Abstract
Present land use in a river basin is consequence of all land development in the past. This study is an attempt to recognize land development of a river basin, focusing on Onga river basin in ancient days (until 6th century). After confirming geological and topographical characteristics, the study pays attention to earthwork capability in Jomon, Yayo i and Kofun era. Leading-edge impl ements in each era support us to make an interpretation of ancient monuments' location and archaeological findings. Especially wooden how/spades in Yayoi era and iron blade edges in Kofu n era had typical impact to expand ricefield towards uncultivated area. The conclution indicates that the a dvanced earthwork implements enabled people shift main paddy field from lower lagoon area to upper alluvial terrains on Onga river basin through ancient days. This ancient land development history has much suggestions for today's river/river basin management.
