.1 | |
1991-2002 | 0.36 | 0.88 | 70.9 | 0.34 | 0.05 | 12.5 | |
2002-2006 | 0.18 | 0.84 | 81.9 | 0.52 | 0.88 | 63.1 | |
2006-2011 | 0.60 | 0.61 | 50.4 | 0.23 | 0.11 | 33.7 | |
2011-2016 | 0.19 | 0.71 | 79.3 | 0.00 | 0.43 | 99.7 | |
2002-2016 | 0.15 | 0.53 | 77.6 | 0.02 | 0.16 | 91.6 | |
Bend 7 | |||||||
1991-1996 | 0.16 | 0.27 | 62.0 | 0.15 | 0.18 | 55.0 | |
1996-1998 | 0.47 | 1.12 | 70.4 | 0.92 | 0.44 | 32.5 | |
1998-2002 | 0.38 | 0.42 | 52.0 | 0.84 | 0.06 | 7.0 | |
1991-2002 | 0.12 | 0.29 | 70.3 | 0.34 | 0.02 | 5.7 | |
2002-2006 | 0.04 | 0.82 | 95.0 | 0.16 | 0.29 | 64.6 | |
2006-2011 | 0.20 | 0.79 | 80.1 | 0.93 | 0.02 | 2.1 | |
2011-2016 | 0.09 | 0.37 | 80.3 | 0.16 | 0.25 | 60.1 | |
2002-2016 | 0.02 | 0.55 | 96.9 | 0.33 | 0.07 | 17.8 | |
Bend 8 | |||||||
1991-1996 | 0.34 | 0.05 | 12.9 | 0.09 | 0.13 | 59.4 | |
1996-1998 | 0.56 | 0.59 | 51.0 | 0.45 | 0.30 | 39.5 | |
1998-2002 | 0.46 | 0.11 | 18.6 | 0.51 | 0.01 | 1.0 | |
1991-2002 | 0.27 | 0.01 | 2.7 | 0.18 | 0.00 | 1.4 | |
2002-2006 | 0.05 | 0.37 | 88.9 | 0.03 | 0.25 | 88.5 | |
2006-2011 | 0.27 | 0.02 | 8.4 | 0.27 | 0.01 | 4.0 | |
2011-2016 | 0.11 | 0.22 | 67.9 | 0.04 | 0.15 | 81.0 | |
2002-2016 | 0.04 | 0.09 | 68.3 | 0.03 | 0.04 | 59.0 | |
Years | Point bar | Concave bank | |||||
Deposition volume (106 m3 yr‒1) | Erosion volume (106 m3 yr‒1) | Erosion as proportion of total volume change (%) | Deposition volume (106 m3 yr‒1) | Erosion volume (106 m3 yr‒1) | Erosion as proportion of total volume change (%) | ||
Bend 9 | |||||||
1991-1996 | 0.94 | 0.47 | 33.4 | 0.34 | 0.33 | 49.4 | |
1996-1998 | 1.59 | 0.85 | 34.8 | 1.58 | 0.30 | 15.8 | |
1998-2002 | 0.46 | 0.11 | 18.6 | 0.74 | 0.32 | 30.1 | |
1991-2002 | 0.86 | 0.11 | 11.1 | 0.43 | 0.08 | 14.8 | |
2002-2006 | 0.34 | 0.74 | 68.3 | 0.38 | 0.33 | 46.4 | |
2006-2011 | 0.34 | 0.13 | 28.2 | 0.43 | 0.16 | 27.0 | |
2011-2016 | 0.19 | 0.46 | 70.9 | 0.11 | 0.46 | 81.3 | |
2002-2016 | 0.13 | 0.27 | 66.9 | 0.12 | 0.14 | 53.4 | |
Bend 10 | |||||||
1991-1996 | 1.28 | 0.63 | 32.7 | 0.21 | 0.27 | 56.2 | |
1996-1998 | 5.47 | 1.45 | 20.9 | 1.29 | 0.48 | 27.0 | |
1998-2002 | 2.42 | 1.24 | 33.9 | 1.30 | 0.74 | 36.3 | |
1991-2002 | 1.56 | 0.17 | 9.7 | 0.35 | 0.01 | 2.4 | |
2002-2006 | 0.52 | 2.47 | 82.5 | 0.08 | 0.46 | 85.0 | |
2006-2011 | 2.26 | 0.71 | 24.0 | 0.16 | 0.30 | 65.2 | |
2011-2016 | 0.88 | 1.83 | 67.5 | 0.02 | 0.67 | 96.6 | |
2002-2016 | 0.60 | 0.94 | 61.1 | 0.01 | 0.40 | 96.9 | |
Bend 11 | |||||||
1991-1996 | 1.29 | 0.07 | 5.4 | 0.55 | 1.01 | 64.9 | |
1996-1998 | 3.94 | 0.05 | 1.2 | 3.39 | 0.91 | 21.1 | |
1998-2002 | 0.26 | 0.81 | 75.9 | 1.30 | 0.74 | 36.3 | |
1991-2002 | 1.08 | 0.00 | 0.2 | 0.61 | 0.24 | 28.3 | |
2002-2006 | 0.18 | 0.78 | 81.0 | 0.25 | 1.81 | 88.0 | |
2006-2011 | 2.26 | 0.71 | 24.0 | 1.27 | 0.40 | 23.9 | |
2011-2016 | 0.25 | 0.78 | 75.9 | 0.90 | 0.62 | 40.9 | |
2002-2016 | 0.16 | 0.59 | 79.1 | 0.49 | 0.52 | 51.7 | |
Bend 12 | |||||||
1991-1996 | 0.39 | 0.67 | 63.1 | 2.70 | 0.96 | 26.2 | |
1996-1998 | 2.10 | 1.65 | 44.1 | 4.36 | 1.21 | 21.7 | |
1998-2002 | 0.40 | 0.75 | 65.0 | 1.80 | 0.66 | 26.9 | |
1991-2002 | 0.39 | 0.57 | 59.3 | 2.14 | 0.37 | 14.6 | |
2002-2006 | 0.05 | 1.64 | 96.8 | 0.25 | 1.81 | 88.0 | |
2006-2011 | 0.33 | 0.96 | 74.3 | 1.07 | 0.19 | 15.4 | |
2011-2016 | 0.11 | 2.30 | 95.3 | 0.75 | 0.41 | 35.5 | |
2002-2016 | 0.08 | 1.54 | 95.3 | 0.82 | 0.20 | 19.6 |
Figure 5 Morphological changes of the point bars and concave banks at bends 1-12 in the Lower Jingjiang Reach from 1991 to 2002 |
Figure 6 Morphological changes of the point bars and concave banks at bends 1-12 in the Lower Jingjiang Reach from 2002 to 2016 |
Table 7 Temporal variation of flow frequency at the Jianli hydrological station before and after the TGP |
Average duration (days) | Before TGP | After TGP | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1991- 1996 | 1997- 1998 | 1999- 2002 | 1991- 2002 | 2003- 2006 | 2007- 2011 | 2012- 2016 | 2003- 2016 | ||||||
<10,000 m3 s‒1 | 186 | 191 | 186 | 187 | 204 | 198 | 176 | 192 | |||||
10,000-15,000 m3 s‒1 | 65 | 79 | 66 | 68 | 63 | 72 | 86 | 74 | |||||
15,000-22,000 m3 s‒1 | 74 | 45 | 64 | 66 | 67 | 63 | 74 | 69 | |||||
>22,000 m3 s‒1 | 40 | 50 | 49 | 44 | 31 | 32 | 29 | 30 |
Figure 7 Annual water discharge and sediment flux before and after TGP (a); Temporal variations in erosion intensity of different discharge classes (b) at the Jianli hydrological station |
Figure 8 Correlation between the QmJP index and the erosion volume changes of point bars and concave banks in the Lower Jingjiang Reach |
Figure 9 Stream power (ω), depth-averaged velocity (Va), the directions (Af, degrees from North) of the depth-averaged flow velocities, and the morphological changes for the surveyed transects from campaign 1 to campaign 2 |
Figure 10 Scatter plots between the volume of erosion as proportion of total volume change for point bars and concave banks in bends 1-12 and the annual average sediment flux of different periods from 1991 to 2016 (a); The meander symmetry index (MSI) of bends 1-12 plotted against width-normalized annual suspended sediment flux (megatons per metre of bankfull channel width per year) (b) |
Figure 11 Scatter plots between the volume of erosion as proportion of total volume change for point bars and concave banks in bends 1-12 and sinuosity and planform type in 1991-2016 |
Figure 12 The meander symmetry index (MSI) of bends 1-12 plotted against sinuosity before and after the TGP |
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