Abstract

Water waves in the ocean can be easily observed at any place regardless of the distance from the shore. However, measurements of wave speeds with respect to the ground can be rather complicated due to the non-trivial oscillation water does. In this article, indirect measurements of the speed of shallow water waves are made after observations of shapes in the undertow water current over the beach sand. The measurements were taken using only a video recorded with a smartphone camera and no additional hardware. These particular shapes take the form of conical shock fronts (also known as Mach cones) which relate the speed of the undertow current with the water wave speed. Using this technique, a Mach number of M = 3.0 ± 0.2 and wave speeds of c wave = (19 ± 2) cm s-1 are obtained which agree with shallow wave speed equations.