The Role of Surges During Periods of Very Shallow Water on Sediment Transport Over Tidal Flats

Periods of very shallow water (water depth in the order of 10 cm) occur daily on tidal flats because of the propagation of tides over very gently sloping beds, leading to distinct morphodynamical phenomena. To improve the understanding of the characteristics of velocity and suspended sediment concentration (SSC) surges and their contribution to sediment transport and local bed changes during periods of very shallow water, measurements of near-bed flow, and SSC were carried out at two cross-shore locations on an intertidal flat along the Jiangsu coast, China. Furthermore, the role of surges in local resuspension and morphological change was explored. Results indicate that flow and SSC surges occurred at both stations during very shallow water periods. On the lower intertidal flat, flood surges were erosive, while weaker surges on the middle intertidal flat were not. Surges on lower intertidal flats resulted in local resuspension and strong turbidity, contributing up to 25% of the onshore-suspended sediment flux during flood tides, even though they last only 10% of the flood duration. When surges travel across the flats, conditions change from erosional to depositional. Velocity surges on the middle intertidal flat were too weak to resuspend bed sediment, and the associated SSC surges were produced by advection.

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Conceptual model of sedimentgraph from flood events in a small agricultural watershed

Annals of Warsaw University of Life Sciences – SGGW Land Reclamation ◽

10.2478/v10060-008-0004-7 ◽

2008 ◽

Vol 39 (1) ◽

pp. 49-57 ◽

Cited By ~ 1

Author(s):

Kazimierz Banasik ◽

J. Mitchell

Keyword(s):

Conceptual Model ◽

Suspended Sediment ◽

Sediment Concentration ◽

Agricultural Watershed ◽

Sediment Flux ◽

Flood Events ◽

Rainfall Events ◽

Sediment Routing ◽

Suspended Sediment Flux ◽

Lag Times

Conceptual model of sedimentgraph from flood events in a small agricultural watershed A procedure for predicting the sediment graph (i.e. the suspended sediment flux), from a small river catchment by heavy rainfall, has been developed using the concept of an instantaneous unit hydrograph (IUH) and dimensionless sediment concentration distribution (DSCD). A formula for instantaneous unit sedimentgraph (IUSG) is presented, and a procedure for estimating the sediment routing coefficient, which is a key parameter of the IUSG, based on measured data of rainfall-runoff-suspended sediment is applied. Field data from a small, field sized agricultural basin, lacated in center of Illinois has been used for analizing lag times for runoff (LAG) and sediment yield (LAGs). Assumptions about sediment generated during rainfall events are discussed.

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Landscape and river self-organization limit the flux of fine particles

10.5194/egusphere-egu2020-12885 ◽

2020 ◽

Author(s):

Colin Phillips ◽

Carlos Rogéliz ◽

Daniel Horton ◽

Jonathan Higgins ◽

Aaron Packman

Keyword(s):

Suspended Sediment ◽

Fine Particle ◽

River Flow ◽

Fine Particles ◽

Strong Support ◽

Sediment Concentration ◽

Sediment Flux ◽

Suspended Sediment Transport ◽

Erosion Rates ◽

Suspended Sediment Flux

<p>Fine particles in rivers comprise a substantial fraction (>50%) of the mass leaving a landscape, while at shorter timescales they represent significant carriers of nutrients and contaminants with the potential to both degrade and enhance aquatic habitats. Predicting fine particle dynamics within rivers remains challenging due to a complex relationship between sediment and water availability from the landscape. This inherent complexity results in watershed-specific understandings of suspended sediment dynamics, typically parameterized as empirical functions of catchment land use, geology, and climate. However, observations of significant fine particle storage within river corridors may indicate that the flux of suspended sediment depends on reach-scale hydraulics. To better understand these dynamics, we synthesized over 40 years of suspended sediment concentration (SSC), hydraulic geometry, river flow, and grainsize data collected by the US Geological Survey from hundreds of rivers spanning a large variety of environments across the continental United States. This data synthesis reveals a strong nonlinear trend between reach-scale hydraulics and the suspended sediment flux, with a secondary dependence on particle properties. The multi-site synthesis reveals that by normalizing the suspended sediment flux by the bankfull shear stress and flux results in a collapse of the observed data onto a single function that describes a self-organizing structure for suspended sediment transport in watersheds. This general relationship indicates strong support for the role of autogenic processes in setting the flux of fine particles and erosion rates of watersheds.</p>

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Suspended sediment fluxes in an Indonesian river draining a rainforested basin subject to land cover change

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-8-7137-2011 ◽

2011 ◽

Vol 8 (4) ◽

pp. 7137-7175 ◽

Cited By ~ 2

Author(s):

F. A. Buschman ◽

A. J. F. Hoitink ◽

S. M. de Jong ◽

P. Hoekstra

Keyword(s):

Land Cover ◽

Suspended Sediment ◽

River Discharge ◽

Soil Loss ◽

Suspended Sediment Concentration ◽

Sediment Concentration ◽

Sediment Flux ◽

Sediment Fluxes ◽

Suspended Sediment Flux ◽

The Impact

Abstract. Forest clearing for reasons of timber production, open pit mining and the establishment of oil palm plantations generally results in excessively high sediment loads in the tropics. The increasing sediment fluxes pose a threat to coastal marine ecosystems such as coral reefs. This study presents observations of suspended sediment fluxes in the Berau river (Indonesia), which debouches into a coastal ocean that can be considered the preeminent center of coral diversity. The Berau is an example of a small river draining a mountainous, relatively pristine basin that receives abundant rainfall. Flow velocity was measured over a large part of the river width at a station under the influence of tides, using a Horizontal Acoustic Doppler Current Profiler (HADCP). Surrogate measurements of suspended sediment concentration were taken with an Optical Backscatter Sensor (OBS). Tidally averaged suspended sediment concentration increases with river discharge, implying that the tidally averaged suspended sediment flux increases non-linearly with river discharge. Averaged over the 6.5 weeks observations covered by the benchmark survey, the tidally averaged suspended sediment flux was estimated at 2 Mt y−1. Considering the wet conditions during the observation period, this figure may be considered as an upper limit of the yearly averaged flux. This flux is significantly smaller than what could have been expected from the characteristics of the catchment. The consequences of ongoing clearing of rainforest were explored using a plot scale erosion model. When rainforest, which still covered 50–60 % of the basin in 2007, is converted to production land, soil loss is expected to increase with a factor between 10 and 100. If this soil loss is transported seaward as suspended sediment, the increase in suspended sediment flux in the Berau river would impose a severe sediment stress on the global hotspot of coral reef diversity. The impact of land cover changes will largely depend on the degree in which the Berau estuary acts as a sediment trap.

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How Sediment Transport Sways Wetland Stability

Eos ◽

10.1029/2016eo046199 ◽

2016 ◽

Vol 97 ◽

Author(s):

Lily Strelich

Keyword(s):

Sediment Transport ◽

Sea Level Rise ◽

Suspended Sediment ◽

Sea Level ◽

Coastal Wetlands ◽

Suspended Sediment Concentration ◽

Sediment Concentration

Scientists examine the role of variables like tides and suspended sediment concentration to improve methods of evaluating coastal wetlands and how they may respond to future sea level rise.

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How do modeling choices and erosion zone locations impact the representation of connectivity and the dynamics of suspended sediments in a multi-source soil erosion model?

Earth Surface Dynamics ◽

10.5194/esurf-9-123-2021 ◽

2021 ◽

Vol 9 (1) ◽

pp. 123-144

Author(s):

Magdalena Uber ◽

Guillaume Nord ◽

Cédric Legout ◽

Luis Cea

Keyword(s):

Sediment Transport ◽

Soil Erosion ◽

Suspended Sediment ◽

Structural Connectivity ◽

Sediment Flux ◽

Suspended Sediment Transport ◽

Sediment Sources ◽

Flux Variability ◽

Suspended Sediment Flux ◽

The Impact

Abstract. Soil erosion and suspended sediment transport understanding is an important issue in terms of soil and water resources management in the critical zone. In mesoscale watersheds (>10 km2) the spatial distribution of potential sediment sources within the catchment associated with rainfall dynamics is considered to be the main factor in the observed suspended sediment flux variability within and between runoff events. Given the high spatial heterogeneity that can exist for such scales of interest, distributed physically based models of soil erosion and sediment transport are powerful tools to distinguish the specific effect of structural and functional connectivity on suspended sediment flux dynamics. As the spatial discretization of a model and its parameterization can crucially influence how the structural connectivity of the catchment is represented in the model, this study analyzed the impact of modeling choices in terms of the contributing drainage area (CDA) threshold to define the river network and of Manning's roughness parameter (n) on the sediment flux variability at the outlet of two geomorphologically distinct watersheds. While the modeled liquid and solid discharges were found to be sensitive to these choices, the patterns of the modeled source contributions remained relatively similar when the CDA threshold was restricted to the range of 15 to 50 ha, with n restricted to the range 0.4–0.8 on the hillslopes and to 0.025–0.075 in the river. The comparison of the two catchments showed that the actual location of sediment sources was more important than the choices made during discretization and parameterization of the model. Among the various structural connectivity indicators used to describe the geological sources, the mean distance to the stream was the most relevant proxy for the temporal characteristics of the modeled sedigraphs.

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The effect of ripple types on cross-shore suspended sediment flux

Earth Surface Dynamics Discussions ◽

10.5194/esurfd-2-215-2014 ◽

2014 ◽

Vol 2 (1) ◽

pp. 215-254

Author(s):

S. R. Kularatne ◽

J. Doucette ◽

C. B. Pattiaratchi

Keyword(s):

Suspended Sediment ◽

Suspended Sediment Concentration ◽

Three Dimensional ◽

Sediment Concentration ◽

Sediment Flux ◽

The Other ◽

Two Dimensional ◽

Significant Difference ◽

Suspended Sediment Flux ◽

The Cross

Abstract. Field measurements, collected at several low energy, microtidal beaches in south-western Australia were used to study the cross-shore transport and sediment resuspension over different sand ripple types. The measurements included simultaneous records of the water surface elevation, cross-shore current velocity, and suspended sediment concentration, as well as free diver measurements of the ripple dimensions. The observed ripples were classified according to their geometry and sediment suspension patterns into six categories: flat bed, post-vortex ripples, two-dimensional (2-D) ripples, two/three-dimensional (2-D/3-D) ripples, three-dimensional (3-D) ripples, and cross ripples. Flat bed conditions were observed under the highest flow mobility numbers. Post-vortex ripples were observed under slightly lower mobility numbers. The other ripple types occurred under low mobility numbers, with no significant difference in the mobility number among them. Two-dimensional ripples were observed more than the other ripple types in the presence of coarse grains. The suspended sediment concentration at ∼0.05 m above the bed was greater over steep ripples. The net cross-shore suspended sediment flux close to the seabed (at ∼0.05 m) in the swell frequency band varied over the different ripples types: onshore over a flat bed, offshore over post-vortex ripples, onshore over 2-D and 2-D/3-D ripples, and offshore over 3-D ripples. The suspended sediment flux direction over the cross ripples varied between onshore and offshore.

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Observations and scaling of tidal mass transport across the lower Ganges–Brahmaputra delta plain: implications for delta management and sustainability

Earth Surface Dynamics ◽

10.5194/esurf-7-231-2019 ◽

2019 ◽

Vol 7 (1) ◽

pp. 231-245 ◽

Cited By ~ 11

Author(s):

Richard Hale ◽

Rachel Bain ◽

Steven Goodbred Jr. ◽

Jim Best

Keyword(s):

Sediment Transport ◽

Suspended Sediment ◽

Suspended Sediment Concentration ◽

Water Discharge ◽

Sediment Concentration ◽

Natural System ◽

Sediment Flux ◽

Sediment Delivery ◽

The Ganges ◽

Tidal Processes

Abstract. The landscape of southwest Bangladesh, a region constructed primarily by fluvial processes associated with the Ganges River and Brahmaputra River, is now maintained almost exclusively by tidal processes as the fluvial system has migrated east and eliminated the most direct fluvial input. In natural areas such as the Sundarbans National Forest, year-round inundation during spring high tides delivers sufficient sediment that enables vertical accretion to keep pace with relative sea-level rise. However, recent human modification of the landscape in the form of embankment construction has terminated this pathway of sediment delivery for much of the region, resulting in a startling elevation imbalance, with inhabited areas often sitting >1 m below mean high water. Restoring this landscape, or preventing land loss in the natural system, requires an understanding of how rates of water and sediment flux vary across timescales ranging from hours to months. In this study, we combine time series observations of water level, salinity, and suspended sediment concentration with ship-based measurements of large tidal-channel hydrodynamics and sediment transport. To capture the greatest possible range of variability, cross-channel transects designed to encompass a 12.4 h tidal cycle were performed in both dry and wet seasons during spring and neap tides. Regional suspended sediment concentration begins to increase in August, coincident with a decrease in local salinity, indicating the arrival of the sediment-laden, freshwater plume of the combined Ganges–Brahmaputra–Meghna rivers. We observe profound seasonality in sediment transport, despite comparatively modest seasonal variability in the magnitude of water discharge. These observations emphasize the importance of seasonal sediment delivery from the main-stem rivers to this remote tidal region. On tidal timescales, spring tides transport an order of magnitude more sediment than neap tides in both the wet and dry seasons. In aggregate, sediment transport is flood oriented, likely as a result of tidal pumping. Finally, we note that rates of sediment and water discharge in the tidal channels are of the same scale as the annually averaged values for the Ganges and Brahmaputra rivers. These observations provide context for examining the relative importance of fluvial and tidal processes in what has been defined as a quintessentially tidally influenced delta in the classification scheme of Galloway (1975). These data also inform critical questions regarding the timing and magnitude of sediment delivery to the region, which are especially important in predicting and preparing for responses of the natural system to ongoing environmental change.

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The influence of turbulent bursting on sediment resuspension under unidirectional currents

Earth Surface Dynamics ◽

10.5194/esurf-5-399-2017 ◽

2017 ◽

Vol 5 (3) ◽

pp. 399-415 ◽

Cited By ~ 13

Author(s):

Sarik Salim ◽

Charitha Pattiaratchi ◽

Rafael Tinoco ◽

Giovanni Coco ◽

Yasha Hetzel ◽

...

Keyword(s):

Sediment Transport ◽

Critical Velocity ◽

Sediment Resuspension ◽

Three Dimensional ◽

Sediment Concentration ◽

Sediment Flux ◽

Experimental Conditions ◽

Bursting Events ◽

Event Based

Abstract. Laboratory experiments were conducted in an open channel flume with a flat sandy bed to examine the role of turbulence on sediment resuspension. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components and acoustic backscatter as a proxy to suspended sediment concentration. Estimates of sediment transport assume that there is a mean critical velocity that needs to be exceeded before sediment transport is initiated. This approach does not consider the turbulent flow field that may initiate sediment resuspension through event-based processes such as the bursting phenomenon. In this paper, laboratory measurements were used to examine the sediment resuspension processes below and above the mean critical velocity. The results within a range above and below the measured mean critical velocity suggested that (1) the contribution of turbulent bursting events remained identical in both experimental conditions, (2) ejection and sweep events contributed more to the total sediment flux than up-acceleration and down-deceleration events, and (3) wavelet transform revealed a correlation between the momentum and sediment flux in both test conditions. Such similarities in conditions above and below the measured mean critical velocity highlight the need to re-evaluate the accuracy of a single time-averaged mean critical velocity for the initiation of sediment entrainment.

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How do modeling choices impact the representation of structural connectivity and the dynamics of suspended sediment fluxes in distributed soil erosion models?

10.5194/esurf-2020-64 ◽

2020 ◽

Author(s):

Magdalena Uber ◽

Guillaume Nord ◽

Cédric Legout ◽

Luis Cea

Keyword(s):

Sediment Transport ◽

Soil Erosion ◽

Suspended Sediment ◽

Structural Connectivity ◽

Sediment Flux ◽

Suspended Sediment Transport ◽

Sediment Sources ◽

Flux Variability ◽

Suspended Sediment Flux ◽

The Impact

Abstract. Soil erosion and suspended sediment transport understanding is an important issue in terms of soil and water resources management in the critical zone. In mesoscale watersheds (> 10 km2) the spatial distribution of potential sediment sources within the catchment associated to the rainfall dynamics are considered as the main factors of the observed suspended sediment ﬂux variability within and between runoff events. Given the high spatial heterogeneity that can exist for such scales of interest, distributed physically based models of soil erosion and sediment transport are powerful tools to distinguish the specific effect of structural and functional connectivity on suspended sediment flux dynamics. As the spatial discretization of a model and its parameterization can crucially influence how structural connectivity of the catchment is represented in the model, this study analyzed the impact of modeling choices in terms of contributing drainage area (CDA) threshold to define the river network and of Manning's roughness parameter (n) on the sediment flux variability at the outlet of two geomorphological distinct watersheds. While the modelled liquid and solid discharges were found to be sensitive to these choices, the patterns of the modeled source contributions remained relatively similar when the CDA threshold was restricted to the range of 15 to 50 ha, n on the hillslopes to the range 0.4–0.8 and to 0.025–0.075 in the river. The comparison of both catchments showed that the actual location of sediment sources was more important than the choices made during discretization and parameterization of the model. Among the various structural connectivity indicators used to describe the geological sources, the mean distance to the stream was the most relevant proxy of the temporal characteristics of the modelled sedigraphs.

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Observations and scaling of tidal mass transport across the lower Ganges-Brahmaputra delta plain: implications for delta management and sustainability

10.5194/esurf-2018-66 ◽

2018 ◽

Author(s):

Richard Hale ◽

Rachel Bain ◽

Steven Goodbred Jr. ◽

Jim Best

Keyword(s):

Sediment Transport ◽

Suspended Sediment ◽

Time Scales ◽

Suspended Sediment Concentration ◽

Water Discharge ◽

Sediment Concentration ◽

Sediment Flux ◽

Sediment Delivery ◽

The Ganges ◽

Tidal Processes

Abstract. The landscape of southwest Bangladesh, a region constructed primarily by fluvial processes associated with the Ganges and Brahmaputra Rivers, is now maintained almost exclusively by tidal processes as the fluvial system has migrated to the east through the Holocene. In natural areas such as the Sundarbans National Forest, year-round spring-tide inundation delivers sufficient sediment for vertical accretion to keep pace with relative sea-level rise. However, recent human modification of the landscape in the form of embankment construction has terminated this pathway of sediment delivery for much of the region, resulting in a startling elevation imbalance, with inhabited areas often sitting > 1 m below mean high water. Restoring this landscape, or preventing land loss in the natural system, requires an understanding of how rates of water and sediment flux vary across time scales ranging from hours to months. In this study, we combine time-series observations of water level, salinity, and suspended sediment concentration, with ship-based measurements of large tidal channel hydrodynamics and sediment transport. To capture the greatest possible range of variability, cross-channel transects designed to encompass a 12.4-h tidal cycle were performed in both dry and wet seasons, during spring and neap tides. Regional suspended sediment concentration begins to increase in August, coincident with a decrease in local salinity, indicating the arrival of the sediment-laden, freshwater plume of the combined Ganges-Brahmaputra-Meghna rivers. We observe profound seasonality in sediment transport, despite somewhat modest seasonal variability in the magnitude of water discharge, indicating the importance of this seasonal sediment delivery. On tidal time-scales, spring tides transport an order of magnitude more sediment than neap tides in both the wet and dry seasons. In aggregate, sediment transport is flood-oriented, likely a result of tidal pumping. Finally, we note that rates of sediment and water discharge in the tidal channels are of the same scale as the annually averaged values for the Ganges or Brahmaputra rivers. These observations provide context for examining the relative importance of fluvial and tidal processes in what has been defined as the quintessential tidal delta in the classification scheme of Galloway. These data also inform critical questions regarding the timing and magnitude of sediment delivery to the region, which are especially important in predicting, and preparing for, future change under changing environmental conditions.

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