scholarly journals Morphological evolution of bifurcations in tide-influenced deltas

2020 ◽  
Vol 8 (2) ◽  
pp. 413-429
Author(s):  
Arya P. Iwantoro ◽  
Maarten van der Vegt ◽  
Maarten G. Kleinhans
Keyword(s):  
River Flow ◽  
Morphological Evolution ◽  
Tidal Flow ◽  
Suspended Load ◽  
Morphological Development ◽  
Relative Role ◽  
Tidal Forcing ◽  
Tidal Influence ◽  
First Case ◽  
Sediment Mobility

Abstract. In river-dominated deltas, bifurcations often develop an asymmetrical morphology; i.e. one of the downstream channels silts up, while the other becomes the dominant one. In tide-influenced systems, bifurcations are thought to be less asymmetric and both downstream channels of the bifurcation remain open. The main aim of this study is to understand how tides influence the morphological development of bifurcations. By using a depth-averaged (2DH, two-dimensional horizontal) morphodynamic model (Delft3D), we simulated the morphological development of tide-influenced bifurcations on millennial timescales. The schematized bifurcation consists of an upstream channel forced by river discharge and two downstream channels forced by tides. Two different cases were examined. In the first case, the downstream channels started with unequal depth or length but had equal tidal forcing, while in the second case the morphology was initially symmetric but the downstream channels were forced with unequal tides. Furthermore, we studied the sensitivity of results to the relative role of river flow and tides. We find that with increasing influence of tides over river, the morphology of the downstream channels becomes less asymmetric. Increasing tidal influence can be achieved by either reduced river flow with respect to the tidal flow or by asymmetrical tidal forcing of the downstream channels. The main reason for this behaviour is that tidal flows tend to be less unequal than river flows when geometry is asymmetric. For increasing tidal influence, this causes less asymmetric sediment mobility and therefore transport in both downstream channels. Furthermore, our results show that bedload tends to divide less asymmetrically compared to suspended load and confirm the stabilizing effect of lateral bed slopes on morphological evolution as was also found in previous studies. We show that the more tide-dominated systems tend to have a larger ratio of bedload-to-suspended-load transport due to periodic low sediment mobility conditions during a transition between ebb and flood. Our results explain why distributary channel networks on deltas with strong tidal influence are more stable than river-dominated ones.

scholarly journals Morphological evolution of bifurcations in tide-influenced deltas

2019 ◽  
Author(s):  
Arya P. Iwantoro ◽  
Maarten van der Vegt ◽  
Maarten G. Kleinhans
Keyword(s):  
River Flow ◽  
Morphological Evolution ◽  
Tidal Flow ◽  
Suspended Load ◽  
Morphological Development ◽  
Relative Role ◽  
Channel Networks ◽  
Tidal Forcing ◽  
Tidal Influence ◽  
First Case

Abstract. In river-dominated deltas, bifurcations often develop an asymmetrical morphology, i.e. one of the downstream channels silts up while the other becomes the dominant one. In tide-influenced systems, bifurcations are thought to be less asymmetric and both downstream channels of the bifurcation remain open. The main aim of this study is to understand how tides influence the morphological development of bifurcations. By using a 2DH morphodynamic model (Delft3D), we simulated the morphological development of tide-influenced bifurcations on millennial time scales. The schematized bifurcation consists of an upstream channel forced by river discharge and two downstream channels forced by tides. Two different cases were examined. In the first case, the downstream channels started with unequal depth or length but had equal tidal forcing, while in the second case the morphology was initially symmetric but the downstream channels were forced with unequal tides. Furthermore, we studied the sensitivity of results to the relative role of river flow and tides. We find that with increasing influence of tides over river, the morphology of the downstream channels becomes less asymmetric. Increasing tidal influence can be achieved by either reduced river flow with respect to the tidal flow, or by asymmetrical tidal forcing of the downstream channels. The main reason for this behaviour is that tidal flows tend to be less unequal than river flows when geometry is asymmetric. For increasing tidal influence, this causes less asymmetric sediment mobility and therefore transport in both downstream channels. Furthermore, our results show that bedload tends to divide less asymmetrical compared to suspended load, showing a possible stabilizing effect of lateral bed slopes on morphological evolution. In our simulations, the more tide-dominated systems tend to have a larger ratio of bedload and suspended load transport. Our results explain why distributary channel networks deltas with strong tidal influence are more stable than river-dominated ones.

scholarly journals Analisa Angkutan Sedimen Pada Hulu Bendung Aepodu Kabupaten Konawe Selatan

2021 ◽  
Vol 2 (1) ◽  
pp. 1-7
Author(s):  
Ramadhan Hidayat Putra ◽  
Amad Syarif Syukri ◽  
Catrin Sudarjat ◽  
Vickky Anggara Ilham
Keyword(s):  
Sediment Transport ◽  
River Flow ◽  
Suspended Load ◽  
Bedload Transport ◽  
Bed Load ◽  
Average Flow ◽  
Load Transport ◽  
Bed Load Transport ◽  
Transport Analysis

Research on Aepodu Weir Sediment Transport Analysis in South Konawe District, based on observations in the field, Aepodu Weir hasa sediment buildup that has now exceeded the height of the weirlight house. The purpose of the study was to analyze the magnitudeof Aepodu river flow and to analyze the amount of sedimenttransport that occurred in the Aepodu dam. The method used todetermine the amount of bed load transport uses stchoklitscht, whilefor transporting suspended load using forcheimer.The results of the analysis of the average flow of the Aepodu riverwere 3,604 m3/ second. Sediment transport that occurs in Aepoduweir is Bedload transport (Qb) of 291625.771 tons / year, andsuspended load transport (Qs) of 16972,423 tons / year, so that thetotal sediment transport (QT) is 308598,194 tons / year.

Morphological Evolution of Low-Grade Silica Fume at Elevated Temperature

2017 ◽  
Vol 36 (6) ◽  
pp. 607-613 ◽  
Author(s):  
Junhong Chen ◽  
Tong Li ◽  
Xiaoping Li ◽  
Kuo-Chih Chou ◽  
Xinmei Hou
Keyword(s):  
Elevated Temperature ◽  
Silica Fume ◽  
Room Temperature ◽  
Morphological Evolution ◽  
Hydroxyl Groups ◽  
Morphological Development ◽  
Low Grade ◽  
Structural Development ◽  
Pollution Problem ◽  
Environmental Pollution Problem

AbstractTo solve the environmental pollution problem caused by low-grade silica fume (SiO2, < 86 mass%) and further expand its application field, the morphological development of low-grade silica fume from room temperature to 900 °C in air was investigated using TG-DTA, SEM and TEM techniques. The structural development of silica fume was further analyzed using FT-IR and Raman spectrum. The results show that silica fume contains many defects of broken bands such as Si-O or ≡Si at room temperature. When exposed to the moister or water, the broken bonds tend to react with water and result in the formation of Si-OH and adjacent hydroxyl groups of Si-OH•OH-Si. At elevated temperature up to 900 °C, the structure of silica fume becomes compact due to the reconstruction of the broken bonds caused by the dehydration reaction.

scholarly journals Upstream Internal Jumps in Stratified Sill Flow: Observations of Formation, Evolution, and Release

2010 ◽  
Vol 40 (6) ◽  
pp. 1419-1426 ◽  
Author(s):  
Patrick F. Cummins ◽  
Laurence Armi
Keyword(s):  
Hydraulic Jump ◽  
Early Stage ◽  
Gravity Current ◽  
Tidal Flow ◽  
Time Dependent ◽  
Upstream Region ◽  
Exchange Flow ◽  
Near Surface ◽  
Undular Bore ◽  
First Case

Abstract The time-dependent response of upstream undular bores and internal hydraulic jumps from initial formation to eventual release is documented. Two events, characterized by qualitatively different responses, are discussed. In the first case, an undular bore develops upstream of the sill crest. This disturbance remains upstream through the ebb tidal flow but is transformed to a hydraulic jump as its amplitude increases. Toward the end of ebb tide, it is released and subsequently disperses into a group of solitary-like waves. During the second event, an upstream jump also develops at an early stage of the tide. However, it is subsequently swept downstream by the tidal flow such that the upstream region then appears featureless. Approaching slack tide, as an exchange flow becomes established, a large bore or gravity current is emitted. The different responses seen in these two events are interpreted in terms of the Froude number associated with the near-surface stratification.

Mechanisms for nitrogen supply to the Australian North West Shelf

1985 ◽  
Vol 36 (6) ◽  
pp. 753 ◽  
Author(s):  
PE Holloway ◽  
SE Humphries ◽  
M Atkinson ◽  
J Imberger
Keyword(s):  
River Flow ◽  
Tidal Flow ◽  
Vertical Mixing ◽  
Low Frequency ◽  
Transport Processes ◽  
Physical Processes ◽  
Mixing Processes ◽  
North West ◽  
Tidal Motion ◽  
The North

An upper bound for the rate of supply of new nitrate required to maintain the observed primary production on the North West Shelf is estimated to be 0.1 g N m-2 day -1. Nitrate concentrations over the shelf and slope regions are high ( > 100 mg N m-3, in water deeper than - 100 m and usually low (~10 mg N m-3), on the shelf. River flow is weak and carries little nutrient into the shelf waters and so it remains for ocean physical processes to advect and mix the nutrient-rich deep waters onto the shallower shelf regions to meet the nutrient demand. Several mechanisms are reviewed to determine their potential in carrying out the required transport processes. Estimates of the advection of nitrate onto the shelf show that both semi-diurnal tidal flow and low-frequency (periods > 35 h) upwelling events can each contribute approximately half the required demand, providing there is rapid use of nutrients. The upwelling events occur in summer and are associated with reversals of the south-west-flowing Leeuwin Current. Tropical cyclones are also shown to be capable of meeting a small, but significant, portion of the demand through enrichment of the surface layers in the offshelf waters by upwelling and vertical mixing. The enriched water can then be advected onto the shelf. Both tidal and internal tidal motion have the potential to transport nitrate onto the shelf from deeper water through vertical and horizontal mixing processes. However, these processes are difficult to quantify accurately. It is concluded that nitrogen is supplied to this shelf ecosystem by physical processes that are regular throughout the year, as opposed to large sporadic events that occur only once or twice a year.

Where Fossils Dare and Males Matter: combined morphological and molecular analysis untangles the evolutionary history of the spider ant genus Leptomyrmex Mayr (Hymenoptera : Dolichoderinae)

2017 ◽  
Vol 31 (6) ◽  
pp. 765 ◽  
Author(s):  
Phillip Barden ◽  
Brendon Boudinot ◽  
Andrea Lucky
Keyword(s):  
Evolutionary History ◽  
Morphological Evolution ◽  
Sister Group ◽  
Morphological Characters ◽  
Fossil Material ◽  
First Case ◽  
History Of ◽  
The Impact ◽  
Surprising Discovery

The distinctive ant genus Leptomyrmex Mayr, 1862 had been thought to be endemic to Australasia for over 150 years, but enigmatic Neotropical fossils have challenged this view for decades. The present study responds to a recent and surprising discovery of extant Leptomyrmex species in Brazil with a thorough evaluation of the Dominican Republic fossil material, which dates to the Miocene. In the first case study of direct fossil inclusion within Formicidae Latreille, 1809, we incorporated both living and the extinct Leptomyrmex species. Through simultaneous analysis of molecular and morphological characters in both Bayesian and parsimony frameworks, we recovered the fossil taxon as sister-group to extant Leptomyrmex in Brazil while considering the influence of taxonomic and character sampling on inferred hypotheses relating to tree topology, biogeography and morphological evolution. We also identified potential loss of signal in the binning of morphological characters and tested the impact of parameterisation on divergence date estimation. Our results highlight the importance of securing sufficient taxon sampling for extant lineages when incorporating fossils and underscore the utility of diverse character sources in accurate placement of fossil terminals. Specifically, we find that fossil placement in this group is influenced by the inclusion of male-based characters and the newly discovered Neotropical ‘Lazarus taxon’.

scholarly journals Effects of Tidally Varying River Flow on Entrainment of Juvenile Salmon into Sutter and Steamboat Sloughs

2020 ◽  
Vol 19 (2) ◽  
Author(s):  
Jason Romine ◽  
◽  
Russell Perry ◽  
Paul Stumpner ◽  
Aaron Blake ◽  
...  
Keyword(s):  
River Flow ◽  
Management Strategies ◽  
Tidal Flow ◽  
Potential Effect ◽  
Rate Of Change ◽  
Sacramento River ◽  
Juvenile Salmon ◽  
Migration Route ◽  
Management Actions ◽  
Hydrodynamic Data

Survival of juvenile salmonids in the Sacramento–San Joaquin Delta (Delta) varies by migration route, and thus the proportion of fish that use each route affects overall survival through the Delta. Understanding factors that drive routing at channel junctions along the Sacramento River is therefore critical to devising management strategies that maximize survival. Here, we examine entrainment of acoustically tagged juvenile Chinook Salmon into Sutter and Steamboat sloughs from the Sacramento River. Because these sloughs divert fish away from the downstream entrances of the Delta Cross Channel and Georgiana Slough (where fish access the low-survival region of the interior Delta), management actions to increase fish entrainment into Sutter and Steamboat sloughs are being investigated to increase through-Delta survival. Previous studies suggest that fish generally “go with the flow”—as net flow into a divergence increases, the proportion of fish that enter that divergence correspondingly increases. However, complex tidal hydrodynamics at sub-daily time-scales may be decoupled from net flow. Therefore, we modeled routing of acoustic tagged juvenile salmon as a function of tidally varying hydrodynamic data, which was collected using temporary gaging stations deployed between March and May of 2014. Our results indicate that discharge, the proportion of flow that entered the slough, and the rate of change of flow were good predictors of an individual’s probability of being entrained. In addition, interactions between discharge and the proportion of flow revealed a non-linear relationship between flow and entrainment probability. We found that the highest proportions of fish are likely to be entrained into Steamboat Slough and Sutter Slough on the ascending and descending limbs of the tidal cycle, when flow changes from positive to negative. Our findings characterize how patterns of entrainment vary with tidal flow fluctuations, providing information critical for understanding the potential effect of management actions (e.g., fish guidance structures) to modify routing probabilities at this location.

Temporal and spatial dynamic of suspended sediments fluxes and sources and morphological evolution of the bed in the middle Loire river

2021 ◽  
Author(s):  
Brahim Hichem Belbal ◽  
Nicole Goutal ◽  
Germain Antoine ◽  
Olivier Cerdan
Keyword(s):  
Power Plants ◽  
River Flow ◽  
Temporal Dynamics ◽  
Morphological Evolution ◽  
Suspended Sediments ◽  
Second Phase ◽  
Temporal Dynamic ◽  
Massif Central ◽  
Catchment Areas ◽  
Loire River

&lt;p&gt;The middle Loire riverbed, after its confluence with Allier, is characterised by a morphology of alternate bars more or less vegetated and possesses riverbank flood protections. The suspended particulate matter (SPM) fluxes are therefore originated from these two catchment areas that drain the eastern and southern parts of the Massif Central. The temporal dynamics of the SPM fluxes are very variable, both on an interannual scale and on the scale of a flood event. Furthermore, SPM fluxes also present high spatial heterogeneities as they are governed by complex processes of production (erosion) and transfer (storage/remobilisation). The Loire river plays an important role in supporting the French energy production by providing cooling water to several Nuclear Power Plants (NPP). However, the cooling systems of the NPPs on the middle Loire are exposed to the risk of silting. In order to ensure a safe management of water intakes and prevent the industrial risks arising from sediment transport, it is therefore imperative to understand the spatio-temporal dynamic of sediment production and transfer.&lt;/p&gt;&lt;p&gt;In this context, the objective of this thesis work is to provide keys to improve sediment management of the river between the two NPPs of Belleville and Dampierre. In a first place, the river flow and SPM data available at the upstream NPP of Belleville will be analysed in order to understand the temporal variations of the incoming SPM fluxes. In a second phase, a soil erosion and hydrological model will be implemented to understand the production processes in the upstream catchments. This second part will allow to determine the interactions of the SPM inputs in the river with the morphodynamics of the bed of the Loire between the two stations. We will present the methodology that has been designed to apprehend these two phases and the first results of the river SPM temporal dynamic at the Belleville NPP station.&lt;/p&gt;

Smoke Screen

2016 ◽  
Author(s):  
Gregory L. Simon
Keyword(s):  
Social Structures ◽  
Relative Role ◽  
The West ◽  
Mountain Pine Beetles ◽  
The Third ◽  
First Case ◽  
Fire Activity ◽  
Pine Beetles ◽  
The Relationship

This chapter presents three cases that illustrate how the underlying drivers of wildland-urban interface (WUI) wildfires frequently mischaracterize the relative role of ecological and social structures of influence. The first case explores the rather unscientific origins of the term firestorm and the credibility it is afforded as a legitimate fire classification through its normative use and acceptance in mainstream fire discourse. This process diminishes the very social and profitable origins of the WUI fire problem and naturalizes these areas as a hazardous by-product of larger, exogenous, and inviolable environmental forces such as climate change. The second case examines recent efforts to study and explain the relationship between mountain pine beetles and fire activity in the western United States. The third case describes the deeply political and protracted process of challenging the economically powerful wood shingle and cedar shake industry. Collectively all three cases illustrate how contemporary discourses on fire tend to truncate the scope of what counts (or is allowed to be brought to the debate table) as an underlying driver of increased fire activity in the West.

scholarly journals Understanding Morphodynamic Changes of a Tidal River Confluence through Field Measurements and Numerical Modeling

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1424 ◽  
Author(s):  
Qiancheng Xie ◽  
James Yang ◽  
Staffan Lundström ◽  
Wenhong Dai
Keyword(s):  
Dominant Role ◽  
Tidal Flow ◽  
River Mouth ◽  
Field Measurements ◽  
Sediment Concentration ◽  
Suspended Load ◽  
Tidal River ◽  
Wet Season ◽  
Run Off ◽  
Tidal Flows

A confluence is a natural component in river and channel networks. This study deals, through field and numerical studies, with alluvial behaviors of a confluence affected by both river run-off and strong tides. Field measurements were conducted along the rivers including the confluence. Field data show that the changes in flow velocity and sediment concentration are not always in phase with each other. The concentration shows a general trend of decrease from the river mouth to the confluence. For a given location, the tides affect both the sediment concentration and transport. A two-dimensional hydrodynamic model of suspended load was set up to illustrate the combined effects of run-off and tidal flows. Modeled cases included the flood and ebb tides in a wet season. Typical features examined included tidal flow fields, bed shear stress, and scour evolution in the confluence. The confluence migration pattern of scour is dependent on the interaction between the river currents and tidal flows. The flood tides are attributable to the suspended load deposition in the confluence, while the ebb tides in combination with run-offs lead to erosion. The flood tides play a dominant role in the morphodynamic changes of the confluence.

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