## 1 Introduction  
Detection and quick mapping of the extent and distribution of overflowed water surfaces during major flood events on urban areas can be significant for quantifying possible hazard maps within spatial and environmental planning strategies [1]. However, the wide lowland areas are characterized by very small gradients and subjected to pervasive minor inundations due to seasonal fluctuations of water levels. These water variations are equally important to be studied and to be spatially defined in comprehensive maps, since the related surface water circulation can adversely interfere with some of the waterside anthropic activities and, at the same time, can severely impact the ecosystem balance of wetlands, influencing the existing bioma. These effects can assume contours that are even more negative if occurring in those areas that suffer the foolish and disrespectful spread of a chaotic residential architecture carried out in an abusive way (settlements without authorizations or controls and with the application of unregulated construction techniques), which is universally named \"informal architecture\". Therefore, the purpose of this paper is to identify, and consequently test, the best survey techniques that are nowadays able to detect the impact degree of various possible levels of inundations in a very short time. Throughout the quick detection of seasonal water fluctuations extent, useful and immediate information can be provided for the realization of a large scale mapping, the collection of local vulnerability related to the urban and natural arrangement, as well as for the criticality categorization to include in ordinary planning and management of extraordinary emergency situations. In such a perspective, the currently available remote sensing space-borne Earth Observation (EO) sensors are useful sources of information on inundation events over wide areas. Both of the two satellite imagery types, i.e., optical and radar data, can help with the rapid tracing of inundated areas by exploiting their time- and cost-efficiency as well as their wide area coverage, and thus, can successfully detect spatial and temporal water level variations and fluctuations extent maps [2; 3]. On the one hand, optical satellite data are usually the best choice for such applications due to their simple readability. On the other hand, overflows often occur in cloudy and rainy periods, which are unfavorable weather conditions for optical images usability because cloud cover prevents good visibility. In this case, radar data acquired by SAR (synthetic aperture radar) satellite sensors offer a valid option for land surface water bodies monitoring and mapping [4]. Water bodies are a specular reflector of the radar signal, resulting in minimal backscattering returned to the satellite. The effectiveness of the radar return is dependent on a number of factors, notably surface roughness, dielectric properties, and local topography in relation to the radar look angle [2]. SAR sensors, in fact, are \"active\" devices that use microwave signals that can operate in all climatic conditions at large scale with good spatial resolution and indifferently during day and night. Easy-to-use and semi-automatic optical imagery- and SAR-based flood mapping approaches, such as texture analysis, change detection, histogram thresholding, have been tested and considerably used in literature in the last years (e.g., [2; 5; 6; 7; 8]).