Mitigating Coastal Erosion in Fort Dauphin, Madagascar
Jean-Jacques Rahobisoa, Voahangy Rambolamanana Ratrimo, and Alfred Ranaivoarisoa
Abstract The city of Fort Dauphin is one of the most attractive tourist spots in Madagascar. In recent years, it has become one of the development centers of the island. However, the city is facing coastal erosion related to human activity as well as natural factors. Mitigation of coastal erosion at the catchment and regional scale is extremely important for the sustainable economic and social development of this region. Spatial analysis using satellite imagery over a long period has been considered as an important tool for determining the extent of the most affected areas and for analyzing how the erosion has developed in the past and at present. Measurement and field work need to be integrated to develop appropriate strategies to mitigate the problems. Satellite imagery analysis in combination with field work and measurement consists of generating long-term information required to determine threats and pressures in time and space. It takes into consideration assessment of land use, the geology of the area, urban planning, local and regional climate, and coastal management. Madagascar faces multiple challenges in mitigating coastal erosion, but the involvement of authorities and local communities plays a key role in long-term shoreline protection.
Keywords Fort Dauphin • Mitigation of coastal erosion • Spatial analysis
Due to its growing intensity, coastal erosion seems to be an abnormal phenomenon, but it is in fact a common occurrence. It has served as the key factor shaping coastal environments throughout history (Niesing 2005; Prasetya and Black 2003). Coastal systems play a variety of roles including assimilation of wave energy, hatching of flora and fauna, and groundwater protection, and they contribute significantly to recreational activities (Niesing 2005). Fort Dauphin is among the coastal zones threatened by coastal erosion. A recent rise in sea level, landslides, and coastal erosion have become serious threats to this municipality. Since 2005, coastal erosion has resulted in loss of housing facilities, four recreational beaches, and road communication links. In 2011 and 2012, widespread diminishing of beaches was observed around the city, with some areas badly damaged. Coastal erosion can be classified as a major risk for the city due to the threat it poses to economic development activities. In light of this, in 2012 the government decided to finance coastal erosion surveys through the PIC (Pole Integré de Croissance) project.
According to the Intergovernmental Panel on Climate Change (IPCC) in its Fourth Assessment Report in 2007, climate change marked by increasing temperature and a rise in sea level will place populations living in coastal areas in grave danger in 80 years' time. Moreover, Key human activities (Neuvy 1981; Schiereck 2004; Williams and Micallef 2009; Brebbia et al. 2009; Kim 2010; Slovinsky 2011) are located in coastal zones. In other words, the pressures of climate change and increase in human activity toward the coasts has turned coastal erosion into a more serious problem, not only for coastal municipalities, but for the world as a whole (Prasetya and Black 2003; Niesing 2005). Coastal erosion is usually the outcome of many factors in combination including natural and human-induced influences operating on different scales (Shore Protection Manual 1984; Ir Zamani Bin Mindu 1988; DGENV European Commission 2004; Williams and Micallef 2009; Slovinsky 2011). In undertaking this case study, therefore, it was necessary to understand the factors responsible for coastal erosion in order to develop mitigation strategies.
Fort Dauphin is an urban municipality in the southern part of Madagascar. According to the administration division, it is the capital of Anosy Region, and Amboasary district is positioned at the south eastern limit of Madagascar, in an area where winds blow from the Indian Ocean (Fig. 13.1). Geomorphologically, this study area is characterized in its eastern part by a small coastal plain dominated by the Anosyan Mountains. Morphological disposition makes the region highly exposed to winds blowing from the east (alize) and orographic lifting occurs frequently (Ratsivalaka Randriamanga 1985). The contacts with the ocean in the eastern and southern parts of the study area constitute cliffs varying between 5 and 10 m in height.
Under the influence of the Indian Ocean and its morphology, this region receives significant rainfall; its average annual rainfall is 1,800 mm/year (Direction de la météorologie 1980). As in the other regions in the country, December and January are the rainy months, comprising the rainy season. As it is exposed to the Indian Ocean, however, rainy and dry seasons are sometimes mixed. Temperature in this area varies between 20 and 26 °C (Direction de la météorologie 1980), where the maximum temperature corresponds to the rainy season and, conversely, the minimum temperature typifies the dry season.
Fig. 13.1 Location of the study area
Fort Dauphin essentially comprises sedimentary rocks that form Pleistocene and Holocene dunes. The eastern and southern areas are characterized by cemented dunes, where limestone playing the role of cement makes relatively hard rock. Due to its hardness, it forms cliffs in some areas. Westward, this formation is topped by unconsolidated recent dune, which occupies three fourths of the area. In the north east of this locality, metamorphic rocks of the Paleoproterozoic Era (1.8 Ga) act as a climatic barrier (Fig. 13.2).