At many river deltas, scientists are missing a major source of sea level rise

Science ◽  
2019 ◽  
Author(s):  
Paul Voosen
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
River Deltas

scholarly journals RESPONSE OF RIVER DELTAS TO SEA LEVEL RISE

2006 ◽  
Vol 62 (2) ◽  
pp. 169-179
Author(s):  
Yoshihisa AKAMATSU ◽  
Gary PARKER ◽  
Tetsuji MUTO
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
River Deltas

scholarly journals Experimental river delta size set by multiple floods and backwater hydrodynamics

2016 ◽  
Vol 2 (5) ◽  
pp. e1501768 ◽  
Author(s):  
Vamsi Ganti ◽  
Austin J. Chadwick ◽  
Hima J. Hassenruck-Gudipati ◽  
Brian M. Fuller ◽  
Michael P. Lamb
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Sustainable Management ◽  
Characteristic Size ◽  
River Delta ◽  
Growth Processes ◽  
River Deltas ◽  
Constant Size ◽  
Stratigraphic Record ◽  
Coastal River

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.

scholarly journals Deltaic Expansions of the Mahanadi Tri-delta and the Chilika Lagoon: Geospatial Approach

2020 ◽  
pp. 46-65
Author(s):  
Binod Kumar Sethi ◽  
Siba Prasad Mishra ◽  
Kabir Sethi ◽  
Kamal Barik
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
River System ◽  
Chilika Lagoon ◽  
Anthropogenic Pressure ◽  
River Deltas ◽  
Gis Tools ◽  
Drainage Channels ◽  
Major River ◽  
Southern Fringe

Prelude: The major river deltas are sinking, shrinking which accommodate ≈40% of global population. The Mahanadi tri-delta along the east coast of India consists of three river deltas i.e. the Mahanadi, the Bramhani and the Baitarani. The tri-delta encompasses many ecological hubs and the 2nd largest lagoon of Asia, the Chilika Lagoon lies in the southern corner of the delta. Presently the Mahanadi tri-delta and its coastal environments are under threat due to coastal vulnerability, population growth, urbanization and industrialization but the expansion of the delta towards south is observed. Scope: Present research is ubiquitous to know the quantity of sinking, shrinking and subsidence of the Mahanadi tri-delta under congregation of different geological setting, damming, LULC changes, soil erosion, regional sea level rise, and anthropogenic pressure. Also geospatial geomorphic changes in the anastomosis of  the rivers and drainage channels are studied along with expansion of the delta to its southern fringe Methodology: The causes of vulnerability of the delta are estimated from sediment inflow and marine transgression is evaluated. The land use and land cover changes has been evaluated and analyzed by using satellite imageries, remote sensing, GIS tools and ERDAS softwares. Results: The study revealed that due to effect of relative sea-level rise, paucity of sediment influx @ 66.7% to the delta are the main causes for the delta vulnerability accompanied by geo-mining and urbanization. The extention of delta to the south is due to emergence of the Makara river system which carries more flood flow than the existing Daya river. Prominent changes in LU & LC are observed from the satellite imageries of two different period. Changes in the LU &LC of the tri-delta has shown the  extension of the Mahanadi tri-delta towards south and shifting of deltaic boundary from 20 m to 50 m contour line in l landward direction during last four to five decades (recasted).

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

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

<p>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.</p>

Landward migration of backwater-mediated delta avulsion sites in response to increase in seasonal lake level: Qaidam Basin, China

2021 ◽  
Author(s):  
Jiaguang Li ◽  
Vamsi Ganti ◽  
Hao Wei ◽  
Chenglong Li
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Satellite Imagery ◽  
Qaidam Basin ◽  
River Mouth ◽  
Flood Hazards ◽  
River Deltas ◽  
The North ◽  
Field Evidence ◽  
Global Increase

<p>River deltas grow through episodic channel-jumping events, called avulsions, which have caused some of the deadliest floods in human history. Climate change is threatening to drown river deltas through a global increase in sea level; however, it is unclear how sea-level rise may affect the location of avulsion sites. Theory and experiments indicate that the avulsion sites on lowland deltas emerge within the backwater zone of coastal rivers because of the morphodynamic feedbacks arising from natural flood discharge variability and the nonuniform flows caused by the standing water level in the receiving basin. Under this backwater hypothesis, marine transgression should cause the landward-migration of lobe-scale avulsion locations; however, we currently lack field evidence for this theoretical prediction. Here, we analyze the location of river avulsions on the Sulengguole River that drains into the North Hubusun Lake, Qaidam Basin, China. Using analysis of time-series satellite imagery, we identified 7 lobe-scale avulsions that occurred in the distal portions of the Sulengguole River during the observation period of 1985 to 2010 CE. Satellite imagery revealed that the areal extent of the seasonal water in the lake increased at a rate of 1.89±0.80 km<sup>2</sup>/yr, likely as a result of increase in extreme precipitation rates. The increase in seasonal lake water areas caused the river mouth of the Sulengguole River to translate landward at a rate of 0.36±0.17 km/yr. We show that the avulsion sites also migrated landward at a commensurate rate of 0.24±0.07 km/yr during this period, consistent with the rate of landward migration of the river mouth. Finally, we show that all 7 avulsions had an avulsion length—streamwise distance of the avulsion site to the river mouth—that scales with the estimated backwater lengthscale (mean of 0.50±0.14 times the backwater lengthscale), consistent with the global compilation of avulsion lengths on large, low-gradient deltas. Our work demonstrates, for the first time, that landward migration of river mouth that would result from relative sea-level rise will cause the avulsion locations to migrate inland in a predictable manner, with implications for the sustainable management of the future of deltas and mitigating flood hazards.</p>

scholarly journals Accelerated river avulsion frequency on lowland deltas due to sea-level rise

2020 ◽  
Vol 117 (30) ◽  
pp. 17584-17590 ◽  
Author(s):  
Austin J. Chadwick ◽  
Michael P. Lamb ◽  
Vamsi Ganti
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Global Climate ◽  
Sediment Supply ◽  
Flood Hazards ◽  
Relative Sea Level ◽  
River Deltas ◽  
Abrupt Changes ◽  
Relative Sea Level Rise ◽  
Coastal Land

Sea-level rise, subsidence, and reduced fluvial sediment supply are causing river deltas to drown worldwide, affecting ecosystems and billions of people. Abrupt changes in river course, called avulsions, naturally nourish sinking land with sediment; however, they also create catastrophic flood hazards. Existing observations and models conflict on whether the occurrence of avulsions will change due to relative sea-level rise, hampering the ability to forecast delta response to global climate change. Here, we combined theory, numerical modeling, and field observations to develop a mechanistic framework to predict avulsion frequency on deltas with multiple self-formed lobes that scale with backwater hydrodynamics. Results show that avulsion frequency is controlled by the competition between relative sea-level rise and sediment supply that drives lobe progradation. We find that most large deltas are experiencing sufficiently low progradation rates such that relative sea-level rise enhances aggradation rates—accelerating avulsion frequency and associated hazards compared to preindustrial conditions. Some deltas may face even greater risk; if relative sea-level rise significantly outpaces sediment supply, then avulsion frequency is maximized, delta plains drown, and avulsion locations shift inland, posing new hazards to upstream communities. Results indicate that managed deltas can support more frequent engineered avulsions to recover sinking land; however, there is a threshold beyond which coastal land will be lost, and mitigation efforts should shift upstream.

Glacial Contributions to 21st Century Sea Level Rise

Eos ◽  
2020 ◽  
Vol 101 ◽  
Author(s):  
Kate Wheeling
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
21St Century ◽  
Mass Change ◽  
Sources Of Uncertainty

Researchers identify the main sources of uncertainty in projections of global glacier mass change, which is expected to add about 8–16 centimeters to sea level, through this century.

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