Sediment is moved along the coastline in a process known as longshore drift. The prevailing wind blows waves carrying sediment into the beach at an angle, the waves break on the shore and as the water runs back into the sea it carries the sediment back down the beach, perpendicular to the angle of the shoreline under the influence of gravity. This results in a zigzag motion as sediment is transported along the coastline. This process means that over time beaches can change shape. Groynes can be built to interrupt the flow of longshore drift, but inevitably some sand and gravel can escape. Longshore drift can form spits were the line of the coast changes sharply, for example at a river estuary. There are several examples of spits along the Welsh coastline.
Students could create diagrams explaining the process of longshore drift, which could include the formation of a spit. Build on this understanding by adding groynes or other features to the diagram and explain how these affect the process. Discuss how measures to halt longshore drift in one area will have an impact further along the coast.