**2. Methodology**

The analysis presented herein has been carried out using the methodology proposed by Miranda and Ferreira [1]. This particular methodology is adjusted so as to be implemented as a micro-scale assessment. In this case, the elements of interest are the historical buildings and the losses, which are mainly defined in terms of physical damage caused to the building fabric, namely, the direct tangible damage. For historic buildings, this damage is deemed the most severe. Moreover, to deal with historic sites, the method addresses direct intangible damage, in terms of losses to the cultural value of heritage buildings.

The vulnerability in this methodology refers to the intrinsic characteristics of the building. Other factors define the social, historical, and economic value of the asset and its interaction with the water. The results can be seen as a synthetic vulnerability function as they are not derived from damage data after flood events. The vulnerability index is a relative measure of the expected severity of the physical *Flood Risk Assessment in Urban Areas: The Historic City Centre of Aveiro as a Case Study DOI: http://dx.doi.org/10.5772/intechopen.109867*

impact of the flood on the building in comparison to other assets ranked. The value of the vulnerability index does not account for the hazard and only partially accounts for the exposure, following an approach that is becoming common in flood risk assessment [6, 7].

As shown in **Figure 1**, the methodology defines flood vulnerability (FV) as the product of the exposure component (EC) and the sensitivity component (SC). Five parameters are considered to define the sensitivity component, each one of them containing four attributes. The exposure parameter refers to the exposure of the building to the flood, which encompasses aspects like the orientation of the most exposed façade to the water flow or the location and dimension of the openings doors and windows [1].

### **2.1 Flood vulnerability**

The goal of vulnerability assessment is to understand how a system will be affected by floods. Even though there are different classes of vulnerability, physical vulnerability is the most commonly assessed because it is the easiest way to characterize it. Furthermore, the nonphysical vulnerability is usually evaluated in terms of economic loss, which is related to the interruption of various activities and is often much more challenging to estimate.

According to Balica [8], flood vulnerability can be determined by a physical approach, where hydrological models are used to estimate flood hazard and economic consequences. Moreover, Balica also mentions an empirical approach related to quantitative or qualitative indicators to rate the vulnerability without inputting the hazard intensity. Regarding the methodology adopted for the present study, no attribute has been assigned the value 0, since it is considered that every historic-building feature measured indicates some degree of vulnerability to the hazard. However, for all the descriptors to contribute equally, a lower boundary of 10 is applied to the rating scale for them, except for the land slope [9].

Based on the estimated individual parameters, the flood vulnerability is computed according to Eq. (1).

Flood Vulnerability FV ð Þ¼ Exposure Component EC ð Þ� Sensitivity Component SC ð Þ (1)

### **2.2 Exposure component**

Exposure analysis aims to examine the economic assets and activities influenced by the flood. Exposure can be determined by geospatial mapping to identify the location of the assets of interest related to the flood hazard. In addition to this, the exposure contemplates some intrinsic characteristics of the elements analyzed.

#### *2.2.1 Wall orientation*

Wall orientation assesses the position of the asset with respect to the expected water flow. This parameter considers that the wall in a plane perpendicular to the water stream direction (fully exposed) presents a bigger pressure load than the ones that are simply immersed. It also considers the presence of openings reachable by the water. The characterization of the buildings as fully or partially exposed without openings is attributed to the ones where the windows and doors are not facing the flow of the water [10]. The assessment is based on the orientation and the characteristics of the main façade. In the case of buildings located in low-lying areas, the class is increased to C or to D for partially and fully exposed buildings.

#### **2.3 Sensitivity component**

#### *2.3.1 Material*

This parameter considers the lateral capacity of the structure, the resilience to ground movement, and the absorption capacity, factors that contribute to the risk of collapse in the short term and degradation in the longer term. In the case of degradation, it depends on two factors: the consequences of improper drying and on the contaminants and salts present in the flow [11].

Among materials, earth is considered the most vulnerable. The materials' porosity determines their absorption capacity, but it can also promote their resilience, as it allows them to tolerate heavy wetting. It should be mentioned that the unbaked earthen structures are the most likely to present disintegration caused by the wetting and water pressure [12].

Masonry buildings are less prone to suffer collapse. However, they can present moisture in the elements and different types of decay such as spalling or exfoliation induced by the presence of salts and contaminants. Previous experiences demonstrated reduction up to 50% of the capacity in dry condition. Therefore, masonry structures should be properly inspected post-event [10].

Modern materials such as steel and concrete are less vulnerable. Moreover, the reparation and replacement of traditional materials may be more expensive. Timber elements are prone to biological attacks, such as fungi and insects. After the flood event, if the element is properly dried, serious damage is not expected. Moreover, saturated elements undergo significant deformation.

*Flood Risk Assessment in Urban Areas: The Historic City Centre of Aveiro as a Case Study DOI: http://dx.doi.org/10.5772/intechopen.109867*

#### *2.3.2 Number of stories*

It is argued that single-story buildings are the most vulnerable, since they do not possess a flood-free story to facilitate the evacuation [13]. Nonetheless, in terms of stability, higher buildings with the same footprint and superficial foundations are more susceptible to the effects of the flood on the subsoil, such as differential settlements [5]. Therefore, for the present study, the vulnerability is considered as increasing with increasing number of stories.

#### *2.3.3 Damage and cracking*

Damage can lead to higher water absorption and lower strength in the materials, such as in the case of wood. Indeed, water ingress can easily occur through cracks, and once inside the building, water can damage movable assets and valuable nonstructural elements, contributing significantly to the economic losses. Therefore, restoration and maintenance measures are essential to prevent water penetration. This indicator includes an assessment of the state and quality of the interventions that can be carried out [6].

#### *2.3.4 Age*

This parameter may represent more valuable assets. This is valid for countries where historic structures have a higher real-estate value, being thus inhabited by higher-income residents [14]. Furthermore, older buildings are likely more prone to suffer flood damage. It is worth noting that the four levels of the age indicator may require an adaptation to the local evolution over time of the investigated building stock.

#### *2.3.5 Heritage status*

The heritage status is directly related to the socioeconomic impact that the preservation of these assets could have. For this reason, a higher value implies higher exposure of the asset. Moreover, the buildings that are listed are often subjected to more requirements, which results in higher intervention costs. In these cases, it is also important to contemplate the nonstructural value of artworks and other movable assets that are hosted in the building, a fact that will increase their vulnerability [15].
