NOTE 1 – SEA WAVES
 Three agents that could transform a coast. Three agents are wind
waves, tides, Tsumanis and currents.
 Wind waves refer to the rise and fall of the water surface in the sea or
ocean when the wind blows over it
 Tides refer to the daily and alternate rise and fall of sea level seen along
ocean coasts primarily due to the gravitational pull of the Moon and, to a
lesser extent, the Sun. These pulls on the Earth and its water produce
two high tides on opposite sides of the Earth when the Moon is very
close to the Earth and low tides when the Moon is further away.
At certain times of the month, when the Earth, the Sun and the Moon
are all in a straight line, extremely high tides (spring tide) are
experienced. While very low tides (neap tide) occurs when the Earth,
Moon and Sun are at right angles to each other. The difference between
the high and low tides is called tidal action and it affects the coastal
processes of erosion and transportation.
 Waves can also be formed below the ocean surface. This type of wave
is known as a tsunami and is usually caused by an earthquake beneath
the ocean floor. The abrupt movement of the ocean floor sends pulses
of energy through the water above it. When tsunamis reach the coast,
they can be as devastating as an earthquake on land

Currents are large-scale and persistent movements of water in the
ocean. It is largely driven by prevailing winds, which can be either
horizontal or vertical. An example is the longshore current that flows
parallel to the coast. It is formed by waves that approach the coast at an
angle. This current can transport an entire section of a sandy beach
several kilometres down the coast within a short period.
 How do waves differ? Wave Size: Wave Energy:
The following factors will affect wave energy:
Speed of wind -The greater the wind speed, the greater the wind
energy.
Duration of wind -The longer the wind blows, the larger the waves and
the greater the energy.
Fetch -The greater the fetch, the greater the wave
Wave Energy:
Although waves
may appear to carry
water towards the
shore, the water
does not actually
move forward
The energy of the
wave moves
towards the shore
but the water
remains in place
As the wave passes, water particles move in a circular path
They swing forward and down with the energy of the wave, then back up to
their original position
Winds affects the water at the surface more than it affects the deep water
Below a certain depth, the water does not move at all
The motion of water on the surface when wind blows across an open
sea.
• When the wind blows over the surface of the water, waves are formed.
• Waves move in a series of circular loop-like motions.
• As waves move through deep water, little energy is lost.
• As waves approach the coast, the water becomes shallower.
• Friction with the sea floor surface slows down the wave movement.
• This frictional force causes the waves to heighten and bend forward.
• As they continue to move forward, they collapse onto the beach, into
foaming water.
• The forward movement of the waves up the shore is called swash.
• Earth's gravity pulls the waves back to the sea; this movement is called
backwash.
What are the characteristics of waves?
Crest is the highest part of a wave
The horizontal distance between crests is the wavelength
Waves are also measured by their frequency, or the number of waves that
pass a point in a certain amount of time
The trough is the lowest part of a wave
The vertical distance from the crest to the trough is the wave height
Three main types of breaking waves are identified by surfers or surf lifesavers.
Their varying characteristics make them more or less suitable for surfing, and
present different dangers.
1. Spilling, or rolling - these are the safest waves on which to surf.
They can be found in most areas with relatively flat shorelines.
They are the most common type of shorebreak. The deceleration
of the wave base is gradual, and the velocity of the upper parts
does not differ much with height. Breaking occurs mainly when
the steepness ratio exceeds the stability limit.
2. Plunging, or dumping: these break suddenly and can "dump"
swimmers—pushing them to the bottom with great force. These
are the preferred waves for experienced surfers. Strong offshore
winds and long wave periods can cause dumpers. They are often
found where there is a sudden rise in the sea floor, such as a
reef or sandbar. Deceleration of the wave base is sufficient to
cause upward acceleration and a significant forward velocity
excess of the upper part of the crest. The peak rises and
overtakes the forward face, forming a "barrel" or "tube" as it
collapses.
3. Surging: these may never actually break as they approach the
water's edge, as the water below them is very deep. They tend to
form on steep shorelines. These waves can knock swimmers
over and drag them back into deeper water.
Constructive and Destructive Waves
Constructive waves are the waves that build up the beaches. They have a
large 'swash', which means they can carry deposits of sand and other
materials far up the beach. They are much lower than destructive waves and
have a longer 'wavelength': this is the distance between the peak of each
wave, or the top. Constructive waves are made when the sea is calm.
Destructive waves are much larger and more powerful and are mostly made
during a storm. They have travelled a long way, and this is what makes them
so powerful. Because they have a stronger backwash than swash, they erode
the coastline because they take the sand back with them into the sea. There is
a shorter distance between their peaks than with constructive waves
(wavelength), and they are much taller.
Wave Refraction
Refraction is the bending of waves because of varying water depths underneath.
The part of a wave in shallow water moves slower than the part of a wave in
deeper water. So when the depth under a wave crest varies along the crest, the
wave bends.
An example of refraction is when waves approach a straight shoreline at an angle.
The part of the wave crest closer to shore is in shallower water and moving slower
than the part away from the shore in deeper water. The wave crest in deeper water
catches up so that the wave crest tends to become parallel to the shore. See below
Must watch real life refraction animation