Coastal Defence Structures Research Articles

Physical Modeling of Landward Scour Due to Tsunami Bore Overtopping Seawall

many of the post tsunami field surveys which conducted by researchers revealed that, the failure due to scour at the landward toe of the seawall due to overtopping of tsunami wave forms one of the important types of coastal defence structures failure and constitutes one of the biggest threats to their structural performance. This study was intended to investigates the scour profile induced by tsunami bores at the landward toe of the vertical seawall and to discuss the effects of the parameters; tide level, incident bore Froude number Fb, incident bore height Hb, overtopping flow Froude number Fo, and overtopping flow depth Ho on the maximum scour depth induced at the landward toe of the seawall. A set of laboratory experiments were conducted at National Hydraulic Research Institute of Malaysia (NAHRIM) with the tichnique of dam break to generate the bore like tsunami. The experiments showed that the initial water level upstream of the seawall has a significant effect on the scour profile and there is a strong negative relationship exists with Froude number of the incident bore and a strong positive relationship exists with Froude number of the overtopping flow depth above the crest of the seawall.

A multifunctional computational approach to waterfront design

ABSTRACTSeawalls and other types of waterfront infrastructures are predominantly designed to counter natural forces and maintain structural stability. Consequently, their defensive and reactive design impedes other types of uses and users. As an alternative to the single-use paradigm, there have been attempts to develop a more ecological, performance-based and civic approach to coastal defence structures that would engage with the diverse needs of human and non-human stakeholders. This paper presents a theoretical and methodological framework for employing computational tools to creatively design the interaction between the sea and the man-made shoreline. The research developed and tested a computational design methodology for the early stages of the seawall architectural design process. The suggested design methodology relies on inputs from a wave and texture taxonomy that was developed using physically based fluid simulation tools. The methodology was tested in a case study design.

Ecological performance of construction materials subject to ocean climate change

Artificial structures will be increasingly utilized to protect coastal infrastructure from sea-level rise and storms associated with climate change. Although it is well documented that the materials comprising artificial structures influence the composition of organisms that use them as habitat, little is known about how these materials may chemically react with changing seawater conditions, and what effects this will have on associated biota. We investigated the effects of ocean warming, acidification, and type of coastal infrastructure material on algal turfs. Seawater acidification resulted in greater covers of turf, though this effect was counteracted by elevated temperatures. Concrete supported a greater cover of turf than granite or high-density polyethylene (HDPE) under all temperature and pH treatments, with the greatest covers occurring under simulated ocean acidification. Furthermore, photosynthetic efficiency under acidification was greater on concrete substratum compared to all other materials and treatment combinations. These results demonstrate the capacity to maximise ecological benefits whilst still meeting local management objectives when engineering coastal defense structures by selecting materials that are appropriate in an ocean change context. Therefore, mitigation efforts to offset impacts from sea-level rise and storms can also be engineered to alter, or even reduce, the effects of climatic change on biological assemblages.

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

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.

Spatial variability of fish communities in a highly urbanised reef system

Rapid coastal development has generated interest in the ecology of human-modified marine environments. Coastal defence structures such as breakwaters and seawalls are increasingly built to reduce erosion and to mitigate the impacts of sea level rise but knowledge on the marine biodiversity around these structures is lacking. Benthic cover and fish community were surveyed at nine offshore sites, comprising seven coral reefs and two seawalls, in the Singapore’s highly urbanised reef system. A total of 4943 fishes from 70 taxa were recorded, dominated by Pomacentridae (56.5%) and Labridae (17.7%). The results showed a clear spatial variation in the fish community structure across the reefs. The southwestern reefs supported fish communities that were significantly different from those in the south. Generic diversity was significantly higher at the southwestern reefs than the southern ones while the abundance and generic richness were similar. The differences in fish community structure were moderately correlated with the abundance of coralline algae, foliose and submassive corals. The seawall sites supported fish communities different from coral reefs that were adjacent to them. While abundance was similar, the former had higher generic richness and diversity than the latter. The difference in community was attributed to two pomacentrid genera (i.e. Neopomacentrus and Pomacentrus) which were more abundant at the reefs. The findings demonstrated that urbanised coastal ecosystems can contribute to supporting fish diversity.

Rock armour for birds and their prey: ecological enhancement of coastal engineering

The authors present key design, construction and ecological enhancement criteria for sustainable coastal defence structures at Hartlepool, UK, a high-energy wave climate. Such ‘ecologically favourable’ coastal defences fulfil the habitats directive and key engineering and cost criteria. Bird, rocky intertidal ecological and biogeomorphological data underpin recommendations for ‘passive’ enhancement mitigation to maximise ecological potential involving rock armour material choice (partially enhanced) and its smart positioning (enhanced). Within 12–18 months of installation, key intertidal species (e.g. limpets, barnacles, fucoid seaweeds) had successfully colonised the rock revetment, matching the initial baseline biotope. However, species abundance and overall mobile and sessile species were not significantly different between the two enhanced treatments after 12–18 months. Importantly, key prey species (the limpet, Patella vulgata) on enhanced rock armour showed statistically significant abundances similar to the baseline shore platform and significantly higher than partially enhanced rock armour. These preliminary data show that well-chosen rock armour material and boulder enhancement using positioning can match baseline biotope conditions in 12–18 months and that for some key prey species, positioning-enhanced rock armour rapidly matches baseline conditions. This facilitates rapid rock revetment colonisation, enabling good recruitment of food species and favourable conditions for internationally designated waterbird species.

Small artificial habitats to enhance the nursery function for juvenile fish in a large commercial port of the Mediterranean

The concentration of human activities along the shoreline induces high levels of pressure, notably seascape urbanization caused by the proliferation of coastal and marine infrastructures such as ports, harbors, marinas and coastal defense structures. Because they are localized in sheltered and shallow coastal areas, these infrastructures inevitably lead to the loss of natural essential habitats once used as nursery ground by juvenile fish. Some studies have reported the presence of high juvenile densities on breakwaters and jetties suggesting those infrastructures could support the nursery function. However, ports seem unlikely to be used by juveniles due to their vertical and featureless docks. Here we explored the feasibility of using small artificial habitats to enhance the ecological value of ports. We set up a total of 108 artificial habitats in three different locations of the large commercial port of Marseille in the northwestern Mediterranean. We then surveyed juvenile fish on the artificial habitats and control docks on 7 different occasions between June and September 2014. Average species richness and densities were higher on the artificial habitats but displayed high spatial and taxa-specific variations. Hence, small artificial habitats are promising ecological engineering tools to enhance the nursery function inside ports and thus reduce the ecological footprint of those infrastructures.

Applications of geosynthetic membranes in soil stabilization and coastal defence structures

Abstract The use of geosynthetic in soil and coastal engineering is increasing and improving due to improvements in its engineering properties and fabrication techniques. While some geosynthetic coastal structures have attained advanced stage in terms of applications and efficiency, others still lack well-structured design formulas and specifications on a sound scientific basis, hence continued experimental works for the better understanding of the hydraulic performance, stability and modes of failure of these structures. Coastal areas are dynamic with unique geomechanical feature such as soil instability, which in any case, may affect the overall performance of coastal defence structures constructed on soft soil or weak foundation. This paper reviews the developments and applications of geosynthetics in soil stabilization and protection of coastal areas with emphasis on shoreline protection. Relevant empirical research data are presented as well as the present and likely future challenges in the use of geosynthetics in soil stabilization and coastal defence structures.

Changing coastlines in NE England: a legacy of colliery spoil tipping and the effects of its cessation

Historical tipping of vast quantities of colliery spoil at various foreshore locations in NE England has changed the morphology and sedimentology of large areas of the shoreline and nearshore sea bed, and has impacted adversely upon the ecology and amenity use of the area. Tipping started early in the 20th Century, well before statutory controls to regulate impacts of activities on the marine environment came into force in the UK in 1974, and ended with the closure of the last colliery in 2005. The spoil tipping acted as a form of artificial sediment recharge to the foreshore, akin to conventional beach recharge schemes that use sand or shingle to replenish foreshores for coastal defence and amenity purposes, but creating a legacy of contaminated beaches and prograding (advancing) shores. Since closure of the collieries, however, the foreshores have received no artificial supply of material, and the shoreline in all former tipping areas has since been in retreat due to natural erosion. This has caused problems where assets are present at the rear of the spoil beaches, requiring coastal defence structures for their protection. As well as collating and analysing historical maps, records, literature and data relating to colliery spoil tipping, the coastal changes that have occurred since its cessation have been assessed by reference to more recent maps, literature, aerial photographs and new and up-to-date beach profile transect survey data from contemporary coastal monitoring programmes. It is envisaged that where sea cliffs are protected by colliery spoil beaches, and hence currently are dormant, they could become re-activated by erosion and start to retreat at short term rates of several metres per year and longer-term rates of up to 0.3 m/year in the foreseeable future.

Role of Beach Morphology in Wave Overtopping Hazard Assessment

Understanding the role of beach morphology in controlling wave overtopping volume will further minimise uncertainties in flood risk assessments at coastal locations defended by engineered structures worldwide. XBeach is used to model wave overtopping volume for a 1:200 year joint probability distribution of waves and water levels with measured, pre- and post-storm beach profiles. The simulation with measured bathymetry is repeated with and without morphological evolution enabled during the modelled storm event. This research assesses the role of morphology in controlling wave overtopping volumes for hazardous events that meet the typical design level of coastal defence structures. Results show that disabling storm-driven morphology under-represents modelled wave overtopping volumes by up to 39% under high H s conditions and has a greater impact on the wave overtopping rate than the variability applied within the boundary conditions due to the range of wave-water level combinations that meet the 1:200 year joint probability criterion. Accounting for morphology in flood modelling is therefore critical for accurately predicting wave overtopping volumes and the resulting flood hazard and to assess economic losses.

Wave setup properties in the surge-wave coupled simulation: a case study of Typhoon Khanun

The accurate prediction of surge height is vitally important in designing coastal defense structures. With the advancement of computation efficiency, many researchers have studied the wave-current interaction on surge height by coupling hydrodynamic and wave models. In this study, Deflt3D Flow model was interacted dynamically with Delft3D Wave model to simulate the storm surge process caused by typhoon Khanun to obtain the spatiotemporal properties on wave setup induced by storm wind. Simulations with and without wave model have been conducted, revealing that the spatiotemporally varying wave setup distribute along the coastal line when typhoon is in the open sea with large wave height and surge height around. The spatial distribution of nearshore wave setup at landfall moment was obtained. Nevertheless the contribution of wave effects on storm surge increases slightly under intensive storm wind, with the maximum wave setup near typhoon center accounting for 10% of the peak surge height.

An Analysis of Fatality Ratios and the Factors That Affected Human Fatalities in the 2011 Great East Japan Tsunami

This study presents a new analysis of spatial variation in fatality ratios in the 2011 Great East Japan tsunami, in order to overcome the limitations of previous studies that tended to underestimate the fatality ratios. In addition, this analysis was performed in a manner that allows the results to be compared to those from analyses of fatality ratios in other historical tsunamis. To do this, it uses population and fatality data at the village scale in areas of less than 3 km2 where the inundation ratio was greater than 70%, rather than the lower-resolution data used in previous studies. The median value of the tsunami inundation depth at each location was extracted at the original 5-m grid resolution. All of the data were obtained from the Reconstruction Support Survey Archive. Based on the results, a strong correlation between the fatality ratio and inundation depth was found only in some areas of the Sendai Plain, whereas no strong correlation was observed along the Sanriku ria coastline. Fatality ratios in Sanriku were likely related not only to the force of the tsunami but also to other factors, such as the ria topography and the population’s experience of past historical tsunamis. Data from other tsunamis in regions where tsunamis frequently occur also indicate that historical tsunami experience is a key factor in reducing fatality ratios. In contrast, the Sendai Plain shows smaller variation in local tsunami amplification effect compared to that of the Sanriku ria coastline, as well as fewer coastal defence structures. Therefore, the fatality ratio in that region was predominantly affected by the force of the tsunami and the residents’ individual characteristics. On the Sendai Plain, Ishinomaki City exhibited a strong correlation between the fatality ratio and inundation depth, as well as between fatality ratio and building damage because its low evacuation ratio meant that many fatalities occurred in victims’ homes. Therefore, the fatality ratio in Ishinomaki City was higher than those in other areas at the same inundation depth. Simple empirical formulas were developed for estimation of human fatalities based on inundation depths and building damage ratios.

Rethinking the role of edaphic condition in halophyte vegetation degradation on salt marshes due to coastal defense structure

Determining how human disturbance affects plant community persistence and species conservation is one of the most pressing ecological challenges. The large-scale disturbance form defense structures usually have a long-term and potential effect on phytocommunity in coastal saltmarshes. Coastal defense structures usually remove the effect of tidal wave on tidal salt marshes. As a consequence, edaphic factors such as the salinity and moisture contents are disturbed by tidal action blocking. However, few previous studies have explicitly addressed the response of halophyte species persistence and dynamics to the changing edaphic conditions. The understanding of the response of species composition in seed banks and aboveground vegetation to the stress is important to identify ecological effect of coastal defense structures and provide usefully insight into restoration. Here, we conducted a field study to distinguish the density, species composition and relationships of seed bank with aboveground vegetation between tidal flat wetlands with and without coastal defense structures. We also addressed the role of edaphic condition in vegetation degradation caused by coastal defense structures in combination with field monitor and greenhouse experiments. Our results showed the density of the seed bank and aboveground vegetation in the tidal flat without coastal defense structures was significantly lower than the surrounded flat with coastal defense structures. A total of 14 species were founded in the surrounded flat seed bank and 11 species in the tidal flat, but three species were only recorded in aboveground vegetation of the tidal flat which was much lower than 24 aboveground species in the surrounded flat. The absent of species in aboveground vegetation contributed to low germination rate which depend on the edaphic condition. The germination of seeds in the seed bank were inhabited by high soil salinity in the tidal flat and low soil moisture in the surrounded flat. Our study supported the hypothesis that the change of edaphic condition caused by coastal defense structures was the main reason for the difference of the species composition similarity between aboveground vegetation and the soil seed bank between the tidal and surrounded flats. Therefore, mitigating the hydrological disturbance and maintaining the original state of edaphic factors would be useful implications for reducing the ecological effect of defense structure to vegetation communities in coastal salt marshes.

Improvement of Tsunami Countermeasures Based on Lessons from The 2011 Great East Japan Earthquake and Tsunami — Situation After Five Years

The 2011 Great East Japan Tsunami exposed many hidden weaknesses in Japan's tsunami countermeasures. Since then, many improvements have been made in both structural measures (numerical simulations, coastal defense structures, building damage assessment and control forests) and nonstructural measures (warning/observation and evacuation). This review summarizes the lessons and improvements in the five-year time period after the 2011 event. After five years, most of the lessons from the 2011 tsunami have been applied, including more realistic tsunami simulations using very fine grids, methods to strengthen coastal defense structures, building evacuations and coastal forests, improved warning content and key points to improve evacuation measures. Nevertheless, large future challenges remain, such as an advanced simulation technique and system for real-time hazard and risk prediction, implementation of coastal defense structures/multilayer countermeasures and encouraging evacuation. In addition, among papers presented at the coastal engineering conference in Japan, the proportion of tsunami-related research in Japan increased from 15% to 35% because of the 2011 tsunami, and approximately 65–70% of tsunami-related studies involve numerical simulation, coastal structures and building damage. These results show the impact of the 2011 tsunami on coastal engineering related to academic institutions and consulting industries in Japan as well as the interest in each tsunami countermeasure.

Failure Mechanisms and Local Scour at Coastal Structures Induced by Tsunami

On 11 March 2011, an exceptionally large tsunami event was triggered by a massive earthquake offshore, the northeast coast of Japan, which affected coastal infrastructure such as seawalls, coastal dikes and breakwaters in the Tohoku region. Such infrastructure was built to protect against the Level 1 tsunamis that previously hit the region, but not for events as significant as the 2011 Tohoku tsunami, which was categorized as a Level 2 tsunami [Shibayama, T., Esteban, M., Nistor, I., Takagi, H., Thao, N. D., Matsumaru, R., Mikami, T., Aranguiz, R., Jayaratne, R. & Ohira, K. [2013] “Classification of tsunami and evacuation areas,” Nat. Hazards 67(2), 365–386], The failure mechanisms of concrete-armored dikes, breakwaters and seawalls due to Level 2 tsunamis are still not fully understood by researchers and engineers. This paper investigates the failure modes and mechanisms of damaged coastal structures in Miyagi and Fukushima Prefectures, following the authors' post-disaster field surveys carried out between 2011 and 2013. Six significant failure mechanisms were identified for the coastal dikes and seawalls affected by this tsunami: (1) Leeward toe scour failure, (2) Crown armor failure, (3) Leeward slope armor failure, (4) Seaward toe scour and slope armor failure, (5) Overturning failure, and (6) Parapet wall failure, in which leeward toe scour being recognized as the major failure mechanism in most surveyed locations. The authors also propose a simple practical mathematical model for predicting the scour depth at the leeward toe of the coastal dikes, by considering the effects of the tsunami hydrodynamics, the soil properties and the type of structure. The key advantage of this model is that it depends entirely on quantities that are measurable in the field. Furthermore this model was further refined by conducting a series of hydraulic model experiments aimed to understand the governing factors of the leeward toe scour failure. Finally, based on the results obtained, key recommendations are given for the design of resilient coastal defense structures that can survive a level 2 tsunami event.

Stakeholder priorities for multi-functional coastal defence developments and steps to effective implementation

To fulfil international conservation commitments, governments have begun to recognise the need for more proactive marine planning policies, advocating sensitive engineering design that can deliver secondary benefits above and beyond the primary purpose of developments. In response, there is growing scientific interest in novel multi-functional coastal defence structures with built-in secondary ecological and/or socio-economic benefits. To ensure research efforts are invested effectively, it is first necessary to determine what secondary benefits can potentially be built-in to engineered coastal defence structures, and further, which of these benefits would be most desirable. It is unlikely that secondary benefits are perceived in the same way across different stakeholder groups. Further, their order of priority when evaluating different options is unlikely to be consistent, since each option will present a suite of compromises and trade-offs. The aim of this study was to investigate stakeholder attitudes towards multi-functional coastal defence developments across different sector groups. A preliminary questionnaire indicated unanimous support for implementing multi-functional structures in place of traditional single-purpose ones. This preliminary survey informed the design of a Delphi-like study, which revealed a more nuanced and caveated level of support from a panel of experts and practitioners. The study also elicited a degree of consensus that the most desirable secondary benefits that could be built-in to developments would be ecological ones – prioritised over social, economic and technical benefits. This paper synthesises these findings, discusses the perceived barriers that remain, and proposes a stepwise approach to effective implementation of multi-functional coastal defence developments.

Longitudinal revetments to mitigate overtopping and flooding: Effectiveness, costs and benefits

Several anthropogenic actions have been weakening sediment supplies to coastal areas, reducing the amount of sediments available on beaches and leading to a general and recurrent retreat of the shoreline position. As a consequence, different coastal defense interventions, oftentimes longitudinal revetments, have been established over the past decades in areas with high erosion rates. However, the lack of monitoring of these coastal defense structures combined with the high exposure of the urban areas to erosion, have led to an increased frequency of damage events in several locations, damaging infrastructures, commercial establishments and housing. This study purposes to assess the effectiveness, costs and benefits of different types of longitudinal revetments that aim to protect urban waterfronts from erosion and overtopping. A statistical analysis was developed and applied in order to assess the overtopping frequency of longitudinal revetments, depending on the seabed depth at the toe of the structure and on the structure's freeboard. Given that wave climate and beach profile are intrinsically associated with overtopping frequency over time, causes for the deepening of the beach profile were identified and various formulations were analyzed in order to estimate the maximum scour depth, to anticipate the frequency of damage events and to assess the severity of overtopping and flooding events. The effectiveness of different interventions to reduce wave overtopping at longitudinal revetments was assessed, including crest elevation, artificial beach profile nourishment and construction of an intermediate berm. A cost-benefit analysis was performed to assess the economic viability of these interventions, based on their additional investment, operation and maintenance costs and corresponding avoided flood damage costs over time. Results for the case of Furadouro beach (Portugal) show that reinforcement of longitudinal revetments is usually economically viable in the mid-term, especially when an increase in overtopping frequency is anticipated. The avoided costs associated with the negative impacts of overtopping tend to break-even with the interventions' costs within a period of around 10 years.

Seawalls as a response to coastal erosion and flooding: a case study from Grande Comore, Comoros (West Indian Ocean)

Many coasts are eroding. In the Comoros, as in many other small island developing states (SIDS), communities frequently respond to coastal erosion by building seawalls—yet seawalls and other coastal defence structure are controversial, especially in a SIDS context, where they typically are poorly designed and constructed and thus tend to increase rather decrease erosion and are often unable to prevent flooding. Through an exploratory qualitative case study of Grande Comore, the main island of the Comoros (West Indian Ocean), we compare and contrast how local stakeholders, national elites and donors understand coastal erosion and flooding in the context of a changing climate and how they experience and perceive seawalls as a response measure. Our analysis suggests that although stakeholders are aware of different drivers of coastal erosion and flooding, including sand mining, seawalls are a frequent and customary response to coastal erosion and flooding. Little is known about their disadvantages or alternative response measures, especially among local community members. Further, a lack of capacity and resources leads not only to poorly designed and constructed seawalls but also to difficulties in enforcing rules and regulations such as bans on sand mining. From our exploratory study, three conclusions emerge: (1) local drivers of coastal erosion and flooding are more visible than global climate change while funding is more readily available for adaptation to climate change; (2) a mix of context and site-specific measures would be needed to adequately respond to coastal erosion and flooding; and (3) further information and knowledge about the extent and causes of coastal erosion and flooding as well as about the effects of different response measures would be needed to allow such context and site-specific measures.

Hidden biodiversity in cryptic habitats provided by porous coastal defence structures

In response to flood risk from rising and stormier seas, increasing amounts of natural coastline worldwide are being replaced by a proliferation of coastal defence structures. While the primary role of defence structures is protecting the coastline, consideration should be given to the biological coastal communities they support. Artificial structures are currently seen as poor habitats for marine organisms. They are constructed in harsh coastal environments, lack structural complexity, and are subjected to episodic disturbance from maintenance, reducing their suitability as habitats for coastal species. Recent work has focused on mitigating the impacts of coastal defence structures, through secondary routes such as enhancing biodiversity by encouraging colonisation of marine biota. Research thus far has focused on enhancements to improve structural complexity on the external surfaces of coastal defences. Many structures are porous with internal compartments. To date no work has been undertaken on the habitat provided by the internal surfaces of the blocks used in building structures.We investigated the role of porous coastal defence structures in habitat provision. Taking advantage of a groyne reduction from 45m to 20m length, we surveyed the internal environment of the structure. We also considered the impacts of maintenance activity on coastal assemblages. Our work shows that the internal environment of artificial structures provides functional habitat space supporting higher species richness and diversity than external surfaces. The more benign environment of internal surfaces protects from desiccation stress and is probably less scoured by mobile sediments, and as such is of unrealised importance to coastal assemblages. External surfaces are also subject to high levels of disturbance from maintenance activities, further limiting the potential ecological contribution this area of the artificial habitat might otherwise develop. These findings reveal the multifunctional role of porous coastal defence structures, acting as engineering protection and habitats for coastal assemblages.

Fresh groundwater resources in a large sand replenishment

Abstract. The anticipation of sea-level rise and increases in extreme weather conditions has led to the initiation of an innovative coastal management project called the Sand Engine. In this pilot project a large volume of sand (21.5 million m3) – also called sand replenishment or nourishment – was placed on the Dutch coast. The intention is that the sand is redistributed by wind, current, and tide, reinforcing local coastal defence structures and leading to a unique, dynamic environment. In this study we investigated the potential effect of the long-term morphological evolution of the large sand replenishment and climate change on fresh groundwater resources. The potential effects on the local groundwater system were quantified with a calibrated three-dimensional (3-D) groundwater model, in which both variable-density groundwater flow and salt transport were simulated. Model simulations showed that the long-term morphological evolution of the Sand Engine results in a substantial growth of fresh groundwater resources, in all adopted climate change scenarios. Thus, the application of a local sand replenishment could provide coastal areas the opportunity to combine coastal protection with an increase of the local fresh groundwater availability.