Author(s): Alejandro Pinilla; Antonio Lastra; Monica Ortega

Linked Author(s):

Keywords: Urban flood risk assessment; Urban drainage overflowing; 2D modelling; Exposure to urban flooding; SIG risk map

Abstract: The aim of this study is to identify and quantify flood risks caused by overflows of the urban drainage network in urban and peri-urban areas of the Madrid region. A total of 136 municipalities whose drainage network is managed by Canal de Isabel II have been individually characterized. Urban flood risk assessment is carried out based on the following risk equation: Risk=Hazard*Exposure*Vulnerability Hazard has been calculated as the flood caused by the drainage overflows that occur by a local 10-year design rainfall. Drainage overflows are obtained by a 1D hydraulic sewage model for a municipality or sanitation system, there is a hydrograph for every manhole and weir overflowing. Those are the input to the 2D hydrological. Flooded area is provided as safe, non-safe and non-flooded areas. Hazard is given in terms of flooding time, water depth and velocity flow. Within the exposure elements there is population weighted by census sections of the city as well as economic activity. In the case of road traffic, it is considered vulnerable according to the damage that the depth of the water and the velocity of the flow could cause to traffic flow or vehicles. Private traffic is weighted by occupancy and dimension of the road while number of public bus lines defines the vulnerability for public transportation. In this study, it was also included the environment, specifically the vulnerability to discharges in natural parks and reservoirs and the affection of the IPPC (integrated pollution prevention and control). The fifth exposure element is a series of 11 categories such a garage and basement floors or strategic infrastructure points. Results for hazard, vulnerability and risk are visually available in an ad-hoc SIG map. They serve to identify flood-prone areas and the risk level over urban sector population, economical, infrastructures (public and private road traffic, rail infrastructures and singular buildings) and the environmental sectors. An urban flood risk map by municipalities is also obtained as well as a hazard-risk scatter diagram that ranks the municipal sewer network. This is useful to prioritize technical improvement measures related to the sanitation system because now the urban flood risk criterion is also included on the decision making. The region has over 800.000 Ha surface area mainly impervious and a total of 6.7 million inhabitants distributed in 179 municipalities. The methodology for assessing the impact methodology of flood was developed and coded in a flexible tool where parameters such as rainfall events or watershed permeability of the watershed can be updated so that the risk map can be recomputed as the municipalities grow and the maintenance of infrastructures evolves.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022870

Year: 2022