Study of Undertow for Different Beach Profile   Undertow, average velocity over one wave period, is dominating in the velocity field in surf zone. It is essential in order to estimate sediment transport as well as beach topography. The objective of the study is to investigate interaction between cross-shore beach profile and undertow in surf zone. In surf zone velocity field consists of steady current, irrotational wave motion, rotational wave motion and turbulence. Laboratory measurement in surf zone is complicated to distinguish components of velocity field. Laser Doppler Velocimeter(LDV), Acoustic Doppler Velocimeter(ADV) etc, are used to record velocity data, but are not efficient after breaking because of bubbles in vortex. Vortex size and velocity of particles in vortex are essential to understand velocity filed. One way is to trace the movement and estimate the density of bubbles in order to quantify vortex size and velocity of bubbles in vortex. Figure: Vortex size is estimated in surf zone captured by High Speed Camera