scholarly journals Quantifying the Effects of Dramatic Changes in Runoff and Sediment on the Channel Morphology of a Large, Wandering River Using Remote Sensing Images

Water ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1767 ◽  
Author(s):  
Zhehui Xie ◽  
He Qing Huang ◽  
Guoan Yu ◽  
Min Zhang
Keyword(s):  
Remote Sensing ◽  
Yellow River ◽  
Sediment Concentration ◽  
Channel Morphology ◽  
Main Channel ◽  
Main Flow ◽  
Remote Sensing Images ◽  
Average Width ◽  
Entire Study ◽  
Morphological Indices

The Yellow River (Huanghe River), which is the second largest river in China, has experienced dramatic changes in both runoff and sediment over the last 60 years. To quantify the effects on the channel morphology of the wandering reach on the Lower Yellow River (LYR), this study extracts morphological indices from Landsat imageries taken between 1979 and 2015. Over the dynamically adjusting complex channel-floodplain system, the spatial distribution of NDVI (Normalized Difference Vegetation Index) is found helpful for identifying the wandering belt created by the frequent migrations of the pathways of the main flow, which are determined from the reflection of the sediment-laded water body in remote sensing images taken at low flows. The extracted results show clearly that the average width and area of the wandering belt over the entire study reach declined in a dramatic fashion between 1979 and 2000 and yet both varied respectively within very narrow ranges from 2000 to 2015. Although the number of bends increased significantly since the 1990s, the sinuosity of the pathways of the main flow remained almost unchanged. By combining the morphological indices extracted from the remote sensing images with field hydrological and geomorphological measurements, our regression analysis identifies that the width of the wandering belt changes at the highest degree of correspondence with the width/depth ratio of the main channel and the variations of both are related most closely to the average flow discharge and then to sediment concentration during the flood seasons. These implicate that a significant reduction of the magnitude of floods and sediment concentration is beneficial not only for making the main channel transit from a wider and shallower cross-section into a narrower and deeper profile but also for narrowing the wandering range of the LYR.

Response of channel geometry to flow and sediment conditions in the lower Yellow River

2020 ◽  
Author(s):  
Huan Jing ◽  
Deyu Zhong ◽  
Hongwu Zhang
Keyword(s):  
Yellow River ◽  
Management Strategies ◽  
Sediment Concentration ◽  
Main Channel ◽  
Channel Stability ◽  
Cross Sectional ◽  
Channel Geometry ◽  
Lower Yellow River ◽  
The Lower Yellow River ◽  
Erosion Intensity

<p>The channel geometry in a fluvial river is significantly affected by the flow and sediment regimes, and the response behavior of channel dimensions usually varies widely to different management strategies from the upstream reservoir. Therefore, it is significantly crucial to investigate the variation of the channel geometry in response to changing flow and sediment conditions and quantify the influence of the latter in the sedimentation reduction and flood releasing in lower reaches downstream of the dam. In this study, three laboratory experiments on the physical model covering the typical braided reach HGK—JHT downstream of the Xiaolangdi Reservoir in the lower Yellow River are carried out, under the discharge of 2000 m<sup>3</sup>/s, 3000 m<sup>3</sup>/s, and 4000 m<sup>3</sup>/s respectively and with the corresponding constant suspended sediment concentration of 8.0 kg/m<sup>3</sup>. Results indicate that (i) spatially, the erosion and deposition in studied channel reach distributed alternately along the course which performs typical evolution properties of the braided river, corresponding to the total erosion amount of 2.27×10<sup>6 </sup>m<sup>3</sup>, 10.29×10<sup>6</sup> m<sup>3</sup>, and 7.98×10<sup>6</sup> m<sup>3</sup> for three magnitude of discharges; and (ii) four representative adjustment patterns are listed based on the observed cross-sectional geometry after each experiment, including the lateral widening pattern, vertical incision pattern, composite pattern and geometrical stable pattern where sectional geometry rarely changes during the period of experiment; and (iii) the quantity <em>ξ=B</em><sup>1/2</sup>/<em>H</em> where <em>B</em> and <em>H</em> is the width and depth of the main channel zone is selected as the typical indicator to determine the variation of the channel stability. It is discovered that <em>ξ </em>in the reaches upstream of section FJS have rather larger values, implying relatively wider and shallower sectional geometry and lower channel stability which is closely associated with the levee safety. And moreover, the quantity <em>ξ </em>generally has lower values, that is, higher channel stability with the increase of experiment discharge; Besides, through the method of nonlinear regression analysis, the empirical relations for HGK—JHT Reach are developed between the main channel dimensions and incoming flow erosion intensity <em>F</em>=(<em>Q</em><sup>2</sup>/<em>S</em>)/10<sup>6</sup> where <em>Q</em> is the discharge and <em>S</em> is the corresponding sediment concentration. In general, the calculated results are generally consistent with the measured values, as the riverbed degradation and the variation of sectional area increase exponentially with a stronger erosion intensity <em>F</em>.This paper may provide some practical basis for the study of channel evolution in sediment-laden rivers.</p>

scholarly journals Response of Erosion and Deposition of Channel Bed, Banks and Floodplains to Water and Sediment Changes in the Lower Yellow River, China

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 357 ◽  
Author(s):  
Xiaofei Liu ◽  
Changxing Shi ◽  
Yuanyuan Zhou ◽  
Zhenkui Gu ◽  
Huijuan Li
Keyword(s):  
Yellow River ◽  
Water Discharge ◽  
Sediment Concentration ◽  
Main Channel ◽  
River Channel ◽  
Lower Yellow River ◽  
Main Research ◽  
The Lower Yellow River ◽  
Water And Sediment ◽  
Geomorphic Units

River channel change can be very sensitive to environmental change and human activities and it has been one of the main research topics in fluvial geomorphology. In this study, repeated channel geometric measurements were used to investigate the channel adjustment to water and sediment changes of the lower Yellow River in China in the past few decades. With a high sediment concentration and large variations of water discharge, the lower Yellow River has a much active channel in its form and location, which has hindered previous research efforts to study long-term differentiated erosion/deposition of different geomorphic units in the channel. In this study, we divided each of four typical channel across-sections at hydrological stations in the lower Yellow River into different units according to the geomorphological features, and give a detailed investigation of erosion/deposition processes of these geomorphic units and the interactions between them besides the influence of incoming water and sediment conditions. The results show that with a significant decreasing trend of both the annual runoff and sediment load of the river and abrupt changes in 1985–1996, the overall siltation trend in the river channel before 1990 had been replaced by a slight erosion trend after 2006. In the earlier period, the siltation in the upstream wandering and transitional reaches mainly occurred on floodplains and that in the downstream straight reaches principally on main channel bed. In the later period, erosion occurred mainly on high and low bank slopes in the wandering reaches and on main channel bed in the transitional reaches. The erosion became weak in the wandering reaches after 2010, continued in the transitional reaches, and was still relatively minor in the straight reaches, reflecting the downstream hysteresis channel response to changes in water and sediment discharges down dams. Our results suggest that the seasonal erosion/deposition of a geomorphic unit of the river channel can be attributed to the changes in water and sediment discharges as well as to the interaction between geomorphic units. Siltation on the main channel bed could be attributed to erosion on the bank slopes in both the sections in the wandering and transitional reaches, and erosion of the main channel bed in flood seasons was negatively related with the mean water discharge at the two sections in the straight reaches. This result implies that fixing the bank slopes in the wandering and transitional reaches and raising the water discharge in the straight reach in flood seasons are favorable options for controlling the development of the two-level perching channel of the lower Yellow River.

scholarly journals Spatiotemporal Changes of Coastline over the Yellow River Delta in the Previous 40 Years with Optical and SAR Remote Sensing

2021 ◽  
Vol 13 (10) ◽  
pp. 1940
Author(s):  
Quantao Zhu ◽  
Peng Li ◽  
Zhenhong Li ◽  
Sixun Pu ◽  
Xiao Wu ◽  
...  
Keyword(s):  
Climate Change ◽  
Remote Sensing ◽  
Human Activities ◽  
Yellow River ◽  
Yellow River Delta ◽  
River Delta ◽  
The Yellow River ◽  
Remote Sensing Images ◽  
The Yellow River Delta ◽  
Spatiotemporal Changes

The integration of multi-source, multi-temporal, multi-band optical, and radar remote sensing images to accurately detect, extract, and monitor the long-term dynamic change of coastline is critical for a better understanding of how the coastal environment responds to climate change and human activities. In this study, we present a combination method to produce the spatiotemporal changes of the coastline in the Yellow River Delta (YRD) in 1980–2020 with both optical and Synthetic Aperture Radar (SAR) satellite remote sensing images. According to the measurement results of GPS RTK, this method can obtain a high accuracy of shoreline extraction, with an observation error of 71.4% within one pixel of the image. Then, the influence of annual water discharge and sediment load on the changes of the coastline is investigated. The results show that there are two significant accretion areas in the Qing 8 and Qingshuigou course. The relative high correlation illustrates that the sediment discharge has a great contribution to the change of estuary area. Human activities, climate change, and sea level rise that affect waves and storm surges are also important drivers of coastal morphology to be investigated in the future, in addition to the sediment transport.

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