Surface runoff in urban catchments: morphological identification of unit hydrographs from urban databanks

In this study, Urban Unit Hydrographs (URBS-UHs), are derived from the analysis of an urban databank for three urban catchments with surface areas ranging from 18 to 180 ha. The geometry of property lots, streets and sewer networks allows for an explicit description of the runoff production areas and their downstream flow channels. The Manningʹs equation is used to compute the flow velocity along the identified channels under rainfall intensities that we related, for purposes of convenience, to return periods. The shape and the scale of the URBS-UH are primarily influenced by catchment morphology, channel roughness and rainfall return period. As a consequence, the transfer function is not unique but rather depends on rainfall characteristics. The URBS-UHs identified without any parameter calibration are encouragingly similar in shape and scale to the unit hydrographs derived from rainfall-runoff measurements over the three studied urban catchments.