Coastal erosion Spain
Of the 7,870 km of coastline (excluding estuaries), about 50% consists of hard and soft cliffs, which are particularly abundant in the Atlantic area and on the Canary and Balearic Islands. A further 35% of the coast is occupied by beaches and some 17% consists of low-lying areas, particularly abundant in the Mediterranean and essentially linked to the existence of sedimentary basins where rivers have formed coastal plains with deltas. 8% are human transformed areas, mainly located along the Mediterranean coastline (1).
The astronomical tidal range along the Atlantic coast varies from 5.40 m at Santander (on the Cantabric northern coast) to 1.6 m at Tarifa, near the Straits of Gibraltar. Along the Mediterranean coast tidal range varies from 0.2-0.8 m. Tidal range at the Canary Islands is about 2.5 m (1).
A common problem, also in the Spanish Mediterranean, is ‘coastal squeeze’ (2), takes place when a coastline is prevented from its landward migration by seawalls or other man-made structures. Erosive processes due to sediment imbalances or associated with sea level rise and increasing storminess can cause the complete disappearance of the beach or salt marsh.
Decreased sediment loads resulting from sediment trapping behind the more than 170 dams in the Ebro drainage basin along with a strong longshore current have resulted in localized erosion and a general transformation from a prograding condition to a destructive phase of the delta (3,4).
Sandy beaches are identified as one of the most threatened coastal habitats of the Basque coast. Sandy beaches on the Basque coast are expected to suffer shoreline retreats of between 25% and 40% of the average beach width in the 21st century (5).
Along the Basque coast, a study of the impacts of 49 cm sea level rise on the Gipuzkoa estuaries revealed that 6.5% of the surface area of wetlands and salt marshes may be affected (6). Average accretion rate of the Basque marshes should be high enough to be able to adjust to the projected rate of sea level rise (7).
Wetlands and marshes in the Basque estuaries are squeezed between the fixed landward boundary and sea level rise (the so-called ‘coastal squeeze’) and by croplands and pastures that lie within the original upper intertidal zone. In the area, these croplands are protected by walls and drained to be used for agriculture purposes, since they lie below the present maximum astronomic high tide level. Hence, these human activities are vulnerable to the sea level rise expected by 2100, especially when extreme events, such as high tides and river floods, occur simultaneously. Likewise, if agriculture activity continues to decline, as throughout the 20th century, these areas may be abandoned and may be susceptible to recolonisation by marsh communities (8). On the basis of these latter socio-economic and climate change scenarios, salt marshes and wetlands might increase, as predicted for other areas (9).
For two micro-tidal sandy beaches located in Mallorca (Balearic Islands, western Mediterranean Sea) the impacts of sea level rise and changes in wave climate on the future coastline have been assessed. Sea level and wave projections were based on an intermediate (RCP4.5) and high-end (RCP8.8) scenario of climate change. Under these scenarios projected regional sea level rise in 2100 is 48 (±23) cm and 67 (±31) cm for RCP4.5 and RCP8.5, respectively. Changes in wave regimes by 2100 reach 0.2 m under calm conditions and up to 0.3 during an extreme event. Currently, the beaches are 35-40 m and 30-50 m wide. The results indicate that, without additional adaptation measures, the studied beaches would suffer a coastal retreat between 7 and up to 50 m, equivalent to half of the present-day aerial beach surface, under the climate scenarios considered (10).
The lack of a general management strategy to fight coastal erosion and the short-term urgency to protect specific stretches has resulted in a reactive approach based initially on hard engineering structures (especially groins, but also seawalls and detached breakwaters). The net longer-term effect was degradation of many coastal areas and sediment starvation, also enhanced by the progressive damming of rivers and associated river regulation policies. Between the second half of the 1980s and the early 1990s, beach nourishment was adopted as a ‘cure-all’ solution for most coastal erosion problems. The number of beaches (400) and the volume of sand (10 million m3 of sand per year) make beach nourishment of the Spanish coast the foremost in Europe, being equivalent to the combined volumes of Italy, Germany, France and the Netherlands (1).
For the functional design of coastal engineering structures, a sea level rise of about 50 cm for the year 2100 is usually taken into account (1).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Spain.
- Gracia et al. (2013)
- Doody (2004), in: Gracia et al. (2013)
- Guillén and Palanques (1992, 1997); Jiménez et al.(1997), all in: Evans (2008)
- Sanchez-Arcilla et al. (1998); McManus (2002), both in: Ericson et al. (2006)
- Chust et al. (2011)
- Chust et al. (2010), in: Chust et al. (2011)
- Leorri et al. (2008), in: Chust et al. (2011)
- Garbutt et al. (2006); Marquiegui and Aguirrezabalaga (2009), both in: Chust et al. (2011)
- Titus et al. (2009), in: Chust et al. (2011)
- Enríquez et al. (2017)