## 1 Introduction  
Floods are probably the most frequently recurring natural phenomena affecting society (humans and goods) in terms of space and time, regardless of their geographical location or socioeconomic development, as shown by the data collected by the International Disasters Database for the period 1900-2018 (CRED, 2020). This is the main reason why flood risk management has become an essential tool from both a social and economic perspective, with the objective of reducing losses associated with both factors. Furthermore, urban historical centers are characterized by the presence of multiple types of cultural heritage sites, which give it a priceless value upon the consideration of the impossibility of the restoration or recovery of the possible damage caused by natural hazards, in this specific case, by river flooding. This abovementioned duality, but also mainly the irreversibility, of flood damage on cultural heritage (which cannot be reproduced once it has been destroyed) makes the prediction and assessment of the flood risks that may affect these sites a critical task for their preservation. Given this situation, the first natural disaster management strategies that included cultural heritage among its objectives began to be developed in the 1990s. Among these initiatives, one could highlight the \"Carta del Rischio\" [1], which has been developed by the Italian Central Institute for Restoration since 1992, or the \"Noah's Ark\" project of the European Union [2], launched in 2002. At specific sites, only a few works provide applications to case studies at different scales (from regional to local scales) [3; 4; 5; 6; 7]. After assessing direct tangible damage (i.e., the direct damage resulting from the physical contact of floodwater with property and its contents), it was found that the economic flood losses have been increasing throughout the past half-century. In the last decade (2008-2018), the economic losses associated with floods exceeded 35 billion USD [8] and, within this period, the flood losses exceeded 19 billion USD in 2012 alone [9; 10; 11]. The design, sizing, implementation and effectiveness of flood damage mitigation measures require rigorous risk analyses [12]. Within the aspects that a flood risk analysis includes, the greatest technical efforts are usually concentrated on flood hazard assessments. Flood vulnerability analysis is the other determining factor regarding the correct estimation of risk, mainly from the use of magnitude-damage models (e.g., [13; 14; 15; 16; 17; 18; 19]). Since the most common methods of flood hazard analysis are based on hydrological and hydraulic models [20], the greatest uncertainties and sources of error may come from the input data to these models. In the case of hydraulic or hydrodynamic models, the geometry of the channel (topography and bathymetry) [21; 22; 23; 24], the boundary conditions (roughness, flow regime, etc. [25]) and the Manning's roughness coefficient (e.g., [26; 27; 28]) are determinants of the goodness of the model and results. In short, the effectiveness of risk mitigation may depend on the correct estimation of parameters such as the roughness of the terrain surface and the detailed bathymetric characterization of the riverbed. In addition to the key points mentioned above, the urban character of cities' historical centers must be taken into account. This latter characteristic determines the preferred flow direction of floods inside the urban areas, turning the streets into improvised river channels. To achieve all these objectives, it is essential to have topographic data that are capable of reproducing the geometry and variability of the terrain [22; 24; 29; 30], with the information coming from LiDAR (light detection and ranging) sensors being the most widely used today to derive DEMs (digital elevation models). However, most LiDAR data are not capable of reproducing the river channel morphology due to its inability to penetrate water bodies.