Hydraulic Planning in Insular Urban Territories: The Case of Madeira Island—Ribeira Brava

Abstract

The main objective of this study was to analyze the flood propensity of the main watercourse of Ribeira Brava drainage basin and, if necessary, to suggest two methodologies to mitigate the impacts, i.e., detention basin sizing and riverbed roughness coefficient adjustment. For the flood propensity assessment, geomorphological data obtained from the watershed characterization process was used through the SIG ArcGIS software and then used for the calculation of the expected peak flow rate for a return period of 100 years using the Gumbel Distribution. Finally, the drainage capacity of the river mouth was verified via the Manning-Strickler equation, with the purpose of establishing whether the river mouth of the watershed has the capacity to drain the entire volume of rainwater in an extreme flood event. In summary, the results indicate that the river mouth of the Ribeira Brava watershed does not have the capacity to drain the rain flow for the pre-established return period; therefore, the detention basin was sized using the Dutch Method and the Simplified Triangular Hydrograph Method, and the roughness coefficient was adjusted in order to ensure the increase in the river mouth’s drainage capacity.