Urban flood modelling has been evolving in recent years, due to computational facilities as well as to the possibility of obtaining detailed terrain data. Flood control techniques have also been evolving to integrate both urban flood and urban planning issues. Land use control and flow generation concerns, as well as a set of possible distributed measures favouring storage and infiltration over the watershed, also gained importance in flood control projects, reinforcing the need to model the entire basin space. However, the use of 2D equations with highly detailed digital elevation models do not guarantee good results by their own. Urban geometry, including buildings shapes, walls, earth fills, and other structures may cause significant interference on flood paths. In this context, this paper presents an alternative urban flood model, focusing on the system behaviour and its conceptual interpretation. Urban Flood Cell Model-MODCEL is a hydrological-hydrodynamic model proposed to represent a complex flow network, with a set of relatively simple information, using average values to represent urban landscape through the flow-cell concept. In this work, to illustrate model capabilities, MODCEL is benchmarked in a test proposed by the British Environmental Agency. Then, its capability to represent storm drains is verified using measured data and a comparison with Storm Water Management Model (SWMM). Finally, it is applied in a lowland area of the Venetian continental plains, representing floods in a complex setup at the city of Noale and in its surroundings.

The development of cities has always had a very close relation with water. However, cities directly impact land use patterns and greatly change natural landscapes, aggravating floods. Considering this situation, this paper intends to discuss lowland occupation and city sustainability in what regards urban stormwater management, fluvial space, and river restoration, aiming at minimizing flood risks and improving natural and built environment conditions. River plains tend to be attractive places for a city to grow. From ancient times, levees have been used to protect lowland areas along major watercourses to allow their occupation. However, urban rivers demand space for temporary flood storage. From a systemic point of view, levees along extensive river reaches act as canalization works, limiting river connectivity with flood plains, rising water levels, increasing overtopping risks and transferring floods downstream. Departing from this discussion, four case studies in the Iguaçu-Sarapuí River Basin, a lowland area of Rio de Janeiro State, Brazil, are used to compose a perspective in which the central point refers to the need of respecting watershed limits and giving space to rivers. Different aspects of low-lying city planning are discussed and analyzed concerning the integration of the built and natural environments.

Unplanned urbanization is one of the main factors responsible for worsening flood-related problems in cities, increasing the frequency of flooding and flooding depths, consequently degrading both the natural and built environment. Considering this, the use of engineering techniques that reduce runoff and promote the urban requalification are an efficient option for managing rainwaters. This paper presents a case study of a flood control project using a storm water detention pond, designed to allow multiple uses of an urban space. The operation of the system is evaluated by an Urban Flow-Cell Model, known as MODCEL. This application seeks the best configuration for the layout of ‘Celso Peçanha’ Detention Basin, considering the local restrictions imposed by the City of Mesquita – Brazil, and optimized to damp storm flows resulting from rainfall events with return periods up to 50 years. The solution proposed considers the possibility of social urban space uses in flood control projects, revitalising degraded areas and giving them multiple functions.

Urban growth usually aggravates flooding problems, disrupting city life and requiring engineering works to ensure safety conditions to lower-lying city areas. Traditionally, canalization works were the preferred choice for flood mitigation. However, increased city growth limits the effectiveness of this approach due to the lack of free spaces. In addition, local canalization practices tend to transfer flooding downstream in a nonsustainable way. In the last 80 years, the town of Cittanova, in the province of Reggio Calabria, Italy, has been subjected to several flooding events related to river overflows or storm drain failures causing significant damages to mobility, households, and even to public safety. This paper focuses on the Forio Creek, which is a tributary of the Vacale River and runs through the city. The study was carried out using mathematical tools within a conceptual framework with the aim of mapping floods to prevent damage to the city and avoid future losses, thus reducing risks. MODCEL was the hydrodynamic model used to map urban floods and to support the use of the Flood Risk Index (FRI), which is a quantitative multicriteria tool relating flood levels to socioeconomic losses. Both the MODCEL and the FRI were previously available, but their combined use and the final integrated analyses carried in this paper introduce a simple and quantifiable flood risk procedure to identify present flood risks and foresee future scenarios while supporting alternative design and prioritizing flood control choices. This framework was applied to Cittanova and validated by practical observations.

Urbanization increases imperviousness and reduces infiltration, retention, and evapotranspiration, frequently aggravating urban flooding due to greater runoff and higher and faster discharge peaks. Effective strategies to mitigate flood risks require a better understanding of the watershed dynamics and space to reverse the negative impacts. However, often cities do not have proper data sets to feed mathematical models that would be helpful in mapping water dynamics. Attempts to reduce flood risks have been made for decades by means of structural interventions but were frequently designed within the logic of a local scale, using limited available spaces and often merely shifting flooding downstream. Therefore, assessing urban floods requires a modeling approach capable of reflecting the watershed scale, considering interactions between hydraulic structures and urban landscape, where best practices and non-structural measures aim to improve community flood resilience through the reduction of social and financial costs in the long run. This paper proposes an integrated approach to analyze low impact development (LID) practices complemented by non-structural measures in a case study in southern Italy, supported by mathematical modeling in a strategy to overcome a context of almost no available data and limited urban open spaces.