Development of Stage-discharge Rating Curve Using Hydraulic Performance Graph Model

The stage-discharge rating curve is widely used in the research for analysis of flow regime and design of hydraulic structure and river channel. To develop the reliable stage-discharge rating curve, numerous discharge data from the lowest to bankful stage should be observed over a long period of time. The river environment and topography of Nakdong River in Korea has been changed drastically due to the Four Major Rivers Restoration Project from the end of 2009 to 2012. Moreover, 8 weirs were built dividing the main river into nine sectors and it led the discontinuous flow and backwater effect for each sector. In such situations, the stage-discharge rating curve should be re-determined with new data for the changed topography and flow characteristics. However, it takes long time to get the new stage-discharge rating curve. In this study, the alternative stage-discharge rating curve was developed using the Hydraulic Performance Graph (HPG). HPG is a plot summarizing all the backwater profile for all possible discharge at a channel reach based on the flow equation that is derived from the energy equation. In this study, the 26 cross sections up to a length of 12.3 km located between Gangjung weir and Dalsung weir in Nakdong River after the project were measured. The HPG for this sector was created. Using the results of discharge and water surface elevation from the HPG, the alternative stage-discharge rating curve was created. Then the discharge from the rating curve was compared with measured data from the several cross sections. The discharge from the rating curve matched the measured data quite well. The alternative stage-discharge rating curve suggested in this study has high applicability for analysis of flow regime and design of hydraulic structure and river channel in drastic environmental changes of the river systems before creating a new stage-discharge rating curve which requires long term measurement data.