I had written earlier that Ramelli's designs for drainage schemes may indicate his presence in the low countries. It seems that he woudn't have had to travel nearly so far to gain such experience. It seems that following the fall of Siena there were renewed efforts to drain the local marshes of the Val-di-Chiana. The best English references seem to be:
Alexander, David (1984). The reclamation of Val-di-Chiana. Annals of the Association of American Geographers. 74.4: 527-550.
Jayawardene, S.A. (1965). Rafael Bobelli, Engineer-Architect: Some Unpublished Documents of the Apostolic Camera. Isis, 56.3: 298-306.