scholarly journals AEOLIAN SEDIMENT TRANSPORT AT A MAN-MADE DUNE SYSTEM; BUILDING WITH NATURE AT THE HONDSBOSSCHE DUNES

2018 ◽  
pp. 83 ◽  
Author(s):  
Marloes Wittebrood ◽  
Sierd De Vries ◽  
Petra Goessen ◽  
Stefan Aarninkhof
Keyword(s):  
Sediment Transport ◽  
Transport Model ◽  
Morphological Changes ◽  
Morphological Evolution ◽  
Sediment Supply ◽  
Dune System ◽  
Morphological Response ◽  
Profile Type ◽  
Building With Nature ◽  
Aeolian Sediment

This paper presents the influence of aeolian sediment transport on the initial morphological evolution of beach and dunes at the man-made dune system ‘Hondsbossche Dunes’ at the Dutch coast. In total 35 million m^3 dredged material was used for the construction of a beach, dune and foreshore system. This study focused on differences in morphological response within the five different realized dune profile types. A conceptual framework was developed, based on the assessment of (1) environmental forcing, (2) sediment supply from aeolian and marine sources and (3) dune types. These three components were quantified from an analysis of measured profile evolution and the application of an aeolian sediment transport model for the first 19 months since the project delivery date in May 2015. Morphological changes were most pronounced in the first seven months after construction. Dune growth of a profile type at this location is determined by a temporal and alongshore variability in local processes that determines the aeolian sediment supply towards the dunes and the dune geometry that determines the capacity of the profile type to capture the sediments. The model simulations managed to qualitatively reproduce alongshore variations in dune growth as a result of spatial variations in sediment availability, grain size, profile shape and interaction with vegetation. Overall, this study shows the relevance of both marine and aeolian processes in such man-made dynamic systems that are comparable to natural systems. Continuing the monitoring and modelling of this system will improve the quantitative knowledge for design optimization of the Building with Nature philosophy.

scholarly journals Modelling of sediment transport and morphological evolution under the combined action of waves and currents

Ocean Science ◽  
2017 ◽  
Vol 13 (5) ◽  
pp. 673-690 ◽  
Author(s):  
Guilherme Franz ◽  
Matthias T. Delpey ◽  
David Brito ◽  
Lígia Pinto ◽  
Paulo Leitão ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Morphological Changes ◽  
Morphological Evolution ◽  
Research Effort ◽  
Beach Erosion ◽  
Model Complexity ◽  
Invariant Equilibrium ◽  
Waves And Currents ◽  
Combined Action ◽  
Modelling System

Abstract. Coastal defence structures are often constructed to prevent beach erosion. However, poorly designed structures may cause serious erosion problems in the downdrift direction. Morphological models are useful tools to predict such impacts and assess the efficiency of defence structures for different scenarios. Nevertheless, morphological modelling is still a topic under intense research effort. The processes simulated by a morphological model depend on model complexity. For instance, undertow currents are neglected in coastal area models (2DH), which is a limitation for simulating the evolution of beach profiles for long periods. Model limitations are generally overcome by predefining invariant equilibrium profiles that are allowed to shift offshore or onshore. A more flexible approach is described in this paper, which can be generalised to 3-D models. The present work is based on the coupling of the MOHID modelling system and the SWAN wave model. The impacts of different designs of detached breakwaters and groynes were simulated in a schematic beach configuration following a 2DH approach. The results of bathymetry evolution are in agreement with the patterns found in the literature for several existing structures. The model was also tested in a 3-D test case to simulate the formation of sandbars by undertow currents. The findings of this work confirmed the applicability of the MOHID modelling system to study sediment transport and morphological changes in coastal zones under the combined action of waves and currents. The same modelling methodology was applied to a coastal zone (Costa da Caparica) located at the mouth of a mesotidal estuary (Tagus Estuary, Portugal) to evaluate the hydrodynamics and sediment transport both in calm water conditions and during events of highly energetic waves. The MOHID code is available in the GitHub repository.

scholarly journals Impacts of storm chronology on the morphological changes of the Formby beach and dune system, UK

2015 ◽  
Vol 15 (7) ◽  
pp. 1533-1543 ◽  
Author(s):  
P. Dissanayake ◽  
J. Brown ◽  
H. Karunarathna
Keyword(s):  
Extreme Event ◽  
Morphological Changes ◽  
Water Levels ◽  
Storm Event ◽  
Dune System ◽  
Morphological Response ◽  
Cumulative Impact ◽  
Dune Erosion ◽  
Sequence Of Events ◽  
Storm Impact

Abstract. Impacts of storm chronology within a storm cluster on beach/dune erosion are investigated by applying the state-of-the-art numerical model XBeach to the Sefton coast, northwest England. Six temporal storm clusters of different storm chronologies were formulated using three storms observed during the 2013/2014 winter. The storm power values of these three events nearly halve from the first to second event and from the second to third event. Cross-shore profile evolution was simulated in response to the tide, surge and wave forcing during these storms. The model was first calibrated against the available post-storm survey profiles. Cumulative impacts of beach/dune erosion during each storm cluster were simulated by using the post-storm profile of an event as the pre-storm profile for each subsequent event. For the largest event the water levels caused noticeable retreat of the dune toe due to the high water elevation. For the other events the greatest evolution occurs over the bar formations (erosion) and within the corresponding troughs (deposition) of the upper-beach profile. The sequence of events impacting the size of this ridge–runnel feature is important as it consequently changes the resilience of the system to the most extreme event that causes dune retreat. The highest erosion during each single storm event was always observed when that storm initialised the storm cluster. The most severe storm always resulted in the most erosion during each cluster, no matter when it occurred within the chronology, although the erosion volume due to this storm was reduced when it was not the primary event. The greatest cumulative cluster erosion occurred with increasing storm severity; however, the variability in cumulative cluster impact over a beach/dune cross section due to storm chronology is minimal. Initial storm impact can act to enhance or reduce the system resilience to subsequent impact, but overall the cumulative impact is controlled by the magnitude and number of the storms. This model application provides inter-survey information about morphological response to repeated storm impact. This will inform local managers of the potential beach response and dune vulnerability to variable storm configurations.

scholarly journals WAVE-CURRENT INTERACTION, SEDIMENT TRANSPORT AND SEABED EVOLUTION IN THE PIRAQUÊ-AÇU/PIRAQUÊ MIRIM ESTUARY (BRAZIL)

2017 ◽  
pp. 32
Author(s):  
Thais Nunes Coutinho ◽  
Leonardo Carvalho De Jesus ◽  
Julio Tomás Aquije Chacaltana
Keyword(s):  
Sediment Transport ◽  
Gravity Waves ◽  
Morphological Changes ◽  
Morphological Evolution ◽  
Seabed Sediment ◽  
Estuary Mouth ◽  
Sediment Mass ◽  
Current Interaction ◽  
Bedload Sediment ◽  
Seabed Evolution

The medium-term seabed evolution of Piraquê-Açú/Piraquê-Mirim estuary (ES/Brazil) is studied numerically in this work. The hydrodynamics is induced by the tide, the river discharges, and the incident water wave. The wave-tide-current interactions are obtained by coupling the shallow water equations with the radiation stress tensor introduced by Longuet-Higgins & Stewart (1960). In this way, the influence of both the tidal current and the current induced by gravity waves on the sediment transport are taken into account. We utilized the Exner (1925) equation, based on the conservation of seabed sediment mass, to calculate the morphological evolution. Seabed morphological changes are accelerated by introducing a time scale factor. Four bedload sediment transport formulations were tested and compared. We found an excellent agreement when numerical results are compared with currents measured in the upper estuary and with sediment transport rates measured at the river’s mouth when using the Engelund and Hansen (1967) sediment transport formulation. We also found that the main morphological changes occurring at the estuary mouth are due to the action of gravity waves. Between the head and mouth of the estuary, the sediment transport rate and morphological seabed changes are controlled exclusively by the tidal currents and the river discharge. In this latter case, we found that the large sandbank located at the estuary mouth is responsible for the absence of wave.

scholarly journals Influence of Sand Trapping Fences on Dune Toe Growth and Its Relation with Potential Aeolian Sediment Transport

2021 ◽  
Vol 9 (8) ◽  
pp. 850
Author(s):  
Christiane Eichmanns ◽  
Holger Schüttrumpf
Keyword(s):  
Sediment Transport ◽  
Meteorological Data ◽  
Coastal Dunes ◽  
Sediment Supply ◽  
Minor Role ◽  
Digital Elevation ◽  
Lower Permeability ◽  
Aerial Vehicle ◽  
A Minor ◽  
Aeolian Sediment

This study provides insights into dune toe growth around and between individual brushwood lines of sand trapping fences at the dune toe of coastal dunes using digital elevation models obtained from repeated unmanned aerial vehicle surveys. Prevailing boundary conditions, especially sediment supply, as well as the porosity and arrangement of the installed sand trapping fences significantly influence the effectiveness of different configurations of sand trapping fences. The dune toe growth is significant immediately after constructing a new sand trapping fence and decreases over time. According to the results presented in this study, for sand trapping fences that have been in place longer, the protruding branch height and the porosity of the remaining branches play a minor role in trapping sand. Sand trapping fences with lower permeability favour localized coastal dune toe growth directly at their brushwood lines, whereas fences with higher porosity allow for more sediment deposition further downwind. The trend in dune toe changes can be roughly predicted by integrating potential sediment transport rates calculated with hourly meteorological data.

scholarly journals Investigating Changes in Aeolian Sediment Transport at Coastal Dunes and Sand Trapping Fences: A Field Study on the German Coast

2020 ◽  
Vol 8 (12) ◽  
pp. 1012
Author(s):  
Christiane Eichmanns ◽  
Holger Schüttrumpf
Keyword(s):  
Sediment Transport ◽  
Wind Profile ◽  
Field Experiments ◽  
Coastal Dunes ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Coastal Protection ◽  
Protection Measures ◽  
Law Of The Wall ◽  
Aeolian Sediment

For the restoration and maintenance of beach and dune systems along the coast, knowledge of aeolian sediment transport and its interaction with coastal protection measures is required. As a nature-based solution, sand trapping fences can be an integral part of coastal protection measures initiating foredune development. There are few detailed studies on aeolian sediment transport rates on coastal dunes and sand trapping fences available to date. Thus, in this work, we present the results of field experiments conducted at the beach, coastal dune, and sand trapping fence on the East Frisian island Langeoog. The vertical sediment flux profile was measured by vertical mesh sand traps, and saltiphones measured the instantaneous sediment transport. A meteorological station was set up to obtain wind data. On the beach, dune toe, and dune crest, the stationary wind profile can be described well by the law of the wall. Saturated aeolian sediment transport rates on the beach and dune toe were predicted by widely used empirical models. Between the sand trapping fence, these empirical transport models could not be applied, as no logarithmic wind profile existed. The upwind sediment supply reduced after each brushwood line of the sand trapping fence, thereby, leading to increased deviation from the saturated conditions.

scholarly journals Modelling of sediment transport and morphological evolution under the combined action of waves and currents

2017 ◽  
Author(s):  
Guilherme Franz ◽  
Matthias T. Delpey ◽  
David Brito ◽  
Lígia Pinto ◽  
Paulo Leitão ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Morphological Changes ◽  
Morphological Evolution ◽  
Research Effort ◽  
Beach Erosion ◽  
Model Complexity ◽  
Invariant Equilibrium ◽  
Waves And Currents ◽  
Combined Action ◽  
Modelling System

Abstract. Coastal defence structures are often constructed to prevent beach erosion. However, poorly designed structures may cause serious erosion problems in the downdrift direction. Morphological models are useful tools to predict such impacts and assess the efficiency of defence structures for different scenarios. Nevertheless, morphological modelling is still a topic under intense research effort. The processes simulated by a morphological model depend on model complexity. For instance, undertow currents are neglected in coastal area models (2DH), which is a limitation for simulating the evolution of beach profiles for long periods. Model limitations are generally overcome by predefining invariant equilibrium profiles that are allowed to shift offshore or onshore. A more flexible approach is described in this paper, which can be generalised to 3D models. The present work is based on the coupling of the MOHID modelling system and SWAN wave model. The impacts of different designs of detached breakwaters and groynes were simulated in a schematic beach configuration following a 2DH approach. The results of bathymetry evolution are in agreement with the patterns found in the literature for several existing structures. The model was also tested in a 3D test case to simulate the formation of sandbars by undertow currents. The findings of this work confirmed the applicability of the MOHID modelling system to study sediment transport and morphological changes in coastal zones under the combined action of waves and currents. The same modelling methodology was applied to a coastal zone (Costa da Caparica) located at the mouth of a mesotidal estuary (Tagus Estuary, Portugal) to evaluate the hydrodynamics and sediment transport in calm water conditions and during events of highly energetic waves.

Aeolian sediment transport on a beach with a varying sediment supply

2014 ◽  
Vol 15 ◽  
pp. 235-244 ◽  
Author(s):  
S. de Vries ◽  
S.M. Arens ◽  
M.A. de Schipper ◽  
R. Ranasinghe
Keyword(s):  
Sediment Transport ◽  
Sediment Supply ◽  
Aeolian Sediment

Sediment supply from shoreface to dunes: linking sediment transport measurements and long-term morphological evolution

Geomorphology ◽  
2004 ◽  
Vol 60 (1-2) ◽  
pp. 205-224 ◽  
Author(s):  
Troels Aagaard ◽  
Robin Davidson-Arnott ◽  
Brian Greenwood ◽  
Jørgen Nielsen
Keyword(s):  
Sediment Transport ◽  
Morphological Evolution ◽  
Sediment Supply ◽  
Transport Measurements

scholarly journals A Numerical Investigation on Tidally Induced Sediment Transport and Morphological Changes with Changing Sea Level in South-East England

Geosciences ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 140
Author(s):  
Nicoletta Leonardi ◽  
Xiaorong Li ◽  
Iacopo Carnacina
Keyword(s):  
Sediment Transport ◽  
Sea Level Rise ◽  
Water Level ◽  
Sea Level ◽  
Large Scale ◽  
Morphological Changes ◽  
Morphological Evolution ◽  
Morphodynamic Equilibrium ◽  
South East England

The impact of tide-induced morphological changes and water level variations on the sediment transport in a tidally dominated system has been investigated using the numerical model Delft3D and South-East England as a test case. The goal of this manuscript is to explore the long-term changes in morphology due to sea level rise and the large-scale morphodynamic equilibrium of the South-East England. Our results suggest that the long term (century scale) tidally-induced morphological evolution of the seabed slows down in time and promotes a vanishing net transport across the large scale system. Century-scale morphologically updated simulations show that both morphological changes and net transport values tend to decrease in time as the system attains a dynamic equilibrium configuration. Results further suggest that the presence of a gradual increase in mean sea level accelerates the initial morphological evolution of the system whose morphological rate of change gradually attains, however, same plateau values as in the absence of sea level rise. Given the same base morphology, increasing water levels enhance residual currents and the net transport near the coastline; and vice-versa, decreasing sea levels minimize both residuals and net transport near the coastline. The areas that are more affected by, water level and morphological changes, are the ones where the net transport is the highest. This manuscript explores and allows extending the idea of morphodynamic equilibrium at a regional scale, larger than the one for which this concept has been generally explored i.e., estuarine scale.

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