Application of morphological approaches to determine unit hydrographs of urban catchments

Deterrmning the hydrological response of urban catchments is of great interest for urban water management. Since most urban catchments are ungauged, this response must be deduced from catchment features, the description of which can be processed more easily today thanks to the availability of urban databases and geographical information systems within many cities. We compare three complementary methods for determining unit hydrographs, with varying degrees of catchment morphology description. The first method, displaying a high degree of description (URBS-UH), is derived from the analysis of urban databases and yields an explicit description of runoff production areas and their downstream flow channels. The second method (H2U), which corresponds to a moderate degree of description, consists of a gamma law whose parameters are based on both the Strahler's catchment order and the average hydraulic length of water paths through the drainage system. The third method, corresponding to a low degree (FDTF), derives the unit hydrograph by means of an iterative deconvolution identification technique using observed rainfall and flow data. The three methods have all been applied to two urban catchments (of 60 and 180 ha), located within the Nantes metropolitan area (western France). Their comparison is discussed and reveals encouraging results: the variability of unit hydrographs due to rainfall intensity is observed with all three of the methods. Deriving unit hydrographs from the morphology of an ungauged catchment would appear beneficial for hydrological purposes, and the degree of information inclusion regarding this morphology can be adapted depending on the availability of geographical data on the catchment studied. Copyright (c) 2005 John Wiley & Sons, Ltd.