Tides and currents

Tides

Periodic rise and fall of sea levels caused by the gravitational pull of the moon and sun, and Earth's rotation.

Types

Tide Type

Description

Moon Position

Spring Tides

Highest high tides and lowest low tides.

Full and new moons (moon and sun aligned).

Neap Tides

Lower high tides and higher low tides.

First and third quarters (moon and sun at 90°).

Diurnal Tides

One high tide and one low tide per day.

No specific moon position; rare globally.

Semi-Diurnal Tides

Two high tides and two low tides of similar height each day.

Common in most locations globally

Onshore Currents

Water moves towards the shore due to wave action. Transports sediment onto the beach, contributing to deposition.

Offshore Currents:

Water moves away from the shore, often caused by strong winds or wave backwash. Removes sediment, contributing to erosion or sediment redistribution.

Rip Currents:

Narrow, fast-flowing offshore currents. Created when waves break strongly in some areas and weaker in others.

Wave Types

Constructive Waves:

  • Low energy, long wavelength, low frequency (6-8 waves per minute).

  • Strong swash → Deposits sediment.

  • Creates wide, gently sloping beaches.

Destructive Waves:

  • High energy, short wavelength, high frequency (10-14 waves per minute).

  • Strong backwash → Removes sediment.

  • Creates steep, narrow beaches.

Concept

Description

Process

Effect

Wave Refraction

Bending of waves as they approach irregular coastlines

Waves slow down in shallow water near headlands (due to friction).

Waves in deeper water around bays continue faster.

Energy concentrates on headlands, causing erosion.

Energy disperses in bays, causing deposition

Leads to the formation of headlands and bays.

Wave Reflection

Waves bounce back after hitting a hard surface like a sea wall or rocky cliff.

Waves reflect off hard surfaces such as sea walls or rocky cliffs.

Intensifies wave energy, increasing erosion at the base of cliffs or structures

Can scour beaches or undermine sea defences.

Wave Orientation

Direction waves approach relative to the coastline.

Oblique Orientation:

  • Waves hit the coast at an angle.

  • Causes longshore drift, moving sediment along the coast.

Perpendicular Orientation:

  • Waves hit the coast head-on.

  • Leads to stronger onshore currents and deposition.