Observed data are required to carry out hydrological simulations 8 in a watershed for use by policy makers. Hydrological simulations thus require 9 a large interdisciplinary knowledge about modeling, computer sciences, data-10 bases, GIS. A Matlab preprocess prior to the hydrological modeling is presented 11 for educational purposes and an easy uptake by non-GIS users. Moreover, this 12 allows for parallel computing. This pre-process builds on two renowned and 13 freely available Matlab toolboxes providing GIS and mesh functionalities. Ad-14 ditional functionalities allow for a decomposition of watersheds with respect to 15 parameterized constraints, including the meshing of the subdomains and the 16 construction of an oriented flow graph. The method is exemplified on a sub-17 basin of the Saar River. 18