Indirect estimation of design flood in urbanized river basins using a distributed hydrological model

A method for indirect estimation of design flood in poorly gauged urbanized river basins by using distributed hydrological modelling is presented. It is based on the critical flood design criterion that maximizes peak flow for a given return period by transforming precipitation of depth duration frequency curve into runoff. Indirect method is compared against direct method based on regional approach and index flood estimation. The paper shows that direct method significantly underestimates design flood in case discharge measurements are strongly affected by artificial alteration of water courses with possible catastrophic consequences in terms of loss of life and damage to property when cause of alteration would be removed. Moreover, the use of a spatially distributed model allows to take into account heterogeneity that generally characterizes river basins with an high degree of urbanization. The presented indirect method, provides design hydrograph that is useful for those cases where design discharge only is not sufficient for designing or planning purposes.