To understand the long term change in river flow is basic information in order to estimate water resources in region and/or watershed. One of ways to obtained above mentioned information from river flow data is the flow-duration curve. It is too difficult to grasp the condition of the watershed using the flow-duration curve because the flow-duration curve depends on rainfall.
In this paper, we propose a new flow-duration curve which does not depend on rainfall. This new flow-duration curve was estimated by runoff ratio using moving average runoff and rainfall.
As a result of new flow-duration curve, the difference among three case study watershed's flow regime can be observed clearly. A new flow-duration curve, which we proposed, could clarify the watershed conditions like land use and/or soil characteristics using only historical river flow and rainfall data.