Experimental river delta size set by multiple floods and backwater hydrodynamics

River deltas worldwide are currently under threat of drowning and destruction by sea-level rise, subsidence, and oceanic storms, highlighting the need to quantify their growth processes. Deltas are built through construction of sediment lobes, and emerging theories suggest that the size of delta lobes scales with backwater hydrodynamics, but these ideas are difficult to test on natural deltas that evolve slowly. We show results of the first laboratory delta built through successive deposition of lobes that maintain a constant size. We show that the characteristic size of delta lobes emerges because of a preferential avulsion node—the location where the river course periodically and abruptly shifts—that remains fixed spatially relative to the prograding shoreline. The preferential avulsion node in our experiments is a consequence of multiple river floods and Froude-subcritical flows that produce persistent nonuniform flows and a peak in net channel deposition within the backwater zone of the coastal river. In contrast, experimental deltas without multiple floods produce flows with uniform velocities and delta lobes that lack a characteristic size. Results have broad applications to sustainable management of deltas and for decoding their stratigraphic record on Earth and Mars.

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Water management plans and sea level rise impacts on seawater intrusion in the Red River Delta, Vietnam

10.5194/egusphere-egu2020-6684 ◽

2020 ◽

Author(s):

Hien Thi Nguyen ◽

Hai Yen Nguyen ◽

Matteo Balistrocchi ◽

Roberto Ranzi

Keyword(s):

Water Management ◽

Sea Level Rise ◽

Sea Level ◽

Seawater Intrusion ◽

River Delta ◽

Red River ◽

Red River Delta ◽

River Deltas ◽

Management Plans ◽

Water Management Plans

Seawater intrusion in coastal areas is now rising as a serious problem for river deltas in the world, especially when high tidal levels occur. Red River Delta plays a paramount role in the economy and society of Vietnam and has already been experiencing the increase in salinity concentrations. The combination of high tidal levels and multi-purposes reservoirs operations in the upstream watershed could exacerbate saltwater intrusion. This research, therefore, analyses the impacts of different water management plans, according to reservoirs operations coupled with sea level rise scenarios, on salinity dynamics in the Red River Delta. Two sea level rise projections referred to RCP4.5 and RCP8.5 emission scenarios have been selected for the simulations of future salinity intrusions in 2050 and 2100. In consideration of the important junction of the 3 main upstream rivers (Lo, Thao and Da River), discharge at Son Tay gauge station is selected as the upstream boundary condition for riverflow. Different discharge scenarios in Son Tay station are, hence, adopted based on statistical analysis of runoff data after the construction of the major reservoirs, started in 1973. Taking into account the 25%, 50%, 75%, 95% exceedance quantiles of the minimum monthly riverflow in Son Tay station combined with 4 downstream sea level rise scenarios, 16 salinity profiles along the Red River Delta reaches were obtained by 1D-hydrodynamic simulations. The results are useful as a guidance to plan multi-purposes reservoirs operations, considering environmental, agricultural, industrial and flood-protection targets.

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Flooded with Error: Handling Uncertainty in SRTM for the Assessment of Sea Level Rise in the Mississippi River Delta

The Professional Geographer ◽

10.1080/00330124.2021.1898992 ◽

2021 ◽

pp. 1-9

Author(s):

Ameen A. Kadhim ◽

Ashton M. Shortridge

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Mississippi River ◽

River Delta ◽

Mississippi River Delta ◽

Error Handling

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Geomophological and vulnerability analysis of a coastal delta under increased hydrological alteration over the past two centuries: Tana River delta, Kenya, East Africa.

10.5194/egusphere-egu21-15404 ◽

2021 ◽

Author(s):

Peter Gitau ◽

Stéphanie Duvail ◽

Dirk Verschuren ◽

Dominique Guillaud

Keyword(s):

Sea Level Rise ◽

East Africa ◽

Sea Level ◽

Coastal Dune ◽

River Delta ◽

River Channels ◽

Dune System ◽

The Past ◽

Tana River ◽

Coastal Dune System

Coastal deltas worldwide are under risk of degradation due to the increasing impacts of sea-level rise, and continuous human alterations of river basin hydrology. This research highlights the geomorphological changes that have occurred within the Tana River delta in Kenya, an important deltaic ecosystem of high biodiversity value in East Africa.The geomorphological features (river channels, floodplain, coastal dune system) and their evolution over the past two centuries were described. Aerial and satellite imagery was used to assess the magnitude and distribution of coastal changes from the 1960s to present. &#160;Additionally, sediment cores recovered within the mangrove environment were analysed to establish the succession of sedimentation periods and patterns. Finally, we explored the response of the coastal processes of deposition and erosion under anthropogenic alterations of the hydrological system.It was established that over the past two centuries Tana River has changed its main channel and outlet to the Indian Ocean on three occasions. A first river avulsion occurred in the 1860s, followed by a second avulsion in the late 1890s that was promoted by human interference through channel expansion and dyke construction. The third change in river course has occurred gradually over the past 20 years, amid human efforts to engineer the river channels.From the sediment analysis and radiocarbon dating, it is ascertained that the lower deltaic region developed rapidly over the past ~180 years, facilitated by increased sedimentation from the main Tana River. On the other hand, analysis of the coastline changes indicate that there has been increased erosion of the coastal dune system and mangrove vegetation along the former river outlet, leading to rapid marine intrusion into local subsistence farming areas. By analysing the combined impacts of both natural river dynamics and human alteration we highlight how the integrity of the Tana River delta has increasingly become vulnerable under present sea level rise and continued upstream river alteration.

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