The impacts of Segura River (Spain) channelization on the coastal seabed

Flood impact on the Spanish Mediterranean coast since 1960 based on the prevailing synoptic patterns

In a changing climate and in social context, tools and databases with high spatiotemporal resolution are needed for increasing the knowledge on the relationship between meteorological events and flood impacts; hence, analysis of high-resolution spatiotemporal databases with detailed information on the frequency, intensity, and impact of floods is necessary. However, the methodological nature of flood databases hinders relating specific flood events to the weather events that cause them; hence, methodologies for classifying flood cases according to the synoptic patterns that generate them are also necessary. Knowing which synoptic patterns are likely to generate risk situations allows for a probabilistic approach with high spatial resolution regarding the timing of occurrence, affected area, and expected damage from floods. To achieve these objectives, we use the SMC-Flood Database, a high-resolution spatiotemporal flood database covering the 1960-2015 period for all municipalities along the Spanish Mediterranean coast. To relate floods with the synoptic conditions that generated them, we used a multivariate analysis method on the corrected daily anomalies of the surface pressure fields, 850 hPa temperature, and 500 hPa geopotential height, all of which were obtained from the 20th Century Reanalysis Project V2. Results show that 12 atmospheric synoptic patterns can statistically explain the 3608 flood cases that occurred in the study area between 1960 and 2015. These flood cases were classified into 847 atmospherically induced flood events. These results reduce the uncertainty during decision making because of the classification of potential risk situations. The Mediterranean Basin is a region where floods have serious socioeconomic impacts; hence, this work helps improving prevention measures and providing information for policymakers, mainly regarding land use planning and early warning systems.

Effects of Anthropogenic Pressures on Dune Systems—Case Study: Calabria (Italy)

During the second half of the last century, considerable anthropization processes were observed throughout most of the Italian territory. These processes have altered the equilibrium conditions of several river and coastal ecosystems, causing the destruction of numerous dune systems. This issue is particularly important in territories such as Calabria, a region in southern Italy subject to considerable anthropogenic pressures and characterized by over 700 km of coast. The aim of the paper was to evaluate the effects of anthropogenic pressures on the Calabrian dune systems, especially in regard to the triggering of coastal erosion processes. For this purpose, historical and current cartographic data, such as shapefiles, cartography, and satellite imagery, were analyzed using QGIS. This evaluation was carried out through the comparison between the current extension of the dune systems and their extensions after the Second World War, before the anthropogenic pressures. This evaluation was also carried out through the analysis of shoreline changes in coastal areas, where dune systems are currently present, and in coastal areas where dune systems have been partially or totally destroyed by anthropogenic causes, compared to the 1950s, thus excluding coastal areas without dune systems in the 1950s, and analyzing what was built in place of the destroyed dune systems. Two criteria were defined to identify the levels of destruction of the dune systems and to identify the coastal erosion processes. The analysis showed a strong correlation between the destruction of dune systems by anthropogenic causes and the triggering of coastal erosion processes.

137Cs estimates of soil erosion rates in a small catchment on a channelized river floodplain in the lower reaches of Yangtze River, China

Channelization significantly affects soil erosion in river floodplains. The object of this study was to use ¹³⁷Cs as a tracer to determine the ¹³⁷Cs inventory and derived soil erosion rates under various land use types in a catchment on channelized river floodplain in the lower reaches of Yangtze River, China. Sampling was carried out to establish a¹³⁷Cs reference inventory in a 70-year old paddy field located on the shoulder-slope of a local hill. The mean reference inventory of ¹³⁷Cs was 1275 Bq m^-2, whereas the ¹³⁷Cs inventory within the catchment ranged from 284 to 1150 Bq m^-2 and the soil erosion rates from -33.3 to -2.4 t ha^-1 yr^-1, respectively. The dominated land use of paddy in cultivated soils contributed relative low soil erosion. Bamboo and castanea mollissima were preferential for local land uses in uncultivated soils in comparison with woodland and Pinnus massoniana. The rates of soil erosion rates in old tea garden were higher than that in new tea garden. Overall, severe soil erosion and no deposition in the entire catchment occurred in the entire catchment due to the human-induced channelization in the 1970s. Our results suggest that restricting farmland being returned to tea plantations, thereby maintaining the current land use types would reduce soil erosion in river floodplain in the future.

Monitoring the dune-beach system of Guardamar del Segura (Spain) using UAV, SfM and GIS techniques

Dune ecosystems play a key role in coastal dynamics, so it is essential to measure their movements with high precision and monitor their changes over time. It is crucial to have a system that allows us to know the natural and anthropic impacts affecting these ecosystems. The aim of this study is to ascertain the historical evolution of the dune system of Guardamar del Segura (Spain) and its relationship with coastal erosion. Likewise, it is also intended to assess the state of the foredune restoration works carried out in 2011. To this end, a comparison of existing cartographic data has been undertaken by using geospatial analysis techniques through Geographic Information Systems (GIS). As a novelty, a low takeoff weight UAV (Unmanned Aerial Vehicle) has been used to produce a high-precision 3D model from two-dimensional images using photogrammetric techniques, such as Structure from Motion (SfM). This technique made it possible to obtain a digital terrain model of high density and precision (30 pt/m² and RMSE Z of 0.173 m). The results show a constant erosion of both the beach and the foredune, with an overall loss of 143,561 m³ of material in the period analyzed (2001-2017). The anthropogenic restoration actions executed within this period have not been effective. In fact, erosion has increased in the period 2016-2017, with a significant reduction in the beach width and sea waves directly affecting the foredune. The main conclusion is that the combined use of UAV and SfM techniques is an excellent procedure to periodically supervise dune ecosystems with high precision and significant time and cost savings.

Factors influencing the rate of beach sand wear: Activation layer thickness and sediment durability

The construction of harbours on the coast and/or dams in river courses prevents the contribution of sediments from rivers and ravines to the coastline and interferes with natural coastal dynamics. In the present study, the main objective is to provide information to the coastal engineer to predict and quantify the wear and tear of sand for artificial beach nourishment, as well as the durability of the intervention. For this purpose: (i) the amount of sample used in laboratory tests is related to the actual activation layer due to waves, and (ii) the material durability (aging) is demonstrated. Sands belonging to 9 beaches in the province of Alicante (Spain) were tested and studied, with different sample quantities (60, 75, 100, 120 and 150 g), the granulometry, calcimetry and wear (using the accelerated particle wear test, APW). The results showed that (generally) the greater the amount of sample used (activation layer), the greater the mass loss (reduction to size <0.063 mm) during the first cycle of the wear test. This may be due to the fact that the greater the amount of material in suspension (as a consequence of greater energy for the same volume of water), the greater the possibility of collision between particles, and therefore, greater particle wear and greater erosion on the beach. In addition, when the same material was subjected to new wear test cycles, that is, without the addition of new material (as is currently happening on the coasts), the durability of the same was compromised up to its wear limit. Particle wear reduces the median sediment size, which encourages movement towards the off-shore zone. Therefore, the wave energy, the material durability and the median sand diameter are elements to be taken into account in a beach nourishment.

Wave farm impacts on coastal flooding under sea-level rise: A case study in southern Spain

Coastal flooding, already an acute problem in many parts of the world, will be exacerbated in the near future by the sea level rise induced by climate change. The influence of wave farms, i.e., arrays of wave energy converters, on coastal processes, in particular sediment transport patterns, has been analysed in recent works; however, their influence on coastal flooding has not been addressed so far. The objective of this work is to investigate whether a wave farm can provide some protection from flooding on the coast in its lee through a case study: a gravel-dominated beach in southern Spain (Playa Granada). We consider three sea-level rise (SLR) scenarios: the present situation (SLR0), an optimistic projection (SLR1) and a pessimistic projection (SLR2). Two state-of-the-art numerical models, SWAN and XBeach-G, are applied to determine the wave propagation patterns, total run-up and flooded dry beach area. The results indicate that the absorption of wave power by the wave farm affects wave propagation in its lee and, in particular, wave heights, with alongshore-averaged reductions in breaking wave heights about 10% (25%) under westerly (easterly) storms. These lower significant wave heights, in turn, result in alongshore-averaged run-up reductions for the three scenarios, which decreases with increasing SLR values from 5.9% (6.8%) to 1.5% (5.1%) for western (eastern) storms. Importantly, the dry beach area flooded under westerly (easterly) storms is also reduced by 5.7% (3.2%), 3.3% (4.9%) and 1.99% (4.5%) in scenarios SLR0, SLR1 and SLR2, respectively. These findings prove that a wave farm can actually reduce coastal flooding on its leeward coast.

Dual wave farms and coastline dynamics: The role of inter-device spacing

In dual wave farms, i.e., arrays of wave energy converters (WECs) with a dual function - generation of renewable power and mitigation of coastal erosion - the spacing between the WECs is a fundamental design parameter. The present research has the objective of establishing how this parameter affects the shoreline evolution behind the array and, on this basis, to propose and apply a method to determine the optimum spacing for coastal protection. The method is demonstrated on a beach subjected to severe erosion. Five case studies are considered: four with different inter-WEC spacings, and one without the wave farm (baseline). A spectral wave propagation model is applied to analyse the variations in significant wave height behind the WEC array. Longshore sediment transport rates are calculated, and a shoreline model is applied. We find that in all the case studies the dry beach area is greater than in the baseline (no farm) case study, which proves the capacity of the dual WEC array to mitigate the erosive trends of the system. Importantly, we obtain that the inter-WEC spacing plays a fundamental role in the evolution of the shoreline and, consequently, in the effectiveness of the WEC array for coastal protection. The case studies with intermediate spacings yield the best performance in terms of dry beach area. More generally, the benefits of dual wave farms in terms of protection of coastal properties and infrastructure, and the ensuing savings in conventional coastal defence measures (coastal structures, beach nourishment, etc.) contribute to the development of wave energy by enhancing its economic viability. The methodology presented in this paper can be used to optimize the design of dual wave farms elsewhere.

Wave farm effects on the coast: The alongshore position

For wave energy to become a fully-fledged renewable and thus contribute to the much-needed decarbonisation of the energy mix, the effects of wave farms (arrays of wave energy converters) on coastal systems must be addressed. The objective of this work is to investigate the effects of wave farms on the longshore sediment transport and shoreline evolution of a gravel-dominated beach and, in particular, its sensitivity to the longshore position of the farm based on eight scenarios. Nearshore wave propagation patterns are computed by means of a spectral wave propagation model (SWAN), variations in sediment transport rates induced by the farm are calculated, and a one-line model is applied to determine the shoreline position and dry beach area. The significant wave height at breaking is reduced in the lee of the wave farm, dampening sediment transport. We find that changes in the dry beach area induced by the wave farm are highly sensitive to its alongshore position, and may result in: (i) erosion relative to the baseline scenario (without wave farm) in three of the eight scenarios, (ii) accretion in three other scenarios, and (iii) negligible effects in the remaining two. These results prove that the alongshore position of the wave farm controls the response of the beach to the extent that it may shift from accretionary to erosionary, and provide evidence of its effectiveness in countering erosion if appropriately positioned. This effectiveness opens up the possibility of using wave farms not only to generate carbon-free energy but also to manage coastal erosion, thus strengthening the case for the development of wave energy.

Mineralogy and morphology of sand: Key parameters in the durability for its use in artificial beach nourishment

Sand is the third most consumed material in the world, although it is a very scarce material. An exhaustive knowledge of sand and its behaviour against the waves is important for selecting the most suitable material to avoid shoreline erosion. To this end, a pattern of behaviour against accelerated wear test has been sought for 26 sand samples with different characteristics and origins (natural, dredged and quarried), with a focus on their mineralogy as well as a comparison of beach evolution carried out by other authors. Several techniques have been applied for characterization: granulometry, calcimetry, XRD and SEM. The results show that the different degrees of sand grain wear are not only due to their size and mineralogy, but also to the morphology of the particles.

Protection of gravel-dominated coasts through wave farms: Layout and shoreline evolution

The impacts of wave farms (arrays of wave energy converters, or WECs) on the nearshore must be fully understood for wave technology to develop and thus contribute to a sustainable, carbon-free energy mix in the near future. The objective of this work is to investigate the role played by the farm layout on the wave propagation patterns leewards and the implications for longshore sediment transport (LST) and shoreline evolution on a gravel-dominated deltaic coast. Changes in wave propagation in four scenarios, corresponding to as many wave farm layouts, are computed by means of a spectral numerical model (Delft3D-WAVE) under (i) low-energy and storm conditions, and (ii) westerly and easterly waves - the two prevailing wave directions. On this basis, sediment transport rates are computed and changes in the shoreline position assessed using a one-line model. To quantify the impact of the wave farm on the nearshore wave conditions, sediment transport and shoreline, we define three ad hoc indicators: the non-dimensional wave height reduction, the non-dimensional LST rate reduction and the non-dimensional shoreline advance. Significant wave heights decrease in the lee of the wave farm, with the consequent reduction in LST rates. As a result, the dry beach area increases in every scenario under both westerly and easterly waves. We find that case studies with the WECs arranged on fewer rows but covering a greater stretch of coastline provide better coastal protection. These results confirm that wave farms can be used not only to generate carbon-free energy but also to protect gravel-dominated coasts.

Causes of the different behaviour of the shoreline on beaches with similar characteristics. Study case of the San Juan and Guardamar del Segura beaches, Spain

Storms can alter the beach shape, relocating large volumes of sediments and generating drastic changes in the coastline. In the last 60years, beaches shoreline behaviour has been different even though the energy of the waves was similar. Therefore, it is necessary to understand the factors that affect the sandy coasts for better future management. In this research, two beaches, with different erosion rate, located in the southeast of Spain (separated by only 40km of distance) have been studied. The beaches: i) have similar orientations, ii) are open to waves with similar sand lengths of 9.8km and 6.6km, and iii) have similar median sediment size (D₅₀). For its study, shoreline evolution has been analysed from 1956 to 2017. From the results obtained, it can be seen that: i) Between 1992 and 2017, San Juan just lost 3% of its surface, while in the previous period (1956-1990) it was 50%, and ii) Guardamar surface lost in 1992-2017 was 18%, and in the previous period it was 14%. For the analysis of the agents involved in both beaches, cross-shore profiles (volume), marine climate, biocenosis and sedimentology studies were carried out. The results showed that the energy on both beaches was very similar. The biocenosis had not changed and, however, the morphology of Guardamar seabed had increased to 1m deep in some places, which had caused part of the beach berm erosion. Furthermore, important differences were found from the sedimentological study, concluding that the content of calcites and the degree of homogeneity of the particles are the real factors that caused these two beaches to behave differently against erosion.

Study of the evolution of gravel beaches nourished with sand

Coastal erosion is a worldwide problem, so accurate knowledge of the factors involved in the shoreline evolution is of great importance. This study analysed three gravel beaches that were nourished with sand from the same source. However, the evolution of their shoreline was different in each case. For its analysis, different factors were studied such as the shoreline and cross-shore profile evolution, the maritime climate, sedimentology and mineralogy. From the results, it should be noted that Centro beach is the most stable with a loss of surface after the first regeneration of 12.8%, while Carrer de mar is the most instable with a loss of 20.9%. The Posidonia oceanica meadow is one of the factors that make Centro beach the most stable despite being the one that receives the most wave energy. Another factor is its mineralogy and more specifically the composition of the particles that form the sample. Thus, it is observed how the cracking or the formation of particles by different minerals with a fragile union, are factors that make the beaches behave differently against erosion. For this reason, it is concluded that in order for the shoreline to be as stable as possible over time, a previous study of the sediment to be used for nourishment is necessary, as well as its possible effect on the ecosystem, since the future shoreline evolution will depend on it.

The effects of the anthropic actions on the sandy beaches of Guardamar del Segura, Spain

There are many activities and uses in the coastal environment, which has historically attracted the humans. This attraction has led to many anthropic actions that have generated imbalances, more important as the human pressure increases. This research focuses on the effects of these pressures along of 11km of the coastline of Guardamar del Segura, a high-value environmental area where is the Segura River mouth and one of the last dune systems of the southeast of Spain. The historic evolution of the shoreline position has been analysed using 60years of aerial images from 1950s to 2014, the seabed depth changes, the maritime climate, the distribution of the sediment grain size and the anthropic actions such as urban development or the channelling of the river. All data were integrated and processed using a Geographic Information System (GIS). The results show that the lack of sediment supply by Segura River and the cut-off in the longshore transport due to the breakwaters and others anthropic actions has led into an increase in the beaches erosion rates, with a loss of >3.2millionm³ of sand in the last 58years (≈55,200m³/year). The conclusions of this research could be useful to the coastal managers at the moment of making the decisions of action and/or conservation on a coastal system to achieve positive results in the medium and long term.

The erosion on the east coast of Spain: Wear of particles, mineral composition, carbonates and Posidonia oceanica

Erosion on sand beaches is a problem worldwide, which together with the shortage of sand justifies the great importance of understanding the processes involved in the regression of the shoreline in order to know and adopt solutions. This study analysed the influence of sediment wear on beaches regression. For this, nine morphological units on Castellón-Valencia and nine on Alicante were analysed. The results of the granulometric and mineralogical analysis and carbonate content, showed that sediments due to different mechanisms of erosion, were worn along the shoreline. This erosion was corroborated by wear obtained in the study of white and blue quartz, where the level of rolling and the particle size were observed. Given the presence of Posidonia oceanica in much of the study area, the mineralogical composition was analysed according to the presence of this seagrass, and it was observed that the closer it gets to the coast the higher the carbonate content. This is an important fact because the increase of CO₂ in the atmosphere has increased the capacity of dilution of carbonates by the seawater. All this leads to the conclusion that different wear mechanisms have caused a decrease in the size of sediments, favouring both longitudinal and transverse transport with the consequent movement of the shoreline. The transverse movement increases as the particles size decrease, and when the particles exceed the depth of closure, they do not return to the shoreline, which faces the direct consequence of the backward movement of the coastline.

The erosion of the beaches on the coast of Alicante: Study of the mechanisms of weathering by accelerated laboratory tests

One of the main problems that coasts around the world present, is the regression and erosion of beaches. However, the factors involved in these processes are unclear. In this study, the influence of sediment erosion on beach regression has been analysed. In order to do that, a three-step investigation has been carried out. Firstly, coastline variations of four Spanish beaches have been analysed. Secondly, a study on sediment position along the beach profile has been developed. Finally, the process that beach sediments undergo along the surf zone when they are hit by the incident waves has been simulated by an accelerated particle weathering test. Samples of sand and shells were subjected to this accelerated particle weathering test. Results were supplemented with those from carbonate content test, XRD, SEM and granulometric analysis. Results shows a cross-shore classification of sediments along the beach profile in which finer particles move beyond offshore limit. Besides, it was observed that sediment erosion process is divided into three sages: i) particles wear due to crashes ii) dissolution of the carbonate fraction, and iii) breakage and separation of mineral and carbonate parts of particles. All these processes lead to a reduction of particle size. The mechanism responsible of beach erosion would consist of multiples and continuous particle location exchanges along the beach profile as a consequence of grain-size decrease due to erosion.

Spatial response surface modelling in the presence of data paucity for the evaluation of potential human health risk due to the contamination of potable water resources

Potential human health risk from waterborne diseases arising from unsatisfactory performance of on-site wastewater treatment systems is driven by landscape factors such as topography, soil characteristics, depth to water table, drainage characteristics and the presence of surface water bodies. These factors are present as random variables which are spatially distributed across a region. A methodological framework is presented that can be applied to model and evaluate the influence of various factors on waterborne disease potential. This framework is informed by spatial data and expert knowledge. For prediction at unsampled sites, interpolation methods were used to derive a spatially smoothed surface of disease potential which takes into account the uncertainty due to spatial variation at any pre-determined level of significance. This surface was constructed by accounting for the influence of multiple variables which appear to contribute to disease potential. The framework developed in this work strengthens the understanding of the characteristics of disease potential and provides predictions of this potential across a region. The study outcomes presented constitutes an innovative approach to environmental monitoring and management in the face of data paucity.

The influence of anthropic actions on the evolution of an urban beach: Case study of Marineta Cassiana beach, Spain

Coastal areas have been historically characterized as being a source of wealth. Nowadays, beaches have become more relevant as a place for rest and leisure. This had led to a very high population pressure due to rapid urbanisation processes. The impacts associated with coastal tourism, demand the development of anthropic actions to protect the shoreline. This paper has studied the impacts of these actions on the Marineta Cassiana beach, in Denia, Spain. This particular Mediterranean beach has traditionally suffered a major shoreline regression, and the beach nourishments carried out in the 1980s would not have achieved the reliability desired. This research has analysed the historic evolution of the beach and its environment for a period of 65years (1950-2015). A Geographic Information System (GIS) has been used to integrate and perform a spatial analysis of urban development, soil erosion, stream flow, swell, longshore transport, submerged vegetation species and shoreline evolution. The results show how the anthropic actions have affected the shoreline. After the excessive urban development of the catchments, there is no natural sediment supply to the beach. The change in the typology of the sediment, from pebbles to sand, during the beach nourishments has led to a crucial imbalance in the studied area. Moreover, the beach area gained has disappeared, affecting the Posidonia oceanica meadow, and incrementing the erosion rates. The findings obtained are relevant, not only in the management and maintenance of the beaches, but also, in the decision-making for future nourishments.

The multifunctional artificial reef and its role in the defence of the Mediterranean coast

Multifunctional artificial reefs (MFAR) are being implemented around the world, due to their ability to provide an environment where a sports-economic-recreational use and environmental improvement is implemented, and are also elements of coastal defence. However, a lot of failures have been recorded, possibly due to disregarded local factors in the formulations used, and there is no method that has encompassed all these factors, in order to take them into account in its design. The aim of this paper was to provide the coastal engineer with a method that would be used for the design of such reefs. To do this, the Babilonia beach of Guardamar del Segura, Alicante (Spain), was chosen because it is a fully anthropised area (with houses in the Maritime-Terrestrial Public Domain, marina, channelling and river mouth) with continuous regression, in which all the elements considered in this study, were treated. Based on the performance obtained in studies and projects worldwide, the climatic characteristics, biocenosis, sediment transport, settlements and liquefaction and the evolution of the coastline, were analysed. The multidisciplinary study carried out showed that with the implementation of a MFAR, the problem was reversed. Furthermore, the area was provided with a playful-economic use, and could be used 60% of the time, by surfers whose skill level were low to intermediate, without forgetting that the diversity of the marine ecosystem in the area was increased.