The urbanization in a watershed generates several modifications that affect hydrological processes, not only increasing the percentage of impervious areas but also altering the structure of the drainage network. The hydrological modeling of small urban and peri-urban watersheds requires a correct representation of the network flow and overland flow between the different hydrological units. This paper presents the application of the width-function to compare drainage networks obtained by different methods in the Mercier peri-urban catchment, Lyon, France. The equivalent natural flow network was generated and its width-function was considered representative of the equivalent natural state. The drainage network representative of the artificialized state was extracted using an “object-oriented” method. Two meshes, pre and post-segmentation, were generated, the second one improving the homogeneity of the units. Their width functions show changes in their structure, as compared with the natural equivalent state. Given the relationship between the width function and the hydrological response, the change in the drainage system also implies a change in the response of the basin. So it is important to consider that when using a hydrological model, its results could be also affected by the methodology of extracting the drainage network.