Interactions between aquatic vegetation, hydraulics and fine sediment

Aquatic vegetation, hydraulics and sediment transport have complex interactions that are not yet well understood. These interactions are important for sediment conveyance, sediment sequestration, phasing of sediment delivery from runoff events, and management of ecosystem health in lowland streams. To address this knowledge gap detailed field measurements of sediment transport through natural flexible aquatic vegetation are required to supplement and validate laboratory results. This paper contributes a field study of suspended sediment transport through aquatic vegetation and includes mechanical removal of aquatic vegetation with a weed cutting boat. It also provides methods to quantify vegetation cover through remote sensing with Unmanned Aerial Vehicles (UAVs) and estimate biomass from ground truth sampling. Suspended sediment concentrations were highly dependent on aquatic vegetation abundance, and the distance upstream that had been cleared of aquatic vegetation. When the study reach was fully vegetated (i.e. cover >80%), the maximum recorded SSC was 14.6 g/m (during a fresh with discharge of 2.47 m/s), during weed cutting operations SSC was 76.8 g/m at 0.84 m/s (weedcutting boat 0.5-1 km upstream from study reach), however following weed cutting operations (4.6 km cleared upstream), SSC was 139.0 g/m at a discharge of 1.52 m/s. The data indicates that fine sediment was being sequestered by aquatic vegetation and likely remobilised after vegetation removal. Investigation of suspended sediment spatial dynamics illustrated changes in particle size distribution due to preferential settling of coarse particles within aquatic vegetation. Hydraulic resistance in the study reach (parameterized by Manning’s n) dropped by over 70% following vegetation cutting. Prior to cutting hydraulic resistance was discharge dependent, while post cutting hydraulic resistance was approximately invariant of discharge. Aerial surveying captured interesting changes in aquatic vegetation cover, where some very dense regions of aquatic vegetation were naturally removed leaving behind unvegetated riverbed and fine sediment.

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North to South Variations in the Suspended Sediment Transport Budget within Large Siberian River Deltas Revealed by Remote Sensing Data

Remote Sensing ◽

10.3390/rs13224549 ◽

2021 ◽

Vol 13 (22) ◽

pp. 4549

Author(s):

Sergey Chalov ◽

Kristina Prokopeva ◽

Michał Habel

Keyword(s):

Remote Sensing ◽

Sediment Transport ◽

Suspended Sediment ◽

Aquatic Vegetation ◽

River Sediments ◽

The Arctic ◽

Suspended Sediment Transport ◽

Forest Steppe ◽

Siberian River ◽

River Deltas

This study presents detailed suspended sediment budget for the four Siberian river deltas, representing contrasting conditions between Northern and Southern environments. Two of the studied rivers empty their water and sediments into the marine located in the permafrost zone in the Arctic region (Lena and Kolyma), and the other two (Selenga and Upper Angara) flow into Lake Baikal located in the steppe and forest-steppe zone of Southern Siberia. For the first time, these poorly monitored areas are analyzed in terms of the long-term and seasonal changes of spatial patterns of suspended sediment concentrations (SSC) over distributaries systems. Remote sensing reflectance is derived from continuous time series of Landsat images and calibrated with the onsite field measurements of SSC. Seasonal variability of suspended sediment changes over deltas was captured for the period from 1989 to 2020. We identify significant variability in the sedimentation processes between different deltas, which is explained by particularities of deltas networks and geomorphology and the existence of specific drivers—continuous permafrost impact in the North and abundant aquatic vegetation and wetland-dominated areas in the South. The study emphasizes that differences exist between Northern and Southern deltas regarding suspended sediments transport conditions. Mostly retention of suspended sediment is observed for Southern deltas due to sediment storage at submerged banks and marshlands located in the backwater zone of the delta during high discharges. In the Northern (arctic) deltas due to permafrost impacts (melting of the permafrost), the absence of sub-aquatic banks and river to ocean interactions of suspended sediment transport is mostly increased downwards, predominantly under higher discharges and along main distributary channels. These results shine light on the geochemical functions of the deltas and patterns of sequestering various metals bound to river sediments.

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Modos de Transporte de Sedimentos Finos no Estuário do Rio Itajaí, SC

Pesquisas em Geociências ◽

10.22456/1807-9806.20282 ◽

2001 ◽

Vol 28 (2) ◽

pp. 151 ◽

Cited By ~ 1

Author(s):

CARLOS AUGUSTO FRANÇA SCHETTINI ◽

ELÍRIO ERNESTINO TOLDO JR

Keyword(s):

Sediment Transport ◽

Suspended Sediment ◽

River Discharge ◽

River Sediment ◽

Drainage Basin ◽

River Estuary ◽

Fine Sediment ◽

Trapping Efficiency ◽

Sediment Delivery ◽

Data Set

This paper presents an assessment about the modes of fine sediment transport in the Itajaí River estuary. ·The available information to approach a conceptual model is derived from three primary sources: (1) the river sediment delivery; (2) the distribution of salinity and particulate suspended mailer (MPS) along the estuary under influence of different river discharge conditions; and (3) near bed hydro-sedimentological processes. The river sediment delivery was achieved by daily monitoring the water and the suspended sediment discharge, since November 1998 at the Indaial lymnimetric station, which represents about 70 % of the drainage basin. The salinity and MPS distribution in the estuary were obtained through 47 weekly surveys along the estuary when vertical profiles of these variables were acquired every 1-1,5 km from the mouth to the upper limit of the salt intrusion. The surveys were carried out between November 1998 and November 1999, using an inflatable boat. The results allowed obtain the relationship between the salt wedge extension as function of the river discharge and the estuarine trapping efficiency. The near-bed hydro-sedimenlological processes were assessed through the deployment of an instrument tripod on the estuarine bed al the channel thalweg 4 km upstream from the mouth. The current speed, water level and MPS data were recorded hourly, 1 m above the bottom, from September to November 1999. Based on this data set, two main modes of fine sediment transport in the Itajaí River estuary were identified: a tidal driven and a fluvial driven mode. The tidal driven mode occurs when the river discharge is bellow 200 m3.s-1. Near bottom sediments arc in all erosion-deposition cycle following the semi-diurnal tides and the anomalistic cycle of spring and neap tides, with net sediment transport landwards. During such periods fine sediment is imported from the inner shelf. This mode occurs at time scales of weeks to months. The fluvial driven mode are fully developed when the river discharge exceeds 1,000 m3.s-1. accompanied by suspended sediment load as high as 10,000 ton.day-1. Fluvial advective process fully dominates the sediment transport resulting in zero trapping efficiency.

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A Quasi-3D Model for Suspended Sediment Transport by Currents and Waves.

Coastal Engineering 1990 ◽

10.1061/9780872627765.163 ◽

1991 ◽

Author(s):

Irene Katopodi ◽

Jan S. Ribberink

Keyword(s):

Sediment Transport ◽

Suspended Sediment ◽

3D Model ◽

Suspended Sediment Transport

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Streamflow and suspended-sediment transport in Garvin Brook, Winona County, southeastern Minnesota: Hydrologic data for 1982

Open-File Report ◽

10.3133/ofr83212 ◽

1983 ◽

Author(s):

G.A. Payne

Keyword(s):

Sediment Transport ◽

Suspended Sediment ◽

Suspended Sediment Transport ◽

Hydrologic Data

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2D and 3D CFD Investigations of Seabed Shear Stresses Around Subsea Pipelines

Volume 4A: Pipeline and Riser Technology ◽

10.1115/omae2013-10626 ◽

2013 ◽

Cited By ~ 1

Author(s):

Wenwen Shen ◽

Terry Griffiths ◽

Mengmeng Xu ◽

Jeremy Leggoe

Keyword(s):

Sediment Transport ◽

Suspended Sediment ◽

Interaction Model ◽

Suspended Sediment Transport ◽

Shear Stresses ◽

Parametric Function ◽

Ample Evidence ◽

North West ◽

Wide Range ◽

Subsea Pipelines

For well over a decade it has been widely recognised that existing models and tools for subsea pipeline stability design fail to account for the fact that seabed soils tend to become mobile well before the onset of pipeline instability. Despite ample evidence obtained from both laboratory and field observations that sediment mobility has a key role to play in understanding pipeline/soil interaction, no models have been presented previously which account for the tripartite interaction between the fluid and the pipe, the fluid and the soil, and the pipe and the soil. There are numerous well developed and widely used theories available to model pipe-fluid and pipe-soil interactions. A challenge lies in the way to develop a satisfactory fluid-soil interaction algorithm that has the potential for broad implementation under both ambient and extreme sea conditions due to the complexity of flow in the vicinity of a seabed pipeline or cable. A widely used relationship by Shields [1] links the bedload and suspended sediment transport to the seabed shear stresses. This paper presents details of computational fluid dynamics (CFD) research which has been undertaken to investigate the variation of seabed shear stresses around subsea pipelines as a parametric function of pipeline spanning/embedment, trench configuration and wave/current properties using the commercial RANS-based software ANSYS Fluent. The modelling work has been undertaken for a wide range of seabed geometries, including cases in 3D to evaluate the effects of finite span length, span depth and flow attack angle on shear stresses. These seabed shear stresses have been analysed and used as the basis for predicting sediment transport within the Pipe-Soil-Fluid (PSF) Interaction Model [2] in determining the suspended sediment concentration and the advection velocity in the vicinity of pipelines. The model has significant potential to be of use to operators who struggle with conventional stabilisation techniques for the pipelines, such as those which cross Australia’s North West Shelf, where shallow water depths, highly variable calcareous soils and extreme metocean conditions driven by frequent tropical cyclones result in the requirement for expensive and logistically challenging secondary stabilisation measures.

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