Longshore drift
Also called: Littoral drift · Topic: Movements of Ocean Water: Waves, Tides and Currents · NCERT: Beyond NCERT
Meaning
Longshore drift is the movement of sand and pebbles along a coast. It happens when waves hit the beach at an angle. The swash (water running up the beach) carries sand up at that angle. The backwash (water running back) pulls it straight down the slope. Step by step, in a zigzag, the sand moves along the shore. It can build features such as spits and bars. When a harbour wall or breakwater blocks this flow, sand piles up on one side and the beach on the other side wears away.
Example
Chennai harbour's breakwaters trap sand carried by longshore drift along the Bay of Bengal coast. This helped build up the wide Marina Beach to the south and caused coastal erosion to the north of the harbour.
Don't confuse with
- Tidal current: water flow caused by the rising and falling tide. Longshore drift is caused by waves striking the shore at an angle.
Related concepts
- Wave
- Orbital motion of water particles
- Fetch
- Wave height
- Wavelength
- Swell
- Breaking of waves
- Kallakkadal