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Journal of Coastal Research, Special Issue 56, 2009

Journal of Coastal Research SI 56 827 - 831 ICS2009 (Proceedings) Portugal ISSN 0749-0258

Coastal hazards of Fajã do Calhau (São Miguel – Azores): a first approach

G. Lameiras†, J. Fontiela†, P. Borges‡, H. Calado†, O. Vieira†, B. Rangel† and A. Gallagher∞ †Geography Section Azores University, 9501-801 Ponta Delgada, Portugal [email protected]

‡Department of Geosciences Azores University, 9501-801 Ponta Delgada, Portugal [email protected]

∞Faculty of Technology Southampton Solent University, Southampton, SO14 0RD, United Kingdom [email protected]

ABSTRACT

LAMEIRAS, G., FONTIELA, J., BORGES, P., CALADO, H., VIEIRA, O., RANGEL, B. and GALLAGHER, A., 2009. Coastal hazards of Fajã do Calhau (São Miguel – Azores): a first approach. Journal of Coastal Research, SI 56 (Proceedings of the 10th International Coastal Symposium), 827 – 831. Lisbon, Portugal, ISSN 0749-0258.

Fajã do Calhau is a supratidal talus-platform located on the South-East coast of São Miguel Island (Azores). Locally called “fajãs”, these flat platforms with hummocky surfaces result from landslides and are relatively common coastal features in the archipelago, occurring on the toe of the cliffed coasts of most Azorean islands. Fajã do Calhau is at the foot of a 380 m high cliff and has an area of approximately 220,000 m2, circa 1300 m length and maximum width of 260 m. The seaward margin of the fajã consists of a scarped active bluff with modal and maximum elevations of 5 and 10 m above sea level, respectively. A gravel beach leans against this bluff. Fajã do Calhau attracted, in recent past, human settling due to its agriculture potential, in spite of the hazards arising from storms and landslides. Nowadays, this area is again increasing in value and attractiveness but as a result of the demand for second housing and seasonal leisure activities. This lead to the on-going construction of a new accessibility, which will further increase the human occupation rates both in space and time.The main coastal hazards of the Fajã do Calhau are coastal erosion (with present-day rates of 0.20 m/yr), coastal storms, mainly from SW, and coastal flooding (on average once every 7 years). Besides these, others with larger recurrence intervals, such as the ones inherent to the genesis of both this feature – landslides and earthquakes – and island volcanism.

ADDITIONAL INDEX WORDS: coastal erosion, coastal storms, coastal flooding, set-back lines.

INTRODUCTION More than 50% of world’s coasts are threatened by

development (PHILLIPS, 2007 personal communication). By 2020, 75% of the world’s population will live within 60 km of the coast (FINKL and KRUEMPEL, 2005).

Coastal communities are more vulnerable to climate change because in addition to meteorological parameters they are also affected by changes in oceanic parameters, especially increases in sea level and wave heights that will, in some cases, represent physical, social and economic impacts on communities.

The Azores archipelago is located in the North Atlantic Ocean approximately 1500 km away from Europe (Figure 1). It comprises nine volcanic islands scattered over 600 km and roughly aligned WNW-ESE. These islands rise from the Azores Plateau, defined by the 2000 m bathymetric contour.

The long fetch that characterises the Azores relative to the North Atlantic explains a high-energy wave climate where both sea and swell are relevant sources of energy to the coast. The steep submarine slopes and absence of shallow shelves produce localised patterns of wave shoaling, refraction and diffraction, which occur just before waves break, especially during storms (BORGES et al., 2002). This leads to the fragmentation of the coast into a number of dynamic cells, limited by virtually impermeable lateral boundaries in terms of sediment movement alongshore. Tides and tidal currents are minor contributors to coastal morphology and sediment dynamics.

The settlements in the Azorean islands are mainly located on the coastal zone, in fact, most of the main municipalities are located on this area. The social and economic growth of the archipelago in the 20th century, and particularly in the last quarter of the century, resulted in accelerated coastal development, which included the construction of communication infrastructures and buildings (BORGES et al., 2002). More recently a boom on the tourism industry brought new pressure to those areas and for that reason, the land-use plans needed to be implemented (VIEIRA et al., 2008).

Supratidal talus-platforms with hummocky surfaces, locally called “fajãs”, resulting from landslides, are relatively common coastal features in the archipelago, occurring in the cliffed coasts of the Azorean islands. On São Miguel Island several of these coastal forms can be seen, such as the Fajã do Calhau.

THE STUDY AREA São Miguel is the largest and the most populated island of the

archipelago, with the Fajã do Calhau being located on its south-east coast as shown in Figure 1.

This is the oldest part of the island being approximately 4 Ma (ABDEL-MONEM et al., 1975), with the local morphology being dominated by the effusive activity of the Nordeste shield volcano (MOORE, 1990) and sea cliffs cutting mainly into weathering lava flows and basaltic pyroclastic deposits and dykes. The local geology is discussed in detail in ZBYSZEWSKI et al. (1958), ZBYSZEWSKI (1961), FERNANDEZ (1982), MOORE (1990; 1991) and FORJAZ (1997).

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Fajã do Calhau is at the toe of a 380 m high cliff and this flat coastal fringe has an area of approximately 220,000 m2, circa 1300 m length and maximum width of 260 m. The seaward margin of the Fajã consists of a scarped active bluff with modal and maximum elevations of 5 and 10 m above sea level, respectively. A gravel beach leans against this bluff (Figure 2).

METHODS AND RESULTS The fieldwork for this research took place during August 2008,

a time of the year when more people can be found staying in Fajã do Calhau due to the summer holidays and for work in the vineries and wineries. The work was divided in two phases: firstly, the recognition of the geological and geomorphological features, including oral surveys concerning the areas flooded and recurrence intervals and an identification of key variables to be used in the investigations to be carried out; and secondly, survey of both population and buildings. With regards to the latter data was gathered on the nature of residency on the Fajã including characteristics present on their properties and buildings (production means, type of ownership) present; the main motivations for coming to Fajã; the opinions of residents about the new accessibility; natural hazards; and finally if they have observed changes in climate in Fajã do Calhau, for the past 10 years. The data collected concerning the building survey was completed with geographical representation using GPS for building positioning, type of buildings (ruins, summer houses, wineries) and their main characteristics (number of floors, buildings materials, color, state of maintenance, integration, type

Figure 1. Location of the Azores archipelago and of the study area.

Figure 2. Geomorphological sketch of Fajã do Calhau, base upon aerial photography of the year 2000 at an approximately scale of 1:5000.

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and characteristics of access, water sources and electricity). In this survey photographs were also taken of every building, to identity and classify them.

In order to collect information systematically, the survey was carried out on an East to West transect. Oral testimonies among older people were also collected.

The results of the field survey were input on a GIS database, a process which is still ongoing, and complemented with aerial photographs from the year 2000 (scale approximately 1:5000).

At Fajã do Calhau 65 buildings have been catalogued, including a small church reduced to ruins. Although Fajã is no longer permanently inhabited (only in seasonal base), the crops and vineyards that formed the focus for development in the first place are still being cultivated. The current use of the buildings by function is: 45 of the 65 buildings are classified as being in ‘good shape’; 18 in ‘bad shape’; and 2 as ‘ruins’.

In what concerns land-use, all properties have vines, on which 43.75% also have vegetable gardens. In fact 93.75% of the respondents of the survey declared that they grow vegetables and/or grapes for their own consumption. Most of these properties, 56.25%, have been bought or loaned and about 50% of the houses have undergone construction or reconstruction works in the past five years.

The population that presently stays in Fajã do Calhau (for the summer or for the harvesting) most of them live in the same rural county (93.75%), the majority of them in the nearby village Água Retorta (81.25%) while the rest – 6.25% – lives in others counties of the island.

The majority of the people that seasonally goes to the Fajã do Calhau are still active workers (74.9%), 12.5% working in the primary economic sector, 31.2% in the secondary and 31.2% in the tertiary economic sector. 81.25% of the fajã-goers have been doing it since their childhood and 37.5% visit the fajã throughout the year, besides the summer time.

The poor accessibility conditions and the noise produced by electric generators were pointed as the main problems of the local. With the construction of the new accessibility, 75% of the surveyed population thinks that some changes will occur in Fajã do Calhau, with 26.6% of them pointing to the rehabilitation of buildings and vineyards as the main changes, thus benefiting this Fajã. In fact, 75% declared that having this new accessibility, they will come more often to Fajã do Calhau.

Part of the data obtained on the surveys, namely the one concerning the perception of the fajã-goers to climate changes and natural hazards of Fajã do Calhau, as well part of the field data concerning the geology, is presently under research.

Figure 2 shows that circa 20% of the houses of Fajã do Calhau are less then 10 m from the edge of the bluff and some of them are less than 0.5 m. The field work also allowed the confirmation of the modal run-ups proposed by BORGES (2003) for coastal flooding consequence of extreme storms and the ‘storm of the century’. Figure 3 shows a plot of the areas of Fajã do Calhau at risk from coastal flooding in an event similar to the 1996 Christmas Day coastal storm in São Miguel and similar to the ‘storm of the century’. These forecasts, however, are based on the run-ups obtained by BORGES (2003) for the extreme event – 1996

Figure 3. Possible extents of flooding of the Fajã do Calhau by extreme coastal storms

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Christmas Day storm – and for the ‘storm of the century’ (e.g. 1840). It assumes that the limits of flooding match the contour line equaling a run-up height of 5 m for the first case and 7 m for the second. Nevertheless, those flooding areas should be taken cautiously due to the simplicity of the approach. The low intensity events produce only slight overtopping of the bluff with some splash therefore causing paltry flooding.

DISCUSSION AND CONCLUSIONS The analysis of the data concerning the current use of the

buildings by function shows that in general the area is still very much a place of active use and productivity, even originating a small and active property market in this fajã. In fact, 50% of the houses have undergone improvements in the last five years, demonstrating the commitment of the fajã-goers with the conservation of the buildings.

The data obtained by the surveys suggests that the majority of the population that presently goes to Fajã do Calhau for the summer or the harvesting, although living most of the year in a rural county, doesn’t work at the primary economic sector signifying that the vineyards and gardening in Fajã do Calhau are hobbies, suggesting a certain nostalgic return to their roots. In fact, an impressive part of the fajã-goers – circa 81% – has a strong connection with this place, in view of the fact that they have been going there since their childhood.

For the generality of the fajã-goers the construction of the new accessibility will bring changes to the Fajã do Calhau such as the rehabilitation of some houses and vineyards, has well the

possibility of going there more often. The first analysis of the data concerning the perception of

coastal hazards and climate changes by the fajã-goers suggests a lack of it, being the elders, however, the ones with a better perception of the phenomena.

The erosion rate proposed by BORGES (2003) for Fajã do Calhau is 0.2 m/yr. If the bluff retreating maintains this rate it implies that in the next 50 years circa 20% of the houses will be at risk of succumbing to erosion and it will be worst in a 100 years scenario (Figure 4), with a coastal land loss of approximately 10,000 m2 and 20,000 m2 respectively, corresponding to a loss of 4.5% and 9.1% of the total surface of Fajã do Calhau. This will lead certainly to the armoring of the bluff with seawalls – presently some sectors of the bluff are already protected by of this type of coastal defense. Although the gravel beach leans against the bluff, this armoring will lead, most certainly, to a seawall saga (e.g. BUSH et al. 1996) and to the ‘newjersyization’ of Fajã do Calhau. Assuming the maintenance bluff retreat rate of 0.2 m/yr, it would be prudent to establish a set-back line of 10 m or 20 m for a 50 years and 100 years period, respectively.

The storm recurrence interval postulate by BORGES (2003) and ANDRADE et al., (2008) for the Azorean archipelago can be applied to Fajã do Calhau. An extreme coastal storm occurs on average once every seven years usually associated with southwesterly waves with maximum significant wave height of 11.7 m and highest wave height occurring in the series of 22.2 m (BORGES, 2003). Usually this event causes coastal flooding, being the scenarios similar to the plots presented on figure 3, with an area of flooding, deduce from the plot, approximately 3000 m2 for

Figure 4. Areas of land loss and set-back lines for 50 and 100 years of coastal bluff erosion at Fajã do Calhau.

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extreme storms and 25,000 m2 for the ‘storm of the century’, corresponding respectively to 1.36% and 11.36% of the total area of the Fajã do Calhau. The flooding limits proposed for the ‘storm of the century’ should be adopted as the set-back line for flooding at Fajã do Calhau.

Additionally to the referred main coastal hazards of Fajã do Calhau – coastal erosion, coastal storms and coastal flooding – there are others with larger recurrence intervals, such as the ones inherent to the genesis of both this feature – landslides, earthquakes and island volcanism – that should also be taken on account. In fact, since the settlement in the mid-15th century São Miguel Island was affected by several volcanic eruptions, earthquakes and landslides. For example Sete Cidades (1439-43?), Fogo (1563), Furnas (1630) and also the Picos Volcanic Complex (1652), have seen plinian to sub-plinian, hydromagmatic and strombolian type basaltic eruptions (FONTIELA & NUNES, 2008). In addition the island was struck by 8 earthquake events with an intensity of greater than VII (MMS; NUNES et al., 2001), the largest being the 1522 event which triggered several massive landslides. São Miguel Island has records of landslide events with different magnitudes, being triggered by several factors like earthquakes (e.g. 1522 Vila Franca Campo), volcanic eruptions (e.g. 1630 Furnas) or heavy rain episodes (e.g. 1997 Ribeira Quente). Those natural hazards although not being typical coastal hazards can occur or affect directly or indirectly the coastal areas of São Miguel namely Fajã do Calhau and vicinities.

Considering that wave climate of the North Atlantic Ocean seems to be increasing (e.g. BACON & CARTER, 1991; BOUWS et al., 1996), the storminess of the Azores archipelago slightly increased in the last 150 years (BORGES, 2003), the climate changes scenarios for São Miguel (SANTOS et al., 2004; SANTOS & MIRANDA, 2006) and the actual global scenarios of climate changes, it’s expected that those factors will in the near future contribute to amplify the magnitude of the coastal hazards of Fajã do Calhau and due to the growing anthropogenic pressure and occupation of that fajã, that will be most certainly amplified by the new accessibility, the coastal risks will also increase and that will be a problem since the Azorean islands aren’t prepared to face these impacts. Therefore it’s urgent that fajã-goers have an awareness/information/formation about the coastal hazards that affect the area, in order to develop strategies, including set-back lines that will minimize the risk, in order to avoid leaving a poisoned heritage to the future generations of fajã-goers.

LITERATURE CITED ABDEL-MONEM, A. A.; FERNANDEZ, L. A. and BOONE, G. M., 1975.

K-Ar ages from the eastern Azores group (Santa Maria, São Miguel and the Formigas Islands). Lithos, 8, pp 247-254.

ANDRADE, C.; TRIGO, R.M.; FREITAS, M.C.; GALLEGO, M.C.; BORGES, P. and RAMOS, A.M., 2008. Comparing historic records of storm frequency and the North Atlantic Oscillation (NAO) chronology for the Azores region. The Holocene, 18(5), pp745-754.

BACON, S. and CARTER, D., 1991. Wave climate changes in the North Atlantic and the North Sea. International Journal of Climatology, 11, pp 545-558.

BORGES, P., 2003. Ambientes litorais nos grupos Central e Oriental do arquipélago dos Açores, conteúdos e dinâmica de microescala. University of Azores. Ph.D. thesis, 413p.

BORGES, P., ANDRADE, C. and FREITAS, C., 2002. Dune, Bluff and Beach erosion due to exhaustive sand mining – the case of Santa Bárbara, S. Miguel (Azores, Portugal). Journal of Coastal Research, Special Issue No. 36, pp 89-95.

BOUWS, E.; JANNINK, D. and KOMEN, G., 1996. The increasing wave height in the North Atlantic. Bulletin American Meteorological Society, 77(10), pp 2275-2277.

BUSH, D.M.; PILKEY, O.H. JR and NEAL, W.J., 1996. Living by the rules of the sea. Duke University Press, Durham, 179pp.

FERNANDEZ, L.A., 1982. The petrologie and geochemestry of the Nordeste Volcanic Complex, S. Miguel, Azores. Arquipélago, 3, pp 145-158.

FINKL, C.W. and KRUEMPEL, C., 2005. Threats, obstacles and barriers to coastal environmental conservation: societal perceptions and managerial positionalities that defeat sustainable development. International Conference on Coastal Conservation and Management in the Atlantic and Mediterranean. (Algarve, Portugal).

FONTIELA, J. and NUNES, J. C., 2008. The B values on the Congro Fracture Zone (S. Miguel Island, Azores) during the period 2003-2007: a first approach. Azores 1998 – International Seminar on seismic risk and rehabilitation of stone masonry housing, (Faial, Azores, Portugal), 6p.

FORJAZ, V.H., 1997. Alguns vulcões da ilha de S. Miguel (Açores). Ponta Delgada, Açores: Edição do Observatório Vulcanológico e Geotérmico dos Açores, 168p.

MOORE, R. B., 1990. Volcanic geology and eruption frequency, São Miguel, Azores. Bulletin of Volcanology, 52, pp 602-614.

MOORE, R. B., 1991. Geologic map of São Miguel, Azores. U.S. Geol. Surv. Misc. Invest. Ser. Map I – 2007, U.S. Geological Survey, Denver, scale 1:50000, 1 sheet.

NUNES, J.C.; FORJAZ., V. H. and FRANÇA, Z., 2001. Principais sismos destrutivos no arquipélago dos Açores – uma revisão. In: FRAGOSO, M. R. (ed.), 5º Encontro Nacional de Sismologia e Engenharia sísmica – SÍSMICA 2001. Laboratório Regional de Engenharia Civil de Ponta Delgada, pp 119-131.

SANTOS, F.D. and MIRANDA, P., 2006. Climate Change in Portugal. Scenarios, Impacts and Adaptation Measures – SIAM II. Gradiva, Lisbon.

SANTOS, F. D.; VALENTE, M. A.; MIRANDA, P. M. A.; AGUIAR, A.; AZEVEDO, E. B.; TOMÉ, A. R. and COELHO, F., 2004. Climate change scenarios in the Azores and Madeira Island. World Resource Review, 16 (4), 473-490.

VIEIRA, O., ALVES, F., SILVA, C., LAMEIRAS, G., RANGEL, B., BOTELHO, A. and CALADO, H. ,2008. Outcome of public participation in small islands – coastal management plans. Littoral 2008. 9th international conference – A changing coast: challenge for the environmental policies (Corila, Veneza, Itália).

ZBTSZEWSKI, G.,1961. Étude geologique de l´íle de S. Miguel (Açores). Comunicações dos Serviços Geológicos de Portugal, 25, pp5-79.

ZBYSZEWSKI, G; ALMEIDA, F. M.; FERREIRA, O. V., and ASSUNÇÃO, C. T., 1958. Carta Geológica de Portugal, notícia explicativa da folha “B” da ilha de S. Miguel (Açores). Serviços Geológicos de Portugal, scale 1:50000.

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