The Youngwal 1, Youngwal 2 and Youngchun gaging stations are observed flood flow and low flow during Mar. 2004~Oct. 2004. They are observed water stages and flow velocities for flood and low flow. The observed data are used to derived rating curve and equations. The HEC-RAS model is applied for hydraulic modeling in gauging stations. The model is designed to perform one-dimensional hydraulic calculations for an river improvement plan in a full network of natural and constructed channels, and is comprised of a graphical user interface(GUI), separate hydraulic analysis components, data storage and management capabilities, graphics and reporting facilities.