Longshore currents are wave-driven currents that flow parallel to the shoreline. Although usually invisible to beachgoers,
they constantly transport sand, reshape beaches, influence coastal erosion and create hazards for swimmers and surfers.
What Is a Longshore Current?
A longshore current is a current that flows parallel to the shoreline inside the surf zone.
It forms when waves approach the beach at an angle rather than straight on. As each wave breaks,
water moves diagonally onto the beach before returning downslope, creating a steady current that runs
along the coast.
Longshore currents are one of the main reasons beaches naturally gain or lose sand over time.
How Longshore Currents Form
- Waves approach the shoreline at an angle.
- Breaking waves push water diagonally onto the beach.
- Gravity pulls water back downslope.
- Repeated wave action creates a current flowing parallel to the shoreline.
- The current transports sand along the coast.
Longshore Drift: Nature’s Sand Conveyor Belt
As longshore currents move water, they also move sand, shells and small pebbles in a process called
longshore drift or littoral drift. Sediment is carried down the coast,
gradually reshaping beaches, spits, barrier islands and coastal inlets.
This natural conveyor belt explains why erosion in one area often leads to sand accumulation farther
down the shoreline.
Why Longshore Currents Matter
- Transport beach sand along the coast.
- Control coastal erosion and deposition.
- Shape barrier islands, spits and sandbars.
- Influence navigation channels and harbor entrances.
- Create challenges for coastal engineering projects.
- Can contribute to swimmer drift and rip current formation.
Longshore Currents vs. Rip Currents
| Longshore Current | Rip Current |
|---|---|
| Flows parallel to shore. | Flows away from shore. |
| Moves sand along beaches. | Returns surf-zone water offshore. |
| Usually broad and steady. | Usually narrow and fast. |
| Shapes coastlines over time. | Major swimming hazard. |
How Longshore Currents Shape Coastlines
Over years to centuries, longshore currents build beaches in some places while eroding others.
They help create:
- Barrier islands
- Sand spits
- Tombolos
- Coastal dunes
- Sandbars
- Beach cusps
Human structures such as groynes, jetties and breakwaters interrupt longshore drift, often causing
erosion farther down the coast.
Longshore Currents and Coastal Erosion
Longshore currents are a major driver of
coastal erosion.
Storm waves can accelerate sediment transport, removing sand from one beach while depositing it
somewhere else.
Beach nourishment projects must account for longshore drift or newly added sand may quickly disappear.
Can Longshore Currents Be Dangerous?
Longshore currents are usually slower than rip currents but can still carry swimmers considerable
distances along the beach. They may also feed water into rip-current channels or make it harder to
return to the original swimming location.
Surfers, paddleboarders and small boats can also be affected during periods of strong wave action.
Related Ocean & Coastal Topics
Frequently Asked Questions
What is a longshore current?
A longshore current is a wave-driven current that flows parallel to the shoreline inside the surf zone.
What causes longshore currents?
They form when waves approach the beach at an angle and repeatedly push water along the shoreline.
What is longshore drift?
Longshore drift is the transport of sand and sediment along the coast by longshore currents and angled waves.
Are longshore currents dangerous?
They are usually less dangerous than rip currents but can carry swimmers, surfers and floating objects
long distances along the shoreline.
Why are longshore currents important?
They shape beaches, transport sediment, influence coastal erosion and affect coastal engineering projects.
