The effects of fluvial and basal sediment properties on the morphodynamics of deltas undergoing sediment supply reduction

2020 ◽  
Author(s):  
Joshua Johnson ◽  
Daniel Parsons ◽  
Christopher Hackney ◽  
Douglas Edmonds ◽  
James Best
Keyword(s):  
River Sediment ◽  
Erosion Resistance ◽  
Sediment Supply ◽  
Coastal Environments ◽  
Land Area ◽  
Sediment Properties ◽  
Delta System ◽  
The Face ◽  
Sediment Reduction ◽  
Supply Reduction

<p>Deltas are home to hundreds of millions of people worldwide and form a key part of many coastal environments. Due to their low elevation, many deltas are threatened by sea level rise as well as direct human influences on flow and subsidence. Added to this, the volume of sediment exported by rivers to the coast has been reduced by around 1.4 billion tons per year, starving deltas of the building material needed to construct and maintain their valuable subaerial land in the face of these challenges. The calibre and cohesivity of sediment have both been shown to be important factors in determining the erosion, deposition and stability regimes within a delta system. However, it has not yet been shown how the qualities of river and substrate sediment affect how resilient deltas are to sediment reduction.</p><p>This study uses numerical modelling to investigate how the cohesivity of incoming river sediment and the erosion resistance of the delta’s substrate affect how deltas respond to a reduction in supplied sediment. Delft3D was used to create a series of stable deltas with varying fluvial and basal sediments, that where then exposed to sediment reduction. The loss of land area, change in channel geometry and other metrics where extracted from model output using Matlab to assess the effects of this sediment reduction, and how these effects varies between deltas.</p>

Alcohol and Drug Problems: Law Enforcement and Legal Policy

2013 ◽  
Author(s):  
Anna Celeste Burke
Keyword(s):  
Twentieth Century ◽  
Law Enforcement ◽  
Drug Policy ◽  
Drug Control ◽  
Demand Reduction ◽  
Prevention And Treatment ◽  
The Face ◽  
Supply Reduction ◽  
Drug Problems ◽  
Over Time

Historically, U.S. policy has been characterized by long-standing ambivalence evident in the changing emphasis placed on prohibition as the aim of drug policy, and in debate about the relative merits of various approaches to drug control. Often characterized as supply reduction versus demand reduction efforts, significant changes have occurred over time in these efforts, and in the emphasis placed on them. In the last quarter of the twentieth century, U.S. drug policy adopted a more prohibitionist stance, with increased reliance on a variety of law enforcement, and even military actions, to control the supply and use of drugs, even in the face of evidence for the effectiveness of prevention and treatment, and high costs associated with the burgeoning incarceration rates.

scholarly journals Million-year lag times in a post-orogenic sediment conveyor

2020 ◽  
Vol 6 (25) ◽  
pp. eaaz8845 ◽  
Author(s):  
R.-H. Fülöp ◽  
A. T. Codilean ◽  
K. M. Wilcken ◽  
T. J. Cohen ◽  
D. Fink ◽  
...  
Keyword(s):  
River Sediment ◽  
River System ◽  
Sediment Supply ◽  
Environmental Forcing ◽  
Murray Darling Basin ◽  
Transit Times ◽  
Lag Times ◽  
Geologic Record ◽  
And Storage ◽  
Multiple Episodes

Understanding how sediment transport and storage will delay, attenuate, and even erase the erosional signal of tectonic and climatic forcings has bearing on our ability to read and interpret the geologic record effectively. Here, we estimate sediment transit times in Australia’s largest river system, the Murray-Darling basin, by measuring downstream changes in cosmogenic 26Al/10Be/14C ratios in modern river sediment. Results show that the sediments have experienced multiple episodes of burial and reexposure, with cumulative lag times exceeding 1 Ma in the downstream reaches of the Murray and Darling rivers. Combined with low sediment supply rates and old sediment blanketing the landscape, we posit that sediment recycling in the Murray-Darling is an important and ongoing process that will substantially delay and alter signals of external environmental forcing transmitted from the sediment’s hinterland.

Maintaining the Resilience and Productivity of Co-culture Systems in the Face of Environmental Change

2021 ◽  
Author(s):  
Angelyn Lao ◽  
Kathleen Aviso ◽  
Heriberto Cabezas ◽  
Raymond Tan
Keyword(s):  
Hybrid Rice ◽  
Ecological Network ◽  
Land Area ◽  
Ecological Network Analysis ◽  
Culture Systems ◽  
Graph Theoretic ◽  
Security Issues ◽  
Key Species ◽  
The Face ◽  
Culture Strategies

Abstract Co-culture systems can address food security issues by intensifying production of crops and animal protein without requiring additional land area. We show how a graph-theoretic optimization model based on ecological network analysis can determine resilient co-culture strategies by controlling the presence of key species. Results of simulations on a hybrid rice and crayfish production system indicate that comparable levels of productivity can be achieved with different ecological system structures.

The Late Cenozoic Eridanos delta system in the Southern North Sea Basin: a climate signal in sediment supply?

2001 ◽  
Vol 13 (3) ◽  
pp. 293-312 ◽  
Author(s):  
I. Overeem ◽  
G. J. Weltje ◽  
C. Bishop-Kay ◽  
S. B. Kroonenberg
Keyword(s):  
North Sea ◽  
Sediment Supply ◽  
Late Cenozoic ◽  
Climate Signal ◽  
Southern North Sea ◽  
Delta System

scholarly journals Global morphodynamic response of deltas to sea-level rise in the 21st century

2020 ◽  
Author(s):  
Jaap Nienhuis ◽  
Roderik van de Wal
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Sediment Supply ◽  
Land Loss ◽  
Land Area ◽  
Rcp Scenarios ◽  
Delta Area ◽  
Future Projections ◽  
Area Change ◽  
Will Force

<p>River deltas are low lying areas that will likely experience significant land loss because of relative sea-level rise. Most future projections of delta land loss, however, assume passive coastal inundation (using so-called “bath-tub” models) and as such they tend to be unvalidated and exclude morphodynamic processes such as sedimentation. To improve future projections of delta land area change, here we apply a morphodynamic model of delta response to RSLR to all 10,000 deltas globally. We use historic RSLR, sediment supply, and observed delta land area change from 1985-2015 to calibrate and validate this model for all these deltas. Applying our model using future RSLR scenarios, we find that by the end of this century deltas globally will have lost land under all RCP scenarios. Land loss is aggravated by river dams that have diminished sediment supply to many deltas. RSLR expected under RCP8.5 will force delta land loss at at rates exceeding 900 km<sup>2</sup>/yr by 2100. We predict cumulative land loss under RCP8.5 up to 2100 of ~35,000 km<sup>2</sup>, or about 4% of total global delta area.</p>

scholarly journals THE 2019 TEXAS COASTAL RESILIENCY MASTER PLAN

2018 ◽  
pp. 25
Author(s):  
Chris Levitz
Keyword(s):  
Coastal Management ◽  
Sediment Supply ◽  
Master Plan ◽  
Coastal Environments ◽  
Public And Private ◽  
Coastal Planning ◽  
Planning Effort ◽  
General Land Office ◽  
Private Entity ◽  
Coastal Hydrodynamics

In 2017, the Texas General Land Office (GLO) released the first Texas Coastal Resiliency Master Plan, an ambitious coastal planning effort to restore, enhance and protect more than 367 miles of coast and some 3,300 miles of bays and estuaries for the State of Texas. The lynchpin of the planning effort is its emphasis on shoring up the coast by using the latest coastal technology backed by research on Texas coastal environments, coastal hydrodynamics and morphology, and sediment supply, among others, in conjunction with federal, public, and private entity coordination. By championing a statewide Plan to guide the future of coastal management, the GLO will assure that Texas continues to restore, enhance, and protect its coastlines and communities.

scholarly journals Detrital signals of coastal erosion and fluvial sediment supply during glacio-eustatic sea-level rise, Southern California, USA

Geology ◽  
2021 ◽  
Author(s):  
G.R. Sharman ◽  
J.A. Covault ◽  
D.F. Stockli ◽  
Z.T. Sickmann ◽  
M.A. Malkowski ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Detrital Zircon ◽  
Coastal Erosion ◽  
Southern California ◽  
Submarine Canyon ◽  
Sediment Supply ◽  
Sediment Budgets ◽  
The Face ◽  
Sea Fan

Coastal erosion, including sea-cliff retreat, represents both an important component of some sediment budgets and a significant threat to coastal communities in the face of rising sea level. Despite the importance of predicting future rates of coastal erosion, few prehistoric constraints exist on the relative importance of sediment supplied by coastal erosion versus rivers with respect to past sea-level change. We used detrital zircon U-Pb geochronology as a provenance tracer of river and deep-sea fan deposits from the Southern California Borderland (United States) to estimate relative sediment contributions from rivers and coastal erosion from late Pleistocene to present. Mixture modeling of submarine canyon and fan samples indicates that detrital zircon was dominantly (55%–86%) supplied from coastal erosion during latest Pleistocene (ca. 13 ka) sea-level rise, with lesser contributions from rivers, on the basis of unique U-Pb age modes relative to local Peninsular Ranges bedrock sources. However, sediment that was deposited when sea level was stable at its highest and lowest points since the Last Glacial Maximum was dominantly supplied by rivers, suggesting decreased coastal erosion during periods of sea-level stability. We find that relative sediment supply from coastal erosion is strongly dependent on climate state, corroborating predictions of enhanced coastal erosion during future sea-level rise.

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