Final answer:
Hard barriers for beach protection include groins, jetties, and breakwaters, which are man-made structures designed to interrupt water flow and absorb wave energy to minimize erosion. Dunes are natural features that also protect the shoreline but are not classified as hard barriers.
Step-by-step explanation:
The types of hard barriers that are commonly used to protect beaches against erosion include groins, jetties, and breakwaters. Groins are structures that extend from the shoreline into the sea and are designed to interrupt water flow and minimize sediment washing away. Jetties are similar to groins but are often placed at the sides of a river or harbor mouth to stabilize the channel and prevent sediment deposition that could block navigation paths.
Breakwaters are constructed offshore to absorb the energy of incoming waves and protect the coast or harbor by creating calm water zones. Unlike these hard structures, dunes are a natural feature that also helps protect the shoreline by acting as a barrier but is not considered a hard barrier as they are made of loose, unconsolidated sand.