scholarly journals Long-term coastal openness variation and its impact on sediment grain-size distribution: a case study from the Baltic Sea

2016 ◽  
Vol 4 (4) ◽  
pp. 773-780 ◽  
Author(s):  
Wenxin Ning ◽  
Jing Tang ◽  
Helena L. Filipsson
Keyword(s):  
Grain Size ◽  
Baltic Sea ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Temporal Dynamics ◽  
Distribution Data ◽  
Sand Content ◽  
Sediment Grain Size ◽  
Study Region

Abstract. We analysed the long-term variations in grain-size distribution in sediments from Gåsfjärden, a fjord-like inlet in the southwestern Baltic Sea, and explored potential drivers of the recorded changes in the sediment grain-size data. Over the last 5.4 thousand years (ky) in the study region, the relative sea level decreased 17 m, which was caused by isostatic land uplift. As a consequence, Gåsfjärden was transformed from an open coastal setting to a semi-closed inlet surrounded by numerous small islands on the seaward side. To quantitatively estimate the morphological changes in Gåsfjärden over the investigated time period and to further link the changes to the grain-size distribution data, a digital elevation model (DEM)-based openness index was calculated. The largest values of the openness indices were found between 5.4 and 4.4 cal ka BP, which indicates relatively high bottom water energy. During the same period, the highest sand content (∼  0.4 %) and silt / clay ratio ( ∼  0.3) in the sediment sequence were also recorded. After 4.4 cal ka BP, the average sand content was halved to ∼  0.2 % and the silt / clay ratio showed a significant decreasing trend over the last 4 ky. These changes were found to be associated with the gradual embayment of Gåsfjärden, as represented by the openness indices. The silt  /  clay ratios exhibited a delayed and relatively slower change compared with the sand content, which indicates different grain-size sediment responses to the changes in hydrodynamic energy. Our DEM-based coastal openness indices have proved to be a useful tool for interpreting the temporal dynamics of sedimentary grain size.

scholarly journals Long-term coastal openness variation and its impact on sediment grain-size distribution: a case study from the Baltic Sea

2016 ◽  
Author(s):  
Wenxin Ning ◽  
Jing Tang ◽  
Helena L. Filipsson
Keyword(s):  
Grain Size ◽  
Baltic Sea ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Morphological Changes ◽  
Land Uplift ◽  
Sediment Grain Size ◽  
Study Region ◽  
Size Data

Abstract. We analysed long-term variations in grain-size distribution in sediments from Gåsfjärden, a fjord-like inlet on the south-west Baltic Sea, and explored potential drivers of the recorded changes in sediment grain-size data. Over the last 5.4 thousand years (ka), the relative sea level decreased 17 m in the study region, caused by isostatic land uplift. As a consequence, Gåsfjärden has been transformed from an open coastal setting into a semi-closed inlet surrounded on the east by numerous small islands. To quantitatively estimate the morphological changes in Gåsfjärden over the last 5.4 ka and to further link the changes to our grain-size data, a digital elevation model (DEM)-based openness index was calculated. In the period between 5.4 and 4.4 ka BP, the inlet was characterised by the largest openness index. During this interval, the highest sand contents (~0.4 %) and silt/clay ratios (~0. 3) in the sediment sequence were recorded, indicating relatively high bottom water energy. After 4.4 ka BP, the average sand content was halved to ~0.2 % and the silt/clay ratios showed a significant decreasing trend over the last 4 ka. These changes are found to be associated with the gradual embayment of Gåsfjärden as represented in the openness index. The silt/clay ratios exhibited a delayed and slower change compared with the sand contents, which further suggest that finer particles are less sensitive to changes in hydrodynamic energy. Our DEM-based coastal openness index has proved to be a useful tool for interpreting the sedimentary grain-size record.

scholarly journals Sediment transport modelling in riverine environments: on the importance of grain-size distribution, sediment density and boundary conditions

2018 ◽  
Author(s):  
Jérémy Lepesqueur ◽  
Renaud Hostache ◽  
Núria Martínez-Carreras ◽  
Emmanuelle Montargès-Pelletier ◽  
Christophe Hissler
Keyword(s):  
Grain Size ◽  
Sediment Transport ◽  
Size Distribution ◽  
Suspended Sediment ◽  
Grain Size Distribution ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Small Scale ◽  
Sediment Grain Size ◽  
Model Based

Abstract. Hydromorphodynamic models are powerful tools to predict the potential mobilization and transport of sediment in river ecosystems. Recent studies even showed that they are able to satisfyingly predict suspended sediment matter concentration in small river systems. However, modelling exercises often neglect suspended sediment properties (e.g. particle site distribution and density), even though such properties are known to directly control the sediment particle dynamics in the water column during rising and flood events. This study has two objectives. On the one hand, it aims at further developing an existing hydromorphodynamic model based on the dynamic coupling of TELEMAC-3D (v7p1) and SISYPHE (v7p1) in order to enable an enhanced parameterisation of the sediment grain size distribution with distributed sediment density. On the other hand, it aims at evaluating and discussing the added-value of the new development for improving sediment transport and riverbed evolution predictions. To this end, we evaluate the sensitivity of the model to sediment grain size distribution, sediment density and suspended sediment concentration at the upstream boundary condition. As a test case, the model is used to simulate a flood event in a small scale river, the Orne River in North-eastern France. The results show substantial discrepancies in bathymetry evolution depending on the model setup. Moreover, the sediment model based on an enhanced sediment grain size distribution (10 classes) and with distributed sediment density outperforms the model with only two sediment grain size classes in terms of simulated suspended sediment concentration.

scholarly journals Estimation of Bed Load Transport in River Osun, South-Western of Nigeria Using Grain Size Distribution Data

2020 ◽  
Vol 2 (2) ◽  
Author(s):  
O.S. Olaniyan
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Bedload Transport ◽  
Cross Sectional Area ◽  
Sediment Supply ◽  
Distribution Data ◽  
Sectional Area ◽  
Cross Sectional ◽  
Standard Methods

Sediment transport rate depends on bed composition, flow hydraulics and sediment supply. There is a paucity of information on bedload transport in River Osun. In this study, bedload in River Osun was estimated using grain size distribution data to predict channel migration and mitigate flooding. Grab sampler was used to collect sediment samples at the sampling point across the river designated as T1-T4. Sieve analysis was carried out in triplicate on sediment from sampling points using standard methods. Discharge and cross-sectional area were measured between December 2017 and December 2018 at sampling stations using standard methods. The seasonal and bedload were estimated using standards equations. The percentage of bed material particles above 5mm and less than or equal to 2mm were 50 and 22.49%, respectively. The average median grain (d50) size was 2.4mm. The discharge and cross-sectional area across River Osun ranged (0.53-17.46) m3/s and (3.83-47.46) m2. The seasonal suspended and bedload across the river were (206.43×103 kg/annum) and 2,538.77×103(kg/annum), respectively. The estimated sediment load of River Osun could be useful in determining the dredging period at any point across the river where deposition of sediment could be monitored.

scholarly journals Basal-crevasse-fill origin of laminated debris bands at Matanuska Glacier, Alaska, U.S.A.

2001 ◽  
Vol 47 (158) ◽  
pp. 412-422 ◽  
Author(s):  
Staci L. Ensminger ◽  
Richard B. Alley ◽  
Edward B. Evenson ◽  
Daniel E. Lawson ◽  
Grahame J. Larson
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Suspended Load ◽  
Isotopic Ratios ◽  
Sediment Grain Size ◽  
Ice Flow ◽  
Stable Isotopic ◽  
Matanuska Glacier ◽  
Thick Layers

AbstractThe numerous debris bands in the terminus region of Matanuska Glacier, Alaska, U.S.A., were formed by injection of turbid meltwaters into basal crevasses. The debris bands are millimeter(s)-thick layers of silt-rich ice cross-cutting older, debris-poor englacial ice. The sediment grain-size distribution of the debris bands closely resembles the suspended load of basal waters, and of basal and proglacial ice grown from basal waters, but does not resemble supraglacial debris, till or the bedload of subglacial streams. Most debris bands contain anthropogenic tritium (3H) in concentrations similar to those of basal meltwater and ice formed from that meltwater, but cross-cut englacial ice lacking tritium. Stable-isotopic ratios (δ18O and δD) of debris-band ice are consistent with freezing from basal waters, but are distinct from those in englacial ice. Ice petrofabric data along one debris band lack evidence of active shearing. High basal water pressures and locally extensional ice flow associated with overdeepened subglacial basins favor basal crevasse formation.

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