For several years, flash floods appear frequently on small dry valleys of the Paris Basin, in the North of France. These “hyper-concentrated stream flows” are defined as floods with sudden apparition, rapid rising time and important specific flow. They are produced by intense rainfall (>50mm.h-1) over small areas (<40km²) and present single features. The catchment morphology is a first-order controlling factor of floods dynamic. For a better understanding of such type of processes, analysing the morphological signature of these catchments becomes of paramount importance. Therefore, classical morphometric methods do not consider the dynamics generated by the catchments structure. So we develop a new tool based on spatial analysis and the cellular automata “Ruicells” is proposed. It allows us to integrate the catchment geometry, the slopes pattern and the drainage network in order to simulate runoff response at different outlets. First results attempt to validate the influence of drainage network on the hydrological response of the catchments, while size of drainage area has a minor influence. Moreover, the application of cellular automata modelling highlights the causes of spatial and temporal variability of flows as for example the relation between the location of streaming areas and water paths.