Rapid assessment of geo-hydrological hazards in Antananarivo (Madagascar) historical centre for damage prevention

Abstract

The historical centre of Antananarivo represents one of the most important cultural heritage sites in Madagascar. During 2015, the whole city area was severely affected by geo-hydrological hazards due to cyclonic rain, resulting in severe flooding, and in widespread shallow landslides along the hillslopes. This event proved the vulnerability to geo-hydrological risk of the Upper town's historical buildings. In October 2017, a geo-hydrological hazard mapping was performed in the Upper Town by combining field surveys, remote sensing and geomatic data analysis in a GIS environment. This provided detailed products such as a geological-geomorphological map, a map of the hydrographic network and of the creek basins, and a geodatabase to be used for detecting areas prone to erosion and geo-hydrological hazards. The final aim was to understand the geological, geomorphological and hydrographic features of the Upper Town, in order locate the more critical areas and to recommend priority works to be carried out, as a first step toward a risk management strategy and a conservation/valorization plan for building the resilience of the site. The results highlighted that a Cultural Heritage site protection strategy can be planned also in case of limited data, which is a frequent condition in developing countries.

Combining InfraRed Thermography and UAV Digital Photogrammetry for the Protection and Conservation of Rupestrian Cultural Heritage Sites in Georgia: A Methodological Application

“…Tangible Cultural Heritage (TCH), such as archaeological and historical sites, plays a key role in building the memory and roots of human society, therefore, its protection and conservation are pressing issues, not only for the conservators'/scientists' community but for the whole society. TCH is often at risk from natural hazards (fires, earthquakes, landslides, flooding, tropical storms) and man-made disasters (destructive sabotage, war), while further damage can arise from the instability of the structures and the fragility of the involved stone materials [1][2][3]. Amongst the latter, volcanic rocks such as tuffs, thanks to their softness and excellent carvability, represent one of the most widely adopted building materials and excavated lithology for rupestrian settlements in the history of man [4,5].…”

Hydrography and geomorphology of Antananarivo High City (Madagascar)

“…above sea level (Figure 1). Antananarivo was called Analamanga (the 'blue forest'), until 1610, when the merina King Andrianjaka built his first wooden royal palace complex (the so-called Rova) and a fortified village on the flat hilltop of the highest relief of the area (Analamanga hill); its privileged position assured an ideal defense and observation post on the lowermost Ikopa river plane (Ciampalini, Frodella, Margottini, & Casagli, 2019) (Figure 2). The first core of the city (the High City) further developed from the hilltop on the hillslopes (Middle town), by the late nineteenth century reaching the river valley during the colonial period (Low town).…”

“…Detailed thematic maps are of basic importance for the study of landslide processes (Calista et al, 2016;Frodella, Morelli, Fidolini, Pazzi, & Fanti, 2014;Smith & Ellison, 1999) and for analysing the landform evolution during the Quaternary (De Muro, Ibba, Simeone, Buosi, & Brambilla, 2017;Karymbalis, Papanastassiou, Gaki-Papanastassiou, Tsanakas, & Maroukian, 2013;Pucci et al, 2015), with special regard to the interactions with human activity (Paliaga, Luino, Turconi, & Faccini, 2018;Roccati, Faccini, Luino, Ciampalini, & Turconi, 2019;Visser, 2014). In this framework, the integration with remote sensing technologies can overcome the limitations of a field approach, by allowing a complete coverage of the analyzed phenomena over wide and inaccessible areas reducing costs and ensuring the safety of the field operators (Bardi et al, 2017;Ciampalini et al, 2019;Del Soldato et al, 2018;Frodella, Gigli, Morelli, Lombardi, & Casagli, 2017a;Gigli et al, 2014). The protection of Cultural Heritage from instability phenomena requires a specific interdisciplinary approach, which should be planned considering the geological and geomorphological characteristics of the site, as well as the typology of the related hazard (Margottini, Fidolini, Iadanza, Trigila, & Ubelmann, 2015a, 2015bNolesini, Frodella, Bianchini, & Casagli, 2016;Pastonchi et al, 2018).…”

“…The rapid urban development of Antananarivo, together with the lack of a proper urban planning, due to political and governance issues, have caused several environmental problems, such as intense deforestation and quarrying, unauthorized slope cutting and terracing for the construction of illegal hovels, moreover, there is a general lack of proper drainage and sewer systems. This context makes the Analamanga hill area particularly prone to soil erosion, landslide and flash flooding phenomena (Ciampalini et al, 2019), especially during the frequent heavy cyclonic rain events affecting the central highlands (Table 1). In this context, in March 2015 Antananarivo was hit by the tropical storm Chedza, resulting in severe flooding in the river plain area of the Low city, and in widespread shallow landslides along the hillslopes of the Middle Town.…”

“…The surveys also enabled the identification of possible new UNESCO Core and Buffer zones. The outcomes of this activity are presented in this work by showing detailed geological and hydrographical maps, which constitute an update of the work of Ciampalini et al (2019). The final purpose was to improve the geological and morphological knowledge of an area characterized by limited scientific data, in order to understand the interaction between the natural landforms, the urban evolution and the acting geomorphological processes, as the first step towards risk management and a conservation strategy of the Antananarivo historical center.…”