But once this self repair mechanism becomes impaired, beaches become more sensitive to weather conditions and climate cycles. The situation is typical for many beaches, all over the world. Note that the rapid oscillations are depicted as growth during one year, followed by shrinking during the next year. What the author intended to show was growth during summer and shrinkage during winter, an oscillation twice as fast. It is a model to sharpen our understanding.
Scientists use such models to study the transport of sediment near beaches.
The size of the boxes could be a part of the beach or the entire beach, and it is called a 'beach cell'. Sand moves towards the beach by wave action and away from the beach by gravity down its gradual slope. In the lower left corner the origin of the sand is shown. Sand arises from coastal erosion and is transported by rivers towards the sea. As rivers deposit sand nearshore and offshore, it enters the corresponding compartments.