Artificial Dune Research Articles

Benthic diatom community response to the sudden rewetting of a coastal peatland

The coastline of the shallow southern Baltic Sea is a highly dynamic system of spits, lagoonal systems and subtidal flats. On the land side, coastal peatlands are common. Intact peatlands provide important ecosystem services, however, many peatlands have been severely degraded due to human activities. Many coastal peatlands are also separated from the Baltic Sea by artificial dunes or dykes in order to facilitate drainage and costal protection measures. Due to their potential to act as carbon sinks, as well as buffer zones against sea level rise and flooding events, there is an increasing interest in the restoration and rewetting of coastal peatlands. Microphytobenthic communities are important primary producers in coastal systems and peatlands and diatoms are often the dominant microphytobenthic group in temperate regions. In November 2019, the removal of the dyke that separated the Polder Drammendorf (a drained, oligohaline peatland), from the adjacent Baltic Sea lagoon Kubitzer Bodden represented a unique chance to study the sudden rewetting of a degraded coastal peatland with brackish water and its effect on the microphytobenthos. The aims of this study were to investigate the poorly known diatom community composition of coastal peatlands, to determine the effects of flooding events on diatom composition and biomass in coastal peatlands as well as the effects of nutrient and substance release from the peatlands on the diatom communities of adjacent coastal waters. We investigated and documented the impact of this sudden rewetting on the benthic diatom communities of the peatland and the adjacent lagoon over the course of one year, applying the latest taxonomy and measuring key environmental factors. The results deepen the understanding of diatom community composition, taxonomy and ecology and explore the influence of land-sea exchange processes on the benthic diatoms of the Baltic Sea coast.

Three years of morphological dune development after planting marram grass on a beach

AbstractCoastal regions globally face escalating challenges from climate change, including rising sea levels and intensified storm events. To address these threats, coastal resilience emerges as a critical paradigm advocating the integration of nature‐based solutions with traditional engineering approaches. Coastal dunes, acting as protective barriers, offer a promising avenue. This three‐year study assesses the efficacy of an artificial dune system to address local sand‐related nuisances on the adjacent seawall featuring planted marram grass in Oosteroever, Belgium. The focus is on understanding sediment accumulation, dune morphology and vegetation development. The results demonstrate a significant increase in dune height, reaching up to 2 m in the zones planted with marram grass, surpassing the height of the adjacent seawall. Comprehensive profiles and drone surveys revealed consistent dune growth of 27 m3/m, which contrasted with the substantial erosion in the adjacent unvegetated beach areas of up to 30 m3/m. One storm event caused dune toe erosion of 1.5 m3/m, but the dune demonstrated rapid recovery through natural aeolian processes. Marram grass development was not impacted by the initial planting configuration and density and was more pronounced at the perimeter edges of the dune. This study highlights the success of the ‘dune‐in‐front‐of‐a‐dike’ approach, offering insights for sustainable coastal resilience strategies.

Exploring The Influence Of Artificial Root Systems Modeled After Marram Grass (Ammophila Arenaria) On Dune Erosion

Vegetated dune systems represent a remarkable landform along numerous coastal areas worldwide. They provide a valuable contribution to local ecosystems and coastal protection. The influence of vegetation on the stability of soils potentially counteracts erosion and, on sandy coasts under suitable conditions, leads to the accumulation of sediments driven by aeolian transport, resulting in dune formation (Feagin et al. 2015). The assessment of the coastal protection potential of dunes is far from being a streamlined, mature procedure, and it will demand more parameters than merely the dunes’ height, dimensions or volume, but tentatively also their vegetation coverage. Artificial dunes or dunes regenerated through sand nourishment often lack additional substrate stabilization since no vegetation bound root systems are present (Nordstrom and Jackson 2022). The role of stabilizing root components in the overall dune body matrix is currently not well understood, in particular, when highly dynamic processes such as wave attack is involved. The hypothesis of this novel work hence is that root systems of dune grass (i.e., A. arenaria) can be quantified for the modelling in experimental campaigns and for more reliable erosion results. To investigate this hypothesis novel physical experiments are currently conducted in the wave flume at the Leichtweiß-Institute for Hydraulic Engineering and Water Resources in Braunschweig (Germany), testing different root surrogate materials and quantities for the first time.

Observations of wave run-up affected by dune scarp during storm conditions: a two dimensional large-scaled movable bed experiment

Artificial dunes serve as essential nature-based defenses against the increasing threats posed by climate change and rising sea levels along coastal regions. However, these man-made dunes are particularly susceptible to erosion during severe storm events, necessitating careful consideration of their design for effective coastal protection. Among the myriad factors influencing artificial dune design, wave run-up stands out as a paramount concern. Not only is wave run-up crucial in assessing the extent of coastal flooding, but it also plays a significant role in shaping shoreline dynamics. During intense storm events, wave run-up amplification leads to substantial erosion of sand dunes, forming dune scarps that resemble cliffs. To address these challenges, we conducted a series of innovative two-dimensional large-scale laboratory experiments using movable beds. These experiments aimed to provide a quantitative understanding of wave run-up characteristics on dune scarps. Additionally, our study explored the feasibility of using existing empirical formulas to predict the 2% exceedance of wave run-up (referred to as R2%) in such scenarios. Our results revealed a consistent trend in R2% values, irrespective of variations in the surf similarity parameter when wave run-up was influenced by a dune scarp. Notably, our findings recommend the adoption of the Stockdon empirical formula, incorporating beach slope from the still water level to the dune scarp toe, as an effective method for predicting R2% during highly erosive conditions. This approach can significantly enhance the design and functionality of artificial dunes, bolstering their capacity to safeguard coastal areas from the impacts of severe storms and erosion, thus contributing to resilient coastal ecosystems and sustainable coastal management.

The importance of grain‐related shear velocity in predicting multi‐monthly dune growth

AbstractThis study assesses the accuracy of the aeolian transport model proposed by van Rijn and Strypsteen in 2020 in predicting sediment transport rates for dune growth, with a focus on the importance of grain‐related shear velocity. A 9‐month dataset of local and regional wind characteristics and dune growth from a new artificial dune with planted marram grass in an environment with minor supply limitations was analysed. The study site is located in Oosteroever, Belgium. The results revealed that utilizing local measured overall shear velocities resulted in significant overprediction of dune volume changes. Incorporating sub‐models for grain‐related bed roughness and shear velocity improved the predictions of dune growth drastically with high statistical results (r2 = 0.98 and RMSE = 0.64 m3/m). The primary driver contributing to dune growth at the study site was due to oblique onshore moderate winds of 10 m/s, as revealed from a frequency‐magnitude analysis. The model could be used with either local wind measurements or regional data transformed to local beach conditions. The study highlights the importance of considering grain‐related shear velocity in future studies to improve the prediction of sand transport rates and enhance our understanding of dune evolution.

COMPOUND URBAN COASTAL FLOOD MODELING: INTEGRATING TIDE, WAVES, PRECIPITATION AND HYDRAULIC INFRASTRUCTURE

Compound coastal flooding considers the joint impacts of marine and hydrologic interactions and has recently been identified as an international research priority. Along the US West Coast, winter storms often bring high marine water levels along with energetic waves and precipitation. Hydrodynamic models have been widely used to estimate flood impacts, including extreme estuarine water levels in compound events (e.g., riverine discharge-tide-storm surge interactions), and produced satisfactory results. However, few studies further consider overland flow routing and high-resolution flood mapping in highly urbanized, low-lying coastal areas. Here, an integrated Delft3D-FM based numerical modeling framework is used to explicitly resolve multi-pathway flood processes (i.e., high marine water levels, waves overtopping, precipitation) and infrastructure (e.g., seawalls, storm drains, artificial dunes).

STRENGTHENING COASTAL DEFENCE WITH ARTIFICIAL DUNES

The Belgian coast is primarily sandy and is locally subject to erosion (Deronde, 2004). Traditionally, erosion was counteracted using hard engineering structures like groynes, seawalls and sea dikes. Nowadays, the Belgian government uses a different strategy by adopting a more soft and dynamic approach where possible. Many ‘soft’ managing activities at the Belgian coast are carried out in the form of regular and routine sand nourishments to cope for future flooding risks and coastal erosion (Houthuys, 2012). This method gives room to a new approach for coastal management where the natural elements and processes facilitate the development of new engineered dune areas at locations where traditional dike structures currently protect the hinterland. In the context of climate change and strict requirements for water safety, these hard to adapt engineering structures will not resist future flood events and more innovative solutions like dune in front of a dike principles to deal with rising sea level are receiving considerable attention. As a result, concepts are worked out in which traditional sea dikes are reinforced with newly created dune systems, offering a high level of protection of coastal infrastructure and at the same time offering a more natural appearance and higher ecological and socio economical values. In the framework of the SARCC project, one pilot site is realized in Raversijde. Besides the coastal defense function of the artificial dune, a second benefit is achieved: mitigating the nuisance, created by aeolian sand transport and preventing roads and tram tracks at the dike crest to be buried in sand.

Early-stage development of an artificial dune with varying plant density and distribution

For the optimal design of artificial dunes, a fundamental understanding of morphological changes throughout the early phases of dune growth is required. This study examines the effect of different vegetation densities and patterns on the subsequent dune development during the first three months following construction. Marram grass (0.40 m in height) was planted in six zones (20 × 20 m2) with three different densities (6, 9 and 15 plants/m2) and four different patterns (gridded, random, clustered, and staggered). Monthly drone surveys were combined with daily to weekly topographic RTK-GNSS surveys along 12 cross-shore profiles (two per zone). Beach wind conditions were continuously monitored with a meteorological station. Additionally, four aeolian sand transport measurements were conducted with Modified Wilson And Cook sand traps. Results demonstrate the importance of using a specific plant density as well as the use of spatial plant distribution. The use of a staggered or random plant distribution leads to the formation of narrower bedforms, while higher vegetation densities also result in narrower bedforms. Bedform height is greater in zones with high vegetation density. Regardless of plant density and distribution, each plantation zone experienced dune development with a volume of 6 m3/m, primarily influenced by the supply of aeolian sand from the adjacent beach. Aeolian sand transport rapidly decreases within a downwind distance of 20 m from the vegetation edge. The ability to trap sand varies between size of the plants, with wider plants being able to trap sand over shorter distances. By the end of the study period, nearly all vegetation zones were completely buried, causing sand to bypass the dune. The future progression of dune development will be determined by the interaction between vegetation growth and sand burial.

Wetland attributes significantly affect patterns of bird species distribution in the Sardinian wetlands (Italy): An uncertain future for waterbird conservation

Abstract The Sardinian wetlands belong to the Sardinia‐Corsica corridor of the central eastern Mediterranean bird flyway. They supply the food and shelter for many waterbird species and act as stopover sites during migratory journeys. Despite policies and laws of the European Union, the Sardinian wetlands are severely threatened by anthropic activities and ongoing climate change, making the condition of the associated avifauna critical. We (a) inventoried the avian metacommunity of the largest coastal wetlands in Sardinia during the summer period, (b) investigated the metacommunity structure, (c) quantified the effects of wetland attributes on avian diversity at species and guild level and (d) predicted future changes in species composition of this metacommunity. We recorded 60 bird species (of which 21 belonged to Annex I of the Birds Directive). The metacommunity structure resulted was significantly nested and non‐modular. Salinity negatively affected the presence of 48 species out of 60, followed by tourism pressure (44 species), wetland isolation (42 species) and water discharges (36 species). The mean water level resulting from artificial regulation for anthropic activities was too high for 63% of the species, which disadvantaged primarily small waders, species feeding on invertebrates and trans‐Saharan migrants. In addition, water‐level fluctuations (that would favour avian diversity) were prevented by artificial regulation during the summer period in many wetlands, producing further negative effects on the avifauna. We found 45% of the recorded bird species at risk of disappearance from this avian metacommunity. Synthesis and applications. Our study indicates that, as things stand, the avian metacommunity of the Sardinian wetlands is destined to experience reductions in the short term and mid‐term. This decline will be accelerated by increased saltwater intrusions due to sea‐level rise. Nevertheless, the nested and non‐modular structure of this avian metacommunity would allow for pro‐active conservation measures (e.g. restriction for tourism activities, construction of artificial dune cordons to minimize saltwater intrusions, water‐level regulation that keeps into account also the ecological requirements of waterbird species) to counteract the effects of current and future threats.

Mollusc shell detritus affects benthic subtidal community dynamics in the Northern Wadden Sea

A shallow subtidal area in the northern Wadden Sea was monitored over 17 years (from 2003 to 2019) for sediment parameters and macrobenthic fauna. Due to the sheltered position of the study area, sediment composition remained rather stable with only minor annual and seasonal variations in sediment granulometry. An intermittend storm (‘Kyrill’) had no significant effect on sediment composition parameters; the construction of an artificial dune along the southern border of the study area had minor transient but no lasting effects on sediment composition. Faunal species richness and total abundance showed the typical seasonality with minimum abundance in late winter and a peak after recruitment in summer. Variations between years in autumn (post-recruitment) abundances were best explained by the number of days with a seawater temperature <1°C during the preceding winter. Temperature during other seasons, salinity, chlorophyll concentration and NAO showed no significant correlations with total abundance, nor did storm (‘Kyrill’) or construction of the artificial dune. Within-site faunal variability was best explained by water depth and velocity of the tidal currents while sediment granulometry was of minor importance. However, the amount of bivalve shell detritus mixed with the sandy sediment proved to be the strongest covariant of species numbers, total abundance, and species-specific abundances. At the sediment surface, shells provide the only anchorage for epibenthic species which in turn attract associated fauna. Shells inside the sediment hamper movement of infaunal predators and epibenthic predators are handicapped in rooting about for prey. Thus, shell material is a highly significant structural factor for the macrozoobenthos in these shallow waters. In a future with increasing ocean acidification, the availability of benthos as a food source for higher trophic levels will depend on the balance between pH-driven shell destruction and the compensatory power of shell-building species.

A modeling application of integrated nature based solutions (NBS) for coastal erosion and flooding mitigation in the Emilia-Romagna coastline (Northeast Italy)

Worldwide, climate change adaptation in coastal areas is a growing challenge. The most common solutions such as seawalls and breakwaters are expensive and often lead to unexpected disastrous effects on the neighboring unprotected areas. In recent years, this awareness has guided coastal managers to adopt alternative solutions with lower environmental impact to protect coastal areas, defined as Nature-Based Solutions (NBSs). NBS are quite popular around the world but are often analyzed and implemented individually at pilot sites. This contribution analyzes the effectiveness of two NBS to mitigate coastal impacts (coastal flooding and erosion) under three historical storms along the Emilia-Romagna coasts and the induced improvements due to their potential integration. Through numerical simulations with XBeach, this study demonstrated that the presence of seagrass meadows of Zostera marina produces an average attenuation of 32 % of the storm peak with a maximum attenuation of 89 % in incoming wave height. Seagrass also mitigates flooded areas and maximum inundation depths by 37 % and 58 % respectively. The artificial dune leads to higher mitigation in terms of inundation of the lagoon (up to 75 %), also avoiding any morphological variations behind it. Seagrass has also been shown to be able to reduce beach erosion volumes up to 55 %. The synergic effect of the two NBS improves the capacity to mitigate both inundation (with a benefit of up to 77 % for flooded area attenuation with respect to cases without any defenses) and coastal erosion. Results of the study suggest that the two NBS will work together to produce co-benefits in terms of preservation of their efficiency, development of habitats for organisms and vegetation species, and thereby offering an important social value in terms of possible tourism, recreation and research.

Estimation of groundwater recharge rates using soil-water isotope profiles: a case study of two contrasting dune types on Langeoog Island, Germany

The creation of artificial dunes for coastal protection may have important consequences for freshwater lenses in coastal aquifers. The objective of this study was to compare the recharge processes below such a young dune with scant vegetation to an older dune covered by grass and herbaceous vegetation. To this aim, soil and water samples were collected from the unsaturated zone at two sites on Langeoog Island in northern Germany, and the soil water was analysed for stable water isotopes and chloride. Recharge rates were calculated by using a new version of HYDRUS-1D, which was modified to simulate isotope fractionation during evaporation. Both the model outcomes and the data highlight the importance of fractionation, which is slightly more pronounced at the older, more vegetated dune. At the newly constructed dune, vegetation dieback seemingly reduces the importance of transpiration during summer. Recharge occurs year-round, albeit predominantly during the winter months. Calculated recharge rates are consistent with lysimeter measurements, but are significantly higher than previously reported rates based on groundwater age data, which is primarily attributed to the absence of dune shrub at the sites investigated here. More data are needed to establish the importance of soil-water repellency and overland flow. Based on the results, it is proposed that repeated isotope sampling can yield important insights into the dynamics of recharge processes, including their response to climate change.

Optimization of Coastal Protections in the Presence of Climate Change

It is generally acknowledged that interdependent critical infrastructure in coastal urban areas is constantly threatened by storm-induced flooding. Due to changing climate effects, such as sea level rise (SLR), the occurrence of catastrophic events will be more frequent and may trigger an increased likelihood of severe hazards. Planning a protective measure or mitigation strategy is a complex problem given the constraints that it must fit within a prescribed and limited fiscal budget and be beneficial to the community it protects both socially and economically. This article proposes a methodology for optimizing protective measures and mitigation strategies for interdependent infrastructures subjected to storm-induced flooding and climate change impacts such as SLR. Optimality is defined in this methodology as a maximum reduction in overall expected losses within a prescribed budget (compared to the expected losses in the case of doing nothing for protection/mitigation). Protective measures can include seawalls, barriers, artificial dunes, restoration of wetlands, raising individual buildings, sealing parts of the infrastructure, strategic retreat, insurance, and many more. The optimal protective strategy can be a combination of several protective measures implemented over space and time. The optimization process starts with parameterizing the protective measures. Storm-induced flooding and SLR, and their corresponding consequences, are estimated using a GIS-based subdivision-redistribution methodology (GISSR) developed by the authors for finding a rough solution in the first brute-force iterations of the optimization loop. A storm surge computational model called GeoClaw is subsequently used to simulate ensembles of synthetic storms in order to fine-tune and achieve the optimal solution. Damage loss, including economic impacts, is quantified based on calculated flood estimates. The suitability of the potential optimal solution is examined and assessed with input from stakeholders' interviews. It should be mentioned that the results and conclusions provided in this work depend on the assumptions made about future sea level rise (SLR). The authors acknowledge that there are other, more severe predictions for sea level rise (SLR), than the one used in this paper.

Uncertainty of Drone-Derived DEMs and Significance of Detected Morphodynamics in Artificially Scraped Dunes

This work capitalises on the morphodynamic study of a scraped artificial dune built on the sandy beach of Porto Garibaldi (Comacchio, Italy) as a barrier to protect the touristic facilities from sea storms during the winter season and contributes to understanding of the role of elevation data uncertainty and uniform thresholds for change detection (TCDs) on the interpretation of volume change estimations. This application relies on products derived from unmanned aerial vehicle (UAV) surveys and on the evaluation of the uncertainty associated with volume change estimations to interpret the case study morphodynamics under non-extreme sea and wind conditions. The analysis was performed by comparing UAV-derived digital elevation models (DEMs)—root mean squared error (RMSE) vs. global navigation satellite system (GNSS) &lt; 0.05 m—and orthophotos, considering the significance of the identified changes by applying a set of TCDs. In this case, a threshold of ~0.15 m was able to detect most of the morphological variations. The set of TCD ≤ 0.15 m was considered to discuss the significance of minor changes and the uncertainty of volume change calculations. During the analysed period (21 December 2016–20 January 2017), water levels and waves affected the front of the artificial dune by eroding the berm area; winds remodelled the entire dune, moving the loose sand around the dune and further inland; sediment volumes mobilised by sea and wind forcing were comparable. This work suggests that UAV-derived coastal morphological variations should be interpreted by integrating: (i) a set of uniform thresholds to detect significant changes; (ii) the uncertainty generated by the propagation of the original uncertainty of the elevation products; (iii) the characteristics of the morphodynamic drivers evaluated by adopting uncertainty-aware approaches. Thus, the contribution of subtle morphological changes—magnitudes comparable with the instrumental accuracy and/or the assessed propagated uncertainty—can be properly accounted for.

ROLE OF SPATIAL VARIABILITY OF SOIL RESISTANCE IN ALONGSHORE VARIABILITY OF COASTAL BARRIERS RESPONSE TO SUPERSTORM SURGES

Sand dunes and other natural coastal barriers (e.g. barrier islands) represent important components of the defense system against consequences of storm surges. However, in many coastal systems, major storm surges represent important drivers of coastal erosion. Increased extreme events potentially result in accelerated coastal erosion, coastal barrier breaching, and coastal flooding. The response of a barrier to a storm surge is often determined by mutual interaction among the driving hydrodynamics, the subsequent morphodynamics, and the local geology, including spatial variations of subaqueous bathymetry and subaerial topography. However, the effect of alongshore variability of soil properties on the alongshore varying response is not yet considered. Therefore, this study examines soil parameters that may affect coastal erosion during major storm surges. Moreover, it applies a novel extension of the numerical model XBeach that accounts for spatial variation of soil properties to an artificial dune system of spatially varying soil permeability. Results showed that variability of soil permeability alongshore the dune results in alongshore varying resistance to erosion so that breaches may occur at the locations of less resistance that are corresponding to locations of higher soil permeability. Outcomes of the numerical simulations proved also that reduced soil permeability represents a nature-based solution that increases the resilience of natural defense systems during major storm surges by mitigating rates of coastal erosion.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/1ERwbW5BmYA

Optimal Strategy to Tackle a 2D Numerical Analysis of Non-Uniform Flow over Artificial Dune Regions: A Comparison with Bibliography Experimental Results

Flow simulation over a dune requires the proper input of roughness coefficients. This study analyzed a numerical simulation of open-channel turbulent flow over two-dimensional fixed dunes to reveal the effect of roughness on the dune bottom, and to determine the optimized combination of the turbulence scheme and the roughness height formula. The most appropriate roughness values and turbulence models were applied using Reynolds-averaged Navier–Stokes models. Seven methods were chosen to estimate the bed roughness properties at the inlet boundary section. The results of all cases calculated with the OpenFOAM toolbox were compared with laboratory experimental data for model validation. The performances of all bed roughness variations were evaluated according to the stream-wise and depth-wise directions with nondimensional values. Consequently, it was revealed that the combination of bottom roughness length scale at the inlet boundary and the k-ω shear-stress transport (SST) model was the most suitable for the flow separation zone and turbulent properties near the channel bottom.

A holistic approach to evaluating dune cores

As population density increases in coastal counties, shoreline stabilization efforts continue to gain momentum to protect infrastructure. Although protection techniques vary from ‘soft’ to ‘hard’ engineering, this paper focuses on a ‘hybrid’ technique utilizing geotubes as artificial dune cores. Previous literature presents conflicting results on the efficacy and potential impacts of dune cores on a beach-dune system. Here we evaluate and quantify the geomorphic impacts following dune core installation and investigate their economic feasibility. This was completed by comparing five case studies: Sea Isle City, NJ; Bolivar Peninsula, TX; Grand Isle, LA; Santa Rosa Beach, FL; and Nantucket Island, MA. An economic assessment was completed to compare dune core installation costs and repairs to alternative shoreline hardening methods. LiDAR data were used to compare dune slope, beach width, and beach volume between digital transects adjacent to and in front of the dune core installations. Digital elevation models (DEMs) were generated to provide a holistic view of geomorphic change and to assess whether erosion occurred landward of the dune core. Results indicate that dune cores are an economically feasible option compared to alternative methods. Limitations include UV exposure, wave influence, and heavy winds. Morphologically, beach width was 29.1% wider in adjacent transects and dune slope was 39.1% steeper in front of the dune core. Beach volume was lower by an overall average of 23.4%. The findings from this study suggest that dune cores are a ‘hard’ or ‘grey’ protection method.

Processes controlling morphodynamics of artificially breached barriers

Naturally and artificially breached tidal inlets can promote fast morphological changes along the adjacent detrital barriers, as they evolve in response to the contemporaneous wave regime. Inlet migration results in downdrift barrier erosion, while updrift sand accumulation and concomitant barrier extension are commonly observed.This study addresses the performance of placement of a sandfill designed to create an artificial dune along the updrift tip of a sand barrier aiming to constrain inlet migration, stabilize its location and reduce sand transfers from the ocean into the lagoon induced by storm overtopping of the barrier. Herein, we investigate the patterns of inlet drifting and processes regulating the progressive loss of efficiency of this soft engineering solution.We show that, besides updrift inlet migration, which occurs with temporary reversal of the prevailing direction of drift currents, meandering of the ebb-channels that envelop the flood delta is quite effective in triggering or enhancing erosion of the updrift barrier tip in periods when the inlet main channel is migrating in the opposite direction. This additional erosional process, which acts along the back-barrier façade, is responsible for the increase of the erosion rate of the artificial dune and regardless of the direction of wave-induced drift direction of the inlet. This finding discloses the relevance of taking into account not only the oceanic processes (waves) but also processes operating on the lagoonal side of the barriers in future engineering operations designed for tidal inlet management.

Remobilizing stabilized island dunes for keeping up with sea level rise?

Dune spits of the island of Sylt (North Sea) persisted through millennia by mobile dunes transferring sand from exposed to sheltered shores. However, 150 years of systematic planting on washovers, blowouts and migrant dunes have almost completely stopped this sand conveyor belt. Spits lost sand until sand replenishments to the exposed side compensated for losses during the last three decades. Based on maps since 1878, aerial images from the 1930s onward as well as botanical ground surveys, we document a long-term shift from loose grass cover to dense heather dominated vegetation. Bare sand areas almost vanished and high shrubs proliferated. Only three dunes continue migrating with about 3 m a-1 since 1936. Mainly artificial dune stabilizations and introduced plants have facilitated succession to an almost complete plant cover. Thus, revitalization of aeolian dynamics would be desirable, and pilot projects may acquire the appropriate knowledge. For a 1.7 × 2.5-km corridor across the island spit, we therefor discuss two suggested experiments: (1) intensify sand nourishments to the eroding beach and stop stabilization measures to allow excess sand blown inland and washovers entering deflation plains, and (2) examine the potential of tunnels for roads to let mobile dunes passing over. Such experiments may not only contribute to dune biodiversity but also to long-ranging adaptations of crowded barrier islands to accelerating sea level rise.

Does the Functional Richness of Plants Reduce Wave Erosion on Embryo Coastal Dunes?

Coastal erosion is a natural process, whose intensity and occurrence have increased due to natural and anthropogenic factors. To protect the coasts, the use of hard infrastructure is a widespread practice that can be effective, mostly at a local scale. However, recent evidence also shows that downstream erosion can be accelerated in adjacent zones. Because of this, natural barriers such as coastal dunes and their plant cover have gained attention, but there is a general lack of information about the role that different species (and combinations of species) play in coastal protection. The aim of this study was to explore if the functional richness of plant species helps reduce wave erosion on embryo coastal dunes. In a wave flume, we set up a 1:1 scale artificial dune covered with different combinations of plant species (Ipomoeae pes-caprae, Sesuvium portulacastrum, and Sporobolus virginicus) and exposed it to simulated “storm waves”. We found that erosion was reduced in dunes covered by plants, but such protection was species-specific and the effectiveness of protection varied over time. Ipomoea was the most effective specie for protection. Differences between species and combinations of species were associated with their physical attributes such as growth form and plant architecture. Although we found that there are species that offer little or no protection from hydrodynamic forces, they may still be important for coastal protection through their ability to build embryo dunes through eolian processes. Indeed, nature-based coastal protection is likely to be an effective alternative to engineered solutions at many sites, but the protection provided is species-specific.