Long-Term Cumulative Effects of Intra-Annual Variability of Unsteady River Discharge on the Progradation of Delta Lobes

Long-Term Cumulative Effects of Intra-Annual Variability of Unsteady River Discharge on the Progradation of Delta Lobes: A Modeling Perspective

Gao, Weilun (Beijing Normal University)
Shao, Dongdong (Beijing Normal University)
Wang, Zhengbing (TU Delft Coastal Engineering; Beijing Normal University)
Nardin, William (University of Maryland Center for Environmental Science)
Rajput, Prateek (Indian Institute of Technology Kanpur)
Yang, Wei (Beijing Normal University)
Sun, Tao (Beijing Normal University)
Cui, Baoshan (Beijing Normal University)

2019

Rivers, regardless of their scales and geographic locations, are characterized with natural and human-induced variability in their discharges. While previous studies have established the effects of both interannual and intra-annual variabilities of unsteady river discharge on delta morphological evolution, the long-term cumulative effects of intra-annual unsteadiness on the progradation of delta lobes has remained hitherto elusive. To address this issue, numerical experiments using simplified unsteady discharges were performed in Delft3D and compared with those assuming constant bank-full discharges. A modified box model was further used to explore the effects of varying intra-annual unsteadiness on the progradation of delta lobes at reduced computational cost. While the overall trends of the progradation and the ultimate area created were found to be similar between the unsteady discharge scenarios and their corresponding constant bank-full discharge scenarios, the nuances of intermittent zig-zag variation in natural delta lobe area were well reproduced by model simulations assuming unsteady river discharges. In addition, long-term predictions suggested the potential existence of a tipping point in the area growth trajectory beyond which the delta lobe area declines during periods of low discharge. When confounding factors such as waves and variable sediment capture ratio were further taken into consideration, simulation results for unsteady river discharge scenarios exhibit significant deviations from constant bank-full discharge scenarios. The implications of the modeling results for delta protection and restoration measures, such as the water-sediment regulation scheme in the Yellow River and artificial channel diversions in the Mississippi River Delta, are also discussed.

delta progradation
delta restoration
numerical modeling
unsteady river discharge

http://resolver.tudelft.nl/uuid:ea44a0be-9eeb-4912-903f-f99f3f47cf42

https://doi.org/10.1029/2017JF004584

2169-9003

Journal of Geophysical Research: Earth Surface, 124 (4), 960-973

Accepted Author Manuscript

Institutional Repository

journal article

© 2019 Weilun Gao, Dongdong Shao, Zhengbing Wang, William Nardin, Prateek Rajput, Wei Yang, Tao Sun, Baoshan Cui