2. Longshore Drift and Beach Drift

3. Wave Front Beach Wind (and wave) direction

4. Beach Wave Front When water depth < 1/2 wavelength, the wave begins to break. It also begins to refract or bend toward the shore as the part of wave in shallow water slows down. As the wave breaks, water moves forward toward the beach.

5. Wave Fronts Beach As successive waves reach shallow water, more water actually begins to move forward and be squeezed along the shore.

6. Wave Fronts Beach

7. Wave Fronts This is called Longshore Drift. As waves bend to meet the shore and begin to break, water is pushed along the shore parallel to the beach. Longshore drift can be a significant contributor to the movement of material along a beach. Swimmers, too, can be carried along the shore.

8. Wave direction Beach Waves approach a bay.

9. As waves approach the bay the “ends” begin to refract and the wave bends.

10. This refraction and the resulting breakers set up longshore currents toward the back of the bay.

11. When the longshore currents meet at the back of the bay, they can create a rip current (also inaccurately called a rip tide) that moves off shore.

12. In deeper water the rip current dissipates into what is called the rip head.

13. Swimmers being carried offshore by a rip current should escape by swimming sideways to the current and not straight back toward the beach. This may exhaust them.

14. Wave Fronts When waves break on shore at an angle, the water rushes up the beach on an angle but gravity tends to draw it straight back down. The flood of water up the beach is called swash and the flow back down is called backwash. Swash Backwash

15. Wave Fronts Any material (sand, etc.) in the breaking wave is, therefore, moved along the beach. This is called beach drift and, coupled with longshore drift, is responsible for the transport of materials along shorelines. Net direction of beach drift