Figure 4 - uploaded by Daan Poppema
Content may be subject to copyright.
Example snapshot of calculated flow field around a cube-shaped building using CFD modelling: a) side view, slice along centre line z/L=0, b) top view, slice along y/L=0.5. Fluid flow from left to right. Blue to red colours indicate low to high flow velocities.
Source publication
The long-term physical existence of sandy shores critically depends on a balanced sediment budget. From the principles of Building with Nature it follows that a sustainable protection of sandy shores should employ some form of shore nourishment. In the spatial design process of urbanized sandy shores, where multiple functions must be integrated, th...
Context in source publication
Context 1
... preliminary result of the use of CFD modelling in the ShoreScape project is shown in Fig. 4. CFD can provide detailed airflow patterns around various geometries and arrangements of beach houses. Aeolian sediment transport can then be computed by using sediment transport equations that are dependent on bed shear stress and near bed flow velocities, which are calculated for each cell in the computational domain of the CFD ...
Citations
... The impact that buildings have on wind flow and sediment deposition patterns around them (Fackrell, 1984;Hunt, 1971;Peterka et al., 1985;Poppema et al., 2021;Pourteimouri et al., 2021) and at the beach or beach-dune interface (Hernández-Calvento et al., 2014;Jackson and Nordstrom, 2011;Nordstrom and McCluskey, 1984;Sanromualdo-Collado et al., 2021;Wijnberg et al., 2021) has been well studied, but there is a lack of knowledge about the impact of smaller structures such as user-made stone wind shelters. Recent work suggests that the decrease of nebkha vegetation is directly linked with an increasing number of stone shelters (Sanromualdo-Collado et al., 2021). ...
Beach users often use a range of strategies to shelter from the wind and blown sand. This involves building structures made of stacking stones. Different from other portable wind blockers, stone-made wind shelters can remain in the landscape for a long time. The process of stone removal from their original place and stone-stacking at another location has well-known effects on rock-dwelling wildlife. Less known are the impacts of stone wind shelters on biogeomorphological processes of beach-dune systems, especially those in arid coastlines, where foredunes formed by nebkhas are naturally discontinuous. This is the case of Playa del Inglés beach (Gran Canaria, Spain), the main sediment input to the Maspalomas dunefield, where the presence of stone wind shelters (goros) made by users has increased in recent decades following an increase of visitors.
This research aims to investigate the effects of stone wind shelters on the dynamics of an arid beach-dune system at various spatiotemporal scales. The methodology includes the use of aerial photography to study the appearance and evolution of stone shelters in Playa del Inglés and some of their long-term effects on the foredune. Field data was also collected to investigate the effects that stone shelters have over a representative foredune nebkha in detail, by monitoring the changes (topography, airflow, and vegetation) of an individual landform as we progressively remove pebbles from a previously built stone shelter.
Results show that stone stacking has an impact on airflow and sediment transport dynamics around landforms, limiting sediment accumulation inside nebkhas and therefore arid foredune growth. Stone stacking also constrict vegetation growth and its ability to retain sediment. The impacts of these artificial structures can be reverted following their removal but that the process of dismantling stones must be carefully planned. We elaborate some recommendations here to do it avoid damaging foredune vegetation.
... Conceptual model of the relationship between beach and dune budget, and expected morphology of the beach-dune system, modified afterPsuty (2004). Reprinted fromWijnberg et al. (2021). ...
Shorelines bordering ebb deltas are often subject to deformation by the approach and attachment of ebb-tidal shoals. Although this is a common behaviour, little attention has been paid to the link between shoal migration and the multi-annual development of the adjacent beach-dune system. This study aims to understand beach-dune systems' behaviour during the approach phase of an ebb-tidal shoal attachment event. Topographic and bathymetric data of the barrier island of Texel (NL) was used to calculate shoreline position, beach and dune volume, dunefoot position, and shoal displacement rates. Two classical beach-dune interaction models were used to understand the observed behaviour: the surfzone-beach-dune model and the sediment budget model. The analysis revealed how a larger bank on the land-facing side of the ebb delta split into two smaller shoals with different morphological behaviors. One of the shoals (S1) moved consistently landwards, recently attaching the shore, whereas the second shoal (S2) is still evolving and presents a milder landward movement than S1. In parallel to the landward movement of S1, the adjacent coastline was subject to erosion, partially counterbalanced by nourishments. However, despite the erosion, dunes are growing in volume, suggesting a net positive transfer of sand from the beach to the dunes. In the surfzone-beach-dune model, regular nourishments positively affect beach state by maintaining sufficient beach size for aeolian sediment transport and reducing shoreline erosion. In the budget model, dune volume growth may occur despite a slightly negative beach budget. Framing Texel in the budget model implies that the beach budget before the start of the approach phase is crucial in defining the behaviour of the dune system during this phase. If the shoal approach significantly reduces the beach budget, the system may cross the budget threshold that dune building is possible. Thus, the dune system may evolve to an erosional state, including dune ridge dissection and blowout development. Hence, nourishments have been essential in keeping the current morphological state during the attachment of the shoal, as they restrict the system from crossing the negative morphological threshold. Thus, without the nourishments, beach erosion driven by the shoal might have led to morphological changes in the dune system that could lead to years of a weakened level of protection until foredune recovery after attachment.
... The dune volume increase shows significant variability in the alongshore direction and peaks in the center of the nourishment around km 24 ( Figure 11). Dune development can be sensitive to beach width, beach sediment budget, shoreline orientation, vegetation and sediment, or surface properties amongst others, e.g., [29,[64][65][66]. For the Hondsbossche Dunes, we observe that dune foot migration is correlated to beach width (r 2 = 0.44, Figure 15b), where larger beach widths result in more seaward migration of the dunefoot. ...
Sandy nourishments can provide additional sediment to the coastal system to maintain its recreational or safety function under rising sea levels. These nourishments can be implemented at sandy beach systems, but can also be used to reinforce gray coastal infrastructure (e.g., dams, dikes, seawalls). The Hondsbossche Dunes project is a combined shoreface, beach, and dune nourishment of 35 million m3 sand. The nourishment was built to replace the flood protection function of an old sea-dike while creating additional space for nature and recreation. This paper presents the evolution of this newly created sandy beach system in the first 5 years after implementation based on bathymetric and topographic surveys, acquired every three to six months. A significant coastline curvature is created by the nourishment leading to erosion in the central 7 km bordered by zones with accretion. However, over the five-year period, net volume losses from the project area were less than 5% of the initial nourished sand volume. The man-made cross-shore beach profile rapidly mimics the characteristics of adjacent beaches. The slope of the surfzone is adjusted within two winters to a similar slope. The initially wide beaches (i.e., up to 225 m) are reduced to about 100 m-wide. Simultaneously, the dune volume has increased and the dune foot migrated seaward at the entire nourished site, regardless of whether the subaqueous profile gained or lost sediment. Our results show that the Hondsbossche Dunes nourishment, built with a natural slope and wide beach, created a positive sediment balance in the dune for a prolonged period after placement. As such, natural forces in the years after implementation provided a significant contribution to the growth in dune volume and related safety against flooding.
Airflow at the beach creates sand deposition patterns around buildings. To assess how initial deposition patterns depend on the orientation of a building relative to the wind direction and on the spacing between buildings, a series of one-day field experiments was conducted with cuboid scale models, in which 34 configurations were tested. Scale models placed further apart than 2 to 3 times the building width created deposition patterns that were similar to those for stand-alone buildings, where downwind deposition tails were the sum of the individual buildings' effects where these overlapped. For smaller spacings, between 0.5 and 2 times the building width, deposition patterns fundamentally differed from those for individual buildings, indicating a different type of airflow developed between the buildings. This created more complex depositional patterns that depended on the gap width. Rotation of an individual building relative to the wind direction induced an asymmetry in the downwind deposition patterns. A new rule of thumb quantitatively relates the asymmetry in the length of the deposition tails behind a building to the angle of the wind relative to the building and the length:width ratio of the building.
