Beyond the Foreshore of some beaches is a backshore zone, characterized by dunes. Dunes are constructed by windblown sediment transported from the foreshore and elsewhere.
Sediment can also be transported to the backshore area during storms, when big waves can reach far inland (note that a storm beach face can be seen well away from the normal beach face).
Not all shorelines are alike. Whereas some shorelines are dominated by deposition (as is the case for sandy beaches), others are dominated by erosion.
Erosional shoreline area
Depositional shoreline area
Shorelines characterized by exposed bedrock and strong wave activity are important suppliers of beach sediment.
Minerals of beach sediment derived mostly from eroded rocks along the coast match those of the source rocks.
Black sand beach, Big Island, Hawaii
…But most sediment supplied to beaches along continental coastlines is delivered to the coast by rivers.
When a river enters a large body of water (e.g. ocean), its flow rapidly decreases, resulting in the deposition of sediment at the river mouth.
The resulting sediment deposit is a delta.
(a river-dominated delta)
If wave action is strong, sediment deposited at a river mouth can be transported along the coastline instead of forming a well-defined delta.
waves and transported
Most waves move toward the shore at a slight angle.
Consequently, the uprush of water (swash) from each breaking wave is oblique.
The direction of swash is oblique.
However, the backwash runs back to the water at a right angle.
Sediment particles are therefore transported in a zig-zag pattern along the beach.
This “beach drift” can carry sand and pebbles hundred to thousands of metres per day.
In a similar manner, water in the shoreface zone flows toward the shore at an angle, and flows back at a right angle to the shore.