A computer-implemented method for civil engineering including obtaining a mesh representing a terrain and a polyline on the mesh, the method further includes computing a contributor of the polyline. The computing of the contributor includes modifying the mesh by determining, based on the polyline, a trench below the polyline. The computing of the contributor further includes computing a watershed segmentation of the terrain based on the modified mesh. The computing of the contributor further includes, based on the computed watershed segmentation, identifying, on the modified mesh, a basin comprising the trench. The contributor corresponds to the identified basin.