This paper presents the TAnaTo2 model. It is based on the open source GIS OrbisGIS, developed at IRSTV institute. TAnaTo2 provides new methods to evaluate the impact of natural and anthropogenic artefacts on the water runoff pathways in a peri-urban basin with a TIN-based model. It allows you to build a drainage network which represents runoff direction computed from the steepest maximum down slope. It is used to pinpoint water flow accumulation and extract watersheds. Tanato2 is applied on the Chézine basin located in north-western France, in the suburbs of Nantes. It is being used to understand the impact of urban development on the topographic course of surface waters.