The Spanish Coastal Systems

The coastline of Galicia is more than 2100 km long (POL Galicia 2010) (Fig. 2.1). Two broad types of coast can be differentiated in the region: zones with rías and zones without rías. Marine inlets dominate in the former, whereas rectilinear stretches dominate in the latter and only small coves or estuaries occur. The megaforms of coastal relief in northwest Spain are clearly determined by the tectonic structure, whereas lithological differentiation has played a predominant role in the genesis of meso and microforms (Pérez-Alberti and Blanco-Chao 2005). In general, different factors are involved in shaping the coastline: the overall structure is determined by tectonic processes; the lithology causes differential erosional processes that define the broad features of the coastal front; and, finally, the succession of geomorphological processes that have taken place over time have determined the specific forms and distribution of the different environments. In addition, human activity has affected many areas, particularly the low-lying coastline.

The Principality of Asturias (or simply Asturias) is a region located in the North of Spain (SW of Europe) limited by the Cantabrian Sea in the North and the Castilla y León, Cantabria and Galicia regions in the South, East and West respectively. The Asturias Coast represents around 30% of the Cantabrian Coast, the northern limit of the Iberian Peninsula, and is surrounded by the Cantabrian Sea. This sea represents the transition of the Atlantic Ocean to the Biscay Gulf, between Spain and France. Towards the South, the Cantabrian Coast is limited by the Cantabrian Mountains, up to 2,648 m altitude, which axis is located only at 20–50 km from the sea.

The Cantabrian Coast is located in the Spanish north littoral, in the southeastern sector of the Bay of Biscay (Cantabrian Sea), conforming the northern border of the Regions of Cantabria and Basque Country, the latter matching Biscay and Guipúzcoa provinces (Fig. 4.1). This coastal strip has an obvious strategic and economic interest and concentrates a variety of activities (urban and industrial development, fishing, tourism, commerce, etc.). This has led to a very intense transformation of coastal areas, particularly during the last decades.

Rocky coasts, widely present along the world shorelines, have been studied from different points of view. Some sectors of rocky coast at Catalonia has been mapped and described by several authors along time. This paper includes a revision of those studies and analyzes some topographical data in order to obtain a global geomorphological characterization of rocky coast including also its relation with other environmental factors such as waves, precipitations and lithology. Remarkable differences between North and South regions have been reported. Moreover, because of the importance of rock fall events as a process affecting this areas, one example of susceptibility analysis to rock fall at Tarragona coast has been presented.

Balearic Islands are located in the centre of Western Mediterranean and is composed by five major islands (from biggest to smallest): Mallorca, Menorca, Ibiza, Formentera and Archipelago of Cabrera. Mallorca located at the centre of archipelago has an extension of 3,636 km2, Menorca, located at the Northeast, has an extension of 695 km2, Ibiza and Formentera, called Pitiuses Islands and located at the South, has an extension of 572 and 82 km2 respectively. Mallorca is the island which have a higher coastal length with 842 km (including Archipelago of Cabrera), Menorca follows with 433 km, Ibiza has 334 km and Formentera 115 km. These coasts, and specially the rocky shores, are the result of the geological and geomorphological characteristics and modelling processes, as fluvial, karst, bioerosion and mass movements, between others conditioned by maritime climate which have configured the structural units of each island. According to general results for the entire archipelago, the percentage between rocky coasts or coasts formed by cohesive materials and beach coasts or coasts formed by non-cohesive materials is 80–20.

Carbonate rocks are omnipresent in the case of the Balearic archipelago. This fact, together with an appropriate climatology, implies that karstic processes are the main responsible for the landscape development as well as the littoral shaping. The special geomorphological and hydrologic conditions of this area, along with sea-level, ecology, or paleoclimate, provokes a littoral complex interaction that give rise to a characteristic coastline. The objective of the present paper deals with the brief description of all related aspects of the endokarstic processes that affect the littoral fringe and summarizing their effects in the morphologic development of the coastline.

The Canary geographic area, an archipelago of 7,447 km2, consists of seven islands, four islets and several seamounts on the eastern edge of the Mid Atlantic (27°–30°N and 13°–16°W), and has a coastal morphology with its own features. This is result of the interference between eruptive activity and marine dynamics. In the Canary Islands, as in Hawaii, the Azores, Madeira and many other oceanic areas of active volcanism, the persistence of eruptive manifestations increases the coastal front. The arrival of lava flows to the sea and the location of emission centers in the sea or its immediate vicinity counteract the retreat of the coastline caused by erosion.

The coast of Galicia corresponds to the NW end of the Iberian Penninsula and extends from the estuary of the Eo River, in the north, to the mouth of the Miño River in the border with Portugal. This coast has distinctive characteristics compared with the rest of the Atlantic Iberian coasts given the importance of geological and structural controls that define the deeply indented coastline. Although is a coast exposed to a energetic storm and swell wave regime, at different scales there are great variations in the orientation of the coastline that causes a high variability in the exposition and the energetic regime.

The main factors that determined the Valencian beaches characteristics are the configuration of relief structures; fluvial sediment supply; low tidal range; the predominance of low energy waves; scarcity of big storms; longshore littoral drift; and human action. There is a significant prevalence of sandy beaches. Nevertheless, both at the northern part of the Gulf of Valencia and in the structural segment, between the Cape Sant Antoni and Alicante city, pebble and gravel beaches are predominant. Most of the Valencian beaches have experienced significant morphological changes during the last decades due to the human interventions -voluntary or involuntary- in the coastal system. The implementation of artificial barriers to longitudinal transport (ports, jetties, groins, etc.) has caused updrift sedimentary accumulations and downdrift accelerated beach erosion, as usual. The urban occupation (especially by the construction of promenades, usually on top of the dunes) destroyed the precarious transversal beach equilibrium. On the other hand, artificial sand nourishments have altered the original texture of many beach segments and punctually modified the previous landscape morphology. In addition, the substantial decrease in new fluvial sediment supply to the coastal system, also by human action, has led to a paradigm shift in the Valencian coasts towards a deficient sedimentary economy that threatens its future sustainability.

On the eastern coast of the Iberian Peninsula—between the Ebro Delta and Cape Palos—the conditions during the Pleistocene, and especially after the Flandrian transgression, favoured the development of beach barrier systems and lagoons along large segments of the coast. The very small tidal range made connections between the sea and lagoons difficult, and this favoured sedimentation processes, which was often accelerated by human activity. Three very different sectors have been differentiated: the Gulf of Valencia, where the largest number of lagoons is found; the cliffed Betic structural sector between Cape Sant Antoni and Cape de les Hortes, in which there are just a few very small lagoons; and the southern sector in which Pleistocene formations occur on the surface or below the current sands. In the Gulf of Valencia there is practically a continuum of Holocene beach barrier-lagoon systems (post-Flandrian) that always start from a Quaternary alluvial structure. The structure and evolution of beach barrier-lagoon systems in this sector reveal the essential role of fluvial sediment supply to the system. The southern sector is formed by systems of a different nature, and in which the recent cumulative processes have played a much less important role, being so much more important the tectonic movements and Quaternary sea level changes. Human action is, in all cases, an essential factor in explaining the current landscapes and development of these ecosystems.

The Balearic Islands coast contains 867 beach systems covering 10% of the coast reflecting the different controls of waves, sediments, geological inheritance and human disturbance. The average length of theses beaches are 169 m, raging from 10 m to more than 5 km, which implies that physical boundaries play a major role in beach length and morphology and wave attenuation; a moderate and seasonal wave climate and sediments composed predominantly of medium to coarse marine biogenic carbonate sands. It also describes the regional distribution, together with the occurrence of wave energy, beach sediments, bar systems and dynamics, rip currents, human disturbance and the influence of geological inheritance and marine biota.

The coast of Malaga is predominantly a low-lying beach and shore platform system exposed to the south and southeast. It is dominated by fluvial sediment input and subject to low energy Mediterranean wave energy conditions. This combined with a microtidal range (average 50 cm) represents the scenario for narrow and relatively steep beaches that are mainly composed by sandy material with sediment sizes of 1.5 mm or more and that are restricted to locations near river mouths and a narrow active nearshore zone.

The coast of Cadiz province (SW Spain) constitutes a complex system with a wide variety of hydrodynamic and geological-geomorphological conditions. Morphodynamic behaviour of beaches in this area shows more dissipative states in the Atlantic coast and more reflective states in the Mediterranean coast. Recent shoreline trends indicate a relatively stable behaviour along most part of Cadiz coast over the last decades, although there are numerous sectors with a clearly erosive trend, mainly in the Northern half of the province. The great spatial and temporal variability of shoreline changes observed is related to the heterogeneity of the coast, as well as to the diversity of factors contributing to erosion processes on each sector. Several coastal hazard hotspots appear along the study zone, mostly related to extreme meteorological events and short-term trends, namely coastal erosion and flooding. The frequency and severity of the risks derived from these hazards have increased over the last decades, mainly due to the increased anthropogenic pressure and urban development on the coast. The coast of Cadiz province (SW Spain) constitutes a complex system with a wide variety of hydrodynamic and geological-geomorphological conditions. Morphodynamic behaviour of beaches in this area shows more dissipative states in the Atlantic coast and more reflective states in the Mediterranean coast. Recent shoreline trends indicate a relatively stable behaviour along most part of Cadiz coast over the last decades, although there are numerous sectors with a clearly erosive trend, mainly in the Northern half of the province. The great spatial and temporal variability of shoreline changes observed is related to the heterogeneity of the coast, as well as to the diversity of factors contributing to erosion processes on each sector. Several coastal hazard hotspots appear along the study zone, mostly related to extreme meteorological events and short-term trends, namely coastal erosion and flooding. The frequency and severity of the risks derived from these hazards have increased over the last decades, mainly due to the increased anthropogenic pressure and urban development on the coast.

The Huelva Coast forms the littoral sector of the SW Iberian Peninsula which extends from the mouth of the Guadiana River, on the border with Portugal, to the mouth of the Guadalquivir River. From a physiographic point of view, the Huelva Coast can be considered a linear, low and sandy coast formed by long beaches, although it could be divided in different sectors according to its topographic configuration and distribution of sedimentary environments.

Canary archipelago is formed by seven main islands and several islets that extends for nearly 500 km across the eastern Atlantic, between latitudes 27°N and 30°N, lying its eastern edge only 100 km from the NW African coast.

The rías on the coast of Galicia make up a series of deep sea inlets along the entire 1720 km long coastline. They are also associated with a complex variety of sedimentary environments, such as bays, intertidal plains, deltas, marshlands, beaches and sand dunes. In plant view, their morphology is cone or funnel-shaped and features two distinct sectors: the first makes up the larger cone, which corresponds to the ría itself, and the second is the smaller cone corresponding to the river channel which discharges into the headwaters. Rías can be classified as drowned river valleys that were flooded by seawater after the last transgression, with rivers at their headwaters, all of which bring about conditions more typically seen in estuaries. Unlike in estuaries, wave action in rías constitutes one of the main processes that control the dynamics of the greater part of this environment. On the contrary, in estuaries, forcing mechanisms are fluvial discharge at the head and daily variations in sea level at the mouth. These differences are what bring about a different distribution of sediments on the bottoms. Over one complete sea-level cycle (sea-level fall to subsequent highstand) two main sedimentary sequences can be differentiated: the ría central basin and the estuarine zone.

Asturias and Cantabria are two Spanish regions (southern Bay of Biscay, NW Iberian Peninsula) with a W-E cliff coast along 422 km. It contains more than 50 estuaries with different features and stages of evolution, including the Rías in Galicia. They have very varied sizes and lengths (Fig. 18.1) as well as sediment types; they are linked to short rivers and, in general, high and low waters allow during high spring tides that mixing waters achieve variable lengths of 5–15 km. This study is focused to join the different studies about Asturias and Cantabria estuaries from the point of view of morphodynamic and sedimentation behavior. Fortunately, in these regions, there are many examples with particular features that can understand the evolution of these sensitive systems to any natural or anthropogenic changes.

The Basque estuaries represent drowned river valleys that were firstly flooded by the sea due to a climate-change-induced sea-level rise 8500 yr ago, and subsequently, infilled with a general shallowing sequence. Basque estuaries developed from an initial fluvial environment followed by a firstly marine and secondly brackish depositional system.During more than 25 years, different boreholes and cores have been drilled and studied along the Basque estuaries by the Harea-Coastal Geology research group of the University of the Basque Country UPV/EHU. In fact, the study of the microfossil content of the Basque estuaries, together with other sedimentological, geochemical or archaeological approaches, has become the main source of geological information in order to reconstruct their Holocene and Anthropocene development and the main drivers behind their environmental evolution. However, much additional knowledge about these variable coastal environments should be gathered in the next years and decades using a multidisciplinary geological approach.

The delta of the Ebro River is located on the Spain Mediterranean coast, in Tarragona province, about 170 km southwest of Barcelona (Fig. 20.1). It is one of the largest deltas of the Mediterranean, began to develop when the last post-glacial eustatic sea level rise was attained (Maldonado in El delta del Ebro: estudio sedimentológico y estratigráfico, 1972). The present extension for the emerged area is 325 km2 and represents only 15% of 2,171 km2 of the whole delta.

The Valencian coastal plains are formed at the end of two important mountain systems: the Iberian Mountain Range to the north and the Baetic Mountains to the south. As a result of tectonic and neotectonic activity, several graben have been formed at the foot of these reliefs, which have been filled with Plio-Quaternary deposits. In all the coastal plains a depositional sequence is repeated in which the river deposits -fan deltas and alluvial plains- alternate with lagoons/marshes. Basin dimensions, sediment input, tectonics and neotectonics in the study area all determine the size, style and characteristics of fluvial forms, which in turn, influence the characteristics of the coast. Ephemeral rivers form prograding fan deltas when there is little subsidence or tectonic stability dominates. Aggrading fan deltas appear when subsidence predominates. The former make the coast protrude, while the latter are associated with straight coasts. On the other hand, due to the runoff scarcity, ephemeral streams provide fewer sediment inputs to the coastal system than perennial rivers. In addition, during flooding, both ephemeral and perennial rivers provide water and sediment to the lagoons, which are filled and transformed into marshes.

The estuary of the Guadalquivir River is the largest in the Gulf of Cadiz, covering an area of some 185,000 ha. From a geological standpoint, the estuary represents the culmination of the marine filling of the Cenozoic Guadalquivir Basin. The present-day configuration of the estuary is the result of the post-glacial transgression of the Atlantic Ocean, starting ca. 15,000 years, that developed during the latest Pleistocene-Holocene up until some 5,500 years ago, when the level of the sea stabilised. The lower Guadalquivir valley was transformed into a wide estuary as the interfluves turned into pronounced headlands. Marine and fluvial dynamics, dependent upon climate and tectonics, thus shaped the present landscape, which features extensive dune systems, marshes and spits, as well as erosion of the headlands (cliff formation).

The estuary of the Odiel and Tinto rivers is located in the southwest of the Iberian Peninsula on the western Gulf of Cadiz (Atlantic Ocean). The Huelva estuary is constituted by the common mouth of the Odiel and Tinto Rivers in a “Y” shape oriented in a N-S direction across 35 km long incised valley. This estuary was generated after the Flandrian Transgression (Holocene), which signified the marine inundation of the main fluvial valleys incised by the rivers during the last Pleistocene lowstand. It extends along the south-western coastal margin of the Guadalquivir sedimentary basin that was incised on Cenozoic non-consolidated sediments during the late Pleistocene and early Holocene when sea level was located up to 100 m below the present position. This estuary is presently completely filled with sediments and has started to prograde to build a delta. The fluvial basin of both rivers is seriously affected by acid mine drainage, so this estuary have a induces important changes in the chemical characteristics of the water, suspended particulate matter (SPM) and sediments.

The Guadiana Estuary is a good example of rock bounded estuary which consists of a single narrow estuarine channel with a meandering morphology imposed by faults systems affecting the hard geology of the substrate. Only along the last kilometers of the estuarine channel, the valley opens when Cenozoic Guadalquivir Basin formations appear. In this area, the Guadiana develops a prograding coastal system constituted by successive sandy barriers separated by salt marshes which configure a wave dominated delta. This progradation is possible thanks an interaction of the coastal agents which enhanced the silting in addition to a good availability of sediments. This chapter explains an explanation of the dynamic functioning of the open coastal environment, so as the resulting facies model.

Aeolian dune fields are relatively well represented along the cliff coast of Asturias and Cantabria (NW Iberian Peninsula) (Fig. 25.1; Tables 25.1 and 25.2). Siliciclastic sands are supplied by large rivers to their estuaries and coastal upwelling and nutrients from some estuaries contribute with the formation of carbonate sands, but inherited and currently generating bioclastic sands are important in several stretches; easterly winds produce upwelling in this coast and shelf mainly in spring and summer (Lavín et al. in The Sea 14, 24: 933–1001, 2004). Most of the Cantabria and Asturias dune fields were formed since the mid-Holocene (Flandrian transgression) once the sea level fell and the prograding processes seaward were favored. It is essential to know the evolutionary patterns from this early stage to those that have occurred since the middle of the 20th century as a result of man's intervention through dredging of the estuaries to which they belong. All dune fields of Asturias and Cantabria have been suffered a natural recession due sea level rise and the continuous surge event, increasingly more often. Policy, laws and management must go hand in hand for try to preserve in the best possible way this type of habitats of great importance for the coast.

The Ebro Delta is one of the most significant coastal sedimentary formations in Spain, not only for being the largest and most important delta in the country, but also for presenting several active dune fields on it. In addition, other ecosystems such as salt marshes and lagoons contribute to conform a characteristic and unique habitat.

The dunes development needs an excess of sediment supply, wind speed able to transport sand to backshore and low atmospheric humidity. Foredunes, dunes fields and Pleistocene fossil dunes are the most characteristics features of the Valencian coast. Fossil dunes are abundant at the southern part. They are the main supply for the Holocene dunes and formed l’Altet field that survived thanks to be just in front of the L’Altet Airport. The foredunes have been mainly destroyed by human action and only few remains still are active. Guardamar and El Saler dune fields had a quite different evolution. Guardamar evolved covering previous fossil dunes and was fixed with pine trees to avoid the sand precipitation into the town. El Saler was mainly destroyed by human impact, but one small area, completely flattened called La Punta del Perellonet, has been transformed during the last 45 years in a natural laboratory to test how dunes have been able to develop once again in a coastal area having a big problem of sediment supply scarcity.

This chapter examines the origin, evolution and present state of the coastal dunes along the South Atlantic Spanish coast around the Strait of Gibraltar. Wind regime in the zone is strongly affected by the North Atlantic Oscillation (NAO). Low or negative NAO index values give rise to the prevalence of westerly humid winds, while during periods with a positive NAO index easterly, dry winds prevail. Several Holocene and historical aeolian phases have been identified in the zone, represented by different aeolian deposits, many of them containing archaeological remains. The oldest one dates to shortly after the mid-Holocene eustatic maximum. During historical times dune-building episodes were associated with a higher frequency and persistence of easterly winds. During the 20th century, and especially in the last few decades, the prevalence of positive values of the NAO index has favoured the growth and advance of mobile dunes in the vicinity of the Strait of Gibraltar. In contrast, dune ridges associated with westerly winds are much less mobile or stable and form shore-parallel ridges covered by vegetation. In the Atlantic side of the Strait, environmental health of coastal dunes is satisfactory, especially those included in the Strait of Gibraltar Natural Park, where more effective protection measures are applied. The Mediterranean side is characterized by a dense population and intense human interventions, leading to erosion problems. Climate change predictions for the next decades suggest an increase in the frequency and intensity of easterly-Levante winds in the Strait. This situation would favour the reinforcement and growth of the Levante-derived dunes around the Strait, and perhaps recovery of the small dunes existing in the Mediterranean side.

Along the last 50 km of Huelva’s east coast and covering more than 430 km2, the aeolian sand sheet of El Abalario-Doñana constitutes the biggest example of an aeolian complex on the whole coast of Spain. In it different sequences or episodes of aeolian formations can be discerned, extending in time from the Late Glacial/Holocene up to the present (Borja and Díaz del Olmo 1996), encompassing areas of entirely stabilised dunes and others where active dunes prevail, including outstanding examples of mobile dunes.

The aeolian sedimentary systems of the Canary Islands have certain natural and socio-economic characteristics that make them differentiated environments, both in the context of the dune fields of Spain and Europe. This is a consequence of their location in intraplate hot spot volcanic islands, their climatic conditions, the high pressure exerted on them by society and the lack of adequate management measures. The relationship between their elements and the continuous change to which they are exposed make them environments with high complexity and fragility. In recent decades, some research lines have been opened around these systems, based on geomorphological, biogeographic, historical, cultural, landscape and socio-ecological analysis. These new approaches have allowed to expand the knowledge about the diversity and complexity of the processes that occur in these systems, as well as to obtain information regarding their management.

The first data available on the interaction between human beings and the Basque estuaries are situated in the Prehistory, after the last glacial maximum.

The Catalan coast is located in the NE Spanish Mediterranean (Fig. 32.1). It has about 600 km long coastline, with about 270 km of beaches. It has a wide variety of temperate coastal systems comprising considerable geo- and biodiversity which is represented in cliffs, rocky coasts, sandy beaches, coastal plains, estuaries, and river deltas. In spite of this natural richness, it can be considered as a paradigm of the highly developed areas of the Mediterranean coastal zone. Accordingly, one of its main characteristics is its high susceptibility to change/damage due to the accumulation of human-induced pressures.

Coastal dunes represent important natural systems for balancing the beach while providing different functions such as protection against erosion and important ecological niches.

This chapter presents the consequences that the traditional land uses had on the Canary Islands’s coastal areas, the policies and strategies of the coastal management, as well as the problems and conflicts that have arisen. Finally, examples of good practices and search for solutions are provided.

Presently, there is a high degree of knowledge about the coastal dynamics of many segments of the coast. The highlights of the functioning of wind, waves, tides and currents in each one of the sectors composing the Spanish coast have been studied and described. The main geomorphologic and sedimentary features of, so as the depositional or erosional trends or each coastal track are also defined. National, regional and local administrations have in their hands the tools to develop a correct Integrated Coastal Zone Management in each one of these coastal tracks. This is vital in Spain, especially, take into account that a big part of the Spanish economy is based in the tourism of sun and beaches. Nowadays, the present coastline suffers the errors committed by the coastal managers in the past. For that, the present Integrated Coastal Zone Management along the Spanish coasts represent an exciting challenge for the competing administrations, since today the entire Coast is public and protected by laws, but with a big responsibility, because now all the scientific knowledge is available for the coastal managers.