The Dutch coastline is expected to change considerably during the next 100 years. Erosion will pr... more The Dutch coastline is expected to change considerably during the next 100 years. Erosion will prevail, although accretion will occur locally.
Pioneer stages in Dutch coastal dunes are under thread. In several areas experiments are executed... more Pioneer stages in Dutch coastal dunes are under thread. In several areas experiments are executed to reactivate dunes. The aim is to restore aeolian processes in order to create new possibilities for the development of pioneer vegetation. How successful are these experiments? This paper compares the results of three different projects from three different areas. The results indicate that large-scale destabilisation of dunes by removal of vegetation leads to a massive increase of dynamic, aeolian processes in an area. In order to achieve durable dune mobility, the sand must stay in movement, either by regular disturbances or by the availability of high, erodable dunes.
Summary Dune mobility; is sand supply through the foredunes the key to success? Bas Arens, Luc Ge... more Summary Dune mobility; is sand supply through the foredunes the key to success? Bas Arens, Luc Geelen, Harrie van der Hagen & Rienk Slings coastal dunes, mobility, aeolian dynamics, restoration In this paper we discuss mechanisms for dune mobility and stability, with special reference to the Dutch situation. Currently in the Netherlands, as in other parts of western Europe, dunes are in a phase of stabilization, which results in loss of biodiversity. Dune grasslands, rich in Red List species disappear gradually because of shrub encroachment. Managers are confronted with this process. Stimulating blowouts inside the system seems not enough to enhance durable rejuvenation of the system. Can we restore dune mobility from the beach land inward into the sand dune ecosystem as a solution to maintain biodiversity? Is dune mobility and hence forth increase of the surface of blowouts realistic under the current climatic and environmental changes? We argue that sand supply and an open sea fro...
This paper presents a new modelling concept for aeolian transport on beaches. Many research is in... more This paper presents a new modelling concept for aeolian transport on beaches. Many research is invested in describing aeolian sediment transport for desert situations. Some of the principles of aeolian sediment transport in deserts are valid for application at the coastal zone but, where in deserts abundant sand is available for transport, in coastal situations sediment availability is limited. Sediment availability (or supply) is limited due to supply limiting factors such as moisture content of the bed, fetch effects and armouring of the surface. We propose a new sediment transport concept where we quantify aeolian sediment transport while quantifying the sediment availability rather than the more conventional (Bagnold, 1954) wind driven transport capacity. The concept is illustrated using field data. The field data is collected during a measurement campaign which has been designed to measure aeolian transport with special focus on sediment availability. Wind and sediment transpor...
Variability in aeolian sediment transport rates have traditionally been explained by variability ... more Variability in aeolian sediment transport rates have traditionally been explained by variability in wind speed. Although it is recognised in literature that limitations in sediment supply can influence sediment transport significantly, most models that predict aeolian sediment transport attribute a dominant role to the magnitude of the wind speed. In this paper it is proposed that spatio-temporal variability of aeolian sediment transport on beaches can be dominated by variations in sediment supply rather than variations in wind speed.
NCK-days 2012 : Crossing borders in coastal research : jubilee conference proceedings, 2012
In the past couple of years, new coastal-dune research has sprung up in the Netherlands. In this ... more In the past couple of years, new coastal-dune research has sprung up in the Netherlands. In this paper, we give an overview of ongoing projects at Wageningen UR, Deltares, TU Delft and UTwente: how these are connected and what type of questions are addressed. There is an increasing demand for the understanding and prediction of coastal dune dynamics, both on the short (year) and long (100 years) term. We approach this from a variety of angles: scientific and applied, short-term and long-term, data-driven and model-based, biotic and abiotic, process-based and rule-based, and focused on components and integrated. We give examples of results and end with a discussion of the benefits of this integrated approach.
ARENS, S.M. and GEELEN, L.H.W.T., 2006. Dune landscape rejuvenation by intended destabilisation i... more ARENS, S.M. and GEELEN, L.H.W.T., 2006. Dune landscape rejuvenation by intended destabilisation in the Amsterdam water supply dunes.
ABSTRACT Near Schoorl in The Netherlands a gap was created in the foredunes during a nature devel... more ABSTRACT Near Schoorl in The Netherlands a gap was created in the foredunes during a nature development project in 1997. This resulted in considerable aeolian sand transport and allowed the sea to enter the swale valley behind the foredunes during storm events. From 1997 to 2002 a monitoring program was carried out and various data sets were collected. This study used a part of those data to investigate the effects of a foredune breach on sand transport dynamics. The main focus was on the aeolian transport of sediment through the gap in the dunes. After the breach calcareous beach sand was transported into the swale valley where exclusively decalcified sand was present. This enabled a study of the spatial aspects of transport based on six data sets of carbonate content that were collected during the 1997¿2002 period. Grids of carbonate content were interpolated and analysed together with data on geomorphology, topography and wind characteristics. The results provided insight on the displacement speed of the deposition front of calcareous sand, the influence of transport barriers and the correlation of transport directions with wind data. In addition, the study led to the observation that the trend of increase of available digital data during the last two decades is significant in facilitating the study of sand transport at the landscape scale. This is encouraging given the fact that the practical use of existing sand transport models in this context remains limited.
Suspended sand is sampled at several heights and positions on a beach and foredune, providing det... more Suspended sand is sampled at several heights and positions on a beach and foredune, providing detailed insight into the vertical and horizontal variation in sand content in the air during landward transport. Grain-size analysis is used to study the changes in grain-size distribution during landward transport. Mean grain size and sorting decrease during transport. Changes in textural parameters follow a gradual and regular path when the sediment is transported into the foredune. Sediment trapped on the seaward slope at a height of 30-50 cm above the surface closely resembles the sediment trapped landward, which implies that changes in the direction of transport are related to vertical changes within the sediment transport profiles. The movement of sand over the vegetated foredunes is induced by turbulent forces created by the air flowing across the vegetation and the foredune, leading to a change from saltation on the beach to modified saltation and suspension on the foredune. Small grains are lifted higher and fall more slowly than coarse grains and therefore are transported further landward, resulting in a gradual decrease in grain size of the landward-deposited sediment. Folk (1971) proposed a quantum model of aeolian deposition: wind deposits consist of a series of quantum bursts or swarms of well-sorted sand grains. Each quantum is carried by a separate gust and deposited as a thin layer of grains. The characteristics of the grains depend on the direction and strength of the gust. The resulting deposit is a mixture of quanta, which is reflected in the polymodal or skewed nature of the frequency curves . For these reasons, samples from beach and foredune are difficult to compare with respect to transport dynamics. Better results will be obtained if only the active layer is sampled . However, in the dune environment, sampling of the active layer is difficult to achieve when the surface is vegetated. In this case, trapping of the sediment when it is transported potentially renders good results.
Vegetation density on foredunes exerts an important control on aeolian sediment transport and dep... more Vegetation density on foredunes exerts an important control on aeolian sediment transport and deposition, and therefore on profile development. In a long-term monitoring field experiment, three plots were planted with regular grids of reed bundles in three different densities: 4, 2 and 1 bundles per m 2 . This study reports on the differences in profile development under the range of vegetation densities.
The Dutch coastline is expected to change considerably during the next 100 years. Erosion will pr... more The Dutch coastline is expected to change considerably during the next 100 years. Erosion will prevail, although accretion will occur locally.
Pioneer stages in Dutch coastal dunes are under thread. In several areas experiments are executed... more Pioneer stages in Dutch coastal dunes are under thread. In several areas experiments are executed to reactivate dunes. The aim is to restore aeolian processes in order to create new possibilities for the development of pioneer vegetation. How successful are these experiments? This paper compares the results of three different projects from three different areas. The results indicate that large-scale destabilisation of dunes by removal of vegetation leads to a massive increase of dynamic, aeolian processes in an area. In order to achieve durable dune mobility, the sand must stay in movement, either by regular disturbances or by the availability of high, erodable dunes.
Summary Dune mobility; is sand supply through the foredunes the key to success? Bas Arens, Luc Ge... more Summary Dune mobility; is sand supply through the foredunes the key to success? Bas Arens, Luc Geelen, Harrie van der Hagen & Rienk Slings coastal dunes, mobility, aeolian dynamics, restoration In this paper we discuss mechanisms for dune mobility and stability, with special reference to the Dutch situation. Currently in the Netherlands, as in other parts of western Europe, dunes are in a phase of stabilization, which results in loss of biodiversity. Dune grasslands, rich in Red List species disappear gradually because of shrub encroachment. Managers are confronted with this process. Stimulating blowouts inside the system seems not enough to enhance durable rejuvenation of the system. Can we restore dune mobility from the beach land inward into the sand dune ecosystem as a solution to maintain biodiversity? Is dune mobility and hence forth increase of the surface of blowouts realistic under the current climatic and environmental changes? We argue that sand supply and an open sea fro...
This paper presents a new modelling concept for aeolian transport on beaches. Many research is in... more This paper presents a new modelling concept for aeolian transport on beaches. Many research is invested in describing aeolian sediment transport for desert situations. Some of the principles of aeolian sediment transport in deserts are valid for application at the coastal zone but, where in deserts abundant sand is available for transport, in coastal situations sediment availability is limited. Sediment availability (or supply) is limited due to supply limiting factors such as moisture content of the bed, fetch effects and armouring of the surface. We propose a new sediment transport concept where we quantify aeolian sediment transport while quantifying the sediment availability rather than the more conventional (Bagnold, 1954) wind driven transport capacity. The concept is illustrated using field data. The field data is collected during a measurement campaign which has been designed to measure aeolian transport with special focus on sediment availability. Wind and sediment transpor...
Variability in aeolian sediment transport rates have traditionally been explained by variability ... more Variability in aeolian sediment transport rates have traditionally been explained by variability in wind speed. Although it is recognised in literature that limitations in sediment supply can influence sediment transport significantly, most models that predict aeolian sediment transport attribute a dominant role to the magnitude of the wind speed. In this paper it is proposed that spatio-temporal variability of aeolian sediment transport on beaches can be dominated by variations in sediment supply rather than variations in wind speed.
NCK-days 2012 : Crossing borders in coastal research : jubilee conference proceedings, 2012
In the past couple of years, new coastal-dune research has sprung up in the Netherlands. In this ... more In the past couple of years, new coastal-dune research has sprung up in the Netherlands. In this paper, we give an overview of ongoing projects at Wageningen UR, Deltares, TU Delft and UTwente: how these are connected and what type of questions are addressed. There is an increasing demand for the understanding and prediction of coastal dune dynamics, both on the short (year) and long (100 years) term. We approach this from a variety of angles: scientific and applied, short-term and long-term, data-driven and model-based, biotic and abiotic, process-based and rule-based, and focused on components and integrated. We give examples of results and end with a discussion of the benefits of this integrated approach.
ARENS, S.M. and GEELEN, L.H.W.T., 2006. Dune landscape rejuvenation by intended destabilisation i... more ARENS, S.M. and GEELEN, L.H.W.T., 2006. Dune landscape rejuvenation by intended destabilisation in the Amsterdam water supply dunes.
ABSTRACT Near Schoorl in The Netherlands a gap was created in the foredunes during a nature devel... more ABSTRACT Near Schoorl in The Netherlands a gap was created in the foredunes during a nature development project in 1997. This resulted in considerable aeolian sand transport and allowed the sea to enter the swale valley behind the foredunes during storm events. From 1997 to 2002 a monitoring program was carried out and various data sets were collected. This study used a part of those data to investigate the effects of a foredune breach on sand transport dynamics. The main focus was on the aeolian transport of sediment through the gap in the dunes. After the breach calcareous beach sand was transported into the swale valley where exclusively decalcified sand was present. This enabled a study of the spatial aspects of transport based on six data sets of carbonate content that were collected during the 1997¿2002 period. Grids of carbonate content were interpolated and analysed together with data on geomorphology, topography and wind characteristics. The results provided insight on the displacement speed of the deposition front of calcareous sand, the influence of transport barriers and the correlation of transport directions with wind data. In addition, the study led to the observation that the trend of increase of available digital data during the last two decades is significant in facilitating the study of sand transport at the landscape scale. This is encouraging given the fact that the practical use of existing sand transport models in this context remains limited.
Suspended sand is sampled at several heights and positions on a beach and foredune, providing det... more Suspended sand is sampled at several heights and positions on a beach and foredune, providing detailed insight into the vertical and horizontal variation in sand content in the air during landward transport. Grain-size analysis is used to study the changes in grain-size distribution during landward transport. Mean grain size and sorting decrease during transport. Changes in textural parameters follow a gradual and regular path when the sediment is transported into the foredune. Sediment trapped on the seaward slope at a height of 30-50 cm above the surface closely resembles the sediment trapped landward, which implies that changes in the direction of transport are related to vertical changes within the sediment transport profiles. The movement of sand over the vegetated foredunes is induced by turbulent forces created by the air flowing across the vegetation and the foredune, leading to a change from saltation on the beach to modified saltation and suspension on the foredune. Small grains are lifted higher and fall more slowly than coarse grains and therefore are transported further landward, resulting in a gradual decrease in grain size of the landward-deposited sediment. Folk (1971) proposed a quantum model of aeolian deposition: wind deposits consist of a series of quantum bursts or swarms of well-sorted sand grains. Each quantum is carried by a separate gust and deposited as a thin layer of grains. The characteristics of the grains depend on the direction and strength of the gust. The resulting deposit is a mixture of quanta, which is reflected in the polymodal or skewed nature of the frequency curves . For these reasons, samples from beach and foredune are difficult to compare with respect to transport dynamics. Better results will be obtained if only the active layer is sampled . However, in the dune environment, sampling of the active layer is difficult to achieve when the surface is vegetated. In this case, trapping of the sediment when it is transported potentially renders good results.
Vegetation density on foredunes exerts an important control on aeolian sediment transport and dep... more Vegetation density on foredunes exerts an important control on aeolian sediment transport and deposition, and therefore on profile development. In a long-term monitoring field experiment, three plots were planted with regular grids of reed bundles in three different densities: 4, 2 and 1 bundles per m 2 . This study reports on the differences in profile development under the range of vegetation densities.
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