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Prof. Stephen Darby
University of Southampton

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Research Keywords & Expertise

0 Physical Geography
0 Sustainability
0 Fluvial and glacial geomorphology and sedimentology
0 Sediment and nutrients transport in rivers
0 Hydrologic and hydrodynamic modelling

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Sustainability
Sediment and nutrients transport in rivers

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Research article
Published: 06 July 2021 in Natural Hazards and Earth System Sciences
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In coastal regions, floods can arise through a combination of multiple drivers, including direct surface run-off, river discharge, storm surge, and waves. In this study, we analyse compound flood potential in Europe and environs caused by these four main flooding sources using state-of-the-art databases with coherent forcing (i.e. ERA5). First, we analyse the sensitivity of the compound flooding potential to several factors: (1) sampling method, (2) time window to select the concurrent event of the conditioned driver, (3) dependence metrics, and (4) wave-driven sea level definition. We observe higher correlation coefficients using annual maxima than peaks over threshold. Regarding the other factors, our results show similar spatial distributions of the compound flooding potential. Second, the dependence between the pairs of drivers using the Kendall rank correlation coefficient and the joint occurrence are synthesized for coherent patterns of compound flooding potential using a clustering technique. This quantitative multi-driver assessment not only distinguishes where overall compound flooding potential is the highest, but also discriminates which driver combinations are more likely to contribute to compound flooding. We identify that hotspots of compound flooding potential are located along the southern coast of the North Atlantic Ocean and the northern coast of the Mediterranean Sea.

ACS Style

Paula Camus; Ivan D. Haigh; Ahmed A. Nasr; Thomas Wahl; Stephen E. Darby; Robert J. Nicholls. Regional analysis of multivariate compound coastal flooding potential around Europe and environs: sensitivity analysis and spatial patterns. Natural Hazards and Earth System Sciences 2021, 21, 2021 -2040.

AMA Style

Paula Camus, Ivan D. Haigh, Ahmed A. Nasr, Thomas Wahl, Stephen E. Darby, Robert J. Nicholls. Regional analysis of multivariate compound coastal flooding potential around Europe and environs: sensitivity analysis and spatial patterns. Natural Hazards and Earth System Sciences. 2021; 21 (7):2021-2040.

Chicago/Turabian Style

Paula Camus; Ivan D. Haigh; Ahmed A. Nasr; Thomas Wahl; Stephen E. Darby; Robert J. Nicholls. 2021. "Regional analysis of multivariate compound coastal flooding potential around Europe and environs: sensitivity analysis and spatial patterns." Natural Hazards and Earth System Sciences 21, no. 7: 2021-2040.

Short communication
Published: 19 May 2021 in Earth and Planetary Science Letters
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The weathering of carbonate rocks with sulfuric acid releases carbon dioxide (CO2) to the atmosphere, offsetting the CO2 drawdown from carbonic acid weathering of silicates thought to regulate global climate. Quantifying CO2 release from sulfuric acid weathering requires the partitioning of riverine sulfate between its two main sources: sedimentary sulfate and sulfide. Although the sulfur (δ34SSO4) and oxygen (δ18OSO4) isotope ratios of sedimentary sulfates (gypsum and anhydrite) of different ages are well constrained, the δ34S of sulfide minerals is highly variable, restricting the utility of δ34S for partitioning sulfur sources. Here, we use oxygen isotope ratios in the river water (δ18OH2O) and sulfate molecules (δ18OSO4) to partition the fraction of sulfate and associated uncertainty delivered by the oxidative weathering of pyrite (fpyr). The partitioning is illustrated using the Mekong River, one of the world's largest river basins, presenting new δ18OSO4, δ18OH2O and δ34SSO4 data collected on 18 tributaries and 6 mainstem sites over two field seasons at peak flux. The geological, geomorphological and climatic diversity of the Mekong River basin make it an ideal field site to quantify the role of sulfuric acid weathering and its implications for the carbon cycle. There is a 12‰ range in both the difference between δ18OSO4 and δ18OH2O (Δ18OSO4−H2O) and δ34S in the river waters of the basin. In the Mekong tributaries, sources of sulfate are highly variable with the fraction of sulfate derived from pyrite oxidation (fpyr) ranging from 0.19 to 0.84. In the mainstem, fpyr reflects the flux-weighted mean of these tributary inputs, with 56±7% (1σ) of the sulfate delivered to the ocean at the Mekong mouth being derived from the oxidative weathering of pyrite. As a result, we estimate that ∼70% of CO2 consumed through silicate weathering in the Mekong basin is offset by the release of CO2 via the dissolution of carbonates by sulfuric acid.

ACS Style

Katy E. Relph; Emily I. Stevenson; Alexandra V. Turchyn; Gilad Antler; Mike J. Bickle; J. Jotautas Baronas; Stephen E. Darby; Daniel R. Parsons; Edward T. Tipper. Partitioning riverine sulfate sources using oxygen and sulfur isotopes: Implications for carbon budgets of large rivers. Earth and Planetary Science Letters 2021, 567, 116957 .

AMA Style

Katy E. Relph, Emily I. Stevenson, Alexandra V. Turchyn, Gilad Antler, Mike J. Bickle, J. Jotautas Baronas, Stephen E. Darby, Daniel R. Parsons, Edward T. Tipper. Partitioning riverine sulfate sources using oxygen and sulfur isotopes: Implications for carbon budgets of large rivers. Earth and Planetary Science Letters. 2021; 567 ():116957.

Chicago/Turabian Style

Katy E. Relph; Emily I. Stevenson; Alexandra V. Turchyn; Gilad Antler; Mike J. Bickle; J. Jotautas Baronas; Stephen E. Darby; Daniel R. Parsons; Edward T. Tipper. 2021. "Partitioning riverine sulfate sources using oxygen and sulfur isotopes: Implications for carbon budgets of large rivers." Earth and Planetary Science Letters 567, no. : 116957.

Journal article
Published: 15 May 2021 in Sustainability
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The development of a coherent and coordinated policy for the management of large socio-agricultural systems, such as the Mekong delta in southern Vietnam, is reliant on aligning the development, delivery, and implementation of policy on national to local scales. Effective decision making is linked to a coherent, broadly-shared vision of the strategic management of socio-agricultural systems. However, when policies are ambiguous, and at worst contradictory, long-term management and planning can consequently suffer. These potential adverse impacts may be compounded if stakeholders have divergent visions of the current and future states of socio-agricultural systems. Herein we used a transferable, scenario-based methodology which uses a standard quadrant matrix in order to explore both anticipated and idealized future states. Our case study was the Mekong delta. The scenario matrix was based upon two key strategic choices (axis) for the delta, derived from analysis of policy documents, literature, stakeholder engagement, and land use models. These are: (i) who will run agriculture in the future, agri-business or the established commune system; and (ii) to what degree sustainability will be incorporated into production. During a workshop meeting, stakeholders identified that agri-business will dominate future agricultural production in the delta but showed a clear concern that sustainability might consequently be undermined despite policy claims of the contrary. As such, our study highlights an important gap between national expectations and regional perspectives. Our results suggest that the new development plans for the Mekong delta (which comprise a new Master Plan and a new 5-year socio-economic development plan), which emphasize agro-business development, should adopt approaches that address concerns of sustainability as well as a more streamlined policy formulation and implementation that accounts for stakeholder concerns at both provincial and national levels.

ACS Style

Craig Hutton; Oliver Hensengerth; Tristan Berchoux; Van Tri; Thi Tong; Nghia Hung; Hal Voepel; Stephen Darby; Duong Bui; Thi Bui; Nguyen Huy; Daniel Parsons. Stakeholder Expectations of Future Policy Implementation Compared to Formal Policy Trajectories: Scenarios for Agricultural Food Systems in the Mekong Delta. Sustainability 2021, 13, 5534 .

AMA Style

Craig Hutton, Oliver Hensengerth, Tristan Berchoux, Van Tri, Thi Tong, Nghia Hung, Hal Voepel, Stephen Darby, Duong Bui, Thi Bui, Nguyen Huy, Daniel Parsons. Stakeholder Expectations of Future Policy Implementation Compared to Formal Policy Trajectories: Scenarios for Agricultural Food Systems in the Mekong Delta. Sustainability. 2021; 13 (10):5534.

Chicago/Turabian Style

Craig Hutton; Oliver Hensengerth; Tristan Berchoux; Van Tri; Thi Tong; Nghia Hung; Hal Voepel; Stephen Darby; Duong Bui; Thi Bui; Nguyen Huy; Daniel Parsons. 2021. "Stakeholder Expectations of Future Policy Implementation Compared to Formal Policy Trajectories: Scenarios for Agricultural Food Systems in the Mekong Delta." Sustainability 13, no. 10: 5534.

Preprint content
Published: 04 March 2021
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Rain-gauge datasets indicate strong increases in both annual mean and extreme precipitation over large parts of the Mainland Southeast Asia (MSEA) including Vietnam and the northwestern part of the peninsula over the last 40 years. Increasing precipitation is associated with increased monsoon intensity in southeast Asia and a northward shift of the monsoon activity centre towards MSEA. Warming-driven evaporation increases over the three main oceanic moisture sources - the Arabian Sea, the Bay of Bengal, and the South China Sea- may partially explain increasing precipitation in large parts of MSEA. Changes in the patterns of the two main modes of natural variability in the tropical Indian Ocean – the Indian Ocean Basin Mode (IOBM) and the Indian Ocean Dipole (IOD) – contribute to surface warming in these oceanic moisture source regions supplying precipitation to MSEA. Climate model projections show robust wide-spread trends in wet season precipitation with increasing frequency and intensity of extreme precipitation events throughout MSEA over the 21st century. Similar to observations, the projected precipitation trends are associated with strong warming-driven increases in evaporation in all major oceanic moisture sources supplying precipitation to MSEA.

ACS Style

Nikolaos Skliris; Robert Marsh; Ivan Haigh; Melissa Wood; Joel Hirschi; Stephen Darby; Nguyen Phu Quynh; Nguyen Nghia Hung. Trends in mean and extreme rainfall over Mainland Southeast Asia associated with warming-driven trends in evaporation . 2021, 1 .

AMA Style

Nikolaos Skliris, Robert Marsh, Ivan Haigh, Melissa Wood, Joel Hirschi, Stephen Darby, Nguyen Phu Quynh, Nguyen Nghia Hung. Trends in mean and extreme rainfall over Mainland Southeast Asia associated with warming-driven trends in evaporation . . 2021; ():1.

Chicago/Turabian Style

Nikolaos Skliris; Robert Marsh; Ivan Haigh; Melissa Wood; Joel Hirschi; Stephen Darby; Nguyen Phu Quynh; Nguyen Nghia Hung. 2021. "Trends in mean and extreme rainfall over Mainland Southeast Asia associated with warming-driven trends in evaporation ." , no. : 1.

Preprint content
Published: 04 March 2021
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Populous deltas exemplify many of the diverse social and environmental changes and challenges that are emerging across the planet during the Anthropocene. Loss of relative elevation due to relative sea-level rise (combining climate and subsidence effects) is one major threat, but there are others such as catchment changes (e.g., water extraction and dam construction) which reduce water and sediment inputs. Rapid socio-economic changes within a delta (e.g., migration, urbanisation, economic transition and land use change) are also widespread and frequently add further pressures on the environmental resources  contained within delta systems. There are long histories of evolving adaptation practice at household to community level. In the long-term (i.e. 2100 and beyond), given relative sea-level rise, there are three distinct (but not necessarily mutually exclusive) policy choices for deltas: (i) retreat and progressive abandonment of the coastal zone; (ii) protection with ever-higher defences, growing pumping needs, and residual risk issues; or (iii) raise land elevation by controlled sedimentation. Building elevation is an attractive option if sufficient sediment is available, and there are now a few innovative examples that show it can be delivered to the delta surface— for example, through strategic raising of agricultural and natural areas with controlled sedimentation. One challenge is to accomplish this in a way which does not disrupt the livelihoods of the delta residents. Further is sufficient sediment available now or in the future, and what about growing urban areas where flood defence is likely to remain the norm? This raises the question about the trade-off between elevation and wealth. Many deltas cope with ‘lost elevation’ via defences: the Netherlands is most advanced in this approach, but such defences are expensive, require access to technology, and require sophisticated governance arrangements to deliver. A range of potential adaptation options at different scales and with different levels of cost will be required to sustain delta futures. This presentation examines potential adaptation options and trade-offs and delta trajectories in a range of examples including the Volta delta, Ghana, the Mahanadi delta, India and the Ganges-Brahmaputra-Meghna delta, India and Bangladesh.

ACS Style

Robert Nicholls; Neil Adger; Craig Hutton; Susan Hanson; Attila Lázár; Katharine Vincent; Andrew Allan; Emma Tompkins; Iñaki Arto; Munsur Rahman; Sugata Hazra; Sam Codjoe; Stephen Darby. Sustainable Deltas in the Anthropocene. 2021, 1 .

AMA Style

Robert Nicholls, Neil Adger, Craig Hutton, Susan Hanson, Attila Lázár, Katharine Vincent, Andrew Allan, Emma Tompkins, Iñaki Arto, Munsur Rahman, Sugata Hazra, Sam Codjoe, Stephen Darby. Sustainable Deltas in the Anthropocene. . 2021; ():1.

Chicago/Turabian Style

Robert Nicholls; Neil Adger; Craig Hutton; Susan Hanson; Attila Lázár; Katharine Vincent; Andrew Allan; Emma Tompkins; Iñaki Arto; Munsur Rahman; Sugata Hazra; Sam Codjoe; Stephen Darby. 2021. "Sustainable Deltas in the Anthropocene." , no. : 1.

Preprint content
Published: 03 March 2021
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The Ganges-Brahmaputra-Meghna (GBM) delta is one of the world’s largest deltas, and consists of large areas of low flat lands formed by the deposition of sediment from the GBM rivers. However, recent estimates have projected between 200~1000 mm of climate-driven sea-level rise by the end of the 21st century, at an average rate of ~6 mm/yr. Eustatic sea-level rise is further compounded by  subsidence of the delta, which in the coastal fringes varies from 0.2 to 7.5 mm/yr, at an average value of ~2.0 mm/yr. Therefore, the combined effect of sea-level rise and subsidence (termed relative sea-level rise, RSLR) is around 8.0 mm/yr. Such high values of RSLR raise the question of whether sediment deposition on the surface of the delta is sufficient to maintain the delta surface above sea level. Moreover, as the total fluvial sediment influx to the GBM delta system is known to be decreasing, the retained portion of fluvial sediment on the delta surface is also likely decreasing, reducing the potential to offset RSLR. Within this context, the potential of various interventions geared at promoting greater retention of sediment on the delta surface is explored using numerical experiments under different flow-sediment regime and anthropogenic interventions.  We find that for the existing, highly managed, conditions, the retained portion of fluvial sediment on the delta surface varies between 22% and 50% during average (when about 20% of the total floodplain in the country is inundated) and extreme (> 60% of the total floodplain in the country is inundated) flood years, respectively. However, the degree to which sediment has the potential to be deposited on the delta surface increases by up to 10% when existing anthropogenic interventions such as polders that act as barriers to delta-plain sedimentation are removed. While dismantling existing interventions is not a politically realistic proposition, more quasi-natural conditions can be reestablished through local- sediment management using tidal river management, cross dams, dredging, bandal-like structures and/or combinations of the above measures.

ACS Style

Stephen Darby; Munsur Rahman; Anisul Haque; Robert Nicholls; Frances Dunn. The physical sustainability of the coastal zone of the Ganges-Brahmaputra-Meghna delta under climatic and anthropogenic stresses. 2021, 1 .

AMA Style

Stephen Darby, Munsur Rahman, Anisul Haque, Robert Nicholls, Frances Dunn. The physical sustainability of the coastal zone of the Ganges-Brahmaputra-Meghna delta under climatic and anthropogenic stresses. . 2021; ():1.

Chicago/Turabian Style

Stephen Darby; Munsur Rahman; Anisul Haque; Robert Nicholls; Frances Dunn. 2021. "The physical sustainability of the coastal zone of the Ganges-Brahmaputra-Meghna delta under climatic and anthropogenic stresses." , no. : 1.

Preprint content
Published: 03 March 2021
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In coastal regions, floods can arise through a combination of multiple drivers, including direct surface run- off, river discharge, storm surge and waves. In this study, we analyse compound flood potential in Europe caused by these four main flooding sources using state-of-the-art databases with homogenous forcing (i.e., ERA5). First, we perform an analysis to assess the sensitivity of the compound flooding potential to several factors: 1) sampling method; 2) time window to select the concurrent event of the conditioned driver; 3) dependence metrics; 4) wave-driven sea level definition. We observe higher correlation coefficients using annual maxima than peaks over threshold. Regarding the other factors, our results show similar spatial distributions of the compound flooding potential. Second, the dependence between the pairs of drivers using the Kendall's rank correlation coefficient and the joint occurrence are synthesized for coherent patterns of compound flooding potential using a clustering technique. This quantitative multi-driver assessment not only distinguishes where overall compound flooding potential is the highest, but also discriminates which driver combinations are more likely to contribute to compound flooding. We identify hotspots of compound flooding potential located along the southern coast of the North Atlantic Ocean and the northern coast of the Mediterranean Sea.

ACS Style

Paula Camus; Ivan D. Haigh; Ahmed Nasr; Thomas Wahl; Stephen E. Darby; Robert J. Nicholls. Regional analysis of multivariate compound flooding potential: sensitivity analysis and spatial patterns. 2021, 2021, 1 -32.

AMA Style

Paula Camus, Ivan D. Haigh, Ahmed Nasr, Thomas Wahl, Stephen E. Darby, Robert J. Nicholls. Regional analysis of multivariate compound flooding potential: sensitivity analysis and spatial patterns. . 2021; 2021 ():1-32.

Chicago/Turabian Style

Paula Camus; Ivan D. Haigh; Ahmed Nasr; Thomas Wahl; Stephen E. Darby; Robert J. Nicholls. 2021. "Regional analysis of multivariate compound flooding potential: sensitivity analysis and spatial patterns." 2021, no. : 1-32.

Preprint content
Published: 03 March 2021
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ACS Style

Paula Camus; Ivan D. Haigh; Ahmed Nasr; Thomas Wahl; Stephen E. Darby; Robert J. Nicholls. Supplementary material to "Regional analysis of multivariate compound flooding potential: sensitivity analysis and spatial patterns". 2021, 1 .

AMA Style

Paula Camus, Ivan D. Haigh, Ahmed Nasr, Thomas Wahl, Stephen E. Darby, Robert J. Nicholls. Supplementary material to "Regional analysis of multivariate compound flooding potential: sensitivity analysis and spatial patterns". . 2021; ():1.

Chicago/Turabian Style

Paula Camus; Ivan D. Haigh; Ahmed Nasr; Thomas Wahl; Stephen E. Darby; Robert J. Nicholls. 2021. "Supplementary material to "Regional analysis of multivariate compound flooding potential: sensitivity analysis and spatial patterns"." , no. : 1.

Preprint content
Published: 05 January 2021
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In the list of challenges facing the world largest deltas, increased salt intrusion and its role in jeopardizing freshwater supply is often ranked very high. Yet, detailed process-based studies of salt intrusion at the whole delta scale are limited and the trends are regularly associated to global sea level rise. Here, using field measurements and a sophisticated 3D model that integrates the riverine, rural, estuarine, and coastal dynamics within one numerical domain, we study salt intrusion at the scale of the Mekong Delta in extensive detail. While many studies down-scale the salt intrusion problem to a topic within an estuary, we show that the continental shelf is an intrinsic component of the delta, and its physical processes, such as monsoon-driven ocean surge, directly influence salinity dynamics within the delta. Typical values of 20–40 cm surge over the continental shelf contribute to up to 10 km of further salt intrusion. The delta's estuarine system is also more sensitive than many other systems to upstream discharge variations. Furthermore, spring-neap variability plays a key role in salt intrusion in the delta. The estuarine variability from a stratified to a mixed system between neap and spring tides develops 3D processes such as estuarine circulation and tidal straining that become the main upstream salt transport mechanisms. The 3D nature of salinity dynamics, and the role of upstream and downstream processes, suggests that compromising on dimension or extent of the numerical domain, can limit the accuracy of predictions of salt intrusion in the delta. The study also showcases that riverbed incision in response to anthropogenic sediment starvation in the last two decades, has increased stratification, and activated or magnified 3D salt transport sub-processes that amplify upstream salt transport. With all the external forces on the delta namely climate change and altered hydrological regime by the upstream dams, due to deeper estuarine channels (driven by sand mining and upstream impoundments), the delta itself is far more vulnerable to even mild natural events. This exemplifies the fundamental importance of preserving the sediment budget and riverbed levels in protecting the world's deltas against salt intrusion.

ACS Style

Sepehr Eslami; Piet Hoekstra; Herman W. J. Kernkamp; Nam Nguyen Trung; Dung Do Duc; Hung Nguyen Nghia; Tho Tran Quang; Arthur van Dam; Stephen E. Darby; Daniel R. Parsons; Grigorios Vasilopoulos; Lisanne Braat; Maarten van der Vegt. Dynamics of salt intrusion in the Mekong Delta; results of field observations and integrated coastal-inland modelling. 2021, 2021, 1 -36.

AMA Style

Sepehr Eslami, Piet Hoekstra, Herman W. J. Kernkamp, Nam Nguyen Trung, Dung Do Duc, Hung Nguyen Nghia, Tho Tran Quang, Arthur van Dam, Stephen E. Darby, Daniel R. Parsons, Grigorios Vasilopoulos, Lisanne Braat, Maarten van der Vegt. Dynamics of salt intrusion in the Mekong Delta; results of field observations and integrated coastal-inland modelling. . 2021; 2021 ():1-36.

Chicago/Turabian Style

Sepehr Eslami; Piet Hoekstra; Herman W. J. Kernkamp; Nam Nguyen Trung; Dung Do Duc; Hung Nguyen Nghia; Tho Tran Quang; Arthur van Dam; Stephen E. Darby; Daniel R. Parsons; Grigorios Vasilopoulos; Lisanne Braat; Maarten van der Vegt. 2021. "Dynamics of salt intrusion in the Mekong Delta; results of field observations and integrated coastal-inland modelling." 2021, no. : 1-36.

Journal article
Published: 18 September 2020 in Journal of Geophysical Research: Earth Surface
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A large portion of freshwater and sediment is exported to the ocean by a small number of major rivers. Many of these mega‐rivers are subject to substantial anthropogenic pressures, which are having a major impact on water and sediment delivery to deltaic ecosystems. Due to hydrodynamic sorting, sediment grain size and composition varies strongly with depth and across the channel in large rivers, complicating flux quantification. To account for this, we modified a semi‐empirical Rouse model, synoptically predicting sediment concentration, grain‐size distribution, and organic carbon (%OC) composition with depth and across the river channel. Using suspended sediment depth samples and flow velocity data, we applied this model to calculate sediment fluxes of the Irrawaddy (Ayeyarwady) and the Salween (Thanlwin), the last two free‐flowing mega‐rivers in Southeast Asia. Deriving sediment‐discharge rating curves, we calculated an annual sediment flux of Mt/yr for the Irrawaddy and Mt/yr for the Salween, together exporting 46% as much sediment as the Ganges‐Brahmaputra system. The mean flux‐weighted sediment exported by the Irrawaddy is significantly coarser (D84 = 193±13 μm) and OC‐poorer (0.29±0.08 wt %) compared to the Salween (112 ± 27 mu μm and 0.59 ± 0.16 wt %, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of Mt C/yr, 53% as much as the Ganges‐Brahmaputra. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment flux, given the increasing anthropogenic pressures on these river basins.

ACS Style

J. Jotautas Baronas; Emily I. Stevenson; Christopher R. Hackney; Stephen E. Darby; Michael J. Bickle; Robert G. Hilton; Christina S. Larkin; Daniel R. Parsons; Aung Myo Khaing; Edward T. Tipper. Integrating Suspended Sediment Flux in Large Alluvial River Channels: Application of a Synoptic Rouse‐Based Model to the Irrawaddy and Salween Rivers. Journal of Geophysical Research: Earth Surface 2020, 125, 1 .

AMA Style

J. Jotautas Baronas, Emily I. Stevenson, Christopher R. Hackney, Stephen E. Darby, Michael J. Bickle, Robert G. Hilton, Christina S. Larkin, Daniel R. Parsons, Aung Myo Khaing, Edward T. Tipper. Integrating Suspended Sediment Flux in Large Alluvial River Channels: Application of a Synoptic Rouse‐Based Model to the Irrawaddy and Salween Rivers. Journal of Geophysical Research: Earth Surface. 2020; 125 (9):1.

Chicago/Turabian Style

J. Jotautas Baronas; Emily I. Stevenson; Christopher R. Hackney; Stephen E. Darby; Michael J. Bickle; Robert G. Hilton; Christina S. Larkin; Daniel R. Parsons; Aung Myo Khaing; Edward T. Tipper. 2020. "Integrating Suspended Sediment Flux in Large Alluvial River Channels: Application of a Synoptic Rouse‐Based Model to the Irrawaddy and Salween Rivers." Journal of Geophysical Research: Earth Surface 125, no. 9: 1.

Report
Published: 18 June 2020 in Changes in hydrology and suspended-sediment transport in the Mississippi River Basin over the past century
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ACS Style

Andrew. Simon; Kimberly. Artita; Gail. Simon; Stephen Darby; Julian. Leyland. Changes in hydrology and suspended-sediment transport in the Mississippi River Basin over the past century. Changes in hydrology and suspended-sediment transport in the Mississippi River Basin over the past century 2020, 1 .

AMA Style

Andrew. Simon, Kimberly. Artita, Gail. Simon, Stephen Darby, Julian. Leyland. Changes in hydrology and suspended-sediment transport in the Mississippi River Basin over the past century. Changes in hydrology and suspended-sediment transport in the Mississippi River Basin over the past century. 2020; ():1.

Chicago/Turabian Style

Andrew. Simon; Kimberly. Artita; Gail. Simon; Stephen Darby; Julian. Leyland. 2020. "Changes in hydrology and suspended-sediment transport in the Mississippi River Basin over the past century." Changes in hydrology and suspended-sediment transport in the Mississippi River Basin over the past century , no. : 1.

Journal article
Published: 01 June 2020 in One Earth
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The world's great rivers are threatened by a range of anthropogenic stresses-of which climate change is just one-that decrease resilience and increase vulnerability to extreme events. Future governance must recognize both the rate of change associated with these stressors and the potential for extreme events to transgress sustainability thresholds.

ACS Style

Jim Best; Stephen E. Darby. The Pace of Human-Induced Change in Large Rivers: Stresses, Resilience, and Vulnerability to Extreme Events. One Earth 2020, 2, 510 -514.

AMA Style

Jim Best, Stephen E. Darby. The Pace of Human-Induced Change in Large Rivers: Stresses, Resilience, and Vulnerability to Extreme Events. One Earth. 2020; 2 (6):510-514.

Chicago/Turabian Style

Jim Best; Stephen E. Darby. 2020. "The Pace of Human-Induced Change in Large Rivers: Stresses, Resilience, and Vulnerability to Extreme Events." One Earth 2, no. 6: 510-514.

Journal article
Published: 27 April 2020 in Journal of Hydrology
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A novel approach of combining regionalization and satellite observations of various hydrological variables were employed to significantly improve prediction of streamflow signatures at “geopolitically ungauged” basins. Using the proposed step-wise physiography and climate-based regionalization approach, the model performance at ungauged basins reached 80% of performance of locally calibrated parameters and significantly outperformed the global regionalization parameters. The proposed water level based flow correlation was found to help diagnose models and outperform the existing performance metrics of simulated water levels at ungauged basins. The study also set up the first multi-national, multi-catchment hydrological model in the Greater Mekong region, the top global biodiversity and major disaster risk hotspot in the world through sequential and iterative refinement of the existing global hydrological model. New model setup or existing models in the poorly-gauged and ungauged basins could benefit from the proposed approach to predict and evaluate models at ungauged basins.

ACS Style

Tien L.T. Du; Hyongki Lee; Duong D. Bui; Berit Arheimer; Hong-Yi Li; Jonas Olsson; Stephen Darby; Justin Sheffield; Donghwan Kim; Euiho Hwang. Streamflow prediction in “geopolitically ungauged” basins using satellite observations and regionalization at subcontinental scale. Journal of Hydrology 2020, 588, 125016 .

AMA Style

Tien L.T. Du, Hyongki Lee, Duong D. Bui, Berit Arheimer, Hong-Yi Li, Jonas Olsson, Stephen Darby, Justin Sheffield, Donghwan Kim, Euiho Hwang. Streamflow prediction in “geopolitically ungauged” basins using satellite observations and regionalization at subcontinental scale. Journal of Hydrology. 2020; 588 ():125016.

Chicago/Turabian Style

Tien L.T. Du; Hyongki Lee; Duong D. Bui; Berit Arheimer; Hong-Yi Li; Jonas Olsson; Stephen Darby; Justin Sheffield; Donghwan Kim; Euiho Hwang. 2020. "Streamflow prediction in “geopolitically ungauged” basins using satellite observations and regionalization at subcontinental scale." Journal of Hydrology 588, no. : 125016.

Journal article
Published: 08 April 2020 in Quaternary Science Reviews
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We provide evidence for a large-scale geomorphic event in Cambodia’s great lake, the Tonlé Sap, during the middle Holocene. The present-day hydrology of the basin is dominated by an annual flood pulse where water from the Mekong River raises the lake level by c. 8 m during the monsoon season. We present new subsurface geophysical data, allied to new and past core studies, which unequivocally show a period of major mid-Holocene erosion across the entire Tonlé Sap basin that is coincident with establishment of the lake’s flood pulse. We argue that this widespread erosion, which removed at least 1.2 m of sediment across the lake’s extent, was triggered by up to three, likely interacting, processes: (1) base-level lowering due to mid-Holocene sea-level fall, leading to (2) capture of the Tonlé Sap drainage by the Mekong River, and (3) a drying climate that also reduced lake level. Longer-term landscape evolution was thus punctuated by a rapid, river capture- and base-level fall- induced, lake drainage that established the ecosystem that flourishes today. The scale of change induced by this mid-Holocene river capture event demonstrates the susceptibility of the Tonlé Sap lake to ongoing changes in local base-level and hydrology induced by anthropogenic activity, such as damming and sand mining, within the Mekong River Basin.

ACS Style

Stephen E. Darby; Peter Langdon; James L. Best; Julian Leyland; Christopher R. Hackney; Mackenzie Marti; Peter R. Morgan; Savuth Ben; Rolf Aalto; Daniel R. Parsons; Andrew P. Nicholas; Melanie J. Leng. Drainage and erosion of Cambodia’s great lake in the middle-late Holocene: The combined role of climatic drying, base-level fall and river capture. Quaternary Science Reviews 2020, 236, 106265 .

AMA Style

Stephen E. Darby, Peter Langdon, James L. Best, Julian Leyland, Christopher R. Hackney, Mackenzie Marti, Peter R. Morgan, Savuth Ben, Rolf Aalto, Daniel R. Parsons, Andrew P. Nicholas, Melanie J. Leng. Drainage and erosion of Cambodia’s great lake in the middle-late Holocene: The combined role of climatic drying, base-level fall and river capture. Quaternary Science Reviews. 2020; 236 ():106265.

Chicago/Turabian Style

Stephen E. Darby; Peter Langdon; James L. Best; Julian Leyland; Christopher R. Hackney; Mackenzie Marti; Peter R. Morgan; Savuth Ben; Rolf Aalto; Daniel R. Parsons; Andrew P. Nicholas; Melanie J. Leng. 2020. "Drainage and erosion of Cambodia’s great lake in the middle-late Holocene: The combined role of climatic drying, base-level fall and river capture." Quaternary Science Reviews 236, no. : 106265.

Preprint content
Published: 23 March 2020
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The Vietnamese Mekong Delta (VMD) is home of 18 million people, provides enough food to cover 50% of the country’s nutritional needs and underpins the welfare of the rapidly growing population of the wider region. The longer-term future sustainability of this great delta, formed over millennia, is uncertain. The region is threatened by climate change induced eustatic sea-level rise (SLR), and by severe land loss. The latter is the result of a number of factors that are, in their majority, driven by human activities. They include dam impoundment that reduces the amount of sediment reaching and slowly building up the delta, sand mining which rapidly depletes the delta from its slowly accumulated sediment reserves and ground water extraction which enhances sediment compaction and accelerates delta subsidence.

In May 2018 we undertook a delta-scale survey to map the bathymetry of all of the main distributary channels of the VMD. Comparisons of these survey data with existing datasets from 1998 and 2018 reveal major increases of channel depth. They show that between 1998 and 2008 the VMD lost in excess of 370 million cubic meters of sediment, while the respective value for the period between 2008 and 2018 is 635 million cubic meters, suggesting an accelerating trend of sediment loss from the system.

We assume a ‘business as usual’ scenario for delta management practices and propagate delta degradation into the future, generating delta analogues for years 2028 and 2038. We combine these delta analogues with projections of SLR for the region for up to year 2098 and a number of boundary condition scenarios into a delta-scale hydraulic model. The fluvial-tidal interactions resolved in our numerical modelling simulations reveal that channel deepening is the key driver of tidal ingress into the delta plain for the next few decades. For the longer-term future (2098), the combined effects of predicted SLR and channel incision can lead to an increase of tidal ingress by 20%. This may destabilise delta bifurcations, is likely to increase bank erosion and flood risk into the future and can have sever implications for saline intrusion into the delta plains.

ACS Style

Grigorios Vasilopoulos; Quan Le Quan; Daniel R. Parsons; Stephen E. Darby; Nguyen N. Hung; Van P. D. Tri; Ivan Haigh; Hal Voepel; Rolf Aalto; Andrew Nicholas. Sediment starvation is the primary factor of tidal ingress in the Mekong delta. 2020, 1 .

AMA Style

Grigorios Vasilopoulos, Quan Le Quan, Daniel R. Parsons, Stephen E. Darby, Nguyen N. Hung, Van P. D. Tri, Ivan Haigh, Hal Voepel, Rolf Aalto, Andrew Nicholas. Sediment starvation is the primary factor of tidal ingress in the Mekong delta. . 2020; ():1.

Chicago/Turabian Style

Grigorios Vasilopoulos; Quan Le Quan; Daniel R. Parsons; Stephen E. Darby; Nguyen N. Hung; Van P. D. Tri; Ivan Haigh; Hal Voepel; Rolf Aalto; Andrew Nicholas. 2020. "Sediment starvation is the primary factor of tidal ingress in the Mekong delta." , no. : 1.

Preprint content
Published: 23 March 2020
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Estuarine systems represent the dynamic transition zone between fluvial and marine systems and as such they are sensitive to changes in both domains resulting from impacts of climate change and human activities related to coastal and water-flow management especially in densely inhabited areas. Further, these tidally influenced systems are subject to a unique set of driving conditions linked to bidirectional flow processes. The potential growing risks of shoreline erosion in coastal, estuarine and inter-tidal environments have been identified by a number of studies in recent years. However, bank erosion processes in tidal settings remain poorly understood, especially when compared to the large volume of research concerning fluvial bank erosion. In general, the well-established fluvial bank erosion literature suggests that bankline erosion involves two main sets of processes: hydraulic erosion and gravitational collapse. Given the additional complexity of the process mechanics involved in tidal settings, arising mainly from the presence of bi-directional flows, process insights gained from studies of fluvial bank erosion might not be appropriately applied in a tidal context.

The present study aims to improve our understanding of estuarine bank mobility dynamics through investigation of the evolution and rates of bank retreat/accretion acting in the Severn Estuary (UK). The Severn Estuary has one of the highest semidiurnal tidal ranges in the world (about 15 m in the outer estuary, up to 8-9 m in the middle parts of the system, and 2 to 3 m in the inner river-dominated sector). Here we estimate bank mobility throughout the estuary from the river-dominated to the tidal-dominated zones during the last 119 years, via analysis of historical maps and recent satellite images. We use the findings from this analysis coupled with recent data collection to propose an empirical model of bank mobility throughout the entire estuary, highlighting the characteristics and the differences between riverine and coastal erosive processes. The model indicates that (i) the highest bank mobility (both in term of erosion and deposition) is located in the mid part of the estuary, close to the bedload convergence zone (BLZ), with other ‘hot spots’ of change linked to major anthropogenic disturbances either in the outer and inner estuary, and (ii) that the erosive mechanics associated to severe lateral land losses in the estuary are mainly driven by impulses in energy delivery to the bank surface in occasion of very high tidal oscillations (particularly in spring overbank tides) and severe storms triggering mass wasting in form of toppling and rotational failures.  

ACS Style

Andrea Gasparotto; Julian Leyland; Stephen Darby; Paul Carling. Bank Erosion Processes, Trends and Impacts in a Hypertidal Estuarine System. 2020, 1 .

AMA Style

Andrea Gasparotto, Julian Leyland, Stephen Darby, Paul Carling. Bank Erosion Processes, Trends and Impacts in a Hypertidal Estuarine System. . 2020; ():1.

Chicago/Turabian Style

Andrea Gasparotto; Julian Leyland; Stephen Darby; Paul Carling. 2020. "Bank Erosion Processes, Trends and Impacts in a Hypertidal Estuarine System." , no. : 1.

Preprint content
Published: 23 March 2020
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A large portion of freshwater and sediment is exported to the ocean by just several of the world's major rivers. Many of these mega-rivers are under significant anthropogenic pressures, such as damming and sand mining, which are having a significant impact on water and sediment delivery to deltaic ecosystems. However, accurately measuring the total sediment flux and its mean physicochemical composition is difficult in large rivers due to hydrodynamic sorting of sediments. To account for this, we developed an updated semi-empirical Rouse modeling framework, which synoptically predicts sediment concentration, grain size distribution, and mean chemical composition (organic carbon wt%, Al/Si ratio) with depth and across the river channel.

We applied this model to derive new sediment flux estimates for the Irrawaddy and the Salween, the last two free-flowing mega-rivers in Southeast Asia, using a newly collected set of suspended sediment depth samples, coupled to ADCP-measured flow velocity data. Constructing sediment-discharge rating curves, we calculated an annual sediment flux of 326 (68% confidence interval of 256-417) Mt/yr for the Irrawaddy and 159 (109-237) Mt/yr for the Salween, together accounting for 2-3% of total global riverine sediment discharge. The mean flux-weighted sediment exported by the Irrawaddy is significantly coarser (D84 = 193 ± 13 µm) and OC-poorer (0.29 ± 0.08 wt%) compared to the Salween (112 ± 27 µm and 0.59 ± 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of 1.9 (1.0-3.3) Mt C/yr, contributing ~1% of the total riverine POC export to the ocean. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment fluxes, given the increasing anthropogenic pressures on these river basins.

ACS Style

J. Jotautas Baronas; Edward T. Tipper; Michael J. Bickle; Robert G. Hilton; Emily I. Stevenson; Christopher Hackney; Daniel Parsons; Stephen Darby; Christina S. Larkin; Aung Myo Khaing. Revised sediment transport model for estimation of suspended sediment flux and chemical composition of the Irrawaddy and Salween rivers. 2020, 1 .

AMA Style

J. Jotautas Baronas, Edward T. Tipper, Michael J. Bickle, Robert G. Hilton, Emily I. Stevenson, Christopher Hackney, Daniel Parsons, Stephen Darby, Christina S. Larkin, Aung Myo Khaing. Revised sediment transport model for estimation of suspended sediment flux and chemical composition of the Irrawaddy and Salween rivers. . 2020; ():1.

Chicago/Turabian Style

J. Jotautas Baronas; Edward T. Tipper; Michael J. Bickle; Robert G. Hilton; Emily I. Stevenson; Christopher Hackney; Daniel Parsons; Stephen Darby; Christina S. Larkin; Aung Myo Khaing. 2020. "Revised sediment transport model for estimation of suspended sediment flux and chemical composition of the Irrawaddy and Salween rivers." , no. : 1.

Journal article
Published: 06 March 2020 in Journal of Geophysical Research: Oceans
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Oceanic density currents in many deep‐water channels are strongly influenced by the Coriolis force. The dynamics of the bottom‐boundary layer in large geostrophic flows, and low Rossby number turbidity currents, are very important for determining the erosion and deposition of sediment in channelized contourite currents and many large‐scale turbidity currents. However, these bottom boundary layers are notoriously difficult to resolve with oceanic field measurements, or in previous small‐scale rotating laboratory experiments. We present results from a large, 13 m diameter, rotating laboratory platform that is able to achieve both stratified and highly turbulent flows in regimes where the rotation is sufficiently rapid that the Coriolis force can potentially dominate. By resolving the dynamics of the turbulent bottom boundary in straight and sinuous channel sections, we find that the Coriolis force can overcome centrifugal force to switch the direction of near‐bed flows in channel bends. This occurs for positive Rossby numbers less than +0.8, defined as , where is the depth‐averaged velocity,the Coriolis parameter. Density and velocity fields decoupled in channel bends, with the densest fluid of the gravity current being deflected to the outer‐bend of the channel by the centrifugal force, while the location of velocity maximum shifted with the Coriolis force, leading to asymmetries between left‐ and right‐ turning bends. These observations of Coriolis effects on gravity currents are synthesized into a model of how sedimentary structures might evolve in sinuous turbidity current channels at various latitudes.

ACS Style

S. Davarpanah Jazi; M. G. Wells; J. Peakall; R. M. Dorrell; R. E. Thomas; G. M. Keevil; S. E. Darby; J. Sommeria; S. Viboud; T. Valran. Influence of Coriolis Force Upon Bottom Boundary Layers in a Large‐Scale Gravity Current Experiment: Implications for Evolution of Sinuous Deep‐Water Channel Systems. Journal of Geophysical Research: Oceans 2020, 125, 1 .

AMA Style

S. Davarpanah Jazi, M. G. Wells, J. Peakall, R. M. Dorrell, R. E. Thomas, G. M. Keevil, S. E. Darby, J. Sommeria, S. Viboud, T. Valran. Influence of Coriolis Force Upon Bottom Boundary Layers in a Large‐Scale Gravity Current Experiment: Implications for Evolution of Sinuous Deep‐Water Channel Systems. Journal of Geophysical Research: Oceans. 2020; 125 (3):1.

Chicago/Turabian Style

S. Davarpanah Jazi; M. G. Wells; J. Peakall; R. M. Dorrell; R. E. Thomas; G. M. Keevil; S. E. Darby; J. Sommeria; S. Viboud; T. Valran. 2020. "Influence of Coriolis Force Upon Bottom Boundary Layers in a Large‐Scale Gravity Current Experiment: Implications for Evolution of Sinuous Deep‐Water Channel Systems." Journal of Geophysical Research: Oceans 125, no. 3: 1.

Research article
Published: 26 February 2020 in PLOS ONE
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The time-averaged and instantaneous flow velocity structures of flood waters are not well understood for irregular surfaces such as are created by the presence of roots and fallen branches on forested floodplains. Natural flow structures commonly depart systematically from those described for idealised roughness elements, and an important knowledge gap exists surrounding the effects of natural flow structures on vertical exchanges of fluid and momentum. An improved understanding of the flow structure is required to model flows over forested floodplains more accurately, and to distinguish their dynamics from non-vegetated floodplains or indeed floodplains with other vegetation types, such as reed or grass. Here we present a quantification of the three-dimensional structure of mean flow velocity and turbulence as measured under controlled conditions in an experimental flume using a physical reproduction of a patch of forested floodplain. The results conform in part to existing models of local flow structure over simple roughness elements in aspects such as flow separation downstream of protruding roots, flow reattachment, and the lowering of the velocity maximum further downstream. However, the irregular shape of the surface of the floodplain with exposed roots causes the three-dimensional flow structure to deviate from that anticipated based on previous studies of flows over idealised two-dimensional roughness elements. The results emphasise varied effects of inheritance of flow structures that are generated upstream—the local response of the flow to similar obstacles depends on their spatial organisation and larger-scale context. Key differences from idealised models include the absence of a fully-developed flow at any location in the test section, and various interactions of flow structures such as a reduction of flow separation due to cross-stream circulation and the diversion of the flow over and around the irregular shapes of the roots.

ACS Style

Arnold Jan H. Reesink; Stephen Darby; David A. Sear; Julian Leyland; Peter R. Morgan; Keith Richardson; James Brasington. Mean flow and turbulence structure over exposed roots on a forested floodplain: Insights from a controlled laboratory experiment. PLOS ONE 2020, 15, e0229306 .

AMA Style

Arnold Jan H. Reesink, Stephen Darby, David A. Sear, Julian Leyland, Peter R. Morgan, Keith Richardson, James Brasington. Mean flow and turbulence structure over exposed roots on a forested floodplain: Insights from a controlled laboratory experiment. PLOS ONE. 2020; 15 (2):e0229306.

Chicago/Turabian Style

Arnold Jan H. Reesink; Stephen Darby; David A. Sear; Julian Leyland; Peter R. Morgan; Keith Richardson; James Brasington. 2020. "Mean flow and turbulence structure over exposed roots on a forested floodplain: Insights from a controlled laboratory experiment." PLOS ONE 15, no. 2: e0229306.

Journal article
Published: 13 January 2020 in Nature Sustainability
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ACS Style

Christopher R. Hackney; Stephen Darby; Daniel R. Parsons; Julian Leyland; James L. Best; Rolf Aalto; Andrew P. Nicholas; Robert C. Houseago. River bank instability from unsustainable sand mining in the lower Mekong River. Nature Sustainability 2020, 3, 217 -225.

AMA Style

Christopher R. Hackney, Stephen Darby, Daniel R. Parsons, Julian Leyland, James L. Best, Rolf Aalto, Andrew P. Nicholas, Robert C. Houseago. River bank instability from unsustainable sand mining in the lower Mekong River. Nature Sustainability. 2020; 3 (3):217-225.

Chicago/Turabian Style

Christopher R. Hackney; Stephen Darby; Daniel R. Parsons; Julian Leyland; James L. Best; Rolf Aalto; Andrew P. Nicholas; Robert C. Houseago. 2020. "River bank instability from unsustainable sand mining in the lower Mekong River." Nature Sustainability 3, no. 3: 217-225.