Final answer:
Swash is the movement of water and sediment onto a beach, while backwash carries sediment back to the sea. Grain size affects sediment transport and deposition, influencing the shape and structure of the beach. Larger grains with more void space tend to remain, while smaller grains are more easily moved away.
Step-by-step explanation:
Swash, Backwash, and Grain Size in Coastal Geography
The terms swash and backwash refer to the movements of water at the coast as waves break. The swash is the movement of water and sediment up the beach after a wave breaks, which can transport particles up the beach slope. The backwash is the water that flows back down the beach into the sea, carrying sediment with it. These two actions can sort sediment by size and determine the shape of the beach.
When considering the relationship between swash, backwash, and grain size, it is understood that the size of sediment grains affects the beach profile and how well impressions or structures like dunes and ripple marks are preserved. Larger grains, such as coarse sand, have greater void space between them, which allows more water to percolate quickly through them during the backwash, diminishing their displacement down the slope. Conversely, smaller grains, like silt and clay, retain water and are more easily moved back to the sea, leading to a gentler beach slope.
Grain size influences a sediment's history, transport, and depositional environment. Larger, coarse-grained sediments suggest a higher energy environment, often closer to the source material, where smaller grains indicate longer transport distances or quieter waters. Structures within sediments, like ripple marks and cross-bedding, are often better formed and preserved in finer sands, typically resulting from symmetrical wave actions in shallow marine environments. As grain size affects the sediment's ability to be transported and deposited, it is a key indicator in geological analyses.