Abstract -- The purpose of this study is to examine the feasibility of Yen's method of using thehydraulic performance graph (HPG) to construct the rating curve for natural rivers.
So far the modification of the derivation for the theoretical rating curve has been completed. The one and two- dimensional water flow models, especially HEC-RAS 2.2 flow models, especially HEC-RAS 2.2 model which is adequately responded to the stage relation between the upstream and the downstream at selected reach, was cooperated, which might be used to provide the flow pattern data for HPG have also been validated through the application to some hypothetical cases. In order to examine the applicability of the HPG to such as Keelung River with natural or human-made including compound cross section channel, bridge, fixed bed, weir, and of a number of reaches together as a system. On the basis of the river cross section investigated a roughly estimated rating curve has been established. However, from the preliminary results obtained one can find that the N-line is not the line paralleled to the Z-line defined by the HPG conception and refer to be determined under the simulation of that the energy slope equals to the averaged bed slope at the downstream location which flow patterns through the natural river reach and the bridge pier and the hydraulic structure neighboring to the gage station has to be computed to derive the more accurate rating curve by using the modified HPG concept which is available after calibrating through the local sensitivity analyses for the hydrologic and hydraulic uncertainties.