Cuadernos de Investigación Geográfica

The complexity of studying coasts: From forms and processes to management

2022-07-14T10:57:26+02:00

Coastal environments are characterized by their high dynamism, related to the interaction between marine agents (winds, waves, currents, sea level changes) and continental forms and processes. The present article summarizes the main morphodynamic characteristics of coasts and the resulting environments. Different oscillations of the sea level are considered, depending on their amplitude and frequency: rapid eustatic fluctuations, energetic tsunamis, storm waves and surges, tides and good weather wind waves. Coastal environments are classified in low, sedimentary coasts, including beaches, dunes, barrier islands, lagoons, salt marshes and river mouths, and high, rocky coasts. Management of coastal zones needs a deep knowledge of all the processes involved at the littoral, especially at the local scale, since coastal processes vary rapidly alongshore. At present the integrated coastal management intends to involve different socioeconomic sectors interested in the occupation and use of coasts. Coastal management must include the adaptation of human activities to the natural processes and associated coastal hazards and the protection of coastal values, both of natural and historical-cultural character. Public administrations at different levels should consider the knowledge of the coastal processes at different scales and their potential interaction with human activities in order to design laws and regulations accordingly.

Response of natural, modified and artificial sandy beaches to sea-level rise

2022-07-14T10:57:27+02:00

Sandy beaches occur in a wide variety of environmental settings and as components of a diverse range of coastal system types. These variations among beaches lead to significant differences in their mesoscale (multi-decadal, km length scale) behaviour, including their response to sea-level rise. In addition to this natural variability, the degree to which the sandy beach system has been or will be modified by humans is a major influence on how it responds to sea-level change. From a spectrum of beach types based on the degree of human modification, three situations (Natural, Modified and Artificial beaches) are considered in order to demonstrate the role of humans as geomorphic agents as sandy beaches respond to rising sea level. The potential trajectories of change are assessed, and future scenarios are presented and discussed. Natural beaches are most likely to survive sea-level rise, while the fate of artificial beaches depends almost entirely on the politics and economics of what lies immediately landward. In all categories of beach, human decision-making is the most important determinant of sandy beach response to sea-level rise.

Methodological proposal for the characterization and typification of the Spanish coasts. Application to the coast of Galicia

2022-07-14T10:57:27+02:00

There are several coastal classifications. Most of them have been elaborated worldwide using tectonic, climatic, topographic, or oceanographic criteria. Other classifications have been generated on a larger scale and focused on classifying the coastal forms, as cliffs, beaches, estuaries, lagoons, or dune complexes in different places.

This project analyzes the types of coastlines, understanding as such each sector that presents certain topographic conditions marked by the elevation and slope, and that was modeled on a concrete type of rock in a specific climatic and marine environment. This paper describes a methodological approach for a detailed scale classification. This approach based on the delimitation of the different coastal systems, exemplified in cliffs and boulder beaches, sandy beaches, and dunes. In this case the shore platforms, marshes and lagoons have not been considered for the technical problems derived from the LiDAR data source, from which the 2 m spatial resolution digital terrain models (DTM) are derived.

The first step in the classification was a manual delimitation combining DTMs and orthophotographs. Subsequently, other typification has been carried out through the automatic creation of Coastal Topographic Units (CTU). This index is the combination of two variables: coastal elevation and slope. The possible integration of others, such as orientation or lithology, is possible, but generate a very high number of units and make it difficult to interpret. For this reason, this study did not consider more variables.

In this project 30 CTUs was generated, and then selecting only those that appear in the cliffs, boulder beaches, sandy beaches, and coastal dunes sectors. The possibility of viewing one or several CTUs in any sector of the coast allows to know more accurately the conditions of each sector and these categories could be improve the coastal management plans.

Historical morphological changes (1956-2017) and future trends at the mouth of the Ebro River delta (NE Spain)

2022-07-14T10:57:28+02:00

The present work focuses on the recent morphological changes recorded in the Ebro River delta, by using aerial photographs in the last six decades and by analyzing changes in the main constitutive features through geomorphological maps. Geomorphological maps of the years 1956 and 2017 are here presented. The results obtained give very valuable clues about the recent trends of the river delta mouth, which can be used to predict future coastal changes to be expected in the following decades. In this sense, by analysing changes in the surface by means of the geomorphological maps together with a shoreline analysis, a differential behavior has been described at both sides of the river mouth: the left side, El Garxal wetland, shows an accretionary trend with rates reaching +40 m/year, while the right side, San Antonio Island, shows erosive trends of more than -20 m/year. This last side also presents a surface reduction of more than 50 ha in the last 60 years. These results suggest that, approximately by the year 2050, the emerged San Antonio Island may disappear if shoreline retreat trends are maintained, making El Garxal exposed to easterly storms, the main erosive dynamic processes in this zone and, therefore changing the entire configuration of the Ebro River delta mouth in the upcoming years. Despite possible solutions have been described in recent works, they may not contribute to a total recovery of the most natural part of the Ebro Delta. Urgent management plans are required to attempting to slow or reverse these trends, otherwise one of the most valuable ecosystems of the delta could disappear.

Analysis of the morphological changes of the beaches along the segment València - Cullera (E Spain) from satellite-derived shorelines

2022-07-14T10:57:29+02:00

Beaches are spaces of paramount importance for coastal societies currently threatened by coastal erosion. Their preservation requires accurate quantification of their changes in order to understand their behavior and to propose efficient solutions. Landsat 8 and Sentinel 2 mid-resolution satellites offer free-of-charge images with great potential for coastal monitoring. From them, it is possible to automatically extract the shoreline position as a quantitative indicator of the beach morphology over large territories and with high temporal frequency.

Beach changes take place at different spatial and temporal scales, typically responding to coastal storms and human interventions on the coast. The collection of large packages of satellite-derived shorelines (SDS) at the coastal sector València-Cullera (W Mediterranean) covering the period 2013-2020 makes it possible to characterize the state of its beaches and their width changes over space and time.

Results reveal a widespread erosional trend, most likely caused by a shortage of sediment in the coastal system. Thus, the majority of the beaches are not capable of restoring their previous conditions after storm-driven retreats. The information provided by the SDS also shows the ineffectiveness of the nourishment actions, at least in the way they have been carried out, and the urgent need for a strategy to address the erosion problem.

Characterization and evolution of the beach-dune system of the Mediterranean coast of Andalusia (Spain): influence of natural and anthropic processes

2022-07-18T06:09:26+02:00

In past decades coastal, erosion related impacts on the world’s shorelines have been significantly growing due to ongoing coastal development and tourist occupation as well as to natural erosion/flooding events exacerbated by climatic change. Ocean coastlines are highly dynamic and changing environments since they show great temporal and spatial variability in response to the action of different and complex coastal processes: at an inter-annual time scales, related to seasonal wave climate variations due to temporal and spatial distributions of high latitude storms and tropical storms/hurricanes, or as a result of events with a large return period, such as the impact of very energetic storms and tsunamis, sea level rise, and variations in rivers’ sediment supplies. In order to prevent and reduce such impacts, coastal managers need to know the sensitivity of natural coastal sectors, which is related to wave energy, beach characteristics/evolution, and sea level trend as well as the potential vulnerability and economic value of the urbanized sectors.

This paper shows coastal evolution and the impacts on it of coastal structures and the characterization and evolution of dune systems along the Mediterranean coast of Andalusia (Spain). For this purpose, an amount of 47 units were defined along the studied coast, and evolution rates (erosion/accretion/stability), for the period 1956-2016, quantified by using the DSAS extension of ArcGIS software. As a result, 9 units recorded accretion, 19 erosion and 19 stability and, concerning the beach surface balance, 17 units presented a positive balance and 28 a negative one and a net balance of -29,738.4 m²/yr. The analysis of coastal evolution evidenced the impact of hard structures: accretion was essentially observed up-drift of ports and groins and in correspondence of breakwaters; erosion was observed down-drift of ports and groins and in correspondence of seawalls and revetments, and at largest river deltas; and stability was observed at pocket beaches and coastal areas locally stabilized by protection structures and nourishment works. These results were used to determine the distribution of swash- and drift-aligned coastal sectors and main direction of sediment transport.

Concerning the characterization and evolution of dune systems, they were mapped different type dunes’ systems as well as dune toe position and fragmentation, and human occupation and evolution from 1977 to 2001 and from 2001 to 2016. In total, they were delimited 53 dune systems along the Mediterranean coast of Andalusia, differentiating three types: Embryo and mobile dunes, grass-fixed dunes and stabilized dunes. It was observed a general decrease in dunes’ surfaces in the 1977-2001 period (-7.5 x 106 m²), linked to the increase of anthropic occupation (+2.3 x 106 m²), and dunes’ fragmentation, especially in Málaga and Almería provinces. During the 2001-2016 period, smaller changes in the level of fragmentation and in dunes’ surfaces were observed. An increase of dunes’ surfaces was only observed on stable or accreting beaches (4 out of 53 dune systems), both in natural and anthropic areas (usually up-drift of ports).

Evolution of the beach-dune systems in the Balearic Islands from their geomorphological management (2000-2021)

2022-07-14T10:57:32+02:00

In order to restore, maintain and protect the beach-dune systems of the Balearic Islands different management techniques have been applied. They have been based on the artificial emulation of natural processes to favour the recovery of the system, on the installation of elements that prevent the frequenting and on trampling of the dune systems. Some techniques are positive while others have aggravated erosive processes due to a lack of geomorphological criteria. This work analyses good and bad practices on beach-dune systems of the Balearic Islands between 2000-2021.

Management of coastal dunes on the Catalan and on the Valencian shorelines (Spain)

2022-07-15T12:39:45+02:00

Coastal areas constitute one of the most difficult domains to manage, due to the several human activities and natural processes concentrated in it. The case of the coastal dunes is special, since they are so fragile and any intervention on them can cause alterations in the landforms and dynamics. This work assesses the level and role of management and the morphological status of coastal dunes on the Catalan and Valencian shorelines. To that end, ten beach-dune systems from Catalan and Valencian shorelines have been studied to guess how management actions determine the morphological status of them. A set of variables, comprising management actions and morphological status, have been selected and analyzed through a Hierarchical Clustering on Principal Components (HCPC). Results show that the beach-dune systems can be gathered in 2 main groups: those where sustainable management measures were not applied and present an advanced erosive state, and the ones where sustainable management measures were applied and present a good state of conservation. The good state of conservation is related to restoring dunes applying nature-based solutions, whereas degraded morphologies appear when artificial management actions have been carried out.