The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. How does beach sand migrate as a result of longshore drift? Explain the sediment budget of a coast. (F)

Longshore drift is a geological process by which sediments, like sand, are transported along the shoreline due to the action of waves and currents. This process is essential in the formation and movement of various coastal features such as beaches, sandbars, and barrier islands.

Longshore drift occurs due to the angle at which waves approach the shore, known as the wave angle. When waves approach the shoreline at an angle, they carry sediment particles up the beach with them (known as swash), and then retreat back down the beach (known as backwash). The backwash typically occurs at a 90-degree angle with the shoreline due to gravity. This continual process results in the sediment gradually moving along the shoreline in a zigzag pattern, in the direction of the longshore current - the water moving parallel to the shore. Factors that influence the rate and direction of longshore drift include the size and angle of the waves, the shape of the coastline, and the composition of the beach material.

The sediment budget of a coast refers to the balance between the amount of sediment being added to (sources) and removed from (sinks) a particular coastal area. The sediment budget can be either positive, negative, or balanced. A positive sediment budget indicates a net gain in sediment, resulting in beach growth. A negative sediment budget indicates a net loss in sediment, resulting in beach erosion. A balanced sediment budget means that the amount of sediment entering and leaving the area is equal, maintaining a stable beach. The sediment budget is influenced by natural factors (e.g., river input, sea-level changes) and human activities (e.g., coastal engineering, mining).

Longshore drift plays a significant role in the sediment budget of a coast. The rate at which sediment is transported along the shoreline by longshore drift can impact the balance between sources and sinks of the sediment. For example, if longshore drift moves sand from one beach to another at a faster rate than sediment can be replenished from other sources (e.g., rivers), this can result in a negative sediment budget and subsequent beach erosion. Conversely, if longshore drift moves sand into an area where there is a net gain in sediment from other sources, this can lead to a positive sediment budget and beach growth. Understanding and managing the interaction between longshore drift and sediment budget is essential for coastal management and the preservation of coastal environments.