The vortex core radius is a radius at the maximum tangential velocity in the vortex flow field.As the vortex motion is complex,it is difficult to determine the vortex core radius by the measurement of the tangential velocity in the whole flow field.Besides,other determinations methods lead to some discrepancies.In this paper,an indirect determination method is proposed. The vortex core radius is calculated by an easily determined characteristic parameter, i.e.The distance from the position of the maximum water surface curvature to the vortex symmetry axis. A order tenth implicit equation between the vortex core radius and the parameter is deduced, and the unique root of the equation is discussed.According to the solution of the equation, a dimensionless curve between the two parameters is plotted.With the proposed method,the vortex core radius is determined by the vortex water surface profile
