Flood Risk and Vulnerability: An Approach to Urban Floods in Ribeira de Machico in the Autonomous Region of Madeira

Introduction

Among all-natural disasters, flooding affects the most people in the world (Moore, 2005). In the Autonomous Region of Madeira – RAM, due to geographical specificities, floods have already caused substantial material damage and a high number of fatalities. It is estimated that public investment in the repair and reconstruction of public infrastructure damaged by floods, since 2020, will exceed 250 million euros. It appears that urban floods have been increasing considerably in RAM, due to pressures exerted by human occupation, weatherproofing sealing, increased population density and disorderly urban occupation. With the increase of this problem at a global level and, mainly in tropical regions, it became necessary to develop measures and devices to mitigate the impacts of floods (Lousada & Castanho, 2021).

Since the beginning of the 19^th century, around 30 alluviums of significant intensity have occurred on Madeira Island, characterized by rapid and violent floods that transport high concentrations of solid material. It is worth mentioning the occurrence of 1803, the year in which about 1000 people died, victims of the catastrophic floods that occurred throughout the island, but with greater intensity in Funchal, Machico and Santa Cruz (Quintal, 1999). Figure 1 shows the most serious recent event that occurred on February 20, 2010.

Figure 1.

Photographs of the alluvium of February 20, 2010

Source: Diário de Notícias

In 2010, an extremely well-known event regionally was the alluvium, which caused damage and losses in several locations on Madeira Island. It took place on February 20, 2010, resulting in the death of 47 people on the island, 600 displaced and 250 injured (RTP, 2016).

Vulnerability represents the degree of loss of component or components exposed to floods, this aspect being different from the concept of risk, being strongly linked to the economic, age, cultural, social characteristics of a society, as well as the occupation of the territory (Ferreira, 2010). Urban flooding in the city of Machico arises since there is a large occupation, somewhat manageable, of potentially floodable areas, where there is a great waterproofing of the soil, associated with the obstruction of several devices responsible for the drainage of the city, namely, culverts and gutters, the high-water table, physical aspects of the city somewhat unfavorable and the bad design of drainage systems.

Associated with the high daily maximum annual rainfall (>200 mm) and the fact that a large part of the city's population is located by the sea (high tides), the risk of flooding in Machico increases, especially during the months of October and November. This phenomenon causes several inconveniences to the lives of many people, especially those who live along the stream and by the sea. Thus, it is extremely important to mitigate these disasters, not only in Machico but throughout the island.

Therefore, this article proposes to describe the indicators of flood vulnerability, also identifying, through Directive 2007/60CE, the Flood Area, the Flood Risk, the Potentially Affected Inhabitants (> 400 inhabitants), the Affected Cultural Heritage (5 buildings), Potentially Affected Roads (> 9 km), Sensitive Potentially Affected Buildings (Machico City Hall, Machico Parish Council, Machico Municipal Fire Department and Machico Health Center) and Potentially Affected Infrastructure.

Ribeira De Machico Hydrographic Basin: Geometric And Physiographic Characteristics

In this stage, will be addressed issues related to:

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  Geometric characteristics of Ribeira de Machico, namely its location, area, perimeter, and shape of the basin;

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  Physiographic characteristics such as geology, soil and vegetation, characteristics that may or may not be favorable to the occurrence of alluvium.