scholarly journals A Tale of Two Deltas: Dam-Induced Hydro-Morphological Evolution of the Volta River Delta (Ghana) and Yellow River Delta (China)

Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3198
Author(s):  
Dongxue Li ◽  
Weilun Gao ◽  
Dongdong Shao ◽  
Mawusi Amenuvor ◽  
Yao Tong ◽  
...  
Keyword(s):  
Yellow River ◽  
Morphological Evolution ◽  
River Mouth ◽  
Yellow River Delta ◽  
Global Scale ◽  
River Delta ◽  
The Yellow River ◽  
Quasi Equilibrium ◽  
The Yellow River Delta ◽  
Future Evolution

Previous studies mostly focus on an individual delta, or deltas at a global scale, to explore dam effects on deltaic hydrological alteration and morphological evolution, while comparative studies on selected similar deltas remain scarce. In this study, we compare the alteration of river discharge and sediment load, as well as the associated deltaic area and shoreline, of two deltas, namely, the Volta River Delta in Ghana and the Yellow River Delta in China, which are subject to similar forcings and mainstem dam influences. The results show that the sediment loads of the Volta River Delta and Yellow River Delta have decreased abruptly and gradually, respectively, to ~10% of the pre-dam level, presumably due to differences in reservoir capacity and upstream dam location. Sediment decline has led to a decrease of the fluvial dominance ratio, which has also been affected by the river mouth location and shoreline orientation. As a consequence, the area of the Volta River Delta has shifted to a new quasi-equilibrium, whereas the Yellow River Delta has kept prograding. This comparative study provides references for understanding the future evolution of similar deltas around the world.

A Tale of Two Deltas: Comparative Study on the Effects of Dam Regulation on Deltaic Hydrological Regime and Morphological Evolution

2021 ◽  
Author(s):  
Weilun Gao ◽  
Dongxue Li ◽  
Mawusi Amenuvor ◽  
Yao Tong ◽  
Dongdong Shao ◽  
...  
Keyword(s):  
Sediment Load ◽  
Yellow River ◽  
Morphological Evolution ◽  
Hydrological Regime ◽  
Yellow River Delta ◽  
River Delta ◽  
The Yellow River ◽  
Quasi Equilibrium ◽  
The Yellow River Delta ◽  
The World

<p>Deltas are among the most populous areas and most productive ecosystems on Earth. Despite their critical importance for human society and coastal ecosystems, many of the world’s deltas are drowning due to substantial decrease in sediment supply, sea level rise, etc. Previous studies have demonstrated the effects of dam regulation on the hydrological regime and morphological evolution of river deltas. However, past attention was mostly paid to individual deltas or deltas at a global scale, while comparative studies on selected deltas are scarce in the literature. In this study, a comparative study on two wave-influenced deltas, namely, the Volta River Delta in Ghana and the Yellow River Delta in China, was conducted. The trend of change of the annual river discharge and sediment load of the two deltas before and after the construction of the major dams were analyzed, and the resultant effects on deltaic morphological evolution were also examined and compared between the two deltas. The results show that the average annual river discharge and sediment load and their inter-annual variation decreased significantly after the construction of major upstream dams for both deltas. However, presumably due to the differences in reservoir capacity and upstream location of the dams, the sediment load of the Volta River Delta decreased abruptly to <10% of the sediment load in the pre-dam period after the construction of the Akosombo Dam in 1964 and became stable afterwards, whereas the sediment load of the Yellow River Delta decreased substantially to ~10% of pre-dam level but in a more gradual stepwise manner since the 1950s. As a result, after the intense shoreline retreat in the 1960s, the delta area of the Volta River Delta appeared to adjust to the reduced yet stable sediment load and shift to a new quasi-equilibrium with minimal change (maximum 0.53%). On the contrary, the Yellow River Delta still kept prograding at the river mouth given the current sediment load. However, it is foreseeable that if the trend of sediment reduction persists, it may potentially turn net delta progradation to erosion and further into a new quasi-equilibrium like the Volta River Delta. Our study provides a new perspective for understanding the future evolution of the Yellow River Delta as well as other deltas around the world that share similar characteristics and forcing factors.</p>

Modelling Morphological Evolution of Deltaic Lobes in the Yellow River Mouth

2021 ◽  
Author(s):  
Wei Li ◽  
Lehong Zhu ◽  
Peng Hu
Keyword(s):  
Time Scales ◽  
Yellow River ◽  
Morphological Evolution ◽  
River Mouth ◽  
Yellow River Delta ◽  
River Delta ◽  
Small Scale ◽  
The Yellow River ◽  
Random Disturbance ◽  
Bed Slope

<p>In history, channel avulsion occurred frequently in the Yellow River Delta featuring by the combination of large-scale north-south shifts and small-scale evolution of “wandering-merging-meandering-diverting” patterns. However, these evolution processes are lack of quantitative investigations due to the complex interactions between riverine and tidal flows, and between sediment-laden flow and river bed as well. Since public observations are scarce, we numerically study this problem focusing on the controlling factors for reproducing the “wandering-merging-meandering” evolution patterns and the characteristics of relative morphological equilibrium under constant discharge and sediment conditions. Using a 2-D depth-averaged fully coupled morphological model, numerical experiments are carried out for a schematic Yellow River Delta. The results show that random disturbance on initial topography is the key factor to initiate wandering patterns. Moreover, the development of river patterns and the associated morphological time scales are strongly related to initial bed slopes and upstream discharge and sediment conditions. Generally, a small bed slope and a low discharge favor the formation of wandering patterns in the early stage, while a large bed slope and a high discharge may accelerate the merging and routing processes. In the case of upstream clear flow, channel formation is dominated by erosion processes. Yet with increasing sediment, it results from the combination of levee lip sedimentation and channel erosion. In addition, the flow routing may be facilitated by enhanced tidal ranges whereas decelerated when subaqueous sedimentation extends to the sea. Regarding the equilibrium state, the morphological time scales are 4~8 years in most cases and the width-depth ratio increases longitudinally following a power-law function.</p>

Effects of reclamation on net ecosystem CO2 exchange in wetland in the Yellow River Delta, China

2013 ◽  
Vol 37 (6) ◽  
pp. 503-516 ◽  
Author(s):  
Li-Qiong YANG ◽  
Guang-Xuan HAN ◽  
Jun-Bao YU ◽  
Li-Xin WU ◽  
Min ZHU ◽  
...  
Keyword(s):  
Yellow River ◽  
Yellow River Delta ◽  
Co2 Exchange ◽  
River Delta ◽  
The Yellow River ◽  
Net Ecosystem Co2 Exchange ◽  
The Yellow River Delta

scholarly journals Impacts of Consolidation Time on the Critical Hydraulic Gradient of Newly Deposited Silty Seabed in the Yellow River Delta

2021 ◽  
Vol 9 (3) ◽  
pp. 270
Author(s):  
Meiyun Tang ◽  
Yonggang Jia ◽  
Shaotong Zhang ◽  
Chenxi Wang ◽  
Hanlu Liu
Keyword(s):  
Yellow River ◽  
Yellow River Delta ◽  
Hydraulic Gradient ◽  
River Delta ◽  
Theoretical Formula ◽  
The Yellow River ◽  
The Yellow River Delta ◽  
Critical Hydraulic Gradient ◽  
Seepage Flows ◽  
The Yrd

The silty seabed in the Yellow River Delta (YRD) is exposed to deposition, liquefaction, and reconsolidation repeatedly, during which seepage flows are crucial to the seabed strength. In extreme cases, seepage flows could cause seepage failure (SF) in the seabed, endangering the offshore structures. A critical condition exists for the occurrence of SF, i.e., the critical hydraulic gradient (icr). Compared with cohesionless sands, the icr of cohesive sediments is more complex, and no universal evaluation theory is available yet. The present work first improved a self-designed annular flume to avoid SF along the sidewall, then simulated the SF process of the seabed with different consolidation times in order to explore the icr of newly deposited silty seabed in the YRD. It is found that the theoretical formula for icr of cohesionless soil grossly underestimated the icr of cohesive soil. The icr range of silty seabed in the YRD was 8–16, which was significantly affected by the cohesion and was inversely proportional to the seabed fluidization degree. SF could “pump” the sediments vertically from the interior of the seabed with a contribution to sediment resuspension of up to 93.2–96.8%. The higher the consolidation degree, the smaller the contribution will be.

scholarly journals Nitrate leaching and NH3 volatilization during soil reclamation in the Yellow River Delta, China

2021 ◽  
pp. 117330
Author(s):  
Wei Zhu ◽  
Jingsong Yang ◽  
Rongjiang Yao ◽  
Xiangping Wang ◽  
Wenping Xie ◽  
...  
Keyword(s):  
Nitrate Leaching ◽  
Yellow River ◽  
Yellow River Delta ◽  
River Delta ◽  
Soil Reclamation ◽  
The Yellow River ◽  
Nh3 Volatilization ◽  
The Yellow River Delta
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