Wave action creates and changes beaches drastically. The sand that makes up beaches is transported along the shoreline by the following wave action. Waves typically approach shorelines at an angle rather than head on. Waves that hit the shoreline are then refracted perpendicular to the shoreline. The change in direction of a wave once it hits the shoreline transports sand grains along the shore. Water flow along shorelines is described with the following terms. Longshore drift is the net flow of water along the shore that results from waves that refract along the shoreline. Longshore drift is parallel to the shoreline in one direction. The direction roughly points towards the same general direction as sand transport and incoming waves. Upstream refers to the direction opposite of longshore drift. Rip currents are strong surface currents. Water that refracts from the shoreline can return out to sea along the surface or along the ocean bottom. Rip currents are the retreating waves that return along the surface. This type of current can be very dangerous to unwary swimmers.