Wave dominated coastlines: Problems and management solutions

Wave dominated coasts = dominant forcing factor is wave energy - drives sediment around and determines if beaches are constructive or destructive

Characterised by:

• High energy
• Sediment and landforms governed by wave energy e.g. cliffs, stacks, arches, wave cut platforms, sand/shingle beaches, spits, tombolas, ridges and sand dunes
• Changes reflecttemporal variations in wave activity and sea levels

Shingle vs sand beaches - 

• Shingle beaches tend to have higher energy
• Both can be managed by groynes to stop or reduce the impacts of long shore drift
• Mainly due to different geology - different rock types are eroded in different ways/ on different time scales
• Shingle beaches are more swash dominant as opposed to backwash
• Angle of repose - have different heights of beaches = sand generally gently sloping, whereas shingle greatly increases in height with movement inland

Sand dunes only form on wave dominated coasts - due to sand supply and the need for strong onshore winds

Can describe waves as plunging, spilling or surging - changes in relation to the steepness of the beach

• Determined by wind strength and seasonality - reflects changes in energy

In open water, waves are variable. Can be affected by:

• Wind velocity
• Weather systems
• Geological events

Nearshore (area where waves start to break) waves are also affected by:

• Fetch - distance and time that wind blows over sea 
• Sea bed topography
• Water depth - relates to sea level changes
• Structures - man made objects in the sea causing waves to break early or reduce velocity

As waves near the shore they may change in height, frequency and the way they break - occurs because of the shallowing BATHYMETRY:

• Movement of water molecules interferes with sea bed generating currents
• Waves start to break and therefore release potential energy
• This moves sediment in the direction of the current
• Happens when the bottom of a wave moves above the wave base as relief of the land increases 

Towards the shore, the sea bed shallows causing more friction

Ellipses become distorted and eventually fail to close leading to the breaking of waves - can be on the forward or backward movement

• Waves approach the shore obliquely (i.e. not perpendicular)
• As sea bed shallows, wave height increases and wave height decreases
• When height to length ratio reaches 1/7, causes instability making the wave break

As the ellipse movement comes in contact with seds energy is transferred from the water to the sed - causes sed movement and energy loss in the water

As waves approach the nearshore zone they generate currents which can take 2 forms:

• Shore-normal currents - waves that hit the shore at a perpendicular angle, break and swash
  • Causes stronger up beach movement from constructive waves = net movement of sediment onto beach
  • Can also cause stronger off beach movements from destructive waves =…