Fundamental characteristics of high velocity flows in a sinuous open channel have been investigated theoretically and experimentally. It was shown that the water surface profiles can be classified into two patterns by using the analytical solutions of linearized shallow water flow equations, and the experimental results agree well with the theoretical findings within the limited range of flow conditions. In this paper, we carried out numerical simulations by using a shallow water flow model to clarify the non-linear characteristics of water surface profile in the vicinity of a resonance relation. The calculated results of water surface profile were visualized and compared with the experimental results to verify the numerical model. It was pointed out that the calculated results elucidated some fundamental nonlinear characteristics such that the flow resistance increases and the phase lag between water surface variations along a side wall and sinuous channel becomes to be π/2 in the neighborhood of a resonance relation.