In order to investigate the circulation dynamics of the Keum River estuary, 300velocity fields obtained at six sites over two tidal cycles by using instantaneous profiling technique were analyzed in detail. In this investigation, the variability of shear velocity, bottom shear stress, drag coefficient, and roughness length scale were confirmed. The measured values of the bottom boundary drag coefficient show wide range of variations, i.e., C$\_$100/=6.78${ imes}$10$^$-5/∼1.15${ imes}$10$^$-1/, and the mean of 300 measurements is 1.6${ imes}$10$^$-2/. The relationship between U* and C$\_$100/ also show the scatter in values. However, overall mean values over two tidal cycles at 6 stations show that if U* 1cm/s, C$\_$100/ is unpredictable, if U* 1cm/s, C$\_$100/ increase with U*. The values of Re$\_$100/ and C$\_$100/ have scatter. But the overall mean values over two tidal cycles show that if Re$\_$100/ 3.6${ imes}$10$^$5/, C$\_$100/ is unpredictable, if Re$\_$100/ 3.6${ imes}$10$^$5/, C$\_$100/=1.4${ imes}$10$^$-2/. Finally the flow regime of the Keum River estuary was classified as "subcritical fully turbulent" flow.